ON ADT7473ARQZ-REEL Remote thermal monitor and fan control Datasheet

ADT7473
Remote Thermal Monitor
and Fan Control
The ADT7473/ADT7473−1 controller is a thermal monitor and
multiple PWM fan controller for noise sensitive or power sensitive
applications requiring active system cooling. The
ADT7473/ADT7473−1 can drive a fan using either a low or high
frequency drive signal, monitor the temperature of up to two remote
sensor diodes plus its own internal temperature, and measure and
control the speed of up to four fans so they operate at the lowest
possible speed for minimum acoustic noise.
The automatic fan speed control loop optimizes fan speed for a
given temperature. A unique dynamic TMIN control mode enables the
system thermals/acoustics to be intelligently managed. The
effectiveness of the system’s thermal solution can be monitored using
the THERM input. The ADT7473/ADT7473−1 also provide critical
thermal protection to the system using the bidirectional THERM pin
as an output to prevent system or component overheating.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Controls and Monitors Up to 4 Fans
High and Low Frequency Fan Drive Signal
1 On-Chip and 2 Remote Temperature Sensors
Series Resistance Cancellation on the Remote Channel
Extended Temperature Measurement Range, Up to 191°C
Dynamic TMIN Control Mode Intelligently Optimizes System
Acoustics
Automatic Fan Speed Control Mode Controls System Cooling Based
on Measured Temperature
Enhanced Acoustic Mode Dramatically Reduces User Perception of
Changing Fan Speeds
Thermal Protection Feature via THERM Output
Monitors Performance Impact of Intel® Pentium® 4 Processor
Thermal Control Circuit via THERM Input
3-wire and 4-wire Fan Speed Measurement
Limit Comparison of All Monitored Values
Meets SMBus 2.0 Electrical Specifications
(Fully SMBus 1.1 Compliant)
These Devices are Pb-Free, Halogen Free/BFR Free and are RoHS
Compliant
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QSOP−16
CASE 492
PIN ASSIGNMENTS
SCL
1
16
SDA
GND
2
15
PWM1/XTO
VCC
3
14
VCCP
TACH3
PWM2/
SMBALERT
TACH1
4
13
D1+
12
D1−
6
11
D2+
TACH2
7
10
D2−
PWM3
8
9
SCL
1
16
SDA
GND
2
15
PWM1/XTO
VCC
TACH3/
ADDR SELECT
PWM2/
THERM_LATCH
TACH1
3
14
VCCP
4
13
D1+
12
D1−
6
11
D2+
TACH2
7
10
D2−
PWM3/
ADDREN
8
9
5
5
ADT7473
(Top View)
ADT7473−1
(Top View)
TACH4/GPIO/
THERM/
SMBALERT
TACH4/GPIO/
THERM/
SMBALERT
TOP MARKING
BOTTOM MARKING
ADT
7473−1
ARQZ
#YYWW
ZZZZ
ZZZZ
ADT7473−1ARQZ
#
YYWW
ZZZZ
= Specific Device Code
= Pb-Free Package
= Date Code
= Assembly Lot Code
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 72 of this data sheet.
© Semiconductor Components Industries, LLC, 2016
November, 2016 − Rev. 11
1
Publication Order Number:
ADT7473/D
ADT7473
*ADDREN
*ADDR SELECT
SCL
SDA
SMBALERT
ADT7473/ADT7473−1
SMBus
ADDRESS SELECTION
PWM1
PWM REGISTERS
AND
CONTROLLERS
(HF & LF)
PWM2
PWM3
ACOUSTIC
ENHANCEMENT
CONTROL
SERIAL BUS
INTERFACE
AUTOMATIC
FAN SPEED
CONTROL
ADDRESS
POINTER
REGISTER
DYNAMIC
TMIN
CONTROL
TACH1
TACH2
PWM
CONFIGURATION
REGISTERS
FAN SPEED
COUNTER
TACH3
INTERRUPT
MASKING
TACH4
PERFORMANCE
MONITORING
*THERM_LATCH
VCC to ADT7473/ADT7473−1
THERMAL
PROTECTION
INTERRUPT
STATUS
REGISTERS
VCC
D1+
D1−
D2+
INPUT
SIGNAL
CONDITIONING
AND
ANALOG
MULTIPLEXER
SRC
D2−
VCCP
LIMIT
COMPARATORS
10-BIT
ADC
VALUE AND
LIMIT
REGISTERS
BAND GAP
REFERENCE
BAND GAP
TEMP. SENSOR
* PIN FUNCTION OLNY AVAILABLE ON THE ADT7473−1
GND
Figure 1. Functional Block Diagram
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameter
Rating
Unit
3.6
V
−0.3 to +3.6
V
Input Current at any Pin
±5.0
mA
Package Input Current
±20
mA
150
°C
−65 to +150
°C
Positive Supply Voltage (VCC)
Voltage on any Input or Output Pin
Maximum Junction Temperature (TJ MAX)
Storage Temperature Range
°C
Lead Temperature, Soldering
IR Reflow Peak Temperature
Lead Temperature (Soldering, 10 sec)
260
300
ESD Rating
1,500
V
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
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2
ADT7473
Table 2. THERMAL CHARACTERISTICS
Package Type
16-lead QSOP
NOTE:
qJA
qJC
Unit
150
39
°C/W
qJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
Table 3. PIN ASSIGNMENT
Pin No.
Mnemonic
1
SCL
Digital Input (Open Drain). SMBus serial clock input. Requires SMBus pullup.
2
GND
Ground Pin.
3
VCC
Power Supply. Powered by 3.3 V.
4
TACH3
ADDR SELECT
5
PWM2
SMBALERT
THERM_LATCH
Description
Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3.
If in address select mode, the logic state of this pin defines the SMBus device address.
Digital Output (Open Drain). ADT7473 default pin function is PWM2. Requires 10 kW typical pullup.
Pulse-width modulated output to control Fan 2 speed. Can be configured as a high or low frequency
drive.
On the ADT7473, this pin can be reconfigured as an SMBALERT interrupt output to signal out-of-limit
conditions.
ADT7473−1 default pin function. THERM_LATCH is a thermal event alert signal when an
overtemperature condition occurs.
6
TACH1
Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1.
7
TACH2
Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 2.
8
PWM3
Digital I/O (Open Drain). Pulse-width modulated output to control the speed of Fan 3 and Fan 4.
Requires 10 kW typical pullup. Can be configured as a high or low frequency drive.
If pulled low on powerup, the ADT7473−1 enters address select mode, and the state of Pin 4
(ADDR SELECT) determines the ADT7473−1 slave address.
ADDREN
9
TACH4
GPIO
THERM
SMBALERT
Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4.
General Purpose Open Drain Digital I/O.
Bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input as well as
to assert when an ADT7473 THERM overtemperature limit is exceeded. For example, the pin can be
connected to the PROCHOT output of an IntelR PentiumR 4 processor or to the output of a trip point
temperature sensor. Can be used as an output to signal overtemperature conditions.
Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt output to signal
out-of-limit conditions.
10
D2−
Cathode Connection to Second Thermal Diode.
11
D2+
Anode Connection to Second Thermal Diode.
12
D1−
Cathode Connection to First Thermal Diode.
13
D1+
Anode Connection to First Thermal Diode.
14
VCCP
Analog Input. Monitors processor core voltage (0 V to 3.0 V).
15
PWM1
16
XTO
Digital Output (Open Drain). Pulse-width modulated output to control Fan 1 speed. Requires 10 kW
typical pullup.
Also functions as the output from the XNOR tree in XNOR test mode.
SDA
Digital I/O (Open Drain). SMBus bidirectional serial data. Requires 10 kW typical pullup.
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3
ADT7473
Table 4. ELECTRICAL CHARACTERISTICS (TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.) (Note 1)
Parameter
Conditions
Min
Typ
Max
Unit
3.0
3.3
3.6
V
Interface Inactive, ADC Active
−
1.5
3.0
mA
0°C ≤ TA ≤ 85°C
−40°C ≤ TA ≤ +125°C
−
−
−
±0.5
−
0.25
±1.5
±2.5
−
°C
0°C ≤ TA ≤ 85°C
−40°C ≤ TA ≤ +125°C
−
−
−
±0.5
−
0.25
±1.5
±2.5
−
°C
First Current
Second Current
Third Current
−
−
−
6
36
96
−
−
−
mA
−
−
±1.5
%
−
−
±1.0
LSB
Power Supply
Supply Voltage
Supply Current, ICC
Temperature-to-Digital Converter
Local Sensor Accuracy
Resolution
Remote Diode Sensor Accuracy
Resolution
Remote Sensor Source Current
Analog-to-Digital Converter (Including MUX and Attentuators)
Total Unadjusted Error (TUE)
Differential Nonlinearity (DNL)
8 Bits
−
±0.1
−
%/V
Conversion Time (Voltage Input)
Averaging Enabled
−
11
−
ms
Conversion Time (Local Temperature)
Averaging Enabled
−
12
−
ms
Conversion Time (Remote Temperature)
Averaging Enabled
−
38
−
ms
Total Monitoring Cycle Time
Averaging Enabled
Averaging Disabled
−
−
145
19
−
−
ms
Input Resistance
For VCCP Channel
70
120
−
kW
0°C ≤ TA ≤ 70°C
−40°C ≤ TA ≤ +120°C
−
−
−
−
±6.0
±10
%
−
−
65,535
−
−
−
−
109
329
5,000
10,000
−
−
−
−
RPM
−
−
8.0
mA
Power Supply Sensitivity
Fan RPM-to-Digital Converter
Accuracy
Full-scale Count
Nominal Input RPM
Fan Count = 0xBFFF
Fan Count = 0x3FFF
Fan Count = 0x0438
Fan Count = 0x021C
Open-Drain Digital Outputs, PWM1 to PWM3, XTO
Current Sink, IOL
Output Low Voltage, VOL
IOUT = −8.0 mA
−
−
0.4
V
High Level Output Current, IOH
VOUT = VCC
−
0.1
20
mA
Open-Drain Serial Data Bus Output (SDA)
Output Low Voltage, VOL
IOUT = −4.0 mA
−
−
0.4
V
High Level Output Current, IOH
VOUT = VCC
−
0.1
1.0
mA
Output High Voltage, VOH
0.75 × VCC
−
−
V
Output Low Voltage, VOL
−
−
0.4
V
Input High Voltage, VIH
2.0
−
−
V
Input Low Voltage, VIL
−
−
0.4
V
Hysteresis
−
500
−
mV
Digital Output Logic Levels, ADT7473−1 (THERM_LATCH) ADTL+
SMBus Digital Inputs (SCL, SDA)
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ADT7473
Table 4. ELECTRICAL CHARACTERISTICS (TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.) (Note 1)
Parameter
Conditions
Min
Typ
Max
Unit
2.0
−
−
−
−
3.6
V
Maximum Input Voltage
−
−0.3
−
−
0.8
−
V
Minimum Input Voltage
−
0.5
−
V p-p
Input High Voltage, VIH
0.75 × VCC
−
−
V
Input Low Voltage, VIL
−
−
0.8
V
Input High Voltage, VIH
−
−
−
Digital Input Logic Levels (TACH Inputs)
Input High Voltage, VIH
Input Low Voltage, VIL
Hysteresis
Digital Input Logic Levels (THERM) ADTL+
Input Low Voltage, VIL
VIN = VCC
−
±1
−
mA
Input Low Current, IIL
VIN = 0
−
±1
−
mA
−
5.0
−
pF
Clock Frequency, fSCLK
10
−
400
kHz
Glitch Immunity, tSW
−
−
50
ns
Bus Free Time, tBUF
4.7
−
−
ms
SCL Low Time, tLOW
4.7
−
−
ms
SCL High Time, tHIGH
4.0
−
50
ms
−
−
1,000
ns
Input Capacitance, CIN
Serial Bus Timing (Note 2) (See Figure 2)
SCL, SDA Rise Time, tr
SCL, SDA Fall Time, tf
Data Setup Time, tSU; DAT
Detect Clock Low Timeout, tTIMEOUT
Can be Optionally Disabled
−
−
300
ms
250
−
−
ns
15
−
35
ms
1. All voltages are measured with respect to GND, unless otherwise noted. Typicals are at TA = 25°C and represent most likely parametric norm.
Logic inputs accept input high voltages up to VMAX, even when the device is operating down to VMIN. Timing specifications are tested at logic
levels of VIL = 0.8 V for a falling edge and VIH = 2.0 V for a rising edge.
2. Serial management bus (SMBus) timing specifications are guaranteed by design and are not production tested.
tF
t LOW
t HD; STA
tR
SCL
t HD; STA
t HD; DAT
t HIGH
t SU; STA
t SU; DAT
t SU; STO
SDA
t BUF
P
S
S
Figure 2. Serial Bus Timing Diagram
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5
P
ADT7473
TYPICAL PERFORMANCE CHARACTERISTICS
0
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
60
40
20
D+ To GND
0
D+ To VCC
−20
−40
−60
0
10
20
30
40
50
60
70
80
−10
−20
−30
−40
−50
−60
90 100
0
2
4
6
RESISTANCE (MW)
10 12 14 16 18 20 22
CAPACITANCE (nF)
Figure 3. Remote Temperature Error vs. PCB
Resistance
Figure 4. Temperature Error vs. Capacitance
Between D+ and D−
30
70
25
100 mV
20
60 mV
15
60
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
8
10
5
0
50
40
30
100 mV
20
40 mV 60 mV
10
0
40 mV
−5
−10
0
100M
200M
300M
400M
500M
600M
0
100M
NOISE FREQUENCY (Hz)
200M
300M
400M
500M
600M
NOISE FREQUENCY (Hz)
Figure 5. Remote Temperature Error vs.
Common-Mode Noise Frequency
Figure 6. Remote Temperature Error vs.
Common-Mode Noise Frequency
1.20
15
TEMPERATURE ERROR (°C)
1.18
1.16
1.14
IDD (mA)
1.12
1.10
1.08
1.06
1.04
1.02
10
5
100 mV
0
250 mV
−5
−10
1.00
0.98
3.0
−15
3.1
3.2
3.3
3.4
3.5
3.6
0
VDD (V)
100M
200M
300M
400M
500M
FREQUENCY (Hz)
Figure 7. Normal IDD vs. Power Supply
Figure 8. Internal Temperature Error vs.
Frequency
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6
600M
ADT7473
TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)
TEMPERATURE ERROR (°C)
6
4
250 mV
2
0
−2
100 mV
−4
−6
−8
−10
−12
0
100M
200M
300M
400M
500M
600M
FREQUENCY (Hz)
Figure 9. Remote Temperature Error vs. Power
Supply Noise Frequency
TEMPERATURE ERROR (°C)
3.0
2.5
2.0
1.5
1.0
0.5
0
−0.5
−1.0
−1.5
−2.0
−40 −20
0
20
40
60
85
105 125
OIL BATH TEMPERATURE (°C)
Figure 10. Internal Temperature Error vs. Temperature
TEMPERATURE ERROR (°C)
3.0
2.5
2.0
1.5
1.0
0.5
0
−0.5
−1.0
−1.5
−40 −20
0
20
40
60
85
105 125
OIL BATH TEMPERATURE (°C)
Figure 11. Remote Temperature Error vs. Temperature
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ADT7473
• A high frequency PWM drive can be independently
Product Description
The ADT7473/ADT7473−1 is a complete thermal
monitor and multiple fan controller for any system requiring
thermal monitoring and cooling. The device communicates
with the system via a serial system management bus. The
serial bus controller has a serial data line for reading and
writing addresses and data (Pin 16), and an input line for the
serial clock (Pin 1). All control and programming functions
for the ADT7473/ADT7473−1 are performed over the serial
bus. Additionally, a pin can be reconfigured as an
SMBALERT output to signal out-of-limit conditions.
Table 5 illustrates the differences between the ADT7473
and the ADT7473−1.
•
•
•
Table 5. ADT7473/ADT7473−1 DEVICE COMPARISON
Feature
ADT7473
•
ADT7473−1
Pin 5
Default: PWM2
Default:
THERM_LATCH
SMBus Address
Fixed Address
Address
selectable
Remote Ch. 2
Therm Limit
= 100°C
= 136°C
Register 0x30,
0x31, 0x32
Default: 0x00
Default: 0xFF
Register 0x3F
Revision Reg
Default: 0x68
Default: 0x69
Register 0x40,
Bit 7
Reserved
(R/W) 1 = Reset
Latch (Lockable)
Register 0x42,
Bit 0
Reserved
•
selected for each PWM channel on the
ADT7473/ADT7473−1. This is not available on the
ADT7467.
The range and resolution of the temperature offset
register can be changed from a ±64°C range at 0.5°C
resolution to a ±128°C range at 1°C resolution. This is
not available on the ADT7467.
THERM overtemperature events can be
disabled/enabled individually on each temperature
channel. This is not available on the ADT7467.
Bit 7 of Configuration Register 1 is no longer supported
because the ADT7473/ADT7473−1 cannot be powered
via a 5.0 V supply.
Bit 0 of Configuration Register 1 (0x40) remains
writable after the lock bit is set. This bit enables
monitoring.
2-wire fan speed measurement is not supported on the
ADT7473/ADT7473−1.
How to Set the Functionality of Pin 9
Pin 9 on the ADT7473/ADT7473−1 has four possible
functions: SMBALERT, THERM, GPIO, and TACH4. The
user chooses the required functionality by setting Bit 0 and
Bit 1 of Configuration Register 4 (0x7D).
Table 6. PIN 9 SETTINGS
(Read-only)
1 = THERM
Limit Latched
Bit 0
Bit 1
0
0
TACH4
0
1
THERM
1
0
GPIO
1
1
SMBALERT
Function
Registers 0x5C,
0x5D, 0x5E
Default: 0x82
Default: 0x62
Register 0x7C,
Bit 4
Reserved
THERM Output
Hysteresis
Register 0x7D,
Bit 4
Reserved
THERM_LATCH
Recommended Implementation
Configuration
Configuring the ADT7473 as shown in Figure 12 allows
the system designer to use the following features:
• Two PWM outputs for fan control of up to three fans.
(The front and rear chassis fans are connected in
parallel.)
• Three TACH fan speed measurement inputs.
• VCC measured internally through Pin 3.
• CPU temperature measured using Remote 1
temperature channel.
• Ambient temperature measured through Remote 2
temperature channel.
• Bidirectional THERM pin. This feature allows
Intel® Pentium® 4 PROCHOT monitoring and can
function as an overtemperature THERM output. It can
alternatively be programmed as an SMBALERT system
interrupt output.
0 = Remote
Channel 2
1 = Remote
Channel 1
and Remote
Channel 2
Comparison Between ADT7467 and
ADT7473/ADT7473−1
The following list shows some comparisons between the
ADT7467 and the ADT7473/ADT7473−1:
• The ADT7473/ADT7473−1 can be powered via a
3.3 V supply only, and does not support 5.0 V
operation, while the ADT7467 does. Violating this
specification results in irreversible damage to the
ADT7473/ADT7473−1. See the Specifications section
for more information.
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ADT7473
CPU FAN
ADT7473
PWM1
TACH2
TACH1
FRONT
CHASSIS
FAN
REAR
CHASSIS
FAN
PWM3
D2+
TACH3
D2−
THERM
CPU
PROCHOT
D1+
AMBIENT
TEMPERATURE
SDA
D1−
SCL
SMBALERT
GND
ICH
Figure 12. ADT7473 Configuration
VCC
Serial Bus Interface
On PCs and servers, control of the ADT7473/ADT7473−1
is carried out using the SMBus. The ADT7473/ADT7473−1
is connected to this bus as a slave device, under the control of
a master controller, which is usually (but not necessarily) the
ICH.
The ADT7473 has a fixed 7-bit serial bus address of
0101110 or 0x2E. The read/write bit must be added to get the
8-bit address (01011100 or 0x5C). When the ADT7473−1
is powered up with Pin 8 (PWM3/ADDREN) high, the
ADT7473−1 has a default SMBus address of 0101110 or
0x2E. If more than one ADT7473−1 is used in a system,
each ADT7473−1 is placed in ADDR SELECT mode by
strapping Pin 8 low on powerup. The logic state of Pin 4
then determines the device’s SMBus address. The logic of
these pins is sampled on powerup.
The device address is sampled on powerup and latched on
the first valid SMBus transaction, more precisely on the
low-to-high transition at the beginning of the eighth SCL
pulse, when the serial bus address byte matches the selected
slave address. The selected slave address is chosen using the
ADDREN pin/ADDR SELECT pin. Any attempted change
in the address has no effect after this.
ADT7473−1
ADDR SELECT
PWM3/
ADDREN
ADT7473−1
ADDR SELECT
PWM3/
ADDREN
0
Low (10 kW to GND)
0101100 (0x2C)
0
High (10 kW Pullup)
0101101 (0x2D)
1
Don’t Care
0101110 (0x2E)
4
10 kW
8
ADDRESS = 0x2C
Figure 14. SMBus Address = 0x2C (Pin 4 = 0)
VCC
ADT7473−1
PWM3/
ADDR_EN
Address
8
Figure 13. Default SMBus Address = 0x2E
ADDR SELECT
Pin 14 State
10 kW
ADDRESS = 0x2E
Table 7. HARDWIRING THE ADT7473−1 SMBUS
DEVICE ADDRESS
Pin 13 State
4
10 kW
4
8
ADDRESS = 0x2D
Figure 15. SMBus Address = 0x2D (Pin 4 = 1)
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ADT7473
data from it, the address pointer register must be set so the
correct data register is addressed, and then data can be
written into that register or read from it. The first byte of a
write operation always contains an address that is stored in
the address pointer register. If data is written to the device,
the write operation contains a second data byte that is written
to the register selected by the address pointer register.
This write operation is shown in Figure 17. The device
address is sent over the bus, and then R/W is set to 0. This
is followed by two data bytes. The first data byte is the
address of the internal data register to be written to, which
is stored in the address pointer register. The second data byte
is the data to be written to the internal data register.
When reading data from a register, there are two
possibilities:
1. If the ADT7473/ADT7473−1’s address pointer
register value is unknown or not the desired value,
it must first be set to the correct value before data
can be read from the desired data register. This is
done by performing a write to the
ADT7473/ADT7473−1, but only the data byte
containing the register address is sent, because no
data is written to the register. This is shown in
Figure 18.
A read operation is then performed consisting of
the serial bus address, R/W bit set to 1, followed
by the data byte read from the data register. This is
shown in Figure 19.
2. If the address pointer register is known to be
already at the desired address, data can be read
from the corresponding data register without first
writing to the address pointer register, as shown in
Figure 19.
VCC
ADT7473−1
ADDR SELECT
PWM3/
ADDREN
10 kW
4
8
NC
DO NOT LEAVE ADDREN
UNCONNECTED! CAN CAUSE
UNPREDICTABLE ADDRESSES.
CARE SHOULD BE TAKEN TO ENSURE THAT PIN 8
(PWM3/ADDREN) IS EITHER TIED HIGH OR LOW. LEAVING PIN 8
FLOATING COULD CAUSE THE ADT7473−1 TO POWER UP WITH
AN UNEXPECTED ADDRESS.
NOTE THAT IF THE ADT7473−1 IS PLACED INTO ADDR SELECT
MODE, PINS 8 AND 4 CAN BE USED AS THE ALTERNATE
FUNCTIONS (PWM3, TACH4/THERM) UNLESS THE CORRECT
CIRCUIT IS MUXED IN AT THE CORRECT TIME OR DESIGNED
TO HANDLE THESE DUAL FUNCTIONS.
Figure 16. Unpredictable SMBus Address if Pin 8
is Unconnected
The ability to make hardwired changes to the SMBus
slave address allows the user to avoid conflicts with other
devices sharing the same serial bus, for example, if more
than one ADT7473−1 is used in a system.
Data is sent over the serial bus in sequences of nine clock
pulses: eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period because a low-to-high
transition when the clock is high might be interpreted as a
stop signal. The number of data bytes that can be transmitted
over the serial bus in a single read or write operation is
limited only by what the master and slave devices can
handle.
When all data bytes have been read or written, stop
conditions are established. In write mode, the master pulls
the data line high during the tenth clock pulse to assert a stop
condition. In read mode, the master device overrides the
acknowledge bit by pulling the data line high during the low
period before the ninth clock pulse; this is known as No
Acknowledge. The master takes the data line low during the
low period before the tenth clock pulse, and then high during
the tenth clock pulse to assert a stop condition.
Any number of bytes of data can be transferred over the
serial bus in one operation, but it is not possible to mix read
and write in one operation, because the type of operation is
determined at the beginning and cannot subsequently be
changed without starting a new operation.
In the ADT7473/ADT7473−1, write operations contain
either one or two bytes, and read operations contain one
byte. To write data to one of the device data registers or read
It is possible to read a data byte from a data register
without first writing to the address pointer register, if the
address pointer register is already at the correct value.
However, it is not possible to write data to a register without
writing to the address pointer register, because the first data
byte of a write is always written to the address pointer
register.
In addition to supporting the send byte and receive byte
protocols, the ADT7473/ADT7473−1 also supports the read
byte protocol. (See System Management Bus (SMBus)
Specifications Version 2 for more information; this
document is available from Intel.)
If several read or write operations must be performed in
succession, the master can send a repeat start condition
instead of a stop condition to begin a new operation.
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10
ADT7473
1
9
9
1
SCL
0
SDA
1
0
1
1
0
1
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ACK. BY
ADT7473/ADT7473−1
ADT7473/ADT7473−1
FRAME 1
FRAME 2
SERIAL BUS ADDRESS BYTE
ADDRESS POINTER REGISTER BYTE
START BY
MASTER
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY STOP BY
FRAME 3 ADT7473/ADT7473−1 MASTER
DATA BYTE
Figure 17. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
9
9
1
SCL
SDA
0
1
0
1
1
1
0
D7
R/W
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ACK. BY
ADT7473/ADT7473−1
FRAME 1
FRAME 2 ADT7473/ADT7473−1
SERIAL BUS ADDRESS BYTE
ADDRESS POINTER REGISTER BYTE
START BY
MASTER
STOP BY
MASTER
Figure 18. Writing to the Address Pointer Register Only
9
1
1
9
SCL
SDA
0
START BY
MASTER
1
0
1
1
1
0
D7 D6 D5 D4 D3 D2 D1 D0
R/W
ACK. BY
NO ACK. BY STOP BY
ADT7473/ADT7473−1
MASTER
MASTER
FRAME 2
FRAME 1
SERIAL BUS ADDRESS BYTE
DATA BYTE FROM ADT7473
Figure 19. Reading Data from a Previously Selected Register
Write Operations
4. The master sends a command code.
5. The slave asserts ACK on SDA.
6. The master asserts a stop condition on SDA and
the transaction ends.
The SMBus specification defines several protocols for
various read and write operations. The ADT7473/
ADT7473−1 uses the following SMBus write protocols. The
following abbreviations are used in the diagrams:
S − Start
P − Stop
R − Read
W − Write
A − Acknowledge
A − No Acknowledge
For the ADT7473/ADT7473−1, the send byte protocol is
used to write a register address to RAM for a subsequent
single-byte read from the same address. This operation is
illustrated in Figure 20.
1
2
3
SLAVE
S
W A
ADDRESS
Send Byte
4
5 6
REGISTER
ADDRESS
A P
Figure 20. Setting a Register Address for
Subsequent Read
In this operation, the master device sends a single
command byte to a slave device, as follows:
1. The master device asserts a start condition on
SDA.
2. The master sends the 7-bit slave address followed
by the write bit (active low).
3. The addressed slave device asserts ACK on SDA.
If the master is required to read data from the register
immediately after setting up the address, it can assert a repeat
start condition immediately after the final ACK and carry
out a single-byte read without asserting an intermediate stop
condition.
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11
ADT7473
Write Byte
connected to a common SMBALERT line connected to the
master. If a device’s SMBALERT line goes low, the
following events occur:
• SMBALERT is pulled low.
• The master initiates a read operation and sends the alert
response address (ARA = 0001 100). This is a general
call address that must not be used as a specific device
address.
• The device whose SMBALERT output is low responds
to the alert response address, and the master reads its
device address. The address of the device is now known
and can be interrogated in the usual way.
• If more than one device’s SMBALERT output is low,
the one with the lowest device address has priority in
accordance with normal SMBus arbitration.
In this operation, the master device sends a command byte
and one data byte to the slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address followed
by the write bit (active low).
3. The addressed slave device asserts ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
6. The master sends a data byte.
7. The slave asserts ACK on SDA.
8. The master asserts a stop condition on SDA, and
the transaction ends.
The single byte write operation is illustrated in Figure 21.
1
2
3
SLAVE
S ADDRESS W A
4
5
REGISTER
ADDRESS
A
6
7
8
DATA A P
Once the ADT7473/ADT7473−1 has responded to the
alert response address, the master must read the status
registers, and the SMBALERT is cleared only if the error
condition is gone.
Figure 21. Single-byte Write to a Register
Read Operations
SMBus Timeout
The ADT7473/ADT7473−1 uses the following SMBus
read protocols.
The ADT7473/ADT7473−1 includes an SMBus timeout
feature. If there is no SMBus activity for 35 ms, the
ADT7473/ADT7473−1 assumes the bus is locked and
releases the bus. This prevents the device from locking or
holding the SMBus expecting data. Some SMBus
controllers cannot work with the SMBus timeout feature, so
it can be disabled.
Receive Byte
This operation is useful when repeatedly reading a single
register. The register address must have been previously set
up. In this operation, the master device receives a single byte
from a slave device, as follows:
1. The master device asserts a start condition on
SDA.
2. The master sends the 7-bit slave address followed
by the read bit (high).
3. The addressed slave device asserts ACK on SDA.
4. The master receives a data byte.
5. The master asserts NO ACK on SDA.
6. The master asserts a stop condition on SDA, and
the transaction ends.
Table 8. CONFIGURATION REGISTER 1 (REG. 0X40)
Bit
<6> TODIS
2
3
SLAVE
S ADDRESS R A
4
5 6
DATA
A P
0: SMBus Timeout Enabled (Default)
1: SMBus Timeout Disabled
Voltage Measurement Input
The ADT7473/ADT7473−1 has one external voltage
measurement channel and can also measure its own supply
voltage, VCC. Pin 14 can measure VCCP. The VCC supply
voltage measurement is carried out through the VCC pin
(Pin 3). The VCCP input can be used to monitor a chipset
supply voltage in computer systems.
In the ADT7473/ADT7473−1, the receive byte protocol
is used to read a single byte of data from a register whose
address has previously been set by a send byte or write byte
operation. This operation is illustrated in Figure 22.
1
Description
Analog-to-Digital Converter
All analog inputs are multiplexed into the on-chip,
successive approximation, analog-to-digital converter.
(ADC) This has a resolution of 10 bits. The basic input range
is 0 V to 2.25 V, but the input has built-in attenuators to
allow measurement of VCCP without any external
components. To allow for the tolerance of the supply
voltage, the ADC produces an output of 3/4 full scale
(768 decimal or 300 hexadecimal) for the nominal input
voltage and thus has adequate headroom to deal with
overvoltages.
Figure 22. Single-byte Read from a Register
Alert Response Address
Alert response address (ARA) is a feature of SMBus
devices that allows an interrupting device to identify itself
to the host when multiple devices exist on the same bus.
The SMBALERT output can be used as either an interrupt
output or an SMBALERT. One or more outputs can be
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12
ADT7473
Input Circuitry
results averaged before being placed into the value register.
When faster conversions are needed, setting BitĂ4 of
Configuration RegisterĂ2 (0x73) turns averaging off. This
effectively gives a reading 16Ătimes faster (711Ăms), but the
reading may be noisier.
The internal structure for the VCCP analog input is shown
in Figure 23. The input circuit consists of an input protection
diode, an attenuator, plus a capacitor to form a first order
low-pass filter that provides the input immunity to high
frequency noise.
Bypass Voltage Input Attenuator
17.5 kW
Setting BitĂ5 of Configuration RegisterĂ2 (0x73) removes
the attenuation circuitry from the VCCP input. This allows
the user to directly connect external sensors or to rescale the
analog voltage measurement inputs for other applications.
The input range of the ADC without the attenuators is 0ĂV
to 2.25ĂV.
VCCP
52.5 kW
35 pF
Figure 23. Structure of Analog Inputs
Single-channel ADC Conversion
Table 9. VOLTAGE MEASUREMENT REGISTERS
Register
Description
Default
0x21
VCCP Reading
0x00
0x22
VCCP Reading
0x00
Setting BitĂ6 of Configuration RegisterĂ2 (0x73) places
the ADT7473/ADT7473−1 into single-channel ADC
conversion mode. In this mode, the ADT7473/ADT7473−1
can be made to read a single voltage channel only. If the
internal ADT7473/ADT7473−1 clock is used, the selected
input is read every 711Ăms. The appropriate ADC channel is
selected by writing to BitsĂ<7:5> of the TACH1 minimum
high byte register (0x55).
VCCP Limit Registers
Associated with the VCCP measurement channel is a high
and low limit register. Exceeding the programmed high or
low limit causes the appropriate status bit to be set.
Exceeding either limit can also generate SMBALERT
interrupts.
Table 11. PROGRAMMING SINGLE-CHANNEL
ADC MODE
Bits <7:5>, Register 0x55
Table 10. VCCP LIMIT REGISTERS
Register
Description
Default
0x46
VCCP Low Limit
0x00
0x47
VCCP High Limit
0xFF
Table 13 shows the input ranges of the analog inputs and
output codes of the 10-bit ADC.
When the ADC is running, it samples and converts a
voltage input in 711Ăms and averages 16Ăconversions to
reduce noise; a measurement takes nominally 11.38Ăms.
Channel Selected
001
VCCP
010
VCC
101
Remote 1 Temperature
110
Local Temperature
111
Remote 2 Temperature
Table 12. CONFIGURATION REGISTER 2 (REG. 0X73)
Bit
Description
<4>
1: Averaging Off
Additional ADC Functions for Voltage Measurements
<5>
1: Bypass Input Attenuators
A number of other functions are available on the
ADT7473/ADT7473−1 to offer the system designer
increased flexibility.
<6>
1: Single-channel Convert Mode
TACH1 Minimum High Byte Register (0x55)
Bits <7:5> select ADC channel for single-channel convert
mode.
Turn-off Averaging
For each voltage measurement read from a value register,
16 readings have actually been made internally and the
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13
ADT7473
Table 13. 10-BIT ADC OUTPUT CODE VS. VIN
ADC Output
VCC (3.3 VIN) (Note 1)
VCCP
Decimal
Binary (10 Bits)
<0.0042
<0.00293
0
00000000 00
0.0042 to 0.0085
0.0293 to 0.0058
1
00000000 01
0.0085 to 0.0128
0.0058 to 0.0087
2
00000000 10
0.0128 to 0.0171
0.0087 to 0.0117
3
00000000 11
0.0171 to 0.0214
0.0117 to 0.0146
4
00000001 00
0.0214 to 0.0257
0.0146 to 0.0175
5
00000001 01
0.0257 to 0.0300
0.0175 to 0.0205
6
00000001 10
0.0300 to 0.0343
0.0205 to 0.0234
7
00000001 11
0.0343 to 0.0386
0.0234 to 0.0263
8
00000010 00
−
−
−
−
1.100 to 1.1042
0.7500 to 0.7529
256 (1/4 scale)
01000000 00
−
−
−
−
2.200 to 2.2042
1.5000 to 1.5029
512 (1/2 scale)
10000000 00
−
−
−
−
3.300 to 3.3042
2.2500 to 2.2529
768 (3/4 scale)
11000000 00
−
−
−
−
4.3527 to 4.3570
2.9677 to 2.9707
1013
11111101 01
4.3570 to 4.3613
2.9707 to 2.9736
1014
11111101 10
4.3613 to 4.3656
2.9736 to 2.9765
1015
11111101 11
4.3656 to 4.3699
2.9765 to 2.9794
1016
11111110 00
4.3699 to 4.3742
2.9794 to 2.9824
1017
11111110 01
4.3742 to 4.3785
2.9824 to 2.9853
1018
11111110 10
4.3785 to 4.3828
2.9853 to 2.9882
1019
11111110 11
4.3828 to 4.3871
2.9882 to 2.9912
1020
11111111 00
4.3871 to 4.3914
2.9912 to 2.9941
1021
11111111 01
4.3914 to 4.3957
2.9941 to 2.9970
1022
11111111 10
>4.3957
>2.9970
1023
11111111 11
1. The VCC output codes listed assume that VCC is 3.3 V.
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14
ADT7473
DV BE + kTńq
Temperature Measurement Method
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, measuring
the base-emitter voltage (VBE) of a transistor operated at
constant current. Unfortunately, this technique requires
calibration to null out the effect of the absolute value of VBE,
which varies from device to device.
The technique used in the ADT7473/ADT7473−1
measures the change in VBE when the device is operated at
three different currents. Previous devices have used only
two operating currents, but the use of a third current allows
automatic cancellation of resistances in series with the
external temperature sensor.
Figure 24 shows the input signal conditioning used to
measure the output of an external temperature sensor. This
figure shows the external sensor as a substrate transistor, but
it could equally be a discrete transistor. If a discrete
transistor is used, the collector is not grounded and should
be linked to the base. To prevent ground noise from
interfering with the measurement, the more negative
terminal of the sensor is not referenced to ground, but is
biased above ground by an internal diode at the D− input. C1
can optionally be added as a noise filter (recommended
maximum value 1,000 pF). However, a better option in
noisy environments is to add a filter, as described in the
Noise Filtering section.
ln(N)
(eq. 1)
where:
k is Boltzmann’s constant.
T is the absolute temperature in Kelvin.
q is the charge on the carrier.
N is the ratio of the two currents.
Figure 24 shows the input signal conditioning used to
measure the output of a remote temperature sensor. This
figure shows the external sensor as a substrate transistor,
provided for temperature monitoring on some
microprocessors. It could also be a discrete transistor such
as a 2N3904/2N3906.
Table 14. TWOS COMPLEMENT TEMPERATURE DATA
FORMAT
Temperature
Local Temperature Measurement
The ADT7473/ADT7473−1 contains an on-chip band gap
temperature sensor whose output is digitized by the on-chip
10-bit ADC. The 8-bit MSB temperature data is stored in the
local temperature register (0x26). Because both positive and
negative temperatures can be measured, the temperature
data is stored in Offset 64 format or twos complement
format, as shown in Table 14 and Table 15. Theoretically,
the temperature sensor and ADC can measure temperatures
from −63°C to +127°C (or −63°C to +191°C in the extended
temperature range) with a resolution of +0.25°C. However,
this exceeds the operating temperature range of the device,
so local temperature measurements outside the
ADT7473/ADT7473−1 operating temperature range are not
possible.
Digital Output (10-bit) (Note 1)
–128°C
1000 0000 00 (Diode Fault)
–63°C
1100 0001 00
–50°C
1100 1110 00
–25°C
1110 0111 00
–10°C
1111 0110 00
0°C
0000 0000 00
10.25°C
0000 1010 01
25.5°C
0001 1001 10
50.75°C
0011 0010 11
75°C
0100 1011 00
100°C
0110 0100 00
125°C
0111 1101 00
127°C
0111 1111 00
1. Bold numbers denote 2 LSBs of measurement in the Extended
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
Table 15. EXTENDED RANGE, TEMPERATURE DATA
FORMAT
Temperature
Digital Output (10-bit) (Note 1)
–64°C
0000 0000 00 (Diode Fault)
–63°C
0000 0001 00
–1°C
0011 1111 00
0°C
0100 0000 00
Remote Temperature Measurement
1°C
0100 0001 00
The ADT7473/ADT7473−1 can measure the temperature
of two remote diode sensors or diode-connected transistors
connected to Pin 10 and Pin 11 or to Pin 12 and Pin 13.
The forward voltage of a diode or diode-connected
transistor operated at a constant current exhibits a negative
temperature coefficient of about −2 mV/°C. Unfortunately,
the absolute value of VBE varies from device to device and
individual calibration is required to null this out, so the
technique is unsuitable for mass production. The technique
used in the ADT7473/ADT7473−1 is to measure the change
in VBE when the device is operated at three different
currents. This is given by:
10°C
0100 1010 00
25°C
0101 1001 00
50°C
0111 0010 00
75°C
1000 1001 00
100°C
1010 0100 00
125°C
1011 1101 00
191°C
1111 1111 00
1. Bold numbers denote 2 LSBs of measurement in the Extended
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
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15
ADT7473
N2 × I
I
N1 × I
VDD
IBIAS
VOUT+
D+
REMOTE
SENSING
TRANSISTOR
To ADC
D−
VOUT−
LOW-PASS FILTER
fC = 65 kHz
Figure 24. Signal Conditioning for Remote Diode Temperature Sensors
waveform to produce a dc voltage proportional to DVBE.
The ADC digitizes this voltage, and a temperature
measurement is produced. To reduce the effects of noise,
digital filtering is performed by averaging the results of 16
measurement cycles.
The results of remote temperature measurements are
stored in 10-bit, twos complement format, as listed in
Table 10. The extra resolution for the temperature
measurements is held in the Extended Resolution Register 2
(0x77). This gives temperature readings with a resolution of
0.25°C.
If a discrete transistor is used, the collector is not grounded
and should be linked to the base. If a PNP transistor is used,
the base is connected to the D– input and the emitter is
connected to the D+ input. If an NPN transistor is used, the
emitter is connected to the D– input and the base is
connected to the D+ input. Figure 25 and Figure 26 show
how to connect the ADT7473/ADT7473−1 to an NPN or
PNP transistor for temperature measurement. To prevent
ground noise from interfering with the measurement, the
more negative terminal of the sensor is not referenced to
ground, but is biased above ground by an internal diode at
the D– input.
Noise Filtering
For temperature sensors operating in noisy environments,
previous practice was to place a capacitor across the D+ pin
and the D− pin to help combat the effects of noise. However,
large capacitances affect the accuracy of the temperature
measurement, leading to a recommended maximum
capacitor value of 1,000 pF. This capacitor reduces the
noise, but does not eliminate it, making use of the sensor
difficult in a very noisy environment.
The ADT7473/ADT7473−1 has a major advantage over
other devices for eliminating the effects of noise on the
external sensor. Using the series resistance cancellation
feature, a filter can be constructed between the external
temperature sensor and the part. The effect of any filter
resistance seen in series with the remote sensor is
automatically canceled from the temperature result.
The construction of a filter allows the ADT7473/
ADT7473−1 and the remote temperature sensor to operate
in noisy environments. Figure 27 shows a low-pass R-C
filter with the following values:
ADT7473/
ADT7473−1
D+
2N3904
NPN
D−
Figure 25. Measuring Temperature by Using an NPN
Transistor
ADT7473/
ADT7473−1
D+
2N3906
PNP
D−
Figure 26. Measuring Temperature by Using a PNP
Transistor
To measure DVBE, the operating current through the
sensor is switched among three related currents. N1 × I and
N2 × I are different multiples of the current I, as shown in
Figure 24. The currents through the temperature diode are
switched between I and N1 × I, giving DVBE1, and then
between I and N2 × I, giving DVBE2. The temperature can
then be calculated using the two DVBE measurements. This
method can also cancel the effect of any series resistance on
the temperature measurement.
The resulting DVBE waveforms are passed through a
65 kHz low-pass filter to remove noise and then to a
chopper-stabilized amplifier. This amplifies and rectifies the
R + 100 W, C + 1 nF
(eq. 1)
This filtering reduces both common-mode noise and
differential noise.
100 W
D+
REMOTE
TEMPERATURE
SENSOR
100 W
1 nF
Figure 27. Filter Between Remote Sensor and
ADT7473/ADT7473−1
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16
D−
ADT7473
Series Resistance Cancellation
programmed to the offset register. It is important to
note that, if more than one offset must be considered,
the algebraic sum of these offsets must be programmed
to the offset register.
Parasitic resistance to the ADT7473/ADT7473−1 D+ and
D− inputs (seen in series with the remote diode) is caused by
a variety of factors including PCB track resistance and track
length. This series resistance appears as a temperature offset
in the remote sensor’s temperature measurement. This error
typically causes a 0.5°C offset per W of parasitic resistance
in series with the remote diode.
The ADT7473/ADT7473−1 automatically cancels out the
effect of this series resistance on the temperature reading,
giving a more accurate result without the need for user
characterization of this resistance. The ADT7473/
ADT7473−1 is designed to automatically cancel up to 3 kW
of resistance, typically. This is transparent to the user by
using an advanced temperature measurement method. This
feature allows resistances to be added to the sensor path to
produce a filter, allowing the part to be used in noisy
environments. See the Noise Filtering section for details.
If a discrete transistor is used with the ADT7473/
ADT7473−1, the best accuracy is obtained by choosing
devices according to the following criteria:
• Base-emitter voltage greater than 0.25 V at 6 mA, at the
highest operating temperature.
• Base-emitter voltage less than 0.95 V at 100 mA, at the
lowest operating temperature.
• Base resistance less than 100 W.
• Small variation in hFE (such as 50 to 150) that indicates
tight control of VBE characteristics.
Transistors, such as 2N3904, 2N3906, or equivalents in
SOT−23 packages, are suitable devices to use.
Factors Affecting Diode Accuracy
Nulling Out Temperature Errors
As CPUs run faster, it becomes more difficult to avoid
high frequency clocks when routing the D+/D– traces
around a system board. Even when recommended layout
guidelines are followed, some temperature errors can still be
attributable to noise coupled onto the D+/D– lines. Constant
high frequency noise usually attenuates or increases
temperature measurements by a linear, constant value.
The ADT7473/ADT7473−1 has temperature offset
registers at Register 0x70 and Register 0x72 for the
Remote 1 and Remote 2 temperature channels. By
performing a one-time calibration of the system, the user can
determine the offset caused by system board noise and null
it out using the offset registers. The offset registers
automatically add a twos complement, 8-bit reading to every
temperature measurement. The LSBs add +0.5°C offset to
the temperature reading so the 8-bit register effectively
allows temperature offsets of up to ±64°C with a resolution
of +0.5°C. This ensures that the readings in the temperature
measurement registers are as accurate as possible.
Remote Sensing Diode
The ADT7473/ADT7473−1 is designed to work with
either substrate transistors built into processors or discrete
transistors. Substrate transistors are generally PNP types with
the collector connected to the substrate. Discrete types can be
either PNP or NPN transistors connected as a diode
(base-shorted to the collector). If an NPN transistor is used,
the collector and base are connected to D+ and the emitter is
connected to D−. If a PNP transistor is used, the collector and
base are connected to D− and the emitter is connected to D+.
To reduce the error due to variations in both substrate and
discrete transistors, a number of factors should be taken into
consideration:
• The ideality factor, nf, of the transistor is a measure of
the deviation of the thermal diode from ideal behavior.
The ADT7473/ADT7473−1 is trimmed for an nf value
of 1.008. Use the following equation to calculate the
error introduced at a temperature, T(°C), when using a
transistor whose nf does not equal 1.008. Refer to the
data sheet for the related CPU to obtain the nf values.
DT + ǒn f * 1.008Ǔń1.008
•
ǒ273.15 K ) TǓ
Table 16. TEMPERATURE OFFSET REGISTERS
(eq. 2)
To factor this in, the user can write the DT value to the
offset register. Then, the ADT7473/ADT7473−1
automatically adds it to or subtracts it from the
temperature measurement.
Some CPU manufacturers specify the high and low
current levels of the substrate transistors. The high
current level of the ADT7473/ADT7473−1, IHIGH, is
96 mA and the low level current, ILOW, is 6 mA. If the
ADT7473/ADT7473−1 current levels do not match the
current levels specified by the CPU manufacturer, it
might be necessary to remove an offset. The CPU’s
data sheet advises whether this offset needs to be
removed and how to calculate it. This offset can be
Register
Description
Default
0x70
Remote 1 Temperature Offset
0x00 (0°C)
0x71
Local Temperature Offset
0x00 (0°C)
0x72
Remote 2 Temperature Offset
0x00 (0°C)
ADT7460/ADT7473/ADT7473−1
Backwards-compatible Mode
By setting Bit 1 of Configuration Register 5 (0x7C), all
temperature measurements are stored in the zone
temperature value registers (Register 0x25, Register 0x26,
and Register 0x27) in twos complement, in the range −63°C
to +127°C. (The ADT7473/ADT7473−1 still makes
calculations based on the Offset 64 extended range and
clamps the results, if necessary.) The temperature limits
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ADT7473
Additional ADC Functions for Temperature
Measurement
must be reprogrammed in twos complement. If a twos
complement temperature below −63°C is entered, the
temperature is clamped to −63°C. In this mode, the diode
fault condition remains −128°C = 1000 0000, while in the
extended temperature range (−64°C to +191°C), the fault
condition is represented by −64°C = 0000 0000.
A number of other functions are available on the
ADT7473/ADT7473−1 to offer the system designer
increased flexibility.
Turn-off Averaging
For each temperature measurement read from a value
register, 16 readings have actually been made internally and
the results averaged before being placed into the value
register. Sometimes it is necessary to take a very fast
measurement. Setting Bit 4 of Configuration Register 2
(0x73) turns averaging off.
Table 17. TEMPERATURE MEASUREMENT
REGISTERS
Register
Description
Default
0x25
Remote 1 Temperature
−
0x26
Local Temperature
−
0x27
Remote 2 Temperature
−
0x77
Extended Resolution 2
0x00
Table 20. CONVERSION TIME WITH AVERAGING
DISABLED
Channel
Table 18. EXTENDED RESOLUTION TEMPERATURE
MEASUREMENT REGISTER BITS
Bit
Mnemonic
<7:6>
TDM2
Measurement Time (ms)
Voltage Channel
0.7
Remote 1 Temperature
Description
Remote 2 Temperature LSBs
Remote 2 Temperature
Local Temperature
<5:4>
LTMP
Local Temperature LSBs
<3:2>
TDM1
Remote 1 Temperature LSBs
7
7
1.3
Table 21. CONVERSION TIME WITH AVERAGING
ENABLED
Temperature Measurement Limit Registers
Associated with each temperature measurement channel
are high and low limit registers. Exceeding the programmed
high or low limit causes the appropriate status bit to be set.
Exceeding either limit can also generate SMBALERT
interrupts.
Channel
Description
Default
0x4E
Remote 1 Temperature Low Limit
0x01
0x4F
Remote 1 Temperature High Limit
0x7F
0x50
Local Temperature Low Limit
0x01
0x51
Local Temperature High Limit
0x7F
0x52
Remote 2 Temperature Low Limit
0x01
0x53
Remote 2 Temperature High Limit
0x7F
11
Remote Temperature
39
Local Temperature
12
Single-channel ADC Conversions
Table 19. TEMPERATURE MEASUREMENT LIMIT
REGISTERS
Register
Measurement Time (ms)
Voltage Channel
Setting Bit 6 of Configuration Register 2 (0x73) places
the ADT7473/ADT7473−1 into single-channel ADC
conversion mode. In this mode, the ADT7473/ADT7473−1
can be made to read a single temperature channel only. The
appropriate ADC channel is selected by writing to Bits
<7:5> of the TACH1 minimum high byte register (0x55).
Table 22. PROGRAMMING SINGLE-CHANNEL ADC
MODE FOR TEMPERATURES
Channel Selected
Bits <7:4>, Register 0x55
Reading Temperature from the ADT7473/ADT7473−1
101
Remote 1 Temperature
It is important to note that the temperature can be read
from the ADT7473/ADT7473−1 as an 8-bit value (with 1°C
resolution) or as a 10-bit value (with 0.25°C resolution). If
only 1°C resolution is required, the temperature readings
can be read back at any time and in no particular order.
If the 10-bit measurement is required, a 2-register read for
each measurement is used. The extended resolution register
(Register 0x77) should be read first. This causes all
temperature reading registers to be frozen until all
temperature reading registers have been read from. This
prevents an MSB reading from being updated while its two
LSBs are being read, and vice versa.
110
Local Temperature
111
Remote 2 Temperature
Configuration Register 2 (0x73)
Bit <4> = 1, Averaging Off.
Bit <6> = 1, Single-channel Convert Mode.
TACH1 Minimum High Byte Register (0x55)
Bits <7:5> select the ADC channel for single-channel
convert mode.
Overtemperature Events
Overtemperature events on any of the temperature
channels can be detected and dealt with automatically in
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ADT7473
automatic fan speed control mode. Register 0x6A to
Register 0x6C are the THERM limits. When a temperature
exceeds its THERM limit, all PWM outputs run at 100%
duty cycle or the maximum PWM duty cycle
(Register 0x38, Register 0x39, and Register 0x3A) if Bit 3
of Configuration Register 4 (0x7D) is set. The fans remain
running at this speed until the temperature drops below
THERM minus hysteresis; this can be disabled by setting the
boost bit in Configuration Register 3 (0x78), Bit 2. The
hysteresis value for that THERM limit is the value
programmed into the hysteresis registers (Register 0x6D
and Register 0x6E). The default hysteresis value is 4°C.
Table 25. THERM LIMIT REGISTER
Register
0x7A
Description
THERM Timer Limit
Default
0x00
16-bit Limits
The fan TACH measurements are 16-bit results. The fan
TACH limits are also 16 bits, consisting of a high byte and
low byte. Because fans running under speed or stalled are
normally the only conditions of interest, only high limits
exist for fan TACHs. Because the fan TACH period is
actually being measured, exceeding the limit indicates a
slow or stalled fan.
THERM LIMIT
Table 26. FAN LIMIT REGISTERS
TEMPERATURE
FANS
Register
HYSTERESIS (°C)
100%
Figure 28. THERM Limit Operation
Limits, Status Registers, and Interrupts
Limit Values
Associated with each measurement channel on the
ADT7473/ADT7473−1 are high and low limits. These can
form the basis of system status monitoring; a status bit can
be set for any out-of-limit condition and is detected by
polling the device. Alternatively, SMBALERT interrupts
can be generated to flag a processor or microcontroller of
out-of-limit conditions.
Default
VCCP Low Limit
0x00
0x47
VCCP High Limit
0xFF
0x48
VCC Low Limit
0x00
0x49
VCC High Limit
0xFF
TACH1 Minimum Low Byte
0xFF
0x55
TACH1 Minimum High Byte
0xFF
0x56
TACH2 Minimum Low Byte
0xFF
0x57
TACH2 Minimum High Byte
0xFF
0x58
TACH3 Minimum Low Byte
0xFF
0x59
TACH3 Minimum High Byte
0xFF
0x5A
TACH4 Minimum Low Byte
0xFF
0x5B
TACH4 Minimum High Byte
0xFF
High limit > comparison performed
Low limit ≤ comparison performed
Table 23. VOLTAGE LIMIT REGISTERS
0x46
0x54
Once all limits have been programmed, the ADT7473/
ADT7473−1 can be enabled for monitoring. The ADT7473/
ADT7473−1 measures all voltage and temperature
measurements in round-robin format and sets the
appropriate status bit for out-of-limit conditions. TACH
measurements are not part of this round-robin cycle.
Comparisons are done differently depending on whether the
measured value is being compared to a high or low limit.
The following is a list of 8-bit limits on the ADT7473/
ADT7473−1.
Description
Default
Out-of-Limit Comparisons
8-bit Limits
Register
Description
Voltage and temperature channels use a window
comparator for error detecting and, therefore, have high and
low limits. Fan speed measurements use only a low limit.
This fan limit is needed only in manual fan control mode.
Analog Monitoring Cycle Time
Table 24. TEMPERATURE LIMIT REGISTERS
Register
Description
0x4E
Remote 1 Temperature Low Limit
0x01
0x4F
Remote 1 Temperature High Limit
0xFF
0x6A
Remote 1 THERM Limit
0xA4
0x50
Local Temperature Low Limit
0x01
0x51
Local Temperature High Limit
0xFF
0x6B
Local THERM Temperature Limit
0xA4
0x52
Remote 2 Temperature Low Limit
0x01
0x53
Remote 2 Temperature High Limit
0xFF
0x6C
Remote 2 THERM Temp. Limit
0xA4
The analog monitoring cycle begins when a 1 is written to
the start bit (Bit 0) of Configuration Register 1 (0x40). By
default, the ADT7473/ADT7473−1 powers up with this bit
set. The ADC measures each analog input in turn and, as
each measurement is completed, the result is automatically
stored in the appropriate value register. This round-robin
monitoring cycle continues unless disabled by writing a 0 to
Bit 0 of Configuration Register 1.
As the ADC is normally left to free-run in this manner, the
time taken to monitor all the analog inputs is normally not
of interest, because the most recently measured value of any
input can be read out at any time.
Default
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ADT7473
For applications where the monitoring cycle time is
important, it can easily be calculated. The total number of
channels measured is:
• One Dedicated Supply Voltage Input (VCCP)
• Supply Voltage (VCC Pin)
• Local Temperature
• Two Remote Temperatures
Table 27. INTERRUPT STATUS REGISTER 1
(REG. 0X41)
As mentioned previously, the ADC performs round-robin
conversions. The total monitoring cycle time for averaged
voltage and temperature monitoring is 146 ms. The total
monitoring cycle time for voltage and temperature
monitoring with averaging disabled is 19 ms. The ADT7473/
ADT7473−1 is a derivative of the ADT7467. As a result, the
total conversion time in the ADT7473/ ADT7473−1 is the
same as the total conversion time of the ADT7467, even
though the ADT7473/ADT7473−1 has fewer monitored
channels.
Fan TACH measurements are made in parallel and are not
synchronized with the analog measurements in any way.
Bit
Mnemonic
Description
7
OOL
1 denotes a bit in Interrupt Status
Register 2 is set and Interrupt Status
Register 2 should be read.
6
R2T
1 indicates that the Remote 2
Temperature High or Low Limit has
been exceeded.
5
LT
4
R1T
1 indicates that the Local Temperature
High or Low Limit has been exceeded.
1 indicates that the Remote 1
Temperature High or Low Limit has
been exceeded.
3
−
2
VCC
Unused
1 indicates that the VCC High or Low
Limit has been exceeded.
1
VCCP
1 indicates that the VCCP High or Low
Limit has been exceeded.
0
−
Unused
Table 28. INTERRUPT STATUS REGISTER 2
(REG. 0X42)
Interrupt Status Registers
The results of limit comparisons are stored in Interrupt
Status Register 1 and Interrupt Status Register 2. The status
register bit for each channel reflects the status of the last
measurement and limit comparison on that channel. If a
measurement is within limits, the corresponding status
register bit is cleared to 0. If the measurement is out of limits,
the corresponding status register bit is set to 1.
The state of the various measurement channels can be
polled by reading the status registers over the serial bus. In
Bit 7 (OOL) of Interrupt Status Register 1 (Reg. 0x41), a 1
means an out-of-limit event has been flagged in Interrupt
Status Register 2. This means the user needs only to read
Interrupt Status Register 2 when this bit is set. Alternatively,
Pin 5 or Pin 9 on the ADT7473 can be configured as an
SMBALERT output, while only Pin 9 can be configured to
be an SMBALERT on the ADT7473−1. This automatically
notifies the system supervisor of an out-of-limit condition.
Reading the status registers clears the appropriate status bit
as long as the error condition that caused the interrupt has
cleared. Status register bits (except OVT) are sticky.
Whenever a status bit is set, indicating an out-of-limit
condition, it remains set even if the event that caused it has
gone away (until read). The only way to clear the status bit
is to read the status register after the event has gone away.
Interrupt mask registers (Register 0x74 and Register 0x75)
allow individual interrupt sources to be masked from
causing an SMBALERT. However, if one of these masked
interrupt sources goes out of limit, its associated status bit is
set in the interrupt status registers. OVT clears
automatically.
Bit
Mnemonic
Description
7
D2
1 indicates an open or short on
D2+/D2− inputs.
6
D1
1 indicates an open or short on
D1+/D1− inputs.
5
F4P
1 indicates that Fan 4 has dropped
below the minimum speed. Alternatively,
indicates that THERM timer limit has
been exceeded if the THERM timer
function is used.
4
FAN3
1 indicates that Fan 3 has dropped
below the minimum speed.
3
FAN2
1 indicates that Fan 2 has dropped
below the minimum speed.
2
FAN1
1 indicates that Fan 1 has dropped
below the minimum speed.
1
OVT
1 indicates that a THERM
overtemperature limit has been
exceeded.
0
THERM
Limit Latch
1 indicates that a Remote Channel 2
latch.
SMBALERT Interrupt Behavior
The ADT747/ADT7473−1 can be polled for status, or an
SMBALERT interrupt can be generated for out-of-limit
conditions. It is important to note how the SMBALERT
output and status bits behave when writing interrupt handler
software.
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20
ADT7473
HIGH LIMIT
HIGH LIMIT
TEMPERATURE
TEMPERATURE
“STICKY”
STATUS BIT
CLEARED ON READ
(TEMP BELOW LIMIT)
CLEARED ON READ
(TEMP BELOW LIMIT)
“STICKY”
STATUS BIT
TEMP BACK IN LIMIT
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
(STATUS BIT STAYS SET)
SMBALERT
SMBALERT
INTERRUPT
MASK BIT SET
Figure 29. SMBALERT and Status Bit Behavior
INTERRUPT MASK BIT
CLEARED
(SMBALERT RE-ARMED)
Figure 29 shows how the SMBALERT output and sticky
status bits behave. Once a limit is exceeded, the
corresponding status bit is set to 1. The interrupt status bit
remains set until the error condition subsides and the
interrupt status register is read. The status bits are referred
to as sticky because they remain set until read by software.
This ensures that an out-of-limit event cannot be missed if
software is polling the device periodically. Note that the
SMBALERT output remains low for the entire duration that
a reading is out of limit and until the interrupt status register
has been read. This has implications on how software
handles the interrupt.
Note that THERM overtemperature events are not sticky,
resetting immediately after the overtemperature condition
ceases. This also applies to SMBALERT if associated with
an OVT event.
Figure 30. How Masking the Interrupt Source Affects
SMBALERT Output
Masking Interrupt Sources
Register 0x74, Interrupt Mask Register 1
Register 0x75, Interrupt Mask Register 2
These registers allow individual interrupt sources to be
masked out to prevent SMBALERT interrupts. Masking an
interrupt source prevents only the SMBALERT output from
being asserted; the appropriate status bit is set normally.
Table 29. INTERRUPT MASK REGISTER 1
(REG. 0X74)
Bit
Mnemonic
Description
To prevent the system from being tied up servicing
interrupts, it is recommended to handle the SMBALERT
interrupt as follows:
1. Detect the SMBALERT assertion.
2. Enter the interrupt handler.
3. Read the status registers to identify the interrupt
source.
4. Mask the interrupt source by setting the
appropriate mask bit in the interrupt mask registers
(Register 0x74 and Register 0x75).
5. Take the appropriate action for a given interrupt
source.
6. Exit the interrupt handler.
7
OOL
0 when one or more alerts are
generated in Interrupt Status Register 2,
assuming all the mask bits in the
Interrupt Mask Register 2 (0x75) = 1;
SMBALERT is still asserted.
1 when one or more alerts are
generated in Interrupt Status Register 2,
assuming all the mask bits in the
Interrupt Mask Register 2 (0x75) = 1;
SMBALERT is not asserted.
6
R2T
1 masks SMBALERT for Remote 2
temperature.
5
LT
4
R1T
Periodically poll the status registers. If the interrupt status
bit has cleared, reset the corresponding interrupt mask bit
to 0. This causes the SMBALERT output and status bits to
behave as shown in Figure 30.
3
−
2
VCC
1 masks SMBALERT for the VCC
channel.
1
VCCP
1 masks SMBALERT for the VCCP
channel.
0
−
Handling SMBALERT Interrupts
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1 masks SMBALERT for Local
temperature.
1 masks SMBALERT for Remote 1
temperature.
Unused
Unused
ADT7473
THERM as an Input
Table 30. INTERRUPT MASK REGISTER 2
(REG. 0X75)
Bit
Mnemonic
Description
7
D2
1 masks SMBALERT for Diode 2 errors.
6
D1
1 masks SMBALERT for Diode 1 errors.
5
FAN4
1 masks SMBALERT for Fan 4 failure. If
the TACH4 pin is being used as the
THERM input, this bit masks
SMBALERT for a THERM event.
4
FAN3
1 masks SMBALERT for Fan 3.
3
FAN2
1 masks SMBALERT for Fan 2.
2
FAN1
1 masks SMBALERT for Fan 1.
1
OVT
1 masks SMBALERT for
overtemperature (exceeding THERM
limits).
0
−
When THERM is configured as an input, the
ADT7473/ADT7473−1 can time assertions on the THERM
pin. This can be useful for connecting to the PROCHOT
output of a CPU to gauge system performance. See the
THERM Timer section for more information.
The user can also set up the ADT7473/ADT7473−1 so
that, when the THERM pin is driven low externally, the fans
run at 100%. The fans run at 100% for the duration of the
time the THERM pin is pulled low. This is done by setting
the BOOST bit (Bit 2) in Configuration Register 3 (0x78)
to 1. This works only if the fan is already running, for
example, in manual mode when the current duty cycle is
above 0x00, or in automatic mode when the temperature is
above TMIN. If the temperature is below TMIN or if the duty
cycle in manual mode is set to 0x00, then pulling the
THERM low externally has no effect. See Figure 31 for
more information.
Unused
Enabling the SMBALERT Interrupt Output
The SMBALERT interrupt function is disabled by default.
Pin 5 or Pin 9 can be reconfigured as an SMBALERT output
to signal out-of-limit conditions. (SMBALERT function is
available only on Pin 9 of ADT7473−1.)
TMIN
Table 31. ADT7473 CONFIGURING PIN 5 AS
SMBALERT OUTPUT
Register
THERM
Bit Setting
Configuration Register 3
(Register 0x78)
<0> ALERT = 1
The ADT7473−1 THERM_LATCH function latches and
asserts when temperature rises 0.25°C above the THERM
limit for the selected remote channel. Due to a THERM
event, the fans spin at full speed. This can be disabled by
setting Bit 2 in Configuration Register 0x7D.
Pin 5 remains latched until temperature falls below
THERM limit for the selected zone, Remote Channel D1 or
Remote Channel D2, and Bit 0 in Status Register 2 is
cleared. By default on the ADT7473−1, the THERM limit is
set as 136°C for Remote Channel 2 and 100°C for Remote
Channel 1.
THERM ASSERTED TO LOW AS
AN INPUT. FANS DO NOT GO
TO 100% BECAUSE TEMPERATURE
IS BELOW TMIN
THERM ASSERTED TO LOW AS
AN INPUT. FANS DO NOT GO TO
100% BECAUSE TEMPERATURE
IS ABOVE TMIN
Figure 31. Asserting THERM Low as an Input in
Automatic Fan Speed Control Mode
THERM Timer
The ADT7473/ADT7473−1 has an internal timer to
measure THERM assertion time. For example, the THERM
input can be connected to the PROCHOT output of a
Pentium® 4 CPU to measure system performance. The
THERM input can also be connected to the output of a trip
point temperature sensor.
The timer is started on the assertion of the
ADT7473/ADT7473−1 THERM input and stopped when
THERM is deasserted. The timer counts THERM times
cumulatively; that is, the timer resumes counting on the next
THERM assertion. The THERM timer continues to
accumulate THERM assertion times until the timer is read (it
is cleared on read) or until it reaches full scale. If the counter
reaches full scale, it stops at that reading until cleared.
The 8-bit THERM timer status register (0x79) is designed
so that Bit 0 is set to 1 on the first THERM assertion. Once
the cumulative THERM assertion time has exceeded
Assigning THERM Functionality to a Pin
Pin 9 on the ADT7473/ADT7473−1 has four possible
functions: SMBALERT, THERM, GPIO, and TACH4. The
user chooses the required functionality by setting Bit 0 and
Bit 1 of Configuration Register 4 (0x7D).
Table 32. CONFIGURATION REGISTER 4 (REG. 0X7D)
Bit 1
Bit 0
Function
0
1
TACH4
0
0
THERM
1
1
SMBusALERT
1
0
GPIO
Once Pin 9 is configured as THERM, it must be enabled
by setting Bit 1 of Configuration Register 3 (0x78).
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ADT7473
45.52 ms, Bit 1 of the THERM timer is set and Bit 0
becomes the LSB of the timer with a resolution of 22.76 ms
(see Figure 32).
When using the THERM timer, be aware of the following.
After a THERM timer read (0x79):
1. The contents of the timer are cleared on read.
2. The F4P bit (Bit 5) of Interrupt Status Register 2
needs to be cleared (assuming that the THERM
timer limit has been exceeded).
THERM timer events. Register 0x7A is the THERM timer
limit register. This 8-bit register allows a limit from 0 sec
(first THERM assertion) to 5.825 sec to be set before an
SMBALERT is generated. The THERM timer value is
compared with the contents of the THERM timer limit
register. If the THERM timer value exceeds the THERM
timer limit value, the F4P bit (Bit 5) of Interrupt Status
Register 2 is set and an SMBALERT is generated. The F4P
bit (Bit 5) of Interrupt Mask Register 2 (0x75) masks out the
SMBALERT if this bit is set to 1; however, the F4P bit of
Interrupt Status Register 2 still is set if the THERM timer
limit is exceeded.
Figure 33 is a functional block diagram of the THERM
timer, limit, and associated circuitry. Writing a value of 0x00
to the THERM timer limit register (0x7A) causes an
SMBALERT to be generated on the first THERM assertion.
A THERM timer limit value of 0x01 generates an
SMBALERT once cumulative THERM assertions exceed
45.52 ms.
If the THERM timer is read during a THERM assertion,
then the following happens:
1. The contents of the timer are cleared.
2. Bit 0 of the THERM timer is set to 1 (because a
THERM assertion is occurring).
3. The THERM timer increments from 0.
4. If the THERM timer limit (Register 0x7A) = 0x00,
the F4P bit is set.
THERM
Configuring the THERM Behavior
THERM
TIMER
(REG. 0x79)
0 0 0 0 0 0 0 1
7 6 5 4 3 2 1 0
1. Configure Pin 9 as a THERM timer input. Setting
Bit 1 (THERM timer enable) of Configuration
Register 3 (0x78) enables the THERM timer
monitoring functionality. This is disabled on Pin 9
by default. Setting Bit 0 and Bit 1 (PIN9FUNC) of
Configuration Register 4 (0x7D) enables THERM
timer/output functionality on Pin 9 (Bit 1 of
Configuration Register 3, THERM, must also be
set). Pin 9 can also be used as TACH4. Setting
Bit 5, Bit 6, and Bit 7 of Configuration Register 5
(0x7C) makes THERM bidirectional. This means
that if the appropriate temperature channel exceeds
the THERM temperature limit, the THERM output
asserts. If the ADT7473 is not pulling THERM low,
but THERM is pulled low by an external device
(such as a CPU overtemperature signal), the
THERM timer also times THERM assertions. If
Bit 5, Bit 6, and Bit 7 of Configuration Register 5
(0x7C) are set to 0, THERM is set as a timer input
only.
2. Select the desired fan behavior for THERM timer
events. Assuming the fans are running, setting
Bit 2 (BOOST) of Configuration Register 3 (0x78)
causes all fans to run at 100% duty cycle whenever
THERM is asserted. This allows fail-safe system
cooling. If this bit is 0, the fans run at their current
settings and are not affected by THERM events. If
the fans are not already running when THERM is
asserted, the fans do not run at full speed.
3. Select whether THERM timer events should
generate SMBALERT interrupts. Bit 5 (F4P) of
Interrupt Mask Register 2 (0x75), when set, masks
out the SMBALERT when the THERM timer limit
value is exceeded. This bit should be cleared if
SMBALERTis based on THERM events required.
THERM ASSERTED
≤22.76 ms
THERM
ACCUMULATE THERM LOW
ASSERTION TIMES
THERM
TIMER
(REG. 0x79)
0 0 0 0 0 0 1 0
7 6 5 4 3 2 1 0
THERM ASSERTED
≥45.52 ms
THERM
ACCUMULATE THERM LOW
ASSERTION TIMES
THERM
TIMER
(REG. 0x79)
0 0 0 0 0 1 0 1
7 6 5 4 3 2 1 0
THERM ASSERTED
≥113.8 ms
(91.04 ms + 22.76 ms)
Figure 32. Understanding the THERM Timer
Generating SMBALERT Interrupts from THERM Timer
Events
The ADT7473/ADT7473−1 can generate an
SMBALERT when a programmable THERM timer limit is
exceeded. This allows the system designer to ignore brief,
infrequent THERM assertions, while capturing longer
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ADT7473
performance is degrading significantly because
THERM is asserting more frequently on an hourly
basis.
Alternatively, OS- or BIOS-level software can
timestamp when the system is powered on. If an
SMBALERT is generated due to the THERM timer
limit being exceeded, another timestamp can be
taken. The difference in time can be calculated for a
fixed THERM timer limit time. For example, if it
takes one week for a THERM timer limit of
2.914 seconds to be exceeded and the next time it
takes only one hour, this is an indication of a
serious degradation in system performance.
4. Select a suitable THERM limit value. This value
determines whether an SMBALERT is generated on
the first THERM assertion, or only if a cumulative
THERM assertion time limit is exceeded. A value of
0x00 causes an SMBALERT to be generated on the
first THERM assertion.
5. Select a THERM monitoring time. This value
specifies how often OS or BIOS level software
checks the THERM timer. For example, BIOS
could read the THERM timer once an hour to
determine the cumulative THERM assertion time.
If, for example, the total THERM assertion time is
<22.76 ms in Hour 1, >182.08 ms in Hour 2, and
>5.825 sec in Hour 3, this can indicate that system
THERM
TIMER LIMIT
(REG. 0x7A)
2.914 s
1.457 s
728.32 ms
364.16 ms
182.08 ms
91.04 ms
45.52 ms
22.76 ms
2.914 s
1.457 s
728.32 ms
364.16 ms
182.08 ms
91.04 ms
45.52 ms
22.76 ms
0 1 2 3 4 5 6 7
THERM TIMER
(REG. 0x79)
THERM
7 6 5 4 3 2 1 0
THERM TIMER CLEARED ON READ
COMPARATOR
IN
OUT
LATCH
F4P BIT (BIT 5)
INTERRUPT STATUS
REGISTER 2
SMBALERT
RESET
CLEARED
ON READ
1 = MASK
F4P BIT (BIT 5)
INTERRUPT MASK REGISTER 2
(REG. 0x75)
Figure 33. Functional Diagram of the ADT7473 THERM Monitoring Circuitry
Configuring the THERM Pin as Bidirectional
are exceeded by 0.25°C. The THERM temperature limit
registers are at Register 0x6A, Register 0x6B, and
Register 0x6C, respectively. Setting Bit 5, Bit 6, and Bit 7 of
Configuration Register 5 (0x7C) makes THERM
bidirectional for the Remote 1, Local, and Remote 2
temperature channels, respectively. Figure 34 shows how the
THERM pin asserts low as an output in the event of a critical
overtemperature.
An alternative method of disabling THERM is to program
the THERM temperature limit to –64°C or less in Offset 64
mode, or −128°C or less in twos complement mode; that is,
for THERM temperature limit values less than –63°C or
–128°C, respectively, THERM is disabled. THERM can
also be disabled by setting Bit 1 of Configuration Register 3
(0x78) to 0.
In addition to monitoring THERM as an input, the
ADT7473/ADT7473−1 can optionally drive THERM low
as an output. When PROCHOT is bidirectional, THERM
can be used to throttle the processor by asserting
PROCHOT. The user can preprogram system-critical
thermal limits. If the temperature exceeds a thermal limit by
0.25°C, THERM asserts low. If the temperature is still above
the thermal limit on the next monitoring cycle, THERM
stays low. THERM remains asserted low until the
temperature is equal to or below the thermal limit. Because
the temperature for that channel is measured only once for
every monitoring cycle after THERM asserts, it is
guaranteed to remain low for at least one monitoring cycle.
The THERM pin can be configured to assert low, if the
Remote 1, Local, or Remote 2 THERM temperature limits
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24
ADT7473
12 V
10 kW
THERM LIMIT
10 kW
12 V
FAN
TACH
TEMP
1N4148
12 V
THERM LIMIT
0.255C
4.7 kW
ADT7473/
ADT7473−1
THERM
3.3 V
10 kW
Q1
NDT3055L
PWM
MONITORING
CYCLE
Figure 35. Driving a 3-wire Fan Using
an N-channel MOSFET
Figure 34. Asserting THERM as an Output, Based on
Tripping THERM Limits
Figure 35 uses a 10 kW pullup resistor for the TACH
signal. This assumes that the TACH signal is an
open-collector from the fan. In all cases, the TACH signal
from the fan must be kept below 3.6 V maximum to prevent
damaging the ADT7473/ADT7473−1. If uncertain as to
whether the fan used has an open-collector or totem pole
TACH output, use one of the input signal conditioning
circuits shown in the Fan Speed Measurement section.
Figure 36 shows a fan drive circuit using an NPN
transistor such as a general-purpose MMBT2222. While
these devices are inexpensive, they tend to have much lower
current handling capabilities and higher on resistance than
MOSFETs. When choosing a transistor, care should be taken
to ensure that it meets the fan’s current requirements.
Ensure that the base resistor is chosen so that the transistor
is saturated when the fan is powered on.
The ADT7473/ADT7473−1 uses pulse-width modulation
(PWM) to control fan speed. This relies on varying the duty
cycle (or on/off ratio) of a square wave applied to the fan to
vary the fan speed. The external circuitry required to drive a
fan using PWM control is extremely simple. For 4-wire fans,
the PWM drive might need only a pullup resistor. In many
cases, the 4-wire fan PWM input has a built-in pullup resistor.
The ADT7473/ADT7473−1 PWM frequency can be set to
a selection of low frequencies or a single high PWM
frequency. The low frequency options are usually used for
3-wire fans, while the high frequency option is usually used
with 4-wire fans.
Note that care must be taken to ensure that the PWM or
TACH pins are not connected to a pullup supply greater than
3.6 V.
Many fans have internal pullups connected to the
TACH/PWM pins to a supply greater than 3.6 V. Clamping
or dividing down the voltage on these pins must be done
where necessary. Clamping these pins with a Zener diode
can also help prevent back-EMF related noise from being
coupled into the system.
For 3-wire fans, a single N-channel MOSFET is the only
drive device required. The specifications of the MOSFET
depend on the maximum current required by the fan being
driven. Typical notebook fans draw a nominal 170 mA;
therefore, SOT devices can be used where board space is a
concern. In desktops, fans can typically draw 250 mA to
300 mA each. If you drive several fans in parallel from a
single PWM output or drive larger server fans, the MOSFET
must handle the higher current requirements. The only other
stipulation is that the MOSFET have a gate voltage drive,
VGS < 3.3 V, for direct interfacing to the PWM output. The
MOSFET should also have a low on resistance to ensure that
there is not significant voltage drop across the FET, which
would reduce the voltage applied across the fan and,
therefore, the maximum operating speed of the fan.
Figure 35 shows how to drive a 3 wire fan using PWM
control.
12 V
12 V
10 kW
10 kW
TACH
TACH
4.7 kW
ADT7473/
ADT7473−1
12 V
FAN
1N4148
Fan Drive Using PWM Control
3.3 V
665 W
PWM
Q1
MMBT2222
Figure 36. Driving a 3-wire Fan Using
an NPN Transistor
Because 4-wire fans are powered continuously, the fan
speed is not switched on or off as with previous PWM
driven/powered fans. This enables it to perform better than
3-wire fans, especially for high frequency applications.
Figure 37 shows a typical drive circuit for 4-wire fans. As
the PWM input on 4-wire fans is usually internally pulled up
to a voltage greater than 3.6 V (the maximum voltage
allowed on the ADT7473/ADT7473−1 PWM output), the
PWM output should be clamped to 3.3 V using a Zener
diode.
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25
ADT7473
12 V
Because the MOSFET can handle up to 3.5 A, it is simply
a matter of connecting another fan directly in parallel with
the first. Care should be taken in designing drive circuits
with transistors and FETs to ensure the PWM pins are not
required to source current and that they sink less than the
8 mA maximum current specified on the data sheet.
12 V
12 V, 4-WIRE FAN
10 kW
VCC
TACH
PWM
10 kW
TACH
TACH
4.7 kW
ADT7473/
ADT7473−1
Driving up to Three Fans from PWM3
TACH measurements for fans are synchronized to
particular PWM channels; for example, TACH1 is
synchronized to PWM1. TACH3 and TACH4 are both
synchronized to PWM3, so PWM3 can drive two fans.
Alternatively, PWM3 can be programmed to synchronize
TACH2, TACH3, and TACH4 to the PWM3 output. This
allows PWM3 to drive two or three fans. In this case, the
drive circuitry looks the same, as shown in Figure 38 and
Figure 39. The SYNC bit in Register 0x62 enables this
function.
Synchronization is not required in high frequency mode
when used with 4-wire fans.
PWM
3.3 V
Figure 37. Driving a 4-wire Fan
Driving Two Fans from PWM3
The ADT7473/ADT7473−1 has four TACH inputs
available for fan speed measurement, but only three PWM
drive outputs. If a fourth fan is used in the system, it should
be driven from the PWM3 output in parallel with the third
fan. Figure 38 shows how to drive two fans in parallel using
low cost NPN transistors. Figure 39 shows the equivalent
circuit using a MOSFET.
Table 33. SYNC: ENHANCED ACOUSTICS
REGISTER 1 (REG. 0X62)
3.3 V
ADT7473/
ADT7373−1
1 kW
PWM3
2.2 kW
3.3 V
1N4148
12 V
TACH3
3.3 V
3.3 V
Q3
MMBT2222
3.3 V
10 kW
TYP
ADT7473/
ADT7473−1
10 kW
TYP
TACH3
3.3 V
3.3 V
TACH
3.3 V
5V
or
12 V
FAN
TACH
1 Synchronizes TACH2, TACH3, and
TACH4 to PWM3.
VCC
12 V
+V
+V
1N4148
3.3 V
SYNC
Pin 4, Pin 6, Pin 7, and Pin 9 (when configured as TACH
inputs) are open-drain TACH inputs intended for fan speed
measurement.
Signal conditioning in the ADT7473/ADT7473−1
accommodates the slow rise and fall times typical of fan
tachometer outputs. The maximum input signal range is 0 V
to 3.6 V. In the event that these inputs are supplied from fan
outputs that exceed 0 V to 3.6 V, either resistive attenuation
of the fan signal or diode clamping must be included to keep
inputs within an acceptable range.
Figure 40 to Figure 43 show circuits for most common fan
TACH outputs.
If the fan TACH output has a resistive pullup to VCC, it can
be connected directly to the fan input, as shown in Figure 40.
Figure 38. Interfacing Two Fans in Parallel to the
PWM3 Output Using Low Cost NPN Transistors
TACH4
<4>
Description
TACH Inputs
Q2
MMBT2222
10 kW
Mnemonic
TACH4
Q1
MMBT3904
10 kW
Bit
PULLUP
4.7 kW
TYP
5V
or
12 V
FAN
TACH
OUTPUT
TACH
10 kW
TYP
PWM3
FAN SPEED
COUNTER
ADT7473/
ADT7473−1
Q1
NDT3055L
Figure 40. Fan with TACH Pullup to VCC
Figure 39. Interfacing Two Fans in Parallel to the
PWM3 Output Using a Single N-channel MOSFET
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26
ADT7473
If the fan output has a resistive pullup to 12 V (or other
voltage greater than 3.6 V), the fan output can be clamped
with a Zener diode, as shown in Figure 41. The Zener diode
voltage should be chosen so that it is greater than VIH of the
TACH input, but less than 3.6 V, allowing for the voltage
tolerance of the Zener. A value of between 3.0 V and 3.6 V
is suitable.
With a pullup voltage of 12 V and pullup resistor less than
1 kW, suitable values for R1 and R2 are 120 kW and 47 kW,
respectively. This gives a high input voltage of 3.35 V.
Fan Speed Measurement
The fan counter does not count the fan TACH output
pulses directly, because the fan speed could be less than
1,000 RPM and it would take several seconds to accumulate
a reasonably large and accurate count. Instead, the period of
the fan revolution is measured by gating an on-chip 90 kHz
oscillator into the input of a 16-bit counter for N periods of
the fan TACH output (see Figure 44), so the accumulated
count is actually proportional to the fan tachometer period,
and inversely proportional to the fan speed.
N, the number of pulses counted, is determined by the
settings of the TACH pulses per revolution register (Register
0x7B). This register contains two bits for each fan, allowing
one, two (default), three, or four TACH pulses to be counted.
VCC
12 V
PULLUP
4.7 kW
TYP
TACH
OUTPUT
TACH
FAN SPEED
COUNTER
ZD1*
ADT7473/
ADT7473−1
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × VCC
Figure 41. Fan with TACH Pullup to Voltage > 3.6 V,
Clamped with Zener Diode
CLOCK
If the fan has a strong pullup (less than 1 kW) to 12 V or
a totem-pole output, a series resistor can be added to limit the
Zener current, as shown in Figure 42.
12 V
PWM
VCC
TACH
1
2
3
TACH
PULLUP
TYP < 1 kW
TACH
OUTPUT
ZD1*
ZENER
OR TOTEM-POLE
4
FAN SPEED
COUNTER
Figure 44. Fan Speed Measurement
ADT7473/
ADT7473−1
Fan Speed Measurement Registers
The fan tachometer readings are 16-bit values consisting
of a 2-byte read from the ADT7473/ADT7473−1.
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × VCC
Figure 42. Fan with Strong TACH. Pullup to > VCC or
Totem-Pole Output, Clamped with Zener and Resistor
12 V
Table 34. FAN SPEED MEASUREMENT REGISTERS
Register
VCC
< 1 kW
TACH
OUTPUT
TACH
FAN SPEED
COUNTER
R1*
R2*
ADT7473/
ADT7473−1
*SEE TEXT
Figure 43. Fan with Strong TACH. Pullup to > VCC or
Totem-Pole Output, Attenuated with R1/R2
Default
0x28
TACH1 Low Byte
0x00
0x29
TACH1 High Byte
0x00
0x2A
TACH2 Low Byte
0x00
0x2B
TACH2 High Byte
0x00
0x2C
TACH3 Low Byte
0x00
0x2D
TACH3 High Byte
0x00
0x2E
TACH4 Low Byte
0x00
0x2F
TACH4 High Byte
0x00
Reading Fan Speed from the ADT7473/ADT7473−1
The measurement of fan speeds involves a 2-register read
for each measurement. The low byte should be read first.
This causes the high byte to be frozen until both high and low
byte registers have been read, preventing erroneous TACH
readings. The fan tachometer reading registers report back
the number of 11.11 ms period clocks (90 kHz oscillator)
gated to the fan speed counter, from the rising edge of the
first fan TACH pulse to the rising edge of the third fan TACH
Alternatively, a resistive attenuator can be used, as shown
in Figure 43. R1 and R2 should be chosen such that
2 V t V PULLUP
Description
R2ńǒR PULLUP ) R1 ) R2Ǔ t 3.6 V (eq. 3)
The fan inputs have an input resistance of nominally
160 kW to ground, which should be taken into account when
calculating resistor values.
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27
ADT7473
Fan Speed (RPM) = (90,000 × 60)/Fan TACH Reading
pulse (assuming two pulses per revolution are being
counted). Because the device is essentially measuring the
fan TACH period, the higher the count value, the slower the
fan is actually running. A 16-bit fan tachometer reading of
0xFFFF indicates either the fan has stalled or is running very
slowly (<100 RPM).
where Fan TACH Reading is the 16-bit fan tachometer
reading.
Example
TACH1 High Byte (Register 0x29) = 0x17
TACH1 Low Byte (Register 0x28) = 0xFF
What is Fan 1 speed in RPM?
Fan 1 TACH Reading = 0x17FF = 6143 (decimal)
RPM = (f × 660)/Fan 1 TACH Reading
RPM = (90000 × 660)/6143
Fan Speed = 879 RPM
High Limit > Comparison Performed
Because the actual fan TACH period is measured, falling
below a fan TACH limit by 1 sets the appropriate status bit
and can be used to generate an SMBALERT.
Measuring Fan TACH
When the ADT7473/ADT7473−1 starts up, TACH
measurements are locked. In effect, an internal read of the
low byte has been made for each TACH input. The net result
of this is that all TACH readings are locked until the high
byte is read from the corresponding TACH registers. All
TACH related interrupts are also ignored until the
appropriate high byte is read.
Once the corresponding high byte has been read, TACH
measurements are unlocked and interrupts are processed as
normal.
Fan Pulses per Revolution
Different fan models can output either one, two, three, or
four TACH pulses per revolution. Once the number of fan
TACH pulses has been determined, it can be programmed
into the fan pulses per revolution register (Register 0x7B)
for each fan. Alternatively, this register can be used to
determine the number or pulses per revolution output by a
given fan. By plotting fan speed measurements at a 100%
speed with different pulses per revolution setting, the
smoothest graph with the lowest ripple determines the
correct pulses per revolution value.
Fan TACH Limit Registers
The fan TACH limit registers are 16-bit values consisting
of two bytes.
Table 36. TACH PULSES/REVOLUTION REGISTER
(REG. 0X7B)
Table 35. FAN TACH LIMIT REGISTERS
Register
Description
Default
0x54
TACH1 Minimum Low Byte
0xFF
0x55
TACH1 Minimum High Byte
0xFF
0x56
TACH2 Minimum Low Byte
0xFF
0x57
TACH2 Minimum High Byte
0xFF
0x58
TACH3 Minimum Low Byte
0xFF
0x59
TACH3 Minimum High Byte
0xFF
0x5A
TACH4 Minimum Low Byte
0xFF
0x5B
TACH4 Minimum High Byte
0xFF
Bit
Mnemonic
<1:0>
FAN1 Default
2 Pulses per Revolution
Description
<3:2>
FAN2 Default
2 Pulses per Revolution
<5:4>
FAN3 Default
2 Pulses per Revolution
<7:6>
FAN4 Default
2 Pulses per Revolution
Table 37. TACH PULSES/REVOLUTION REGISTER
BIT VALUES
Value
Fan Speed Measurement Rate
The fan TACH readings are normally updated once every
second.
The FAST bit (Bit 3) of Configuration Register 3 (0x78),
when set, updates the fan TACH readings every 250 ms.
If any of the fans are not being driven by a PWM channel
but are powered directly from 5.0 V or 12 V, their associated
dc bit in Configuration Register 3 should be set. This allows
TACH readings to be taken on a continuous basis for fans
connected directly to a dc source. For optimal results, the
associated dc bit should always be set when using 4-wire
fans.
Description
00
1 Pulse per Revolution
01
2 Pulses per Revolution
10
3 Pulses per Revolution
11
4 Pulses per Revolution
Fan Spin-up
The ADT7473/ADT7473−1 has a unique fan spin-up
function. It spins the fan at 100% PWM duty cycle until two
TACH pulses are detected on the TACH input. Once two
TACH pulses are detected, the PWM duty cycle goes to the
expected running value, for example, 33%. The advantage
is that fans have different spin-up characteristics and take
different times to overcome inertia. The ADT7473/
ADT7473−1 runs the fans just fast enough to overcome
inertia and is quieter on spin-up than fans programmed for
a given spin-up time.
Calculating Fan Speed
Assuming a fan has two pulses per revolution (and two
pulses per revolution being measured), fan speed is
calculated by:
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ADT7473
Fan Startup Timeout
Table 40. PWM FREQUENCY REGISTERS
(REG. 0X5F TO 0X61)
To prevent the generation of false interrupts as a fan spins
up (because it is below running speed), the ADT7473/
ADT7473−1 includes a fan startup timeout function. During
this time, the ADT7473/ADT7473−1 looks for two TACH
pulses. If two TACH pulses are not detected, an interrupt is
generated. Using Configuration Register 1 (0x40), Bit 5
(FSPDIS), this functionality can be changed (see the
Disabling Fan Startup Timeout section).
Table 38. PWM1 TO PWM3 CONFIGURATION
(REG. 0X5C TO 0X5E)
Bit
Mnemonic
<2:0>
FREQ
Description
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz
100 = 35.3 Hz (Default)
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
Fan Speed Control
Bit
Mnemonic
Description
<2:0>
SPIN
These bits control the startup timeout for PWM1 (0x5C),
PWM2 (0x5D), PWM3 (0x5E).
000 = No Startup Timeout
001 = 100 ms
010 = 250 ms (Default)
011 = 400 ms
100 = 667 ms
101 = 1 s
110 = 2 s
111 = 4 s
The ADT7473/ADT7473−1 controls fan speed using
automatic and manual modes.
In automatic fan speed control mode, fan speed is
automatically varied with temperature and without CPU
intervention, once initial parameters are set up. The
advantage of this is that, if the system hangs, the user is
guaranteed the system is protected from overheating. The
automatic fan speed control incorporates a feature called
dynamic TMIN calibration. This feature reduces the design
effort required to program the automatic fan speed control
loop. For more information and procedures on how to
program the automatic fan speed control loop and dynamic
TMIN calibration, see the Programming the Automatic Fan
Speed Control Loop section.
In manual fan speed control mode, the ADT7473/
ADT7473−1 allows the duty cycle of any PWM output to be
manually adjusted. This can be useful if the user wants to
change fan speed in software or adjust the PWM duty cycle
output for test purposes. Bits <7:5> of Register 0x5C to
Register 0x5E (PWM configuration registers) control the
behavior of each PWM output.
Disabling Fan Startup Timeout
Although fan startup makes fan spin-ups much quieter
than fixed-time spin-ups, the option exists to use fixed
spin-up times. Setting Bit 5 (FSPDIS) to 1 in Configuration
Register 1 (0x40) disables the spin-up for two TACH pulses.
Instead, the fan spins up for the fixed time as selected in
Register 0x5C to Register 0x5E.
PWM Logic State
The PWM outputs can be programmed high for a 100%
duty cycle (non-inverted) or low for a 100% duty cycle
(inverted).
Table 41. PWM CONFIGURATION
(REG. 0X5C TO 0X5E) BITS
Table 39. PWM1 TO PWM3 CONFIGURATION
(REG. 0X5C TO 0X5E) BITS
Bit
Mnemonic
Description
4
INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
Bit
Mnemonic
<7:5>
BHVR 111
Description
Manual Mode
Once under manual control, each PWM output can be
manually updated by writing to Register 0x30 to Register
0x32 (PWM current duty cycle registers).
Low Frequency Mode PWM Drive Frequency
The PWM drive frequency can be adjusted for the
application. Register 0x5F to Register 0x61 configure the
PWM frequency for PWM1 to PWM3, respectively. In high
frequency mode, the PWM drive frequency is always
22.5 kHz.
Programming the PWM Current Duty Cycle Registers
The PWM current duty cycle registers are 8-bit registers
that allow the PWM duty cycle for each output to be set
anywhere from 0% to 100% in steps of 0.39%.
The value to be programmed into the PWMMIN register is
given by:
High Frequency Mode PWM Drive
Value (decimal) + PWM MINń0.39
Setting Bit 3 of Register 0x5F, 60H or 61H enables high
frequency mode for fans 1, 2 and 3.
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29
(eq. 4)
ADT7473
Example 1
Sleep States
For a PWM duty cycle of 50%
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 0x80 (hex)
The ADT7473/ADT7473−1 has been specifically
designed to operate from a 3.3 V STBY supply. In
computers that support S3 and S5 states, the core voltage of
the processor is lowered in these states. If using the dynamic
TMIN mode, lowering the core voltage of the processor
changes the CPU temperature and the dynamics of the
system under dynamic TMIN control. Likewise, when
monitoring THERM, the THERM timer should be disabled
during these states.
Example 2
For a PWM duty cycle of 33%
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 0x54 (hex)
Table 42. PWM CURRENT DUTY CYCLE REGISTERS
Register
Description
Default
0x30
PWM1 Duty Cycle
0xFF (0%)
0x31
PWM2 Duty Cycle
0xFF (0%)
0x32
PWM3 Duty Cycle
0xFF (0%)
Dynamic TMIN Control Register 1 (0X36)
Bit <1> VCCPLO = 1
When the VCCP voltage drops below the VCCP low limit,
the following occurs:
1. Status Bit 1 (VCCP) in Status Register 1 is set.
2. SMBALERT is generated, if enabled.
3. THERM monitoring is disabled. The THERM
timer should hold its value prior to the S3 or S5
state.
4. Dynamic TMIN control is disabled. This prevents
TMIN from being adjusted due to an S3 or S5 state.
5. The ADT7473/ADT7473−1 is prevented from
entering the shutdown state.
By reading the PWMx current duty cycle registers, the
user can keep track of the current duty cycle on each PWM
output, even when the fans are running in automatic fan
speed control mode or acoustic enhancement mode. See the
Programming the Automatic Fan Speed Control Loop
section for details.
Fan Presence Detect
This feature can be used to determine if a 4-wire fan is
directly connected to a PWM output. This feature does not
work for 3-wire fans. To detect whether a 4-wire fan is
connected directly to a PWM output, the following steps
must be performed in this order:
1. Drive the appropriate PWM outputs to 100% duty
cycle.
2. Set Bit 0 of Configuration Register 2 (0x73).
3. Wait 5 ms.
4. Program the fans to run at a different speed if
necessary.
5. Read the state of Bits <3:1> of Configuration
Register 2 (0x73). The state of these bits reflects
whether a 4-wire fan is directly connected to the
PWM output.
Once the core voltage, VCCP, goes above the VCCP low
limit, everything is re-enabled, and the system resumes
normal operation.
XNOR Tree Test Mode
The ADT7473/ADT7473−1 includes an XNOR tree test
mode. This mode is useful for in-circuit test equipment at
board-level testing. By applying stimulus to the pins
included in the XNOR tree, it is possible to detect opens or
shorts on the system board.
Figure 45 shows the signals that are exercised in the
XNOR tree test mode. The XNOR tree test is invoked by
setting Bit 0 (XEN) of the XNOR tree test enable register
(0x6F).
TACH1
TACH2
As the detection time only takes 5 ms, programming the
PWM outputs to 100% and then back to their normal speed
is not noticeable in most cases.
TACH3
Description of How Fan Presence Detect Works
TACH4
Typical 4-wire fans have an internal pull up to 4.75 V
±10%, which typically sources 5 mA. While the detection
cycle is on, an internal current sink is turned on, sinking
current from the fan’s internal pullup. By driving some of the
current from the fan’s internal pullup (~100 mA), the logic
buffer switches to a defined logic state. If this state is high,
a fan is present; if it is low, no fan is present.
The PWM input voltage should be clamped to 3.3 V. This
ensures the PWM output is not pulled to a voltage higher
than the maximum allowable voltage on that pin (3.6 V).
PWM2
PWM3
PWM1/XTO
Figure 45. XNOR Tree Test
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30
ADT7473
Power-on Default
Programming the Automatic Fan Speed Control Loop
When the ADT7473 is powered up, it polls the VCCP
input. By default, the ADT7473−1 powers up with fans
running, eliminating the need for polling of VCCP.
If VCCP stays below 0.75 V (the system CPU power rail
is not powered up), the ADT7473 assumes the functionality
of the default registers after the ADT74731 is addressed via
any valid SMBus transaction.
If VCC goes high (the system processor power rail is
powered up), a fail-safe timer begins to count down. If the
ADT7473 is not addressed by any valid SMBus transactions
before the fail-safe timeout (4.6 seconds) lapses, the
ADT7473 drives the fans to full speed. If the ADT7473 is
addressed by a valid SMBus transaction after this point, the
fans stop, and the ADT7473 assumes its default settings and
begins normal operation.
If VCCP goes high (the system processor power rail is
powered up), then a fail-safe timer begins to count down. If
the ADT7473 is addressed by a valid SMBus transaction
before the fail-safe timeout (4.6 seconds) lapses, then the
ADT7473 operates normally, assuming the functionality of
all the default registers. See the flow chart in Figure 46.
To understand the automatic fan speed control loop, it is
strongly recommended to use the ADT7473/ADT7473−1
evaluation board and software while reading this section.
This section provides the system designer with an
understanding of the automatic fan control loop, and
provides step-by-step guidance on effectively evaluating
and selecting critical system parameters. To optimize the
system characteristics, the designer needs to consider the
system configuration, including the number of fans, where
they are located, and what temperatures are measured in the
particular system.
The mechanical or thermal engineer who is tasked with
the system thermal characterization should also be involved
at the beginning of the process.
Automatic Fan Control Overview
The ADT7473/ADT7473−1 can automatically control the
speed of fans based on the measured temperature. This is
done independently of CPU intervention once initial
parameters are set up.
The ADT7473/ADT7473−1 has a local temperature
sensor and two remote temperature channels that can be
connected to a CPU on-chip thermal diode (available on
Intel Pentium class CPUs and other CPUs). These three
temperature channels can be used as the basis for automatic
fan speed control to drive fans using PWM.
Automatic fan speed control reduces acoustic noise by
optimizing fan speed according to accurately measured
temperature. Reducing fan speed can also decrease system
current consumption. The automatic fan speed control mode
is very flexible due to the number of programmable
parameters, including TMIN and TRANGE. The TMIN and
TRANGE values for a temperature channel and, therefore, for
a given fan, are critical because they define the thermal
characteristics of the system. The thermal validation of the
system is one of the most important steps in the design
process, so these values should be selected carefully.
Figure 47 gives a top-level overview of the automatic fan
control circuitry on the ADT7473/ADT7473−1. From a
systems-level perspective, up to three system temperatures
can be monitored and used to control three PWM outputs.
The three PWM outputs can be used to control up to four
fans. The ADT7473/ADT7473−1 allows the speed of four
fans to be monitored. Each temperature channel has a
thermal calibration block, allowing the designer to
individually configure the thermal characteristics of each
temperature channel. For example, a designer can decide to
run the CPU fan when CPU temperature increases above
60°C, and a chassis fan when the local temperature increases
above 45°C. At this stage, the designer has not assigned
these thermal calibration settings to a particular fan drive
(PWM) channel. The right side of Figure 47 shows controls
that are fan-specific. The designer has individual control
over parameters such as minimum PWM duty cycle, fan
ADT7473/ADT7473−1 IS POWERED UP
Y
HAS THE ADT7473/
ADT7473−1 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
N
IS VCCP ABOVE 0.75 V?
CHECK VCCP
Y
START FAIL-SAFE TIMER
Y
HAS THE ADT7473/
ADT7473−1 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
FAIL-SAFE TIMER
ELAPSES AFTER THE
FAIL-SAFE TIMEOUT
HAS THE ADT7473/
ADT7473−1 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
Y
N
RUNS THE FANS
TO FULL SPEED
HAS THE ADT7473/
ADT7473−1 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
Y
START UP THE ADT7473/
ADT7473−1 NORMALLY
SWITCH OFF FANS
Figure 46. Power-on Flow Chart
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31
ADT7473
speed failure thresholds, and even ramp control of the PWM
outputs. Automatic fan control, then, ultimately allows
graceful fan speed changes that are less perceptible to the
system user.
THERMAL CALIBRATION
S
REMOTE1
TEMP
TMIN
TRANGE
PWM
MIN
THERMAL CALIBRATION
S
MUX
TMIN
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
REMOTE2
TEMP
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM1
0%
100%
LOCAL
TEMP
PWM
CONFIG
PWM
MIN
100%
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 3
AND 4
MEASUREMENT
0%
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM2
TACH2
PWM
CONFIG
PWM
GENERATOR
PWM3
TACH3
Figure 47. Automatic Fan Control Block Diagram
Step 1: Hardware Configuration
This influences the choice of whether to use the
TACH4 pin or to reconfigure it for the THERM
function.
3. Is the CPU fan to be controlled using the
ADT7473/ADT7473−1 or will it run at full speed
100% of the time?
If run at full speed, 100% of the time, this frees up
a PWM output, but the system is louder.
4. Where will the ADT7473/ADT7473−1 be
physically located in the system?
This influences the assignment of the temperature
measurement channels to particular system
thermal zones. For example, locating the
ADT7473/ADT7473−1 close to the VRM
controller circuitry allows the VRM temperature to
be monitored using the local temperature channel.
During system design, the motherboard sensing and
control capabilities should be addressed early in the design
stages. Decisions about how these capabilities are used
should involve the system thermal/mechanical engineer.
Consider the following questions:
1. What ADT7473/ADT7473−1 functionality will be
used?
• PWM2 or SMBALERT for ADT7473?
• THERM_LATCH or PWM2 for ADT7473−1?
• TACH4 fan speed measurement or
over-temperature THERM function?
The ADT7473/ ADT7473−1 offers multifunctional
pins that can be reconfigured to suit different
system requirements and physical layouts. These
multifunction pins are software programmable.
2. How many fans will be supported in the system,
three or four?
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32
ADT7473
THERMAL CALIBRATION
PWM
MIN
100%
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
0%
100%
LOCAL =
VRM TEMP
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
MUX
PWM
MIN
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
100%
S
TMIN
TRANGE
TACH1
PWM
GENERATOR
PWM
CONFIG
CPU FAN SINK
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
PWM
CONFIG
TACHOMETER2
MEASUREMENT
0%
THERMAL CALIBRATION
PWM
GENERATOR
TACHOMETER1
MEASUREMENT
PWM
MIN
THERMAL CALIBRATION
TMIN
PWM
CONFIG
PWM3
TACH3
REMOTE2 =
CPU TEMP
REAR CHASSIS
Figure 48. Hardware Configuration Example
ADT7473
FRONT
CHASSIS
FAN
TACH2
PWM1
TACH1
CPU FAN
PWM3
REAR
CHASSIS
FAN
TACH3
D2+
D2−
THERM
PROCHOT
D1+
AMBIENT
TEMPERATURE
CPU
D1−
SDA
SCL
SMBALERT
GND
Figure 49. Recommended Implementation 1
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33
ICH
ADT7473
Recommended Implementation 1
multiple temperature channels. The mux is the bridge
between temperature measurement channels and the three
PWM outputs.
Bits <7:5> (BHVR) of Register 0x5C, Register 0x5D, and
Register 0x5E (PWM configuration registers) control the
behavior of the fans connected to the PWM1, PWM2, and
PWM3 outputs. The values selected for these bits determine
how the mux connects a temperature measurement channel
to a PWM output.
Configuring the ADT7473, as in Figure 49 provides the
system designer with the following features:
• Two PWM outputs for fan control of up to three fans.
(The front and rear chassis fans are connected in
parallel.)
• Three TACH fan speed measurement inputs.
• VCC measured internally through Pin 4.
• CPU core voltage measurement (VCORE).
• VRM temperature using local temperature sensor.
• CPU temperature measured using the Remote 1
temperature channel.
• Ambient temperature measured through the Remote 2
temperature channel.
• Bidirectional THERM pin allows the monitoring of
PROCHOT output from an Intel® Pentium® 4
processor, for example, or can be used as an
overtemperature THERM output.
• SMBALERT system interrupt output.
Automatic Fan Control Mux Options
Bits <7:5> (BHVR), Register 0x5C, Register 0x5D,
Register 0x5E.
000 = Remote 1 temperature controls PWMx
001 = Local temperature controls PWMx
010 = Remote 2 temperature controls PWMx
101 = Fastest speed calculated by local and Remote 2
temperature controls PWMx
110 = Fastest speed calculated by all three temperature
channel controls PWMx
The fastest speed calculated options pertain to controlling
one PWM output based on multiple temperature channels.
The thermal characteristics of the three temperature zones
can be set to drive a single fan. An example is the fan turning
on when Remote 1 temperature exceeds 60°C, or if the local
temperature exceeds 45°C.
Step 2: Configuring the Mux
After the system hardware configuration is determined,
the fans can be assigned to particular temperature channels.
Not only can fans be assigned to individual channels, but the
behavior of the fans is also configurable. For example, fans
can be run under automatic fan control, manually (under
software control), or at the fastest speed calculated by
MUX
THERMAL CALIBRATION
PWM
MIN
100%
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
S
MUX
LOCAL =
VRM TEMP
S
REMOTE2 =
CPU TEMP
TACHOMETER2
MEASUREMENT
PWM
MIN
100%
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
0%
THERMAL CALIBRATION
TMIN
TACHOMETER1
MEASUREMENT
PWM
MIN
100%
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
0%
THERMAL CALIBRATION
TMIN
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
Figure 50. Assigning Temperature Channels to Fan Channels
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34
CPU FAN SINK
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
PWM3
TACH3
REAR CHASSIS
ADT7473
Other Mux Options
Bits <7:5> (BHVR), Register 0x5C, Register 0x5D,
Register 0x5E.
011 = PWMx runs full speed (default for ADT7473−1)
100 = PWMx disabled (default for ADT7473)
111 = manual mode
Remote 2 (processor) temperature. In this case, the
CPU fan sink is also used to cool the VRM.
PWM2 (front chassis fan) is controlled by the Remote 1
temperature (ambient).
PWM3 (rear chassis fan) is controlled by the Remote 1
temperature (ambient).
•
•
In normal mode, PWMx runs under software control. In
this mode, PWM duty cycle registers (Register 0x30 to
Register 0x32) are writable and control the PWM outputs.
Example Mux Settings
Bits <7:5> (BHVR), PWM1 Configuration Register (0x5C)
101 = Fastest speed calculated by local and Remote 2
temperature controls PWM1
Bits <7:5> (BHVR), PWM2 Configuration Register (0x5D)
000 = Remote 1 temperature controls PWM2
Bits <7:5> (BHVR), PWM3 Configuration Register (0x5E)
000 = Remote 1 temperature controls PWM3
Mux Configuration Example
This is an example of how to configure the mux in a
system using the ADT7473/ADT7473−1 to control three
fans. The CPU fan sink is controlled by PWM1, the front
chassis fan is controlled by PWM2, and the rear chassis fan
is controlled by PWM3. The mux is configured for the
following fan control behaviors:
• PWM1 (CPU fan sink) is controlled by the fastest speed
calculated by the local (VRM temperature) and
These settings configure the mux, as shown in Figure 51.
THERMAL CALIBRATION
PWM
MIN
100%
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
MUX
S
LOCAL =
VRM TEMP
TACHOMETER2
MEASUREMENT
PWM
MIN
100%
S
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
0%
THERMAL CALIBRATION
TMIN
TACHOMETER1
MEASUREMENT
PWM
MIN
100%
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
0%
THERMAL CALIBRATION
TMIN
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM
GENERATOR
PWM1
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
CPU FAN SINK
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
Figure 51. Mux Configuration Example
Step 3: TMIN Settings for Thermal Calibration Channels
REAR CHASSIS
the TMIN value is exceeded, the fan turns on and runs at the
minimum PWM duty cycle. The fan turns off once the
temperature drops below TMIN − THYST.
To overcome fan inertia, the fan is spun up until two valid
TACH rising edges are counted. See the Fan Startup
Timeout section for more details. In some cases, primarily
for psycho-acoustic reasons, it is desirable that the fan never
switches off below TMIN. Bits <7:5> of Enhanced Acoustics
Register 1 (0x62), when set, can keep the fans running at the
PWM minimum duty cycle, if the temperature falls below
TMIN.
TMIN is the temperature at which the fans start to turn on
under automatic fan control. The speed at which the fan runs
at TMIN is programmed later. The TMIN values chosen are
temperature channel specific, for example, 25°C for
ambient channel, 30°C for VRM temperature, and 40°C for
processor temperature.
TMIN is an 8-bit value, either twos complement or Offset
64, that can be programmed in 1°C increments. A TMIN
register is associated with each temperature measurement
channel: Remote 1 local and Remote 2 temperature. Once
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35
ADT7473
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty
cycle below TMIN − THYST.
Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty
cycle below TMIN − THYST.
Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty
cycle below TMIN − THYST.
Table 43. TMIN REGISTERS
Register
Description
Default
0x67
Remote 1 Temperature TMIN
0x9A (90°C)
0x68
Local Temperature TMIN
0x9A (90°C)
0x69
Remote 2 Temperature TMIN
0x9A (90°C)
Enhanced Acoustics Register 1 (0x62)
Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
PWM DUTY CYCLE
100%
0%
TMIN
THERMAL CALIBRATION
PWM
MIN
100%
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
TMIN
TRANGE
LOCAL =
VRM TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
MUX
TRANGE
TACHOMETER1
MEASUREMENT
PWM
MIN
100%
TMIN
TACHOMETER2
MEASUREMENT
0%
PWM
MIN
THERMAL CALIBRATION
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
100%
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
PWM1
0%
THERMAL CALIBRATION
REMOTE2 =
CPU TEMP
PWM
GENERATOR
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
CPU FAN SINK
PWM3
TACH3
Figure 52. Understanding the TMIN Parameter
REAR CHASSIS
Step 4: PWMMIN for Each PWM (Fan) Output
PWMMIN is the minimum PWM duty cycle at which each
fan in the system runs. It is also the start speed for each fan
under automatic fan control once the temperature rises
above TMIN (see Figure 53). For maximum system acoustic
benefit, PWMMIN should be set as low as possible.
Depending on the fan used, the PWMMIN setting is usually
in the 20% to 33% duty cycle range. This value can be found
through fan validation.
PWM DUTY CYCLE
100%
PWMMIN
0%
TMIN
TEMPERATURE
Figure 53. PWMMIN Determines Minimum
PWM Duty Cycle
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36
ADT7473
not equate to running the fan at 33% speed. Driving a fan at
33% PWM duty cycle actually runs the fan at closer to 50%
of its full speed. This is because fan speed in %RPM
generally relates to the square root of PWM duty cycle.
Given a PWM square wave as the drive signal, fan speed in
RPM approximates to:
More than one PWM output can be controlled from a
single temperature measurement channel. For example,
Remote 1 temperature can control PWM1 and PWM2
outputs. If two different fans are used on PWM1 and PWM2,
the fan characteristics can be set up differently. As a result,
Fan 1 driven by PWM1 can have a different PWMMIN value
than that of Fan 2 connected to PWM2. Figure 54 illustrates
this as PWM1MIN (front fan) is turned on at a minimum duty
cycle of 20%, while PWM2MIN (rear fan) turns on at a
minimum of 40% duty cycle. However, both fans turn on at
exactly the same temperature, defined by TMIN.
% fanspeed + ǸPWM duty cycle
PWMMAX is the maximum duty cycle at which each fan
in the system runs under the automatic fan speed control
loop. For maximum system acoustic benefit, PWMMAX
should be as low as possible, but should be capable of
maintaining the processor temperature limit at an acceptable
level. If the THERM temperature limit is exceeded, the fans
are still boosted to 100% for fail-safe cooling (see
Figure 55).
There is a PWMMAX limit for each fan channel. The
default value of this register is 0xFF and thus has no effect
unless it is programmed.
PWM DUTY CYCLE
PWM2
PWM1
PWM1MIN
0%
TMIN
(eq. 5)
Step 5: PWMMAX for PWM (Fan) Outputs
100%
PWM2MIN
10
TEMPERATURE
100%
PWM DUTY CYCLE
Figure 54. Operating Two Different Fans from a
Single Temperature Channel
Programming the PWMMIN Registers
The PWMMIN registers are 8-bit registers that allow the
minimum PWM duty cycle for each output to be configured
anywhere from 0% to 100%. This allows the minimum
PWM duty cycle to be set in steps of 0.39%.
The value to be programmed into the PWMMIN register is
given by:
Value (decimal) = PWMMIN/0.39
PWMMAX
PWMMIN
0%
TMIN
TEMPERATURE
Figure 55. PWMMAX Determines Maximum PWM Duty
Cycle Below the THERM Temperature Limit
Example 1
Programming the PWMMAX Registers
For a minimum PWM duty cycle of 50%
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
The PWMMAX registers are 8-bit registers that allow the
maximum PWM duty cycle for each output to be configured
anywhere from 0% to 100%. This allows the maximum
PWM duty cycle to be set in steps of 0.39%.
The value to be programmed into the PWMMAX register
is given by:
Value (decimal) = PWMMAX/0.39
Example 2
For a minimum PWM duty cycle of 33%
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 54 (hex)
Example 1
Table 44. PWMMIN REGISTERS
Register
Description
For a maximum PWM duty cycle of 50%
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Default
0x64
PWM1 Minimum Duty Cycle
0x80 (50%)
0x65
PWM2 Minimum Duty Cycle
0x80 (50%)
0x66
PWM3 Minimum Duty Cycle
0x80 (50%)
Example 2
For a minimum PWM duty cycle of 75%
Value (decimal) = 75/0.39 = 85 (decimal)
Value = 192 (decimal) or C0 (hex)
Note on Fan Speed and PWM Duty Cycle
The PWM duty cycle does not directly correlate to fan
speed in RPM. Running a fan at 33% PWM duty cycle does
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37
ADT7473
4. Graphically program and visualize this
functionality using the ADT7473/ADT7473−1
evaluation software.
Table 45. PWMMAX REGISTERS
Register
Description
Default
0x38
PWM1 Maximum Duty Cycle
0xFF (100%)
0x39
PWM2 Maximum Duty Cycle
0xFF (100%)
0x3A
PWM3 Maximum Duty Cycle
0xFF (100%)
Figure 57 shows how adjusting PWMMIN affects TRANGE.
TRANGE is implemented as a slope, which means that as
PWMMIN is changed, TRANGE changes, but the actual slope
remains the same. The higher the PWMMIN value, the
smaller the effective TRANGE, that is, the fan reaches full
speed (100%) at a lower temperature. Figure 58 shows how
increasing PWMMIN changes the effective TRANGE.
See the Note on Fan Speed and PWM Duty Cycle section.
Step 6: TRANGE for Temperature Channels
TRANGE is the range of temperature over which automatic
fan control occurs once the programmed TMIN temperature
is exceeded. TRANGE is a temperature slope, not an arbitrary
value, that is, a TRANGE of 40°C holds true only for
PWMMIN = 33%. If PWMMIN is increased or decreased, the
effective TRANGE changes. Refer to Figure 56.
PWM DUTY CYCLE
100%
TRANGE
PWM DUTY CYCLE
100%
50%
33%
25%
10%
0%
30°C
40°C
45°C
54°C
PWMMIN
0%
TMIN
TMIN
Figure 58. Increasing PWMMIN Changes Effective
TRANGE
TEMPERATURE
Figure 56. TRANGE Parameter Affects Cooling Slope
For a given TRANGE value, the temperature at which the
fan runs at full speed for different PWMMIN values can be
easily calculated as follows:
TMAX = TMIN + (Max DC − Min DC) × TRANGE /170
where:
TMAX is the temperature at which the fan runs full speed.
TMIN is the temperature at which the fan turns on.
Max DC is the maximum duty cycle (100%) = 255 decimal.
Min DC is equal to PWMMIN.
TRANGE is the duty PWM duty cycle vs. temperature slope.
The TRANGE or fan control slope is determined by the
following procedure:
1. Determine the maximum operating temperature for
that channel (for example, 70°C).
2. Determine experimentally the fan speed (PWM
duty cycle value) that does not exceed the
temperature at the worst-case operating points (for
example, 70°C is reached when the fans are
running at 50% PWM duty cycle).
3. Determine the slope of the required control loop to
meet these requirements.
Example 1
50%
Calculate T, given that TMIN = 30°C, TRANGE = 40°C, and
PWMMIN = 10% duty cycle = 26 (decimal).
TMAX = TMIN + (Max DC − Min DC) × TRANGE /170
TMAX = 30°C + (100% − 10%) × 40°C/170
TMAX = 30°C + (255 − 26) × 40°C/170
TMAX = 84°C (effective TRANGE = 54°C)
33%
Example 2
PWM DUTY CYCLE
100%
Calculate TMAX, given that TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 25% duty cycle = 64 (decimal).
TMAX = TMIN + (Max DC − Min DC) × TRANGE /170
TMAX = 30°C + (100% − 25%) × 40°C/170
TMAX = 30°C + (255 − 64) × 40°C/170
TMAX = 75°C (effective TRANGE = 45°C)
0%
30°C
40°C
TMIN
Figure 57. Adjusting PWMMIN Affects TRANGE
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ADT7473
Example 3
Increasing or decreasing PWMMIN changes the effective
TRANGE, although the fan control still follows the same
PWM duty cycle to temperature slope. The effective
TRANGE for different PWMMIN values can be calculated
using Equation 7.
Calculate TMAX, given that TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 33% duty cycle = 85 (decimal).
TMAX = TMIN + (Max DC − Min DC) × TRANGE /170
TMAX = 30°C + (100% − 33%) × 40°C/170
TMAX = 30°C + (255 − 85) × 40°C/170
TMAX = 70°C (effective TRANGE = 40°C)
T MAX + T MIN ) ǒMax DC * Min DCǓ
(eq. 7)
where (Max DC − Min DC) × TRANGE/170 is the effective
TRANGE value.
See the Note on Fan Speed and PWM Duty Cycle section.
Figure 59 shows PWM duty cycle vs. temperature for each
TRANGE setting. The lower graph shows how each TRANGE
setting affects fan speed vs. temperature. As indicated by the
graph, the effect on fan speed is nonlinear.
The graphs in Figure 59 assume the fan starts from 0%
PWM duty cycle. Clearly, the minimum PWM duty cycle,
PWMMIN, needs to be factored in to see how the loop
actually performs in the system. Figure 60 shows how
TRANGE is affected when the PWMMIN value is set to 20%.
It can be seen that the fan actually runs at about 45% fan
speed when the temperature exceeds TMIN.
Example 4
Calculate TMAX, given that TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 50% duty cycle = 128 (decimal).
TMAX = TMIN + (Max DC − Min DC) × TRANGE /170
TMAX = 30°C + (100% − 50%) × 40°C/170
TMAX = 30°C + (255 − 128) × 40°C/170
TMAX = 60°C (effective TRANGE = 30°C)
Selecting a TRANGE Slope
The TRANGE value can be selected for each temperature
channel: Remote 1, local, and Remote 2. Bits <7:4>
(TRANGE) of Register 0x5F to Register 0x61 define the
TRANGE value for each temperature channel.
Table 46. SELECTING A TRANGE VALUE
TRANGE (5C)
100
0000
2
90
0001
2.5
80
3.33
0011
4
PWM DUTY CYCLE (%)
Bits <7:4> (Note 1)
0010
25C
2.55C
3.335C
45C
55C
70
6.675C
85C
60
105C
50
0100
5
0101
6.67
0110
8
0111
10
1000
13.33
10
1001
16
0
1010
20
1011
26.67
1100
32 (Default)
1101
40
1110
53.33
1111
80
13.35C
165C
40
205C
30
26.65C
325C
20
405C
53.35C
0
20
40
60
80
100
120
805C
TEMPERATURE ABOVE TMIN
25C
100
2.55C
FAN SPEED (% OF MAX)
90
1. Register 0x5F configures Remote 1 TRANGE; Register 0x60
configures local TRANGE; Register 0x61 configures Remote 2
TRANGE.
Summary of TRANGE Function
When using the automatic fan control function, the
temperature at which the fan reaches full speed can be
calculated by:
T MAX + T MIN ) T TRANGE
T TRANGEń170
3.335C
45C
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
325C
20
405C
10
0
(eq. 6)
53.35C
805C
0
20
40
60
80
100
120
TEMPERATURE ABOVE TMIN
Equation 6 holds true only when PWMMIN is equal to
33% PWM duty cycle.
Figure 59. TRANGE vs. Actual Fan Speed Profile
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ADT7473
25C
100
3.335C
90
45C
80
PWM DUTY CYCLE (%)
PWM DUTY CYCLE (%)
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
325C
20
70
60
50
40
30
20
405C
10
0
100
2.55C
90
10
53.35C
805C
0
20
40
60
80
100
0
120
0
10
TEMPERATURE ABOVE TMIN
25C
45C
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
325C
20
405C
10
60
80
100
60
70
80
90
100
120
90
100
80
70
60
50
40
30
20
10
53.35C
40
50
90
3.335C
FAN SPEED (% MAX RPM)
FAN SPEED (% OF MAX)
90
20
40
100
2.55C
0
30
TEMPERATURE ABOVE TMIN
100
0
20
805C
0
0
10
20
30
40
50
60
70
80
TEMPERATURE ABOVE TMIN
TEMPERATURE ABOVE TMIN
Figure 60. TRANGE and % Fan Speed Slopes with
PWMMIN = 20%
Figure 61. TRANGE and % Fan Speed Slopes for VRM,
Ambient, and CPU Temperature Channels
Example: Determining TRANGE for Each Temperature
Channel
Step 7: TTHERM for Temperature Channels
TTHERM is the absolute maximum temperature allowed
on a temperature channel. When operating above this
temperature, a component such as the CPU or VRM might
be beyond its safe operating limit. When the temperature
measured exceeds TTHERM all fans are driven at 100%
PWM duty cycle (full speed) to provide critical system
cooling.
The fans remain running at 100% until the temperature
drops below TTHERM − hysteresis, where hysteresis is the
number programmed into the hysteresis registers
(Register 0x6D and Register 0x6E). The default hysteresis
value is 4°C.
The TTHERM limit should be considered the maximum
worst-case operating temperature of the system. Because
exceeding any TTHERM limit runs all fans at 100%, it has
very negative acoustic effects. Ultimately, this limit should
be set up as a fail-safe, and it should not be exceeded under
normal system operating conditions.
Note that the TTHERM limits are nonmaskable and affect
the fan speed no matter how the automatic fan control
settings are configured. This allows some flexibility because
a TRANGE value can be selected based on its slope, while a
The following example shows how the different TMIN and
TRANGE settings can be applied to three different thermal
zones. In this example, the following TRANGE values apply:
TRANGE = 80°C for ambient temperature
TRANGE = 53.3°C for CPU temperature
TRANGE = 40°C for VRM temperature
This example uses the mux configuration described in the
Step 2: Configuring the Mux section, with the ADT7473/
ADT7473−1 connected as shown in Figure 61. Both CPU
temperature and VRM temperature drive the CPU fan
connected to PWM1.
Ambient temperature drives the front chassis fan and rear
chassis fan connected to PWM2 and PWM3. The front
chassis fan is configured to run at PWMMIN = 20%. The rear
chassis fan is configured to run at PWMMIN = 30%. The
CPU fan is configured to run at PWMMIN = 10%.
Note on 4-wire Fans
The control range for 4-wire fans is much wider than that
for 3-wire fans. In many cases, 4-wire fans can start with a
PWM drive of as little as 20%.
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ADT7473
Hysteresis Registers
hard limit (such as 70°C), can be programmed as TMAX (the
temperature at which the fan reaches full speed) by setting
TTHERM to that limit (for example, 70°C).
Register 0x6D, Remote 1 Local Temperature Hysteresis
Register
Bits <7:4> Remote 1 temperature hysteresis (4°C default)
Bits <3:0> Local temperature hysteresis (4°C default)
Register 0x6E, Remote 2 Temperature Hysteresis Register
Bits <7:4> Remote 2 temperature hysteresis (4°C default)
Table 47. THERM REGISTERS
Register
Description
Default
0x6A
Remote 1 THERM
Temperature Limit
0xA4 (100°C)
0x6B
Local THERM Temperature
Limit
0xA4 (100°C)
0x6C
Remote 2 THERM
Temperature Limit
0xA4 (100°C)
Because each hysteresis setting is four bits, hysteresis
values are programmable from 1°C to 15°C. It is not
recommended that hysteresis values be programmed to 0°C,
because this disables hysteresis. In effect, this would cause
the fans to cycle between normal speed and 100% speed,
creating unsettling acoustic noise.
TRANGE
PWM DUTY CYCLE
100%
0%
TMIN
TTHERM
THERMAL CALIBRATION
PWM
MIN
100%
S
TMIN
TRANGE
PWM
MIN
100%
S
MUX
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM1
0%
THERMAL CALIBRATION
REMOTE2 =
CPU TEMP
PWM
CONFIG
TACHOMETER1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
Figure 62. How TTHERM Relates to Automatic Fan Control
Step 8: THYST for Temperature Channels
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
CPU FAN SINK
PWM3
TACH3
REAR CHASSIS
The THYST value chosen determines the amount of time
needed for the system to cool down or heat up as the fan turns
on and off. Values of hysteresis are programmable in the
range 1°C to 15°C. Larger values of THYST prevent the fans
from chattering on and off. The THYST default value is set
at 4°C.
THYST is the amount of extra cooling a fan provides after
the temperature measured has dropped back below TMIN
before the fan turns off. The premise for temperature
hysteresis (THYST) is that, without it, the fan would merely
chatter or cycle on and off regularly whenever temperature
is hovering at about the TMIN setting.
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ADT7473
The THYST setting applies not only to the temperature
hysteresis for fan on/off, but the same setting is used for the
TTHERM hysteresis value, described in Step 6: TRANGE for
Temperature Channels section. Therefore, programming
Register 0x6D and Register 0x6E sets the hysteresis for both
fan on/off and the THERM function.
Bits <3:0>, Local temperature hysteresis (4°C default)
Register 0x6E, Remote 2 Temperature Hysteresis Register
Bits <7:4>, Remote 2 temperature hysteresis (4°C default)
In some applications, it is required that fans not turn off
below TMIN, but remain running at PWMMIN. Bits <7:5> of
the Enhanced Acoustics Register 1 (0x62) allow the fans to
be turned off or to be kept spinning below TMIN. If the fans
are always on, the THYST value has no effect on the fan when
the temperature drops below TMIN.
Hysteresis Registers
Register 0x6D, Remote 1, Local Hysteresis Register
Bits <7:4>, Remote 1 temperature hysteresis (4°C default)
TRANGE
PWM DUTY CYCLE
100%
0%
TMIN
TTHERM
THERMAL CALIBRATION
PWM
MIN
100%
S
TMIN
TRANGE
PWM
MIN
100%
S
MUX
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM1
0%
THERMAL CALIBRATION
REMOTE2 =
CPU TEMP
PWM
CONFIG
TACHOMETER1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
CPU FAN SINK
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
REAR CHASSIS
Figure 63. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
Enhanced Acoustics Register 1 (0x62)
Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty
cycle below TMIN − THYST.
Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty
cycle below TMIN − THYST.
Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when
temperature is below TMIN − THYST.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty
cycle below TMIN − THYST.
Dynamic TMIN Control Mode
In addition to the automatic fan speed control mode
described in the Automatic Fan Control Overview section,
the ADT7473/ADT7473−1 has a mode that extends the
basic automatic fan speed control loop. Dynamic TMIN
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ADT7473
control allows the ADT7473/ADT7473−1 to intelligently
adapt the system’s cooling solution for best system
performance or lowest possible system acoustics, depending
on user or design requirements. Use of dynamic TMIN
control alleviates the need to design for worst-case
conditions and significantly reduces system design and
validation time.
Worst-case Processor Power Consumption
Designing for Worst-case Conditions
The tendency is to design to data sheet maximums for
peripheral components, again overcooling the system.
This data sheet maximum does not necessarily reflect the
true processor power consumption. Designing for
worst-case CPU power consumption can result in a
processor becoming overcooled (generating excess system
noise).
Worst-case Peripheral Power Consumption
System design must always allow for worst-case
conditions. In PC design, the worst-case conditions include,
but are not limited to, the following:
Worst-case Assembly
Every system is unique because of manufacturing
variations. Heat sinks may be loose fitting or slightly
misaligned. Too much or too little thermal grease might be
used, or variations in application pressure for thermal
interface material could affect the efficiency of the thermal
solution. Accounting for manufacturing variations in every
system is difficult; therefore, the system must be designed
for the worst-case conditions.
Worst-case Altitude
A computer can be operated at different altitudes. The
altitude affects the relative air density, which alters the
effectiveness of the fan cooling solution. For example,
comparing 40°C air temperature at 10,000 feet to 20°C air
temperature at sea level, relative air density is increased by
40%. This means that the fan can spin 40% slower and make
less noise at sea level than at 10,000 feet while keeping the
system at the same temperature at both locations.
TA
HEAT
SINK
Worst-case Fan
INTEGRATED
HEAT
SPREADER
GOOD CPU AIRFLOW
CPU
DRIVE
BAYS
FAN
CPU
DRIVE
BAYS
VENTS
GOOD VENTING = GOOD AIR
EXCHANGE
qJA
qTIMC
PROCESSOR
TTIM
TJ
Dynamic TMIN control mode builds on the basic
automatic fan control loop by adjusting the TMIN value
based on system performance and measured temperature.
This is important because, instead of designing for the worst
case, the system thermals can be defined as operating zones.
The ADT7473/ADT7473−1 can self-adjust its fan control
loop to maintain either an operating zone temperature or a
system target temperature. For example, it can be specified
that the ambient temperature in a system should be
maintained at 50°C. If the temperature is below 50°C, the
fans might not need to run, or might run very slowly. If the
temperature is higher than 50°C, the fans need to throttle up.
The challenge presented by any thermal design is finding
the right settings to suit the system’s fan control solution.
This can involve designing for the worst case, followed by
weeks of system thermal characterization, and finally fan
acoustic optimization (for psycho-acoustic reasons).
POWER
SUPPLY
POOR CPU
AIRFLOW
TC
Dynamic TMIN Control Overview
FAN
VENTS
qCTIM
Although a design usually accounts for worst-case
conditions in all these cases, the actual system is almost
never operated at worst-case conditions. The alternative to
designing for the worst case is to use the dynamic TMIN
control function.
I/O CARDS
POWER
SUPPLY
qCA
qCS
Figure 65. Thermal Model
The same motherboard can be used in a number of
different chassis configurations. The design of the chassis
and the physical location of fans and components determine
the system thermal characteristics. Moreover, for a given
chassis, the addition of add-in cards, cables, or other system
configuration options can alter the system airflow and
reduce the effectiveness of the system cooling solution. The
cooling solution can also be inadvertently altered by the end
user. (For example, placing a computer against a wall can
block the air ducts and reduce system airflow.)
I/O CARDS
TTIM
qJTIM
SUBSTRATE
EPOXY
THERMAL INTERFACE MATERIAL
Worst-case Chassis Airflow
FAN
TS
qTIMS
THERMAL
INTERFACE
MATERIAL
Due to manufacturing tolerances, fan speeds in RPM are
normally quoted with a tolerance of ±20%. The designer
needs to assume that the fan RPM can be 20% below
tolerance. This translates to reduced system airflow and
elevated system temperature. Note that fans 20% out of
tolerance can negatively impact system acoustics because
they run faster and generate more noise.
VENTS
qSA
POOR VENTING = POOR AIR
EXCHANGE
Figure 64. Chassis Airflow Issues
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ADT7473
Getting the most benefit from the automatic fan control
mode involves characterizing the system to find the best
TMIN and TRANGE settings for the control loop, and the best
PWMMIN value for the quietest fan speed setting. Using the
ADT7473/ADT7473−1’s dynamic TMIN control mode,
however, shortens the characterization time and alleviates
tweaking the control loop settings because the device can
self-adjust during system operation.
Dynamic TMIN control mode is operated by specifying the
operating zone temperatures required for the system.
Associated with this control mode are three operating point
registers, one for each temperature channel. This allows the
system thermal solution to be broken down into distinct
thermal zones. For example, CPU operating temperature is
70°C, VRM operating temperature is 80°C, and ambient
operating temperature is 50°C. The ADT7473/ADT7473−1
dynamically alters the control solution to maintain each
zone temperature as closely as possible to its target operating
point.
Table 49 provides a brief description of each parameter.
Table 49. TMIN CONTROL LOOP PARAMETERS
Parameter
Table 48. OPERATING POINT REGISTERS
Register
Description
Remote 1 Operating Point
0xA4 (100°C)
Local Temp. Operating Point
0xA4 (100°C)
0x35
Remote 2 Operating Point
0xA4 (100°C)
Figure 66 shows an overview of the parameters that affect
the operation of the dynamic TMIN control loop.
THIGH
If the temperature exceeds the THIGH limit, an
error flag is set in a status register and an
SMBALERT interrupt can be generated.
TMIN
The temperature at which the fan turns on
under automatic fan speed control.
Operating
Point
The target temperature for a particular
temperature zone. The ADT7473/ADT7473−1
attempts to maintain system temperature at
about the operating point by adjusting the TMIN
parameter of the control loop.
TTHERM
If the temperature exceeds this critical limit, the
fans can be run at 100% for maximum cooling.
TRANGE
Programs the PWM duty cycle vs. temperature
control slope.
Step 9: Operating Points for Temperature Channels
PWM DUTY CYCLE
The operating point for each temperature channel is the
optimal temperature for that thermal zone. The hotter each
zone is allowed to be, the quieter the system, because the
fans are not required to run as fast. The ADT7473/
ADT7473−1 increases or decreases fan speeds as necessary
to maintain the operating point temperature, allowing for
system-to-system variation and removing the need for
worst-case design. If a sensible operating point value is
chosen, any TMIN value can be selected in the system
characterization. If the TMIN value is too low, the fans run
sooner than required, and the temperature is below the
operating point. In response, the ADT7473/ADT7473−1
increases TMIN to keep the fans off longer and to allow the
temperature zone to get closer to the operating point.
Likewise, too high a TMIN value causes the operating point
to be exceeded, and in turn, the ADT7473/ADT7473−1
reduces TMIN to turn the fans on sooner to cool the system.
TEMPERATURE
TTHERM
THIGH
If the temperature drops below the TLOW limit,
an error flag is set in a status register and an
SMBALERT interrupt can be generated.
Because the dynamic TMIN control mode is a basic
extension of the automatic fan control mode, program the
automatic fan control mode parameters first, as described in
the Step 1: Hardware Configuration section to the Step 8:
THYST for Temperature Channels section, then proceed with
dynamic TMIN control mode programming.
Default
0x34
TMIN OPERATING
POINT
TLOW
Dynamic TMIN Control Programming
0x33
TLOW
Description
TRANGE
Figure 66. Dynamic TMIN Control Loop
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ADT7473
Programming Operating Point Registers
Table 50. OPERATING POINT REGISTERS
There are three operating point registers, one for each
temperature channel. These 8-bit registers allow the
operating point temperatures to be programmed with 1°C
resolution.
Register
THERMAL CALIBRATION
0xA4 (100°C)
0x34
Local Operating Point
0xA4 (100°C)
0x35
Remote 2 Operating Point
0xA4 (100°C)
OPERATING
POINT
PWM
MIN
100%
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
S
TRANGE
TACHOMETER2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
100%
TMIN
TACHOMETER1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
MUX
TMIN
PWM
GENERATOR
PWM1
0%
THERMAL CALIBRATION
REMOTE2 =
CPU TEMP
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
S
TRANGE
Default
Remote 1 Operating Point
PWM
MIN
100%
TMIN
Description
0x33
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
CPU FAN SINK
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
REAR CHASSIS
Figure 67. Operating Point Value Dynamically Adjusts Automatic Fan Control Settings
Step 10: High and Low Limits for Temperature
Channels
Table 51. TEMPERATURE LIMIT REGISTERS
Register
The low limit defines the temperature at which the TMIN
value starts to be increased, if temperature falls below this
value. This has the net effect of reducing the fan speed,
allowing the system to get hotter. An interrupt can be
generated when the temperature drops below the low limit.
The high limit defines the temperature at which the TMIN
value starts to be reduced, if temperature increases above
this value. This has the net effect of increasing fan speed to
cool down the system. An interrupt can be generated when
the temperature rises above the high limit.
Description
Default
0x4E
Remote 1 Temperature Low Limit
0x01
0x4F
Remote 1 Temperature High Limit
0x7F
0x50
Local Temperature Low Limit
0x01
0x51
Local Temperature High Limit
0x7F
0x52
Remote 2 Temperature Low Limit
0x01
0x53
Remote 2 Temperature High Limit
0x7F
How Dynamic TMIN Control Works
The basic premise is as follows:
1. Set the target temperature for the temperature
zone, which could be, for example, the Remote 1
thermal diode. This value is programmed to the
Remote 1 operating temperature register.
Programming High and Low Limits
There are six limit registers; a high limit and low limit are
associated with each temperature channel. These 8-bit
registers allow the high and low limit temperatures to be
programmed with 1°C resolution.
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ADT7473
2. As the temperature in that zone (Remote 1
temperature) rises toward and exceeds the
operating point temperature, TMIN is reduced, and
the fan speed increases.
3. As the temperature drops below the operating
point temperature, TMIN is increased, and the fan
speed is reduced.
WAIT n
MONITORING
CYCLES
CURRENT
TEMPERATURE
MEASUREMENT
T1(n)
However, the loop operation is not as simple as described
in these steps. A number of conditions govern the situations
in which TMIN can increase or decrease.
IS T1(n) − T1(n − 1)
≤ 0.255C
YES
IS T1(n) - T1(n - 1) = 0.5 - 0.755C
IS T1(n) - T1(n - 1) = 1.0 - 1.755C
IS T1(n) - T1(n - 1) > 2.05C
Long Cycle
8 cycles
1 sec
16 cycles
2 sec
001
16 cycles
2 sec
32 cycles
4 sec
010
32 cycles
4 sec
64 cycles
8 sec
DECREASE TMIN BY 15C
DECREASE TMIN BY 25C
DECREASE TMIN BY 45C
Figure 69 shows the steps taken during the long cycle.
WAIT 2n
MONITORING
CYCLES
CURRENT
TEMPERATURE
MEASUREMENT
T1(n)
OPERATING
POINT
TEMPERATURE
OP1
IS T1(n) > OP1
YES
DECREASE TMIN
BY 15C
NO
IS T1(n) < LOW TEMP LIMIT
AND
TMIN < HIGH TEMP LIMIT YES
AND
TMIN < OP1
AND
T1(n) > TMIN
Secs
000
DO NOTHING
(SYSTEM IS
COOLING OFF
FOR CONSTANT)
Figure 68. Short Cycle Steps
Table 52. CYCLE BIT ASSIGNMENTS
Secs
DO NOTHING
NO
The ADT7473/ADT7473−1 implements two loops: a
short cycle and a long cycle. The short cycle takes place
every n monitoring cycles. The long cycle takes place every
2n monitoring cycles. The value of n is programmable for
each temperature channel. The bits are located at the
following register locations:
Remote 1 = CYR1 = Bits <2:0> of Dynamic TMIN Control
Register 2 (0x37).
Local = CYL = Bits <5:3> of Dynamic TMIN Control
Register 2 (0x37).
Remote 2 = CYR2 = Bits <7:6> of Dynamic TMIN Control
Register 2 (0x37) and Bit 0 of Dynamic TMIN Control
Register 1 (0x36).
Short Cycle
NO
YES
PREVIOUS
TEMPERATURE
MEASUREMENT
T1 (n − 1)
Short Cycle and Long Cycle
Code
IS T1(n) >
(OP1 − HYS)
OPERATING
POINT
TEMPERATURE
OP1
INCREASE
TMIN BY 15C
NO
DO NOT
CHANGE
011
64 cycles
8 sec
128 cycles
16 sec
100
128 cycles
16 sec
256 cycles
32 sec
Figure 69. Long Cycle Steps
101
256 cycles
32 sec
512 cycles
64 sec
110
512 cycles
64 sec
1024 cycles
128 sec
111
1024 cycles
128 sec
2048 cycles
256 sec
The following examples illustrate some of the
circumstances that might cause TMIN to increase, decrease,
or stay the same.
Example 1: Normal Operation − No TMIN Adjustment
Care should be taken when choosing the cycle time. A
long cycle time means that TMIN is updated less often. If
your system has very fast temperature transients, the
dynamic TMIN control loop is always lagging. If a cycle time
is chosen that is too fast, the full benefit of changing TMIN
might not be realized and needs to change again on the next
cycle; in effect, it is overshooting. It is necessary to carry out
some calibration to identify the most suitable response time.
Figure 68 shows the steps taken during the short cycle.
• If measured temperature never exceeds the
•
programmed operating point minus the hysteresis
temperature, then TMIN is not adjusted; that is, it
remains at its current setting.
If measured temperature never drops below the low
temperature limit, then TMIN is not adjusted.
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ADT7473
Example 3: Increase TMIN Cycle
THERM LIMIT
HIGH TEMP LIMIT
OPERATING
POINT
When the temperature drops below the low temperature
limit, TMIN can increase in the long cycle. Increasing TMIN
has the effect of running the fan slower and, therefore,
quieter. The long cycle diagram in Figure 69 shows the
conditions required for TMIN to increase. A quick summary
of those conditions and the reasons they need to be true
follows.
TMIN can increase if:
• The measured temperature falls below the low temperature
limit. This means the user must choose the low limit
carefully. It should not be so low that the temperature
never falls below it because TMIN would never increase,
and the fans would run faster than necessary.
• TMIN is below the high temperature limit. TMIN is
never allowed to increase above the high temperature
limit. As a result, the high limit should be sensibly
chosen because it determines how high TMIN can go.
• TMIN is below the operating point temperature. TMIN
should never be allowed to increase above the operating
point temperature because the fans would not switch on
until the temperature rose above the operating point.
• The temperature is above TMIN. The dynamic TMIN
control is turned off below TMIN.
HYSTERESIS
ACTUAL TEMP
LOW TEMP LIMIT
TMIN
Figure 70. Temperature Between the Operating Point
and the Low Temperature Limit
Because neither the operating point minus the hysteresis
temperature nor the low temperature limit has been
exceeded, the TMIN value is not adjusted, and the fan runs at
a speed determined by the fixed TMIN and TRANGE values
defined in the automatic fan speed control mode.
Example 2: Operating Point Exceeded − TMIN Reduced
When the measured temperature is below the operating
point temperature minus the hysteresis, TMIN remains the
same.
Once the temperature exceeds the operating temperature
minus the hysteresis (OP − Hyst), TMIN starts to decrease.
This occurs during the short cycle (see Figure 68). The rate
at which TMIN decreases depends on the programmed value
of n. It also depends on how much the temperature has
increased between this monitoring cycle and the last
monitoring cycle; that is, if the temperature has increased by
1°C, then TMIN is reduced by 2°C. Decreasing TMIN has the
effect of increasing the fan speed, thus providing more
cooling to the system.
If the temperature slowly increases only in the range
(OP − Hyst), that is, ≤0.25°C per short monitoring cycle,
then TMIN does not decrease. This allows small changes in
temperature in the desired operating zone without changing
TMIN. The long cycle makes no change to TMIN in the
temperature range (OP − Hyst) because the temperature has
not exceeded the operating temperature.
Once the temperature exceeds the operating temperature,
the long cycle causes TMIN to be reduced by 1°C every long
cycle while the temperature remains above the operating
temperature. This takes place in addition to the decrease in
TMIN that occurs due to the short cycle. In Figure 71, because
the temperature is increasing at a rate ≤0.25°C per short cycle,
no reduction in TMIN takes place during the short cycle.
Once the temperature falls below the operating
temperature, TMIN stays the same. Even when the
temperature starts to increase slowly, TMIN stays the same
because the temperature increases at a rate ≤0.25°C per cycle.
THERM
LIMIT
HIGH TEMP
LIMIT
OPERATING
POINT
HYSTERESIS
ACTUAL
TEMP
NO CHANGE IN TMIN HERE
DUE TO ANY CYCLE BECAUSE
T1(n) - T1 (n - 1) ≤ 0.255C
AND T1(n) < OP = > T MIN
STAYS THE SAME
TMIN
LOW TEMP
LIMIT
DECREASE HERE DUE TO
SHORT CYCLE ONLY
T1(n) - T1 (n - 1) = 0.55C
OR 0.755C = > TMIN
DECREASES BY 15C
EVERY SHORT CYCLE
DECREASE HERE DUE TO
LONG CYCLE ONLY
T1(n) - T1 (n - 1) ≤ 0.255C
AND T1(n) > OP = > T MIN
DECREASES BY 15C
EVERY LONG CYCLE
Figure 71. Effect of Exceeding Operating Point Minus
Hysteresis Temperature
www.onsemi.com
47
ADT7473
the Pentium® 4 is connected to the THERM input of the
ADT7473/ADT7473−1.
The operating point for the processor can be determined
by allowing the current temperature to be copied to the
operating point register when the PROCHOT output pulls
the THERM input low on the ADT7473/ADT7473−1. This
gives the maximum temperature at which the Pentium® 4
can run before clock modulation occurs.
Figure 72 shows how TMIN increases when the current
temperature is above TMIN and below the low temperature
limit, and TMIN is below the high temperature limit and
below the operating point. Once the temperature rises above
the low temperature limit, TMIN stays the same.
THERM
LIMIT
HIGH TEMP
LIMIT
OPERATING
POINT
LOW TEMP
LIMIT
Enabling the THERM Trip Point as the Operating Point
HYSTERESIS
Bits <4:2> of Dynamic TMIN Control Register 1 (0x36)
enable/disable THERM monitoring to program the
operating point.
ACTUAL
TEMP
Dynamic TMIN Control Register 1 (0x36)
TMIN
Bit <4> PHTR2 = 1, copies the Remote 2 current
temperature to the Remote 2 operating point register, if
THERM is asserted. The operating point contains the
temperature at which THERM is asserted. This allows the
system to run as quietly as possible without affecting system
performance.
PHTR2 = 0, ignores any THERM assertions. The Remote 2
operating point register reflects its programmed value.
Bit <3> PHTL = 1, copies the local current temperature to
the local temperature operating point register if THERM is
asserted. The operating point contains the temperature at
which THERM is asserted. This allows the system to run as
quietly as possible without affecting system performance.
PHTL = 0, ignores any THERM assertions. The local
temperature operating point register reflects its programmed
value.
Bit <2> PHTR1 = 1, copies the Remote 1 current
temperature to the Remote 1 operating point register if
THERM is asserted. The operating point contains the
temperature at which THERM is asserted. This allows the
system to run as quietly as possible without affecting system
performance.
PHTR1 = 0, ignores any THERM assertions. The Remote 1
operating point register reflects its programmed value.
Figure 72. Increasing TMIN for Quieter Operation
Example 4: Preventing TMIN from Reaching Full Scale
Because TMIN is dynamically adjusted, it is undesirable
for TMIN to reach full scale (127°C) because the fan would
never switch on. As a result, TMIN is allowed to vary only
within a specified range:
• The lowest possible value for TMIN is −127°C (twos
complement mode) or −64°C (Offset 64 mode).
• TMIN cannot exceed the high temperature limit.
• If the temperature is below TMIN, the fan is switched
off or runs at minimum speed and dynamic TMIN
control is disabled.
THERM
LIMIT
OPERATING
POINT
LOW TEMP
LIMIT
HYSTERESIS
ACTUAL
TEMP
HIGH TEMP
LIMIT
TMIN
TMIN PREVENTED
FROM INCREASING
Figure 73. TMIN Adjustments Limited by the High
Temperature Limit
Enabling Dynamic TMIN Control Mode
Bits <7:5> of the Dynamic TMIN Control Register 1 (0x36)
enable/disable dynamic TMIN control on the temperature
channels.
Step 11: Monitoring THERM
Using the operating point limit ensures that the dynamic
TMIN control mode operates in the best possible acoustic
position while ensuring that the temperature never exceeds
the maximum operating temperature. Using the operating
point limit allows TMIN to be independent of system-level
issues because of its self-corrective nature. In PC design, the
operating point for the chassis is usually the worst-case
internal chassis temperature.
The optimal operating point for the processor is
determined by monitoring the thermal monitor in the Intel®
Pentium® 4 processor. To do this, the PROCHOT output of
Dynamic TMIN Control Register 1 (0x36)
Bit <7> R2T = 1, enables dynamic TMIN control on the
Remote 2 temperature channel. The chosen TMIN value is
dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
R2T = 0, disables dynamic TMIN control. The TMIN value
chosen is not adjusted and the channel behaves as described
in the Automatic Fan Control Overview section.
www.onsemi.com
48
ADT7473
Bit <6> LT = 1, enables dynamic TMIN control on the local
temperature channel. The chosen TMIN value is dynamically
adjusted based on the current temperature, operating point,
and high and low limits for this zone.
LT = 0, disables dynamic TMIN control. The TMIN value
chosen is not adjusted and the channel behaves as described
in the Automatic Fan Control Overview section.
Bit <5> R1T = 1, enables dynamic TMIN control on the
Remote 1 temperature channel. The chosen TMIN value is
dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
R1T = 0, disables dynamic TMIN control. The TMIN value
chosen is not adjusted, and the channel behaves as described
in the Automatic Fan Control Overview section.
mechanical engineer evaluating best settings for the system.
Having determined the optimal settings for the thermal
solution, the engineer can adjust the system acoustics. The
goal is to implement a system that is acoustically pleasing
without causing user annoyance due to fan cycling. It is
important to realize that although a system might pass an
acoustic noise requirement specification (for example,
36 dB), if the fan is annoying, it fails the consumer test.
Approaches to System Acoustic Enhancement
There are two different approaches to implementing
system acoustic enhancement: temperature-centric and
fan-centric.
The temperature-centric approach involves smoothing
transient temperatures as they are measured by a
temperature source (for example, Remote 1 temperature).
The temperature values used to calculate the PWM duty
cycle values are smoothed, reducing fan speed variation.
However, this approach causes an inherent delay in updating
fan speed and causes the thermal characteristics of the
system to change. It also causes the system fans to stay on
longer than necessary because the fan’s reaction is merely
delayed. The user has no control over noise from different
fans driven by the same temperature source. Consider, for
example, a system in which control of a CPU cooler fan (on
PWM1) and a chassis fan (on PWM2) use Remote 1
temperature. Because the Remote 1 temperature is
smoothed, both fans are updated at exactly the same rate. If
the chassis fan is much louder than the CPU fan, there is no
way to improve its acoustics without changing the thermal
solution of the CPU cooling fan.
Enhancing System Acoustics
Automatic fan speed control mode reacts instantaneously
to changes in temperature; that is, the PWM duty cycle
responds immediately to temperature change. Any impulses
in temperature can cause an impulse in fan noise. For
psycho-acoustic reasons, the ADT7473/ADT7473−1 can
prevent the PWM output from reacting instantaneously to
temperature changes. Enhanced acoustic mode controls the
maximum change in PWM duty cycle at a given time. The
objective is to prevent the fan from cycling up and down,
annoying the user.
Acoustic Enhancement Mode Overview
Figure 74 gives a top-level overview of the automatic fan
control circuitry on the ADT7473/ADT7473−1 and shows
where acoustic enhancement fits in. Acoustic enhancement
is intended as a post design tweak made by a system or
ACOUSTIC
ENHANCEMENT
THERMAL CALIBRATION
PWM
MIN
100%
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
PWM
MIN
100%
S
MUX
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM1
0%
THERMAL CALIBRATION
TMIN
PWM
CONFIG
TACHOMETER1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACH1
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM2
TACH2
FRONT CHASSIS
PWM
GENERATOR
TACHOMETER3
AND 4
MEASUREMENT
0%
CPU FAN SINK
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
Figure 74. Acoustic Enhancement Smoothes Fan Speed Variations
Under Automatic Fan Speed Control
www.onsemi.com
49
REAR CHASSIS
ADT7473
The fan-centric approach to system acoustic enhancement
controls the PWM duty cycle, driving the fan at a fixed rate
(for example, 6%). Each time the PWM duty cycle is
updated, it is incremented by a fixed 6%. As a result, the fan
ramps smoothly to its newly calculated speed. If the
temperature starts to drop, the PWM duty cycle immediately
decreases by 6% at every update. Therefore, the fan ramps
smoothly up or down without inherent system delay.
Consider, for example, controlling the same CPU cooler fan
(on PWM1) and chassis fan (on PWM2) using Remote 1
temperature. The TMIN and TRANGE settings have already
been defined in automatic fan speed control mode, that is,
thermal characterization of the control loop has been
optimized. Here, the chassis fan is noisier than the CPU
cooling fan. Using the fan-centric approach, PWM2 can be
placed into acoustic enhancement mode independently of
PWM1. The acoustics of the chassis fan can, therefore, be
adjusted without affecting the acoustic behavior of the CPU
cooling fan, even though both fans are controlled by
Remote 1 temperature. The fan-centric approach is how
acoustic enhancement works on the ADT7473/
ADT7473−1.
If the PWM duty cycle value needs to be decreased, it is
decreased by eight time slots. Figure 76 shows how the
enhanced acoustics mode algorithm operates.
The enhanced acoustics mode algorithm calculates a new
PWM duty cycle based on the temperature measured. If the
new PWM duty cycle value is greater than the previous
PWM value, then the previous PWM duty cycle value is
incremented by either 1, 2, 3, 5, 8, 12, 24, or 48 time slots,
depending on the settings of the enhanced acoustics
registers. If the new PWM duty cycle value is less than the
previous PWM value, the previous PWM duty cycle is
decremented by 1, 2, 3, 5, 8, 12, 24, or 48 time slots. Each
time the PWM duty cycle is incremented or decremented, its
value is stored as the previous PWM duty cycle for the next
comparison. A ramp rate of 1 corresponds to one time slot,
which is 1/255 of the PWM period. In enhanced acoustics
mode, incrementing or decrementing by 1 changes the PWM
output by 1/255 × 100%.
READ
TEMPERATURE
CALCULATE
NEW PWM
DUTY CYCLE
Enabling Acoustic Enhancement for Each PWM
Output
Enhanced acoustics Register 1 (0x62)
Bit 3 = 1, enables acoustic enhancement on PWM1 output
IS
NEW PWM
VALUE >
PREVIOUS
VALUE?
Enhanced acoustics Register 2 (0x63)
Bit 7 = 1, enables acoustic enhancement on PWM2 output
Bit 3 = 1, enables acoustic enhancement on PWM3 output
Effect of Ramp Rate on Enhanced Acoustics Mode
DECREMENT
PREVIOUS
PWM VALUE
BY RAMP RATE
YES
The PWM signal driving the fan has a period, T, given by
the PWM drive frequency, f, because T = 1/f. For a given
PWM period, T, the PWM period is subdivided into 255
equal time slots. One time slot corresponds to the smallest
possible increment in the PWM duty cycle. A PWM signal
of 33% duty cycle is, therefore, high for 1/3 × 255 time slots
and low for 2/3 × 255 time slots. Therefore, a 33% PWM
duty cycle corresponds to a signal that is high for 85 time
slots and low for 170 time slots.
INCREMENT
PREVIOUS
PWM VALUE
BY RAMP RATE
Figure 76. Enhanced Acoustics Algorithm
Step 12: Ramp Rate for Acoustic Enhancement
The optimal ramp rate for acoustic enhancement can be
found through system characterization after the thermal
optimization has been finished. The effect of each ramp rate
should be logged, if possible, to determine the best setting
for a given solution.
PWM_OUT
33% DUTY
CYCLE
85
TIME SLOTS
NO
170
TIME SLOTS
Enhanced Acoustics Register 1 (0x62)
PWM OUTPUT (ONE PERIOD)
= 255 TIME SLOTS
Bits <2:0> ACOU, select the ramp rate for PWM1.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Figure 75. 33% PWM Duty Cycle Represented in
Time Slots
The ramp rates in the enhanced acoustics mode are
selectable from the values 1, 2, 3, 5, 8, 12, 24, and 48. The
ramp rates are discrete time slots. For example, if the ramp
rate is 8, then eight time slots are added to the PWM high duty
cycle each time the PWM duty cycle needs to be increased.
www.onsemi.com
50
ADT7473
Enhanced Acoustics Register 2 (0x63)
Figure 78 shows how changing the ramp rate from 48 to
8 affects the control loop. The overall response of the fan is
slower. Because the ramp rate is reduced, it takes longer for
the fan to achieve full running speed. In this case, it takes
approximately 4.4 seconds for the fan to reach full speed.
RTEMP(°C)
100
RTEMP(°C)
80
80
60
PWM DUTY CYCLE (%)
60
40
40
20
20
0
0
0
4.4
TIME (s)
Figure 78. Enhanced Acoustics Mode with
Ramp Rate = 8
Figure 79 shows the PWM output response for a ramp rate
of 2. In this instance, the fan takes about 17.6 seconds to
reach full running speed.
140
120
RTEMP(°C)
120
RTEMP(°C)
100
80
80
60
60
PWM DUTY CYCLE (%)
40
120
20
100
0
40
PWM CYCLE (%)
100
20
RTEMP(°C)
120
0
100
80
80
60
60
PWM CYCLE (%)
40
40
PWM CYCLE (%)
0
RTEMP(°C)
120
100
Another way to view the ramp rates is to measure the time
it takes for the PWM output to ramp up from 0% to 100%
duty cycle for an instantaneous change in temperature. This
can be tested by putting the ADT7473/ADT7473−1 into
manual mode and changing the PWM output from 0% to
100% PWM duty cycle. The PWM output takes 35 seconds
to reach 100% when a ramp rate of 1 time slot is selected.
Figure 77 shows remote temperature plotted against
PWM duty cycle for enhanced acoustics mode. The ramp
rate is set to 48, which corresponds to the fastest ramp rate.
Assume that a new temperature reading is available every
115 ms. With these settings, it takes approximately
0.76 seconds to go from 33% duty cycle to 100% duty cycle
(full speed). Even though the temperature increases very
rapidly, the fan ramps up to full speed gradually.
140
140
120
PWM CYCLE (%)
Bits <2:0> ACOU3, select the ramp rate for PWM3.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Bits <6:4> ACOU2, select the ramp rate for PWM2.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Figure 79. Enhanced Acoustics Mode with
Ramp Rate = 2
Figure 80 shows how the control loop reacts to
temperature with the slowest ramp rate. The ramp rate is set
to 1, while all other control parameters remain the same.
With the slowest ramp rate selected, it takes 35 seconds for
the fan to reach full speed.
20
20
0
0
TIME (s)
TIME (s)
17.6
0
0.76
Figure 77. Enhanced Acoustics Mode with
Ramp Rate = 48
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51
ADT7473
RTEMP(°C)
100
Slower Ramp Rates
120
The ADT7473/ADT7473−1 can be programmed for
much longer ramp times by slowing the ramp rates. Each
ramp rate can be slowed by a factor of 4.
100
80
RTEMP(°C)
140
80
60
60
40
40
PWM DUTY CYCLE (%)
20
0
0
TIME (s)
PWM CYCLE (%)
120
PWM1 Configuration Register (0x5C)
Bit <3> SLOW, 1 slows the ramp rate for PWM1 by 4.
PWM2 Configuration Register (0x5D)
Bit <3> SLOW, 1 slows the ramp rate for PWM2 by 4.
20
PWM3 Configuration Register (0x5E)
0
Bit <3> SLOW, 1 slows the ramp rate for PWM3 by 4.
The following sections list the ramp-up times when the
SLOW bit is set for each PWM output.
35
Figure 80. Enhanced Acoustics Mode with
Ramp Rate = 1
Enhanced Acoustics Register 1 (0x62)
As Figure 77 to Figure 80 show, the rate at which the fan
reacts to temperature change is dependent on the ramp rate
selected in the enhanced acoustics registers. The higher the
ramp rate, the faster the fan reaches the newly calculated fan
speed.
90
90
PWM DUTY CYCLE (%)
80
70
70
60
60
50
50
40
RTEMP(°C)
40
30
30
20
20
10
10
0
PWM CYCLE (%)
RTEMP(°C)
80
Bits <2:0> ACOU, select the ramp rate for PWM1.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 sec
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
Enhanced Acoustics Register 2 (0x63)
Bits <2:0> ACOU3, select the ramp rate for PWM3.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 sec
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
Bits <6:4> ACOU2, select the ramp rate for PWM2.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 sec
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
0
TIME (s)
Figure 81. How Fan Reacts to Temperature Variations
in Enhanced Acoustics Mode
Figure 81 shows the behavior of the PWM output as
temperature varies. As the temperature increases, the fan
speed ramps up. Small drops in temperature do not affect the
ramp-up function because the newly calculated fan speed is
still higher than the previous PWM value. Enhanced
acoustics mode allows the PWM output to be made less
sensitive to temperature variations. This is dependent on the
ramp rate selected and programmed into the enhanced
acoustics registers.
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52
ADT7473
Register Tables
Table 53. ADT7473/ADT7473−1 REGISTERS
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
0x21
R
VCCP
Reading
9
8
7
6
5
4
3
2
0x00
−
0x22
R
VCC
Reading
9
8
7
6
5
4
3
2
0x00
−
0x25
R
Remote 1
Temp.
9
8
7
6
5
4
3
2
0x01
−
0x26
R
Local
Temp.
9
8
7
6
5
4
3
2
0x01
−
0x27
R
Remote 2
Temp.
9
8
7
6
5
4
3
2
0x01
−
0x28
R
TACH1 Low
Byte
7
6
5
4
3
2
1
0
0x00
−
0x29
R
TACH1
High Byte
15
14
13
12
11
10
9
8
0x00
−
0x2A
R
TACH2 Low
Byte
7
6
5
4
3
2
1
0
0x00
−
0x2B
R
TACH2
High Byte
15
14
13
12
11
10
9
8
0x00
−
0x2C
R
TACH3 Low
Byte
7
6
5
4
3
2
1
0
0x00
−
0x2D
R
TACH3
High Byte
15
14
13
12
11
10
9
8
0x00
−
0x2E
R
TACH4 Low
Byte
7
6
5
4
3
2
1
0
0x00
−
0x2F
R
TACH4
High Byte
15
14
13
12
11
10
9
8
0x00
−
0x30
R/W
PWM1
Current
Duty Cycle
7
6
5
4
3
2
1
0
0x00/0
xFF
−
0x31
R/W
PWM2
Current
Duty Cycle
7
6
5
4
3
2
1
0
0x00/0
xFF
−
0x32
R/W
PWM3
Current
Duty Cycle
7
6
5
4
3
2
1
0
0x00/0
xFF
−
0x33
R/W
Remote 1
Operating
Point
7
6
5
4
3
2
1
0
0xA4
Yes
0x34
R/W
Local Temp
Operating
Point
7
6
5
4
3
2
1
0
0xA4
Yes
0x35
R/W
Remote 2
Operating
Point
7
6
5
4
3
2
1
0
0xA4
Yes
0x36
R/W
Dynamic
TMIN
Control
Reg. 1
R2T
LT
R1T
PHTR2
PHTL
PHTR1
VCCPLO
CYR2
0x00
Yes
0x37
R/W
Dynamic
TMIN
Control
Reg. 2
CYR2
CYR2
CYL
CYL
CYL
CYR1
CYR1
CYR1
0x00
Yes
0x38
R/W
PWM1 Max
Duty Cycle
7
6
5
4
3
2
1
0
0xFF
−
0x39
R/W
PWM2 Max
Duty Cycle
7
6
5
4
3
2
1
0
0xFF
−
0x3A
R/W
PWM3 Max
Duty Cycle
7
6
5
4
3
2
1
0
0xFF
−
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53
ADT7473
Table 53. ADT7473/ADT7473−1 REGISTERS (continued)
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
0x3D
R
Device ID
Register
7
6
5
4
3
2
1
0
0x73
−
0x3E
R
Company
ID Number
7
6
5
4
3
2
1
0
0x41
−
0x3F
R
Revision ID
Register
7
6
5
4
3
2
1
0
0x68/0
x69
−
0x40
R/W
Config.
Register 1
ADT7473:
RES
ADT7473−1:
Latch Reset
TODIS
FSPDIS
Vx1
FSPD
RDY
LOCK
STRT
0x01
Yes
0x41
R
Interrupt
Status
Register 1
OOL
R2T
LT
R1T
RES
VCC
VCCP
RES
0x00
−
0x42
R
Interrupt
Status
Register 2
D2
D1
F4P
FAN3
FAN2
FAN1
OVT
ADT7473:
RES
ADT7473−1:
THERM
Limit Latch
0x00
−
0x46
R/W
VCCP Low
Limit
7
6
5
4
3
2
1
0
0x00
−
0x47
R/W
VCCP High
Limit
7
6
5
4
3
2
1
0
0xFF
−
0x48
R/W
VCC Low
Limit
7
6
5
4
3
2
1
0
0x00
−
0x49
R/W
VCC High
Limit
7
6
5
4
3
2
1
0
0xFF
−
0x4E
R/W
Remote 1
Temp. Low
Limit
7
6
5
4
3
2
1
0
0x01
−
0x4F
R/W
Remote 1
Temp. High
Limit
7
6
5
4
3
2
1
0
0xFF
−
0x50
R/W
Local Temp.
Low Limit
7
6
5
4
3
2
1
0
0x01
−
0x51
R/W
Local Temp.
High Limit
7
6
5
4
3
2
1
0
0xFF
−
0x52
R/W
Remote 2
Temp. Low
Limit
7
6
5
4
3
2
1
0
0x01
−
0x53
R/W
Remote 2
Temp. High
Limit
7
6
5
4
3
2
1
0
0xFF
−
0x54
R/W
TACH1
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x55
R/W
TACH1
Minimum
High Byte
15
14
13
12
11
10
9
8
0xFF
−
0x56
R/W
TACH2
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x57
R/W
TACH2
Minimum
High Byte
15
14
13
12
11
10
9
8
0xFF
−
0x58
R/W
TACH3
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x59
R/W
TACH3
Minimum
High Byte
15
14
13
12
11
10
9
8
0xFF
−
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54
ADT7473
Table 53. ADT7473/ADT7473−1 REGISTERS (continued)
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
0x5A
R/W
TACH4
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x5B
R/W
TACH4
Minimum
High Byte
15
14
13
12
11
10
9
8
0xFF
−
0x5C
R/W
PWM1
Config.
Register
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82/0
x62
Yes
0x5D
R/W
PWM2
Config.
Register
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82/0
x62
Yes
0x5E
R/W
PWM3
Config.
Register
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82/0
x62
Yes
0x5F
R/W
Remote 1
TRANGE/
PWM 1
Frequency
RANGE
RANGE
RANGE
RANGE
HF/LF
Fan 1
FREQ
FREQ
FREQ
0xCC
Yes
0x60
R/W
Local
TRANGE/
PWM 2
Frequency
RANGE
RANGE
RANGE
RANGE
HF/LF
Fan 2
FREQ
FREQ
FREQ
0xCC
Yes
0x61
R/W
Remote 2
TRANGE/
PWM 3
Frequency
RANGE
RANGE
RANGE
RANGE
HF/LF
Fan 3
FREQ
FREQ
FREQ
0xCC
Yes
0x62
R/W
Enhanced
Acoustics
Reg. 1
MIN3
MIN2
MIN1
SYNC
EN1
ACOU
ACOU
ACOU
0x00
Yes
0x63
R/W
Enhanced
Acoustics
Reg. 2
EN2
ACOU2
ACOU2
ACOU2
EN3
ACOU3
ACOU3
ACOU3
0x00
Yes
0x64
R/W
PWM1 Min
Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x65
R/W
PWM2 Min
Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x66
R/W
PWM3 Min
Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x67
R/W
Remote 1
Temp. TMIN
7
6
5
4
3
2
1
0
0x9A
Yes
0x68
R/W
Local Temp.
TMIN
7
6
5
4
3
2
1
0
0x9A
Yes
0x69
R/W
Remote 2
Temp. TMIN
7
6
5
4
3
2
1
0
0x9A
Yes
0x6A
R/W
Remote 1
THERM
Temp. Limit
7
6
5
4
3
2
1
0
0xA4
Yes
0x6B
R/W
Local
THERM
Temp. Limit
7
6
5
4
3
2
1
0
0xA4
Yes
0x6C
R/W
Remote 2
THERM
Temp. Limit
7
6
5
4
3
2
1
0
0xA4/0
xC8
Yes
0x6D
R/W
Remote 1
and Local
Temp/TMIN
Hysteresis
HYSR1
HYSR1
HYSR1
HYSR1
HYSL
HYSL
HYSL
HYSL
0x44
Yes
0x6E
R/W
Remote 2
Temp/TMIN
Hysteresis
HYSR2
HYSR2
HYSR2
HYRS2
RES
RES
RES
RES
0x40
Yes
0x6F
R/W
XNOR Tree
Test Enable
RES
RES
RES
RES
RES
RES
RES
XEN
0x00
Yes
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ADT7473
Table 53. ADT7473/ADT7473−1 REGISTERS (continued)
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
0x70
R/W
Remote 1
Temp.
Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x71
R/W
Local Temp.
Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x72
R/W
Remote 2
Temp.
Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x73
R/W
Config.
Register 2
SHDN
CONV
ATTN
AVG
FAN3
Detect
FAN2
Detect
FAN1
Detect
FAN
Presence
DT
0x00
Yes
0x74
R/W
Interrupt
Mask
Register 1
OOL
R2T
LT
R1T
RES
VCC
VCCP
RES
0x00
−
0x75
R/W
Interrupt
Mask
Register 2
D2
D1
F4P
FAN3
FAN2
FAN1
OVT
RES
0x00
−
0x76
R
Extended
Resolution
1
RES
RES
VCC
VCC
VCCP
VCCP
RES
RES
0x00
−
0x77
R
Extended
Resolution
2
TDM2
TDM2
LTMP
LTMP
TDM1
TDM1
RES
RES
0x00
−
0x78
R/W
Config.
Register 3
DC4
DC3
DC2
DC1
FAST
BOOST
THERM
ALERT
Enable
0x00
Yes
0x79
R
THERM
Timer
Status
Register
TMR
TMR
TMR
TMR
TMR
TMR
TMR
ASRT/
TMRO
0x00
−
0x7A
R/W
THERM
Timer Limit
Register
LIMT
LIMT
LIMT
LIMT
LIMT
LIMT
LIMT
LIMT
0x00
−
0x7B
R/W
TACH
Pulses per
Revolution
FAN4
FAN4
FAN3
FAN3
FAN2
FAN2
FAN1
FAN1
0X55
−
0x7C
R/W
Config.
Register 5
R2 THERM
Local
THERM
R1
THERM
ADT7473: RES
ADT7473−1:
THERM HYSTR
GPIOP
GPIOD
Temp
Offset
TWOS
COMPL
ADT
7473:
0x00
Yes
0x7D
R/W
Config.
Register 4
RES
RES
BpAtt
VCCP
ADT7473: RES
ADT7473−1:
THERM_LATCH
CONFIG
Max/
Full on
THERM
THERM
Disable
PIN9
FUNC
PIN9
FUNC
0x00
Yes
0x7E
R
Test
Register 1
DO NOT WRITE TO THESE REGISTERS
0x00
Yes
0x7F
R
Test
Register 2
DO NOT WRITE TO THESE REGISTERS
0x00
Yes
0x80
R
Test
Register 3
DO NOT WRITE TO THESE REGISTERS
0x10
Yes
Table 54. VOLTAGE READING REGISTERS (POWER-ON DEFAULT = 0X00) (Note 1)
Register Address
R/W
Description
0x21
Read-only
Reflects the voltage measurement at the VCCP input on Pin 14 (8 MSB of reading). (Note 2)
0x22
Read-only
Reflects the voltage measurement at the VCC input on Pin 3 (8 MSB of reading). (Note 3)
1. If the extended resolution bits of these readings are also being read, the extended resolution registers (Register 0x76 and Register 0x77)
must be read first. Once the extended resolution registers have been read, the associated MSB reading registers are frozen until read. Both
the extended resolution registers and the MSB registers are frozen.
2. If VCCPLO (Bit 1 of the Dynamic TMIN Control Register 1, 0x36) is set, VCCP can control the sleep state of the ADT7473/ADT7473−1.
3. VCC (Pin 3) is the supply voltage for the ADT7473/ADT7473−1.
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ADT7473
Table 55. TEMPERATURE READING REGISTERS (POWER-ON DEFAULT = 0X01) (Note 1 and 2)
Register Address
R/W
0x25
Read-only
Remote 1 Temperature Reading (8 MSB of Reading) (Note 3 and 4)
Description
0x26
Read-only
Local Temperature Reading (8 MSB of Reading)
0x27
Read-only
Remote 2 Temperature Reading (8 MSB of Reading) (Note 3 and 4)
1. These temperature readings can be in twos complement or Offset 64 format; this interpretation is determined by Bit 0 of Configuration
Register 5 (0x7C).
2. If the extended resolution bits of these readings are also being read, the extended resolution registers (Register 0x76 and Register 0x77)
must be read first. Once the extended resolution registers have been read, all associated MSB reading registers are frozen until read. Both
the extended resolution registers and the MSB registers are frozen.
3. In twos complement mode, a temperature reading of −128°C (0x80) indicates a diode fault (open or short) on that channel.
4. In Offset 64 mode, a temperature reading of −64°C (0x00) indicates a diode fault (open or short) on that channel.
Table 56. FAN TACHOMETER READING REGISTERS (POWER-ON DEFAULT = 0X00) (Note 1)
Register Address
R/W
0x28
Read-only
TACH1 Low Byte
Description
0x29
Read-only
TACH1 High Byte
0x2A
Read-only
TACH2 Low Byte
0x2B
Read-only
TACH2 High Byte
0x2C
Read-only
TACH3 Low Byte
0x2D
Read-only
TACH3 High Byte
0x2E
Read-only
TACH4 Low Byte
0x2F
Read-only
TACH4 High Byte
1. These registers count the number of 11.11 ms periods (based on an internal 90 kHz clock) that occur between a number of consecutive fan TACH
pulses (default = 2). The number of TACH pulses used to count can be changed using the TACH pulses per revolution register (Register 0x7B).
This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes are read, the low byte
must be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until the first valid fan
TACH measurement is read into these registers. This prevents false interrupts from occurring while the fans are spinning up. A count of 0xFFFF
indicates a fan is one of the following:
• Stalled or blocked (object jamming the fan).
• Failed (internal circuitry destroyed).
• Not populated. (The ADT7473/ADT7473−1 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH
minimum high and low bytes should be set to 0xFFFF.)
• Alternate function, for example, TACH4 reconfigured as THERM pin.
Table 57. CURRENT PWM DUTY CYCLE REGISTERS
(ADT7473 POWER-ON DEFAULT = 0X00, ADT7473−1 POWER-ON DEFAULT = 0XFF) (Note 1)
Register Address
R/W
0x30
R/W
PWM1 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)
0x31
R/W
PWM2 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)
0x32
R/W
PWM3 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)
Description
1. These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the
ADT7473/ADT7473−1 reports the PWM duty cycles back through these registers. The PWM duty cycle values vary according to temperature
in automatic fan speed control mode. During fan startup, these registers report back 0x00. In software mode, the PWM duty cycle outputs
can be set to any duty cycle value by writing to these registers.
Table 58. OPERATING POINT REGISTERS (POWER-ON = 0XA4) (Note 1, 2 and 3)
Register Address
R/W (Note 3)
0x33
R/W
Remote 1 Operating Point Register (Default = 100°C)
Description
0x34
R/W
Local Temperature Operating Point Register (Default = 100°C)
0x35
R/W
Remote 2 Operating Point Register (Default = 100°C)
1. These registers set the target operating point for each temperature channel when the dynamic TMIN control feature is enabled.
2. The fans being controlled are adjusted to maintain temperature about an operating point.
3. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any subsequent attempts to write to these registers
fail.
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ADT7473
Table 59. REGISTER 0X36 − DYNAMIC TMIN CONTROL REGISTER 1 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<0>
CYR2
R/W
MSB of 3-bit Remote 2 cycle value. The other two bits of the code reside in Dynamic TMIN
Control Register 2 (Reg. 0x37). These three bits define the delay time between making
subsequent TMIN adjustments in the control loop, in terms of the number of monitoring
cycles. The system has associated thermal time constants that need to be found to optimize
the response of fans and the control loop.
<1>
VCCPLO
R/W
VCCPLO = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP)
drops below its VCCP low limit value (Register 0x46), the following occurs:
Status Bit 1 in Interrupt Status Register 1 is set.
SMBALERT is generated, if enabled.
PROCHOT monitoring is disabled.
Dynamic TMIN control is disabled.
The device is prevented from entering shutdown.
Everything is re-enabled once VCCP increases above the VCCP low limit.
<2>
PHTR1
R/W
PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point
register if THERM is asserted. The operating point contains the temperature at which
THERM is asserted, allowing the system to run as quietly as possible without affecting
system performance.
PHTR1 = 0 ignores any THERM assertions on the THERM pin. The Remote 1 operating
point register reflects its programmed value.
<3>
PHTL
R/W
PHTL = 1 copies the local channel’s current temperature to the local operating point register
if THERM is asserted. The operating point contains the temperature at which THERM is
asserted. This allows the system to run as quietly as possible without affecting system
performance.
PHTL = 0 ignores any THERM assertions on the THERM pin. The local temperature
operating point register reflects its programmed value.
<4>
PHTR2
R/W
PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point
register if THERM is asserted. The operating point contains the temperature at which
THERM is asserted, allowing the system to run as quietly as possible without affecting
system performance.
PHTR2 = 0 ignores any THERM assertions on the THERM pin. The Remote 2 operating
point register reflects its programmed value.
<5>
R1T
R/W
R1T = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen
TMIN value is dynamically adjusted based on the current temperature, operating point, and
high and low limits for this zone.
R1T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the
channel behaves as described in the Fan Speed Control section.
<6>
LT
R/W
LT = 1 enables dynamic TMIN control on the local temperature channel. The chosen TMIN
value is dynamically adjusted based on the current temperature, operating point, and high
and low limits for this zone.
LT = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the
channel behaves as described in the Fan Speed Control section.
<7>
R2T
R/W
R2T = 1 enables dynamic TMIN control on the Remote 2 temperature channel. The chosen
TMIN value is dynamically adjusted based on the current temperature, operating point, and
high and low limits for this zone.
R2T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted and the
channel behaves as described in the Fan Speed Control section.
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any subsequent attempts to write to this register fail.
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ADT7473
Table 60. REGISTER 0X37 − DYNAMIC TMIN CONTROL REGISTER 2 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<2:0>
CYR1
R/W
3-bit Remote 1 cycle value. These three bits define the delay time between making
subsequent TMIN adjustments in the control loop for the Remote 1 channel, in terms of
number of monitoring cycles. The system has associated thermal time constants that need to
be found to optimize the response of fans and the control loop.
Bits
Decrease Cycle
Increase Cycle
000
001
010
011
100
101
110
111
<5:3>
CYL
R/W
CYR2
R/W
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
2048 cycles (256 sec)
3-bit Local temperature cycle value. These three bits define the delay time between making
subsequent TMIN adjustments in the control loop for the local temperature channel, in terms
of number of monitoring cycles. The system has associated thermal time constants that need
to be found to optimize the response of fans and the control loop.
Bits
Decrease Cycle
Increase Cycle
000
001
010
011
100
101
110
111
<7:6>
8 cycles (1 sec)
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
8 cycles (1 sec)
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
2048 cycles (256 sec)
2 LSBs of 3-bit Remote 2 cycle value. The MSB of the 3-bit code resides in Dynamic TMIN
Control Register 1 (Register 0x36). These three bits define the delay time between making
subsequent TMIN adjustments in the control loop for the Remote 2 channel, in terms of
number of monitoring cycles. The system has associated thermal time constants that need to
be found to optimize the response of fans and the control loop.
Bits
000
001
010
011
100
101
110
111
Decrease Cycle
8 cycles (1 sec)
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
Increase Cycle
16 cycles (2 sec)
32 cycles (4 sec)
64 cycles (8 sec)
128 cycles (16 sec)
256 cycles (32 sec)
512 cycles (64 sec)
1024 cycles (128 sec)
2048 cycles (256 sec)
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any subsequent attempts to write to this register fail.
Table 61. MAXIMUM PWM DUTY CYCLE REGISTERS (POWER-ON DEFAULT = 0XFF) (Note 1, 2, and 3)
Description
Register Address
R/W (Note 2)
0x38
R/W
Maximum Duty Cycle for PWM1 Output, Default = 100% (0xFF)
0x39
R/W
Maximum Duty Cycle for PWM2 Output, Default = 100% (0xFF)
0x3A
R/W
Maximum Duty Cycle for PWM3 Output, Default = 100% (0xFF)
1. These registers set the maximum PWM duty cycle of the PWM output.
2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any subsequent attempts to write to this register fail.
3. If Bit 3 of Configuration Register 4 (0x7D) is set, then on a THERM overtemperature event, fans go to their maximum programmed PWM value
as programmed here. If Bit 3 of Configuration Register 4 (0x7D) is 0, then on a THERM overtemperature event, fans go to 100% PWM.
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ADT7473
Table 62. REGISTER 0X40 − CONFIGURATION REGISTER 1 (POWER-ON DEFAULT = 0X01)
Bit No.
Mnemonic
R/W
<0>
STRT
R/W
Description
<1>
LOCK
Write Once
Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers
become read-only and cannot be modified until the ADT7473/ADT7473−1 is powered down
and powered up again. This prevents rogue programs, such as viruses, from modifying
critical system limit settings. (This is a lockable bit.)
<2>
RDY
Read-only
This bit is set to 1 by the ADT7473/ADT7473−1 to indicate only that the device is fully
powered up and ready to begin system monitoring.
<3>
FSPD
R/W
When set to 1, this bit runs all fans at maximum speed as programmed in the maximum
PWM duty cycle registers (0x30, 0x38, 0x39 and 0x3A ). Power-on default = 0. This bit is not
locked at any time.
<4>
Vx1
R/W
BIOS should set this bit to a 1 when the ADT7473/ADT7473−1 is configured to measure
current from an ADI ADOPTt VRM controller and to measure the CPU’s core voltage. This
bit allows monitoring software to display CPU watts usage. (This is a lockable bit.)
<5>
FSPDIS
R/W
Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs go high for the
entire fan spin-up timeout selected.
<6>
TODIS
R/W
When this bit is set to 1, the SMBus timeout feature is enabled. This allows the
ADT7473/ADT7473−1 to be used with SMBus controllers that cannot handle SMBus
timeouts. (This is a lockable bit.)
<7>
RES
Latch Reset
−
Logic 1 enables monitoring and PWM control outputs based on the limit settings
programmed. Logic 0 disables monitoring and PWM control based on the default powerup
limit settings. This bit is not locked when Bit 1 (LOCK bit) has been written. This bit remains
writable after lock bit is set.
Reserved on the ADT7473.
On the ADT7473−1, resets latch conditions when set to 1.
Table 63. REGISTER 0X41 − INTERRUPT STATUS REGISTER 1 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<1>
VCCP
Read-only
VCCP = 1 indicates the VCCP high or low limit has been exceeded. This bit is cleared on a
read of the status register only if the error condition has subsided.
<2>
VCC
Read-only
VCC = 1 indicates the VCC high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<4>
R1T
Read-only
R1T = 1 indicates the Remote 1 low or high temperature has been exceeded. This bit is
cleared on a read of the status register only if the error condition has subsided.
<5>
LT
Read-only
LT = 1 indicates the local low or high temperature has been exceeded. This bit is cleared on
a read of the status register only if the error condition has subsided.
<6>
R2T
Read-only
R2T = 1 indicates the Remote 2 low or high temperature has been exceeded. This bit is
cleared on a read of the status register only if the error condition has subsided.
<7>
OOL
Read-only
OOL = 1 indicates an out-of-limit event has been latched in Interrupt Status Register 2
(0x42). This bit is a logical OR of all status bits in Interrupt Status Register 2. Software can
test this bit in isolation to determine whether any of the voltage, temperature, or fan speed
readings represented by Interrupt Status Register 2 are out-of-limit, which saves the need to
read Interrupt Status Register 2 every interrupt or polling cycle.
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Table 64. REGISTER 0X42 − INTERRUPT STATUS REGISTER 2 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
<0>
RES
THERM
Limit Latch
Read-only
Reserved on the ADT7473
On the ADT7473−1, THERM Limit Latch = 1 indicates Remote Channel 2 latch. This is a
THERM limit condition.
<1>
OVT
Read-only
OVT = 1 indicates one of the THERM overtemperature limits is exceeded. This bit is cleared
on a read of the status register when the temperature drops below THERM – THYST.
<2>
FAN1
Read-only
FAN1 = 1 indicates Fan 1 has dropped below minimum speed or has stalled. This bit is not
set when the PWM1 output is off.
<3>
FAN2
Read-only
FAN2 = 1 indicates Fan 2 has dropped below minimum speed or has stalled. This bit is not
set when the PWM2 output is off.
<4>
FAN3
Read-only
FAN3 = 1 indicates Fan 3 has dropped below minimum speed or has stalled. This bit is not
set when the PWM3 output is off.
<5>
F4P
Read-only
F4P = 1 indicates Fan 4 has dropped below minimum speed or has stalled. This bit is not set
when the PWM3 output is off.
When Pin 9 is programmed as a GPIO output, writing to this bit determines the logic output of
the GPIO.
If Pin 9 is configured as the THERM timer input for THERM monitoring, then this bit is set
when the THERM assertion time exceeds the limit programmed in the THERM timer limit
register (Reg. 0x7A).
R/W
Read-only
Description
<6>
D1
Read-only
D1 = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs.
<7>
D2
Read-only
D2 = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
Table 65. VOLTAGE LIMIT REGISTERS (Note 1)
Register Address
R/W
0x46
R/W
VCCP Low Limit
Description (Note 2)
Power-On Default
0x00
0x47
R/W
VCCP High Limit
0xFF
0x48
R/W
VCC Low Limit
0x00
0x49
R/W
VCC High Limit
0xFF
1. Setting the Configuration Register 1 Lock bit has no effect on these registers.
2. High limits: an interrupt is generated when a value exceeds its high limit (> comparison). Low limits: an interrupt is generated when a value
is equal to or below its low limit (≤ comparison).
Table 66. TEMPERATURE LIMIT REGISTERS (Note 1)
Register Address
R/W
0x4E
R/W
Remote 1 Temperature Low Limit
Description (Note 2)
Power-On Default
0x01
0x4F
R/W
Remote 1 Temperature High Limit
0xFF
0x50
R/W
Local Temperature Low Limit
0x01
0x51
R/W
Local Temperature High Limit
0xFF
0x52
R/W
Remote 2 Temperature Low Limit
0x01
0x53
R/W
Remote 2 Temperature High Limit
0xFF
1. Exceeding any of these temperature limits by 1°C causes the appropriate status bit to be set in the interrupt status register. Setting the
Configuration Register 1 Lock bit has no effect on these registers.
2. High limits: an interrupt is generated when a value exceeds its high limit (> comparison). Low limits: an interrupt is generated when a value
is equal to or below its low limit (≤ comparison).
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Table 67. FAN TACHOMETER LIMIT REGISTERS (Note 1)
Register Address
R/W
0x54
R/W
TACH1 Minimum Low Byte
Description
Power-On Default
0xFF
0x55
R/W
TACH1 Minimum High Byte/Single-channel ADC Channel Select
0xFF
0x56
R/W
TACH2 Minimum Low Byte
0xFF
0x57
R/W
TACH2 Minimum High Byte
0xFF
0x58
R/W
TACH3 Minimum Low Byte
0xFF
0x59
R/W
TACH3 Minimum High Byte
0xFF
0x5A
R/W
TACH4 Minimum Low Byte
0xFF
0x5B
R/W
TACH4 Minimum High Byte
0xFF
1. Exceeding any of the TACH limit registers by 1 indicates that the fan is running slowly or has stalled. The appropriate status bit is set in
Interrupt Status Register 2 to indicate the fan failure. Setting the Configuration Register 1 Lock bit has no effect on these registers.
Table 68. REGISTER 0X55 − TACH1 MINIMUM HIGH BYTE (POWER-ON DEFAULT = 0XFF)
Bit No.
Mnemonic
R/W
Description
<4:0>
Reserved
Read-only
These bits are reserved when Bit 6 of Configuration Register 2 (0x73) is set (single-channel
ADC mode). Otherwise, these bits represent Bits <4:0> of the TACH1 minimum high byte.
<7:5>
SCADC
R/W
When Bit 6 of Configuration Register 2 (0x73) is set (single-channel ADC mode), these bits
are used to select the only channel from which the ADC makes measurements. Otherwise,
these bits represent Bits <7:5> of the TACH1 minimum high byte.
Table 69. PWM CONFIGURATION REGISTERS
Register Address
R/W (Note 1)
Description
Power-On Default
0x5C
R/W
PWM1 Configuration
ADT7473: 0x82
ADT7473−1: 0x62
0x5D
R/W
PWM2 Configuration
ADT7473: 0x82
ADT7473−1: 0x62
0x5E
R/W
PWM3 Configuration
ADT7473: 0x82
ADT7473−1: 0x62
1. These registers become read-only when the Configuration Register 1 Lock bit is set. Any further attempts to write to these registers have
no effect.
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Table 70. REGISTER 0X5C, REGISTER 0X5D, AND REGISTER 0X5E − CONFIGURATION REGISTERS
(ADT7473 POWER-ON DEFAULT = 0X82, ADT7473−1 POWER-ON DEFAULT = 0X62)
Bit No.
Mnemonic
R/W
<2:0>
SPIN
R/W
Description
These bits control the startup timeout for PWMx. The PWM output stays high until two valid
TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan
TACH measurement directly after the fan startup timeout period, then the TACH
measurement reads 0xFFFF and Interrupt Status Register 2 reflects the fan fault. If the
TACH minimum high and low bytes contain 0xFFFF or 0x0000, then the Interrupt Status
Register 2 bit is not set, even if the fan has not started.
Bit Code
Startup Time
000
001
010
011
100
101
110
111
No Startup Timeout
100 ms
250 ms (Default)
400 ms
667 ms
1 sec
2 sec
4 sec
<3>
SLOW
R/W
SLOW = 1 makes the ramp rates for acoustic enhancement four times longer.
<4>
INV
R/W
This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for
100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle
corresponds to a logic low output.
<7:5>
BHVR
R/W
These bits assign each fan to a particular temperature sensor for localized cooling.
000 = Remote 1 temperature controls PWMx (automatic fan control mode).
001 = Local temperature controls PWMx (automatic fan control mode).
010 = Remote 2 temperature controls PWMx (automatic fan control mode).
011 = PWMx runs full speed (default for ADT7473−1).
100 = PWMx disabled (default for ADT7473).
101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx.
110 = Fastest speed calculated by all three temperature channel controls PWMx.
111 = Manual mode. PWM duty cycle registers (Register 0x30 to Register 0x32) become
writable.
Table 71. TEMPERATURE TRANGE/PWM FREQUENCY REGISTERS
Register Address
R/W (Note 1)
Description
Power-On Default
0x5F
R/W
Remote 1 TRANGE/PWM1 Frequency
0xCC
0x60
R/W
Local Temperature TRANGE/PWM2 Frequency
0xCC
0x61
R/W
Remote 2 TRANGE/PWM3 Frequency
0xCC
1. These registers become read-only when the Configuration Register 1 Lock bit is set. Any further attempts to write to these registers have
no effect.
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Table 72. REGISTER 0X5F, REGISTER 0X60, AND REGISTER 0X61 − TEMP TRANGE/PWM FREQUENCY
REGISTERS, (POWER-ON DEFAULT = 0XCC)
Bit No.
Mnemonic
R/W
<2:0>
FREQ
R/W
Description
These bits control the PWMx frequency.
Bit Code
Frequency
000
001
010
011
100
101
110
111
11.0 Hz
14.7 Hz
22.1 Hz
29.4 Hz
35.3 Hz (Default)
44.1 Hz
58.8 Hz
88.2 Hz
<3>
HF/LF
R/W
HF/LF = 1, high frequency PWM output for 4-wire fans. Once enabled, 3-wire fan-specific
settings have no effect.
0x5F, HF/LF = 1, Enables High Frequency Mode for Fan 1
0x60, HF/LF = 1, Enables High Frequency Mode for Fan 2
0x61, HF/LF = 1, Enables High Frequency Mode for Fan 3
<7:4>
RANGE
R/W
These bits determine the PWM duty cycle vs. the temperature slope for automatic fan control.
Bit Code
Temperature
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8°C
10°C
13.33°C
16°C
20°C
26.67°C
32°C (Default)
40°C
53.33°C
80°C
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Table 73. REGISTER 0X62 − ENHANCED ACOUSTICS REGISTER 1 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W (Note 1)
Description
<2:0>
ACOU
R/W
These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping
instantaneously to its newly calculated speed, PWM1 ramps gradually at the rate determined
by these bits. This feature enhances the acoustics of the fan being driven by the PWM1
output.
Time Slot Increase
Time for 33% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
35 sec
17.6 sec
11.8 sec
7.0 sec
4.4 sec
3.0 sec
1.6 sec
0.8 sec
<3>
EN1
R/W
When this bit is 1, acoustic enhancement is enabled on PWM1 output.
<4>
SYNC
R/W
SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3.
This allows up to three fans to be driven from PWM3 output and their speeds to be measured.
SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output.
<5>
MIN1
R/W
When the ADT7473/ADT7473−1 is in automatic fan control mode, this bit defines whether
PWM1 is off (0% duty cycle) or at PWM1 minimum duty cycle when the controlling
temperature is below its TMIN – hysteresis value.
0 = 0% duty cycle below TMIN − hysteresis.
1 = PWM1 minimum duty cycle below TMIN − hysteresis.
<6>
MIN2
R/W
When the ADT7473/ADT7473−1 is in automatic fan speed control mode, this bit defines
whether PWM2 is off (0% duty cycle) or at PWM2 minimum duty cycle when the controlling
temperature is below its TMIN − hysteresis value.
0 = 0% duty cycle below TMIN − hysteresis.
1 = PWM 2 minimum duty cycle below TMIN − hysteresis.
<7>
MIN3
R/W
When the ADT7473/ADT7473−1 is in automatic fan speed control mode, this bit defines
whether PWM3 is off (0% duty cycle) or at PWM3 minimum duty cycle when the controlling
temperature is below its TMIN − hysteresis value.
0 = 0% duty cycle below TMIN − hysteresis.
1 = PWM3 minimum duty cycle below TMIN − hysteresis.
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
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Table 74. Register 0x63 − Enhanced Acoustics Register 2 (Power-On Default = 0x00)
Bit No.
Mnemonic
R/W (Note 1)
<2:0>
ACOU3
R/W
Description
These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping
instantly to its newly calculated speed, PWM3 ramps gradually at the rate determined by
these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output.
Time Slot Increase
Time for 33% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
35 sec
17.6 sec
11.8 sec
7.0 sec
4.4 sec
3.0 sec
1.6 sec
0.8 sec
<3>
EN3
R/W
When this bit is 1, acoustic enhancement is enabled on PWM3 output.
<6:4>
ACOU2
R/W
These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping
instantly to its newly calculated speed, PWM2 ramps gradually at the rate determined by
these bits. This effect enhances the acoustics of the fans being driven by the PWM2 output.
Time Slot Increase
Time for 33% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
<7>
EN2
R/W
35 sec
17.6 sec
11.8 sec
7.0 sec
4.4 sec
3.0 sec
1.6 sec
0.8 sec
When this bit is 1, acoustic enhancement is enabled on PWM2 output.
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
Table 75. PWM MINIMUM DUTY CYCLE REGISTERS
Register Address
R/W (Note 1)
0x64
R/W
PWM1 Minimum Duty Cycle
Description
0x80 (50% Duty Cycle)
Power-On Default
0x65
R/W
PWM2 Minimum Duty Cycle
0x80 (50% Duty Cycle)
0x66
R/W
PWM3 Minimum Duty Cycle
0x80 (50% Duty Cycle)
1. These registers become read-only when the Configuration Register 1 Lock bit is set. Any further attempts to write to these registers have
no effect.
Table 76. REGISTER 0X64, REGISTER 0X65, AND REGISTER 0X66 - PWM MINIMUM DUTY CYCLE REGISTERS
(POWER-ON DEFAULT = 0X80, 50% DUTY CYCLE)
Bit No.
Mnemonic
R/W
<7:0>
PWM Duty Cycle
R/W
Description
These bits define the PWMMIN duty cycle for PWMx.
0x00 = 0% Duty Cycle (Fan Off)
0x40 = 25% Duty Cycle
0x80 = 50% Duty Cycle
0xFF = 100% Duty Cycle (Fan Full Speed)
Table 77. TMIN REGISTERS (Note 1)
Register Address
R/W (Note 2)
0x67
R/W
Remote 1 Temperature TMIN
Description
Power-On Default
0x9A (90°C)
0x68
R/W
Local Temperature TMIN
0x9A (90°C)
0x69
R/W
Remote 2 Temperature TMIN
0x9A (90°C)
1. These are the TMIN registers for each temperature channel. When the temperature measured exceeds TMIN, the appropriate fan runs at
minimum speed and increases with temperature according to TRANGE.
2. These registers become read-only when the Configuration Register 1 Lock bit is set. Any further attempts to write to these registers have
no effect.
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Table 78. THERM LIMIT REGISTERS (Note 1)
Register Address
R/W (Note 2)
0x6A
R/W
Remote 1 THERM Limit
Description
0x6B
R/W
Local THERM Limit
0x6C
R/W
Remote 2 THERM Limit
Power-On Default
0xA4 (100°C)
0xA4 (100°C)
ADT7473: 0xA4 (100°C)
ADT7473−1: 0xC8 (136°C)
1. If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism
incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software
or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below THERM
Limit − Hysteresis. If the THERM pin is programmed as an output, then exceeding these limits by 0.25°C can cause the THERM pin to assert
low as an output.
2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have
no effect.
Table 79. TEMPERATURE/TMIN HYSTERESIS REGISTERS (Note 1)
Register Address
Bit Name
0x6D
R/W (Note 2)
R/W
Description
Remote 1 and local temperature hysteresis.
HYSL
<3:0>
Local temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the local temperature
AFC and dynamic TMIN control loops.
HYSR1
<7:4>
Remote 1 temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the Remote 1
temperature AFC and dynamic TMIN control loops.
0x6E
R/W
HYSR2
<7:4>
Remote 2 temperature hysteresis.
Power-On Default
0x44
0x40
Local temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the local temperature
AFC and dynamic TMIN control loops.
1. Each 4 bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that
channel falls below its TMIN value, the fan remains running at PWMMIN duty cycle until the temperature = TMIN – hysteresis. Up to 15°C of
hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel, if its THERM
limit is exceeded. The PWM output being controlled goes to 100%, if the THERM limit is exceeded and remains at 100% until the temperature
drops below THERM – hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4°C.
Setting the hysteresis value lower than 4°C causes the fan to switch on and off regularly when the temperature is close to TMIN.
2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have
no effect.
Table 80. XNOR TREE TEST REGISTER
Register Address
Bit Name
0x6F
R/W (Note 1)
R/W
Description
XNOR tree test enable register.
XEN <0>
If the XEN bit is set to 1, the device enters the XNOR
tree test mode. Clearing the bit removes the device
from the XNOR tree test mode.
Res <7:1>
Unused. Do not write to these bits.
Power-On Default
0x00
1. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have
no effect.
Table 81. REMOTE 1 TEMPERATURE OFFSET REGISTER (0X70)
Register Address
R/W (Note 1)
<7:0>
R/W
Description
Allows a twos complement offset value to be automatically added to
or subtracted from the Remote 1 temperature reading. This is to
compensate for any inherent system offsets such as PCB trace
resistance. LSB value = 0.5°C.
Power-On Default
0x00
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
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Table 82. LOCAL TEMPERATURE OFFSET REGISTER (0X71)
Register Address
R/W (Note 1)
Description
Power-On Default
<7:0>
R/W
Allows a twos complement offset value to be automatically added to
or subtracted from the local temperature reading. LSB value = 0.5°C.
0x00
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
Table 83. REMOTE 2 TEMPERATURE OFFSET REGISTER (0X72)
Register Address
R/W (Note 1)
<7:0>
R/W
Description
Power-On Default
Allows a twos complement offset value to be automatically added to
or subtracted from the Remote 2 temperature reading. This is to
compensate for any inherent system offsets such as PCB trace
resistance. LSB value = 0.5°C.
0x00
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
Table 84. REGISTER 0X73 − CONFIGURATION REGISTER 2 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W (Note 1)
Description
<0>
FanPresDT
R/W
When FanPresenceDT = 1, the state of Bits <3:1> of Register 0x73 reflects the presence of a
4-wire fan on the appropriate TACH channel.
<1>
Fan1Detect
Read-only
Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM1 input.
<2>
Fan2Detect
Read-only
Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM2 input.
<3>
Fan3Detect
Read-only
Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM3 input.
<4>
AVG
R/W
AVG = 1, averaging on the temperature and voltage measurements is turned off. This allows
measurements on each channel to be made much faster.
<5>
ATTN
R/W
ATTN = 1, the ADT7473/ADT7473−1 removes the attenuators from the VCCP input. The
VCCP input can be used for other functions such as connecting up external sensors.
<6>
CONV
R/W
CONV = 1, the ADT7473/ADT7473−1 is put into a single-channel ADC conversion mode. In
this mode, the ADT7473/ADT7473−1 can be made to read continuously from one input only,
for example, Remote 1 temperature. The appropriate ADC channel is selected by writing to
Bits <7:5> of TACH1 minimum high byte register (0x55).
Bits <7:5>, Register 0x55
000
001
010
011
100
101
110
111
<7>
Shutdown
R/W
Reserved
VCCP
VCC (3.3 V)
Reserved
Reserved
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
SHDN = 1, ADT7473/ADT7473−1 goes into shutdown mode. All PWM outputs assert low or
high, depending on the state of the INV bit, to switch off all fans.
1. This register becomes read-only when the Configuration Register 1Lock bit is set to 1. Any further attempts to write to this register have no
effect.
Table 85. REGISTER 0X74 − INTERRUPT MASK REGISTER 1 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
<1>
VCCP
R/W
VCCP = 1, masks SMBALERT for out-of-limit conditions on the VCCP channel.
Description
<2>
VCC
R/W
VCC = 1, masks SMBALERT for out-of-limit conditions on the VCC channel.
<4>
R1T
R/W
R1T = 1, masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel.
<5>
LT
R/W
LT = 1, masks SMBALERT for out-of-limit conditions on the local temperature channel.
<6>
R2T
R/W
R2T = 1, masks SMBALERT for out-of-limit conditions on the Remote 2 temperature channel.
<7>
OOL
R/W
OOL = 0, then when one or more alerts are generated in Interrupt Status Register 2, assuming
all the mask bits in the Interrupt Mask Register 2 (0x75) = 1, SMBALERT are still asserted.
OOL = 1, then when one or more alerts are generated in Interrupt Status Register 2, assuming
all the mask bits in the Interrupt Mask Register 2 (0x75) = 1, SMBALERT are not asserted.
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Table 86. REGISTER 0X75 − INTERRUPT MASK REGISTER 2 (POWER-ON DEFAULT <7:0> = 0X00)
Bit No.
Mnemonic
R/W
<1>
OVT
R/W
OVT = 1, masks SMBALERT for overtemperature THERM conditions.
Description
<2>
FAN1
R/W
FAN1 = 1, masks SMBALERT for a Fan 1 fault.
<3>
FAN2
R/W
FAN2 = 1, masks SMBALERT for a Fan 2 fault.
<4>
FAN3
R/W
FAN3 = 1, masks SMBALERT for a Fan 3 fault.
<5>
F4P
R/W
F4P = 1, masks SMBALERT for a Fan 4 fault. If the TACH4 pin is being used as the THERM
input, this bit masks SMBALERT for a THERM timer event.
<6>
D1
R/W
D1 = 1, masks SMBALERT for a diode open or short on a Remote 1 channel.
<7>
D2
R/W
D2 = 1, masks SMBALERT for a diode open or short on a Remote 2 channel.
Table 87. REGISTER 0X76 − EXTENDED RESOLUTION REGISTER 1 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<3:2>
VCCP
Read-only
VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP measurement.
<5:4>
VCC
Read-only
VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement.
1. If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table 88. REGISTER 0X77 − EXTENDED RESOLUTION REGISTER 2 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<3:2>
TDM1
Read-only
Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature
measurement.
<5:4>
LTMP
Read-only
Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement.
<7:6>
TDM2
Read-only
Remote 2 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature
measurement.
1. If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table 89. REGISTER 0X78 − CONFIGURATION REGISTER 3 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W (Note 1)
Description
<0>
ALERT
Enable
R/W
ALERT = 0 (default), ADT7473 Pin 5 is configured as PWM2.
ALERT = 1, Pin 5 for ADT7473 (PWM2/SMBALERT) is configured as an SMBALERT
interrupt output to indicate out-of-limit error conditions.
ALERT = 0 (default), ADT7473−1 Pin 5 is configured as. THERM_LATCH.
ALERT = 1, Pin 5 for ADT7473−1 (THERM_LATCH/PWM2) is configured as PWM2.
<1>
THERM
R/W
THERM Enable = 1 enables THERM functionality on Pin 9. Also determined by Bit 0 and
Bit 1 (PIN9FUNC) of Configuration Register 4. Direction is controlled by Bit 5, Bit 6, and Bit 7
of Configuration Register 5 (0x7C). When THERM is asserted, if the fans are running and the
boost bit is set, the fans run at full speed. THERM can also be programmed so that a timer
monitors the duration THERM has been asserted.
<2>
BOOST
R/W
When THERM is an input and BOOST = 1, assertion of THERM causes all fans to run at the
maximum programmed duty cycle for fail-safe cooling.
<3>
FAST
R/W
FAST = 1, enables fast TACH measurements on all channels. This increases the TACH
measurement rate from once per second to once every 250 ms (4x).
<4>
DC1
R/W
DC1 = 1, enables TACH measurements to be continuously made on TACH1. Fans must be
driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven
motors.
<5>
DC2
R/W
DC2 = 1, enables TACH measurements to be continuously made on TACH2. Fans must be
driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven
motors.
<6>
DC3
R/W
DC3 = 1, enables TACH measurements to be continuously made on TACH3. Fans must be
driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven
motors.
<7>
DC4
R/W
DC4 = 1, enables TACH measurements to be continuously made on TACH4. Fans must be
driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven
motors.
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have no
effect.
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ADT7473
Table 90. REGISTER 0X79 − THERM TIMER STATUS REGISTER (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
<7:1>
TMR
R
Times how long THERM input is asserted. These seven bits read 0 until the THERM
assertion time exceeds 45.52 ms.
Description
<0>
ASRT/
TMR0
R
This bit is set high on the assertion of the THERM input and is cleared on read. If the THERM
assertion time exceeds 45.52 ms, this bit is set and becomes the LSB of the 8-bit TMR
reading. This allows THERM assertion times from 45.52 ms to 5.82 sec to be reported back
with a resolution of 22.76 ms.
Table 91. REGISTER 0X7A − THERM TIMER LIMIT REGISTER (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<7:0>
LIMT
R/W
Sets maximum THERM assertion length allowed before an interrupt is generated. This is an
8-bit limit with a resolution of 22.76 ms allowing THERM assertion limits of 45.52 ms to
5.82 seconds to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P)
of Interrupt Status Register 2 (Reg. 0x42) is set. If the limit value is 0x00, an interrupt is
generated immediately on the assertion of the THERM input.
Table 92. REGISTER 0X7B − TACH PULSES PER REVOLUTION REGISTER (POWER-ON DEFAULT = 0X55)
Bit No.
Mnemonic
R/W
<1:0>
FAN1
R/W
Description
Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to
determine fan pulses per revolution for unknown fan type.
Bit Code
Pulses Counted
00
01
10
11
<3:2>
FAN2
R/W
Sets number of pulses to be counted when measuring Fan 2 speed. Can be used to
determine fan pulses per revolution for unknown fan type.
Bit Code
Pulses Counted
00
01
10
11
<5:4>
FAN3
R/W
FAN4
R/W
1
2 (Default)
3
4
Sets number of pulses to be counted when measuring Fan 3 speed. Can be used to
determine fan pulses per revolution for unknown fan type.
Bit Code
Pulses Counted
00
01
10
11
<7:6>
1
2 (Default)
3
4
1
2 (Default)
3
4
Sets number of pulses to be counted when measuring Fan 4 speed. Can be used to
determine fan pulses per revolution for unknown fan type.
Bit Code
Pulses Counted
00
01
10
11
1
2 (Default)
3
4
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ADT7473
Table 93. REGISTER 0X7C − CONFIGURATION REGISTER 5 (ADT7473POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W (Note 1)
<0>
TWOS
COMPL
R/W
Description
<1>
Temp Offset
−
TempOffset = 0 sets offset range to ±64°C at 0.5°C resolution.
TempOffset = 1 sets offset range to ±128°C at 1°C resolution.
<2>
GPIOD
−
GPIO direction. When GPIO function is enabled, this determines whether the GPIO is an
input (0) or an output (1).
<3>
GPIOP
−
GPIO polarity. When the GPIO function is enabled and is programmed as an output, this bit
determines whether the GPIO is active low (0) or high (1).
<4>
RES
THERM
Hysteresis
R/W
Reserved on the ADT7473 On the ADT7473−1:
0 = THERM hysteresis disabled
1 = THERM hysteresis enabled
<5>
R1 THERM
R/W
R1 THERM = 1, THERM temperature limit functionality enabled for Remote 1 temperature
channel; that is, THERM is bidirectional. R1 THERM = 0, THERM is a timer input only.
THERM can also be disabled on any channel by:
Writing −64°C to the appropriate THERM temperature limit in Offset 64 mode.
Writing −128°C to the appropriate THERM temperature limit in twos complement mode.
<6>
Local
THERM
R/W
Local THERM = 1, THERM temperature limit functionality enabled for the local temperature
channel; that is, THERM is bidirectional. Local THERM = 0, THERM is a timer input only.
THERM can also be disabled on any channel by:
Writing −64°C to the appropriate THERM temperature limit in Offset 64 mode.
Writing −128°C to the appropriate THERM temperature limit in twos complement mode.
<7>
R2 THERM
R/W
R2 THERM = 1, THERM temperature limit functionality enabled for Remote 2 temperature
channel; that is, THERM is bidirectional. R2 THERM = 0, THERM is a timer input only.
THERM can also be disabled on any channel by:
Writing −64°C to the appropriate THERM temperature limit in Offset 64 mode.
Writing −128°C to the appropriate THERM temperature limit in twos complement mode.
Twos complement = 1, sets the temperature range to twos complement temperature range.
Twos complement = 0, changes the temperature range to Offset 64. When this bit is
changed, the ADT7473/ADT7473−1 interprets all relevant temperature register values as
defined by this bit.
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
Table 94. REGISTER 0X7D − CONFIGURATION REGISTER 4 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W (Note 1)
Description
<1:0>
Pin9FUNC
R/W
These bits set the functionality of Pin 9.
00 = TACH4 (Default)
01 = THERM
11 = SMBALERT
10 = GPIO
<2>
THERM
Disable
R/W
THERM Disable = 1, disables THERM overtemperature output features.
<3>
Max/Full on
THERM
R/W
Max/Full on THERM = 0; when THERM temperature limit is exceeded, fans go to full speed.
Max/Full on THERM = 1; when THERM temperature limit is exceeded, fans go to maximum
programmed fan speed.
Max/Full on THERM = 1; when THERM limit is exceeded, fans go to maximum speed as
defined in Register 0x38, Register 0x39, Register 0x3A.
<4>
RES
THERM
Config
<5>
BpAttVCCP
<6>
RES
Reserved
<7>
RES
Reserved
Unused on ADT7473. On the ADT7473−1:
0 = Remote Channel 2 (Default)
1 = Remote Channel 1 and Remote Channel 2
R/W
Bypass VCCP attenuator. When set, the measurement scale for this channel changes from
0 V (0x00) to 2.2965 V (0xFF).
1. This register becomes read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to this register have
no effect.
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71
ADT7473
Table 95. REGISTER 0X7E − MANUFACTURER’S TEST REGISTER 1 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
<7:0>
Reserved
Read-only
Description
Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and
should not be written to under normal operation.
Table 96. REGISTER 0X7F − MANUFACTURER’S TEST REGISTER 2 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
<7:0>
Reserved
Read-only
Description
Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and
should not be written to under normal operation.
Table 97. REGISTER 0X80 − MANUFACTURER’S TEST REGISTER 3 (POWER-ON DEFAULT = 0X10)
Bit No.
Mnemonic
R/W
<7:0>
Reserved
Read-only
Description
Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and
should not be written to under normal operation.
Table 98. ORDERING INFORMATION
Package Type
Package Option
Shipping†
ADT7473ARQZ−REEL
16-lead QSOP
RQ−16
2,500 Tape & Reel
ADT7473ARQZ−1RL
16-lead QSOP
RQ−16
2,500 Tape & Reel
Device Order Number*
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*These are Pb-Free packages.
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72
ADT7473
PACKAGE DIMENSIONS
QSOP16
CASE 492
ISSUE A
2X
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b DOES NOT INCLUDE DAMBAR
PROTRUSION.
4. DIMENSION D DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH,
PROTRUSIONS, OR GATE BURRS SHALL NOT EX­
CEED 0.005 PER SIDE. DIMENSION E1 DOES NOT
INCLUDE INTERLEAD FLASH OR PROTRUSION. IN­
TERLEAD FLASH OR PROTRUSION SHALL NOT EX­
CEED 0.005 PER SIDE. D AND E1 ARE DETERMINED
AT DATUM H.
5. DATUMS A AND B ARE DETERMINED AT DATUM H.
0.20 C D
D
16
L2
D
A
9
GAUGE
PLANE
SEATING
PLANE
E
E1
C
C
L
2X
DETAIL A
0.20 C D
2X 10 TIPS
1
8
0.25 C D
16X
e
B
b
0.25
M
C A-B D
h x 45 _
A2
0.10 C
0.10 C
16X
H
A
A1
C
SEATING
PLANE
DETAIL A
M
DIM
A
A1
A2
b
c
D
E
E1
e
h
L
L2
M
INCHES
MIN
MAX
0.053
0.069
0.004
0.010
0.049
---0.008
0.012
0.007
0.010
0.193 BSC
0.237 BSC
0.154 BSC
0.025 BSC
0.009
0.020
0.016
0.050
0.010 BSC
0_
8_
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
1.24
---0.20
0.30
0.19
0.25
4.89 BSC
6.00 BSC
3.90 BSC
0.635 BSC
0.22
0.50
0.40
1.27
0.25 BSC
0_
8_
SOLDERING FOOTPRINT
16X
16X
0.42
16
1.12
9
6.40
1
8
0.635
PITCH
DIMENSIONS: MILLIMETERS
*For additional information on our Pb-Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
Pentium is a registered trademark of Intel Corporation.
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ADT7473/D