ADT7475 D

ADT7475
Remote Thermal Monitor
and Fan Controller
The ADT7475 controller is a thermal monitor and multiple PWM
fan controller for noise-sensitive or power-sensitive applications
requiring active system cooling. The ADT7475 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 that they operate at
the lowest possible speed for minimum acoustic noise.
The automatic fan speed control loop optimizes fan speed for a
given temperature. The effectiveness of the system’s thermal solution
can be monitored using the THERM input. The ADT7475 also
provides critical thermal protection to the system using the
bidirectional THERM pin as an output to prevent system or
component overheating.
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QSOP−16
CASE 492
PIN ASSIGNMENT
Features
SCL
1
16
SDA
•
•
•
•
•
GND
2
15
PWM1/XTO
•
•
•
•
•
•
•
•
Controls and Monitors Up to 4 Fans
High and Low Frequency Fan Drive Signal
1 On-Chip and 2 Remote Temperature Sensors
Extended Temperature Measurement Range, Up to 191°C
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
VCC
3
14
VCCP
TACH3
PWM2/
SMBALERT
TACH1
4
13
D1+
12
D1−
6
11
D2+
TACH2
7
10
D2−
PWM3
8
9
5
ADT7475
(Top View)
TACH4/GPIO/
THERM/
SMBALERT
MARKING DIAGRAM
ADT7475
ARQZ
#YYWW
ADT7475ARQZ
#
YYWW
= Specific Device Code
= Pb-Free Package
= Date Code
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 57 of this data sheet.
© Semiconductor Components Industries, LLC, 2013
August, 2018 − Rev. 8
1
Publication Order Number:
ADT7475/D
ADT7475
SCL
SDA SMBALERT
ADT7475
SERIAL BUS
INTERFACE
PWM1
PWM2
PWM3
PWM REGISTERS
AND
CONTROLLERS
(HF & LF)
ADDRESS
POINTER
REGISTER
AUTOMATIC
FAN SPEED
CONTROL
ACOUSTIC
ENHANCEMENT
CONTROL
PWM
CONFIGURATION
REGISTERS
TACH1
TACH2
FAN SPEED
COUNTER
TACH3
TACH4
INTERRUPT
MASKING
PERFORMANCE
MONITORING
THERMAL
PROTECTION
THERM
VCC
INTERRUPT
STATUS
REGISTERS
VCC to ADT7475
D1+
D1−
D2+
INPUT
SIGNAL
CONDITIONING
AND
ANALOG
MULTIPLEXER
D2−
VCCP
BAND GAP
TEMP. SENSOR
LIMIT
COMPARATORS
10-BIT
ADC
VALUE AND
LIMIT
REGISTERS
BAND GAP
REFERENCE
GND
Figure 1. Functional Block Diagram
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameter
Rating
Unit
Positive Supply Voltage (VCC)
3.6
V
−0.3 to +3.6
V
Input Current at Any Pin
±5
mA
Package Input Current
±20
mA
150
°C
−65 to +150
°C
Voltage on Any Input or Output Pin
Maximum Junction Temperature (TJ MAX)
Storage Temperature Range
Lead Temperature, Soldering
IR Reflow Peak Temperature
Lead Temperature (Soldering, 10 sec)
°C
260
300
ESD Rating
1,500
V
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
Table 2. THERMAL CHARACTERISTICS
Package Type
16-lead QSOP (Note 1)
qJA
qJC
Unit
150
39
°C/W
1. qJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
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ADT7475
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. VCC is also monitored through this pin.
4
TACH3
Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3.
5
PWM2
PWM2: Digital Output (Open Drain). Requires 10 kW typical pullup. Pulse-width modulated output to
control Fan 2 speed. Can be configured as a high or low frequency drive.
SMBALERT: Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt
output to signal out-of-limit conditions.
B
SMBALERT
Description
6
TACH1
Digital Input (Open Drain). Fan tachometer input to measure the speed of Fan 1.
7
TACH2
Digital Input (Open Drain). Fan tachometer input to measure the 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.
9
TACH4
THERM
TACH4: Digital Input (Open Drain). Fan tachometer input to measure the speed of Fan 4.
THERM: Digital I/O (Open Drain). Alternatively, this pin can be reconfigured as a bidirectional THERM
pin that can be used to time and monitor assertions on the THERM input. For example, the pin can be
connected to the PROCHOT output of an Intel® Pentium® 4 processor or to the output of a trip point
temperature sensor. This pin can be used as an output to signal overtemperature conditions.
GPIO: General-Purpose Open Drain Digital I/O.
SMBALERT: Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt
output to signal out-of-limit conditions.
GPIO
SMBALERT
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
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.
16
B
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ADT7475
Table 4. ELECTRICAL CHARACTERISTICS (TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.) (Note 1)
Parameter
Conditions
Min
Typ
Max
Unit
Power Supply
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
High Level
Low Level
−
−
180
11
−
−
mA
−
−
±1.5
%
−
−
±1
LSB
−
±0.1
−
%/V
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 ATTENUATORS)
Total Unadjusted Error (TUE)
Differential Non-linearity (DNL)
8 Bits
Power Supply Sensitivity
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
±10
%
−
−
65,535
−
−
−
−
109
329
5,000
10,000
−
−
−
−
RPM
−
−
8.0
mA
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
Input High Voltage, VIH
2.0
−
−
V
Input Low Voltage, VIL
−
−
0.4
V
Hysteresis
−
500
−
mV
Maximum Input Voltage
2.0
−
−
−
−
3.6
V
Minimum Input Voltage
−
−0.3
−
−
0.8
−
V
−
0.5
−
V p-p
Input High Voltage, VIH
0.75 × VCC
−
−
V
Input Low Voltage, VIL
−
−
0.8
V
SMBus DIGITAL INPUTS (SCL, SDA)
DIGITAL INPUT LOGIC LEVELS (TACH INPUTS)
Input High Voltage, VIH
Input Low Voltage, VIL
Hysteresis
DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+
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ADT7475
Table 4. ELECTRICAL CHARACTERISTICS (TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.) (Note 1)
Parameter
Conditions
Min
Typ
Max
Unit
DIGITAL INPUT CURRENT
Input High Current, IIH
VIN = VCC
−
±1
−
mA
Input Low Current, IIL
VIN = 0 V
−
±1
−
mA
−
5
−
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
SCL, SDA Rise Time, tR
−
−
1,000
ns
SCL, SDA Fall Time, tF
−
−
300
ms
250
−
−
ns
15
−
35
ms
Input Capacitance, CIN
SERIAL BUS TIMING (Note 2) (See Figure 2)
Data Setup Time, tSU: DAT
Detect Clock Low Timeout, tTIMEOUT
Can be Optionally Disabled
1. All voltages are measured with respect to GND, unless otherwise specified. Typicals are at TA = 25°C and represent the most likely
parametric norm. Logic inputs accept input high voltages of 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. SMBus timing specifications are guaranteed by design and are not production tested.
t LOW
tF
t HD; STA
tR
SCL
t HD; STA
t HD; DAT
t HIGH
t SU; STA
t SU; DAT
t SU; STO
SDA
P
t BUF
S
S
Figure 2. Serial Bus Timing Diagram
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P
ADT7475
0
30
−10
20
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
TYPICAL PERFORMANCE CHARACTERISTICS
−20
−30
−40
−50
−60
0
2
4
6
8
10
D+ To GND
0
−20
−30
−40
10 12 14 16 18 20 22
D+ To VCC
−10
0
40
60
80
100
LEAKAGE RESISTANCE (MW)
CAPACITANCE (nF)
Figure 3. Temperature Error vs. Capacitance
Between D+ and D−
Figure 4. Remote Temperature Error vs. PCB
Resistance
30
70
25
100 mV
20
60 mV
15
60
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
20
10
5
0
50
40
30
0
100M
200M
300M
400M
500M
40 mV 60 mV
10
0
40 mV
−5
100 mV
20
−10
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.
Differential-Mode Noise Frequency
1.20
15
TEMPERATURE ERROR (°C)
1.18
1.16
IDD (mA)
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
0.98
3.0
3.1
3.2
3.3
3.4
3.5
10
5
0
−10
VDD (V)
0
100M
200M
300M
400M
500M
600M
FREQUENCY (Hz)
Figure 7. Normal IDD vs. Power Supply
B
250 mV
−5
−15
3.6
100 mV
Figure 8. Internal Temperature Error vs. Power
Supply Noise
B
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ADT7475
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
−40 −20
0
20
40
60
85
105 125
OIL BATH TEMPERATURE (°C)
Figure 10. Internal Temperature Error vs. ADT7475
Temperature
3.0
TEMPERATURE ERROR (°C)
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 11. Remote Temperature Error vs. ADT7475
Temperature
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ADT7475
Product Description
The ADT7475 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 ADT7475
are performed over the serial bus. In addition, a pin can be
reconfigured as an SMBALERT output to signal
out-of-limit conditions.
specification results in irreversible damage to the ADT7475.
Signal pins (TACH/PWM) should be pulled up or clamped
to 3.6 V maximum. See the Specifications Section for more
information.
Recommended Implementation
Configuring the ADT7475 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 the Remote 1
temperature channel.
• Ambient temperature measured through the Remote 2
temperature channel.
• Bidirectional THERM pin. This feature allows
Intel® Pentium® 4 PROCHOT monitoring and can
function as an overtemperature THERM output. The
THERM pin can alternatively be programmed as an
SMBALERT system interrupt output.
Quick Comparison Between ADT7473 and ADT7475
• The ADT7473 supports advanced dynamic TMIN
•
•
•
•
features while the ADT7475 does not.
Acoustic smoothing is improved on the ADT7475.
THERM can be selected as an output only on the
ADT7475.
The ADT7475 has two additional configuration
registers.
The ADT7475 has other minor register changes.
The ADT7475 is similar to the ADT7473 in that it is
powered by a supply no greater than 3.6 V. Exceeding this
FRONT
CHASSIS
FAN
REAR
CHASSIS
FAN
PWM3
D2+
TACH3
D2−
THERM
AMBIENT
TEMPERATURE
CPU FAN
ADT7475
PWM1
TACH2
TACH1
PROCHOT
CPU
SDA
D1+
SCL
D1−
SMBALERT
GND
ICH
Figure 12. ADT7475 Configuration
Serial Bus Interface
because a low-to-high transition when the clock is high may
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 are 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
On PCs and servers, control of the ADT7475 is carried out
using the SMBus. The ADT7475 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 ADT7475 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). Data is sent over the serial
bus in sequences of nine clock pulses, that is, 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
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ADT7475
stored in the address pointer register. The second data byte
is the data to write to the internal data register.
When reading data from a register, there are two
possibilities:
1. If the ADT7475 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 ADT7475 as before, but
only the data byte containing the register address
is sent, because no data is written to the register
see Figure 14.
A read operation is then performed consisting of
the serial bus address; the R/W bit set to 1,
followed by the data byte read from the data
register see Figure 15.
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 see
Figure 15.
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 ADT7475, 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 data from it,
the address pointer register must be set so that the correct
data register is addressed, and then data can be written to 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 to be 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 13. 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 write to, which is
1
9
9
1
SCL
0
SDA
1
START BY
MASTER
0
1
1
0
1
R/W
D7
FRAME 1
SERIAL BUS ADDRESS BYTE
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7475
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY
ADT7475
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY STOP BY
ADT7475 MASTER
FRAME 3
DATA BYTE
Figure 13. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
9
9
1
SCL
SDA
0
START BY
MASTER
1
0
1
1
1
0
FRAME 1
SERIAL BUS ADDRESS BYTE
D7
R/W
ACK. BY
ADT7475
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7475
FRAME 2
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 14. Writing to the Address Pointer Register Only
9
1
1
9
SCL
SDA
START BY
MASTER
0
1
0
1
1
1
0
FRAME 1
SERIAL BUS ADDRESS BYTE
D7
R/W
ACK. BY
ADT7475
D6
D5
D4
D3
D2
D1
D0
NO ACK. BY
MASTER
FRAME 2
DATA BYTE FROM ADT7475
Figure 15. Reading Data from a Previously Selected Register
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STOP BY
MASTER
ADT7475
Write Byte
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 ADT7475 also supports the read byte protocol
(for more information, see System Management Bus
Specifications Rev. 2.0, 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.
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 (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 byte write operation is shown in Figure 17.
Write Operations
The SMBus specification defines several protocols for
different types of read and write operations. The ones used
in the ADT7475 are discussed in this section. The following
abbreviations are used in the diagrams:
S − Start
P − Stop
R − Read
W − Write
A − Acknowledge
A − No acknowledge
The ADT7475 uses the following SMBus write protocols.
1
S
SLAVE
W A
ADDRESS
4
5 6
REGISTER
ADDRESS
A P
5
A
6
7
8
DATA A P
The ADT7475 uses the following SMBus read protocols.
Receive Byte
This operation is useful when repeatedly reading a single
register. The register address must be set up previously. 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.
In the ADT7475, 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 shown in Figure 18.
For the ADT7475, 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 shown in Figure 16.
3
4
REGISTER
ADDRESS
Read Operations
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 (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 asserts a stop condition on SDA and
the transaction ends.
2
3
Figure 17. Single-byte Write to a Register
Send Byte
1
2
SLAVE
S ADDRESS W A
1
2
3
SLAVE
S ADDRESS R A
4
5 6
DATA
A P
Figure 18. Single-byte Read from a Register
Figure 16. Setting a Register Address for
Subsequent Read
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
connected to a common SMBALERT line connected to the
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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ADT7475
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 (decimal 768 or 300 hex)
for the nominal input voltage and so has adequate headroom
to deal with overvoltages.
master. If a device’s SMBALERT line goes low, the
following events occur:
1. SMBALERT is pulled low.
2. The master initiates a read operation and sends the
alert response address (ARA = 0001 100). This
general call address must not be used as a specific
device address.
3. 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.
4. 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.
5. Once the ADT7475 has responded to the alert
response address, the master must read the status
registers, and the SMBALERT is cleared only if
the error condition has gone away.
Input Circuitry
The internal structure for the VCCP analog input is shown
in Figure 19. The input circuit consists of an input protection
diode, an attenuator, and a capacitor to form a first-order,
low-pass filter that gives the input immunity to high
frequency noise.
52.5 kW
Table 6. VOLTAGE MEASUREMENT REGISTERS
The ADT7475 includes an SMBus timeout feature. If
there is no SMBus activity for 35 ms, the ADT7475 assumes
that the bus is locked and releases the bus. This prevents the
device from locking or holding the SMBus expecting data.
Some SMBus controllers cannot handle the SMBus timeout
feature, so it can be disabled.
Register
Description
Default
0x21
VCCP Reading
0x00
0x22
VCCP Reading
0x00
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 5. CONFIGURATION REGISTER 1 (REG. 0X40)
<6> TODIS
35 pF
Figure 19. Structure of Analog Inputs
SMBus Timeout
Bit
17.5 kW
VCCP
Description
0: SMBus Timeout Enabled (Default)
1: SMBus Timeout Disabled
Table 7. VCCP LIMIT REGISTERS
Register
Virus Protection
To prevent rogue programs or viruses from accessing
critical ADT7475 register settings, the lock bit can be set.
Setting Bit 1 of Configuration Register 1 (0x40) sets the
lock bit and locks critical registers. In this mode, certain
registers can no longer be written to until the ADT7475 is
powered down and powered up again. For more information
on which registers are locked, see the Register Tables
section.
Description
Default
0x46
VCCP Low Limit
0x00
0x47
VCCP High Limit
0xFF
Table 10 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 16 conversions to
reduce noise; a measurement takes nominally 11.38 ms.
Extended Resolution Registers
Voltage Measurement Input
Voltage measurements can be made with higher accuracy
using the extended resolution registers (0x76 and 0x77).
Whenever the extended resolution registers are read, the
corresponding data in the voltage measurement registers is
locked until their data is read. That is, if extended resolution
is required, then the extended resolution register must be
read first, immediately followed by the appropriate voltage
measurement register.
The ADT7475 has one external voltage measurement
channel. It 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.
Analog-to-Digital Converter
All analog inputs are multiplexed into the on-chip,
successive approximation, analog-to-digital converter. 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
Additional ADC Functions for Voltage Measurements
A number of other functions are available on the
ADT7475 to offer the system designer increased flexibility.
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ADT7475
Turn-off Averaging
channel is selected by writing to Bits <7:5> of the TACH1
minimum high byte register (0x55).
For each voltage measurement read from a value register,
16 readings have been made internally, and the
results averaged, before being placed into the value register.
For instances where faster conversions are needed, setting
Bit 4 of Configuration Register 2 (0x73) turns averaging
off. This effectively gives a reading 16 times faster (711 ms),
but the reading may be noisier.
Table 8. SINGLE-CHANNEL ADC CONVERSION
Register 0x55, Bits <7:5>
Bypass Voltage Input Attenuator
Setting Bit 5 of Configuration Register 2 (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 0 V
to 2.25 V.
Channel Selected
001
VCCP
010
VCC
101
Remote 1 Temperature
110
Local Temperature
111
Remote 2 Temperature
Table 9. CONFIGURATION REGISTER 2 (REG. 0X73)
Bit
Single-Channel ADC Conversion
Setting Bit 6 of Configuration Register 2 (0x73) places
the ADT7475 into single-channel ADC conversion mode. In
this mode, the ADT7475 can be made to read a single
voltage channel only. If the internal ADT7475 clock is used,
the selected input is read every 711Ăms. The appropriate ADC
Description
<4>
1: Averaging Off
<5>
1: Bypass Input Attenuators
<6>
1: Single-channel Convert Mode
TACH1 Minimum High Byte (0x55)
Bits <7:5> select the ADC channel for single-channel
convert mode.
Table 10. 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 and that VCC should never exceed 3.6 V.
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ADT7475
Temperature Measurement Method
However, this exceeds the operating temperature range of
the device, so local temperature measurements outside the
ADT7475 operating temperature range are not possible.
Local Temperature Measurement
The ADT7475 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 temperature
registers (0x25, 0x26, and 0x27). 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 11 and Table 12.
Theoretically, the temperature sensor and ADC can
measure temperatures from −128°C to +127°C (or −64°C to
+191°C in the extended temperature range) with a
resolution of 0.25°C.
I
CPU
THERMDA
REMOTE
SENSING
TRANSISTOR
N×I
Remote Temperature Measurement
The ADT7475 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. Because the
absolute value of VBE varies from device to device and
individual calibration is required to null this out, the
technique is unsuitable for mass production.
VDD
IBIAS
D+
VOUT+
To ADC
THERMDC
D−
VOUT−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
Figure 20. Signal Conditioning for Remote Diode Temperature Sensors
To measure DVBE, the sensor is switched between
operating currents of I and N × I. The resulting waveform is
passed through a 65 kHz low-pass filter to remove noise and
to a chopper stabilized amplifier that performs the functions
of amplification and rectification of the waveform to
produce a dc voltage proportional to DVBE. This voltage is
measured by the ADC to give a temperature output in 10-bit,
twos complement format. To further reduce the effects of
noise, digital filtering is performed by averaging the results
of 16 measurement cycles.
A remote temperature measurement takes nominally
38 ms. The results of remote temperature measurements are
stored in 10-bit, twos complement format, as shown in
Table 11. 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.
The technique used in the ADT7475 is to measure the
change in VBE when the device is operated at two different
currents.
This is given by:
DV BE + kTńq
ln(N)
(eq. 1)
where:
k is Boltzmann’s constant.
q is the charge on the carrier.
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
Figure 20 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.
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 to the
D+ input. If an NPN transistor is used, the emitter is
connected to the D− input and the base to the D+ input.
Figure 21 and Figure 22 show how to connect the ADT7475
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 D− pin to help combat the effects of noise. However,
large capacitance’s 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.
Sometimes, this sensor noise is a problem in a very noisy
environment. In most cases, a capacitor is not required
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ADT7475
because differential inputs, by their very nature, have a high
immunity to noise.
algebraic sum of these offsets must be programmed to
the offset register.
If a discrete transistor is used with the ADT7475, the best
accuracy is obtained by choosing devices according to the
following criteria:
• Base-emitter voltage greater than 0.25ĂV at 11ĂmA, at
the highest operating temperature.
• Base-emitter voltage less than 0.95ĂV at 180ĂmA, at the
lowest operating temperature.
• Base resistance less than 100 W.
• Small variation in hFE (approximately 50 to 150) that
indicates tight control of VBE characteristics.
ADT7475
2N3904
NPN
D+
D−
Figure 21. Measuring Temperature by Using
an NPN Transistor
ADT7475
2N3906
PNP
D+
Transistors, such as 2N3904, 2N3906, or equivalents in
SOT−23 packages, are suitable devices to use.
D−
Figure 22. Measuring Temperature by Using
a PNP Transistor
Table 11. TWOS COMPLEMENT TEMPERATURE DATA
FORMAT
Factors Affecting Diode Accuracy
Temperature
Remote Sensing Diode
The ADT7475 is designed to work with either substrate
transistors built into processors or with 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
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 ADT7475 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. See the processor data sheet for
the nf values.
DT + ǒn f * 1.008Ǔ
•
ǒ273.15 k ) TǓ
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 (0x77) with 0.25°C resolution.
Table 12. EXTENDED RANGE, TEMPERATURE DATA
FORMAT
Temperature
(eq. 2)
To factor this in, the user can write the DT value to the
offset register. The ADT7475 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 ADT7475, IHIGH, is 180ĂmA and the
low level current, ILOW, is 11ĂmA. If the ADT7475
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 programmed to the offset
register. If more than one offset must be considered, the
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
1°C
0100 0001 00
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 (0x77) with 0.25°C resolution.
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ADT7475
Nulling Out Temperature Errors
Temperature Measurement Limit Registers
As CPUs run faster, it is 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 ADT7475 has two temperature offset registers,
Register 0x70 and Register 0x72, for the Remote 1 and
Remote 2 temperature channels. By doing 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.
Changing Bit 1 of Configuration Register 5 (0x7C)
changes the resolution and therefore the range of the
temperature offset as either having a range of –63°C to
+127°C, with a resolution of 1°C, or having a range of −63°C
to +64°C, with a resolution of 0.5°C. This temperature offset
can be used to compensate for linear temperature errors
introduced by noise.
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 (depending on the way the interrupt mask register
is programmed and assuming that SMBALERT is set as an
output on the appropriate pin).
Table 16. TEMPERATURE MEASUREMENT LIMIT
REGISTERS
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)
By setting Bit 0 of Configuration Register 5 (0x7C), all
temperature measurements are stored in the zone temperature
value registers (0x25, 0x26, and 0x27) in twos complement
in the range −128°C to +127°C. The temperature limits must
be reprogrammed in twos complement.
If a twos complement temperature below −128°C is
entered, the temperature is clamped to −128°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.
Default
0x25
Remote 1 Temperature
−
0x26
Local Temperature
−
0x27
Remote 2 Temperature
−
0x77
Extended Resolution 2
0x00
Mnemonic
<7:6>
TDM2
Remote 2 Temperature LSBs
<5:4>
LTMP
Local Temperature LSBs
<3:2>
TDM1
Remote 1 Temperature LSBs
0x4F
Remote 1 Temperature High Limit
0x7F
0x50
Local Temperature Low Limit
0x81
0x51
Local Temperature High Limit
0x7F
0x52
Remote 2 Temperature Low Limit
0x81
0x53
Remote 2 Temperature High Limit
0x7F
A number of other functions are available on the
ADT7475 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. The default round-robin cycle
time takes 146.5 ms.
Table 17. CONVERSION TIME WITH AVERAGING
DISABLED
Channel
Table 15. EXTENDED RESOLUTION TEMPERATURE
MEASUREMENT REGISTER BITS
Bit
0x81
Additional ADC Functions for Temperature
Measurement
Table 14. TEMPERATURE MEASUREMENT
REGISTERS
Description
Default
Remote 1 Temperature Low Limit
It is important to note that temperature can be read from
the ADT7475 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, this involves a
two-register read for each measurement. The Extended
Resolution Register 2 (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.
ADT7463/ADT7475 Backwards Compatible Mode
Register
Description
0x4E
Reading Temperature from the ADT7475
Table 13. TEMPERATURE OFFSET REGISTERS
Register
Register
Voltage Channels
Description
0.7
Remote Temperature 1
7
Remote Temperature 2
7
Local Temperature
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Measurement Time (ms)
1.3
ADT7475
When Bit 7 of Configuration Register 6 (0x10) is set, the
default round-robin cycle time increases to 240 ms.
THERM LIMIT
TEMPERATURE
Table 18. CONVERSION TIME WITH AVERAGING
ENABLED
Channel
Measurement Time (ms)
Voltage Channels
11
Remote Temperature 1
39
Remote Temperature 2
39
Local Temperature
12
FANS
THERM can be disabled on specific temperature channels
using Bits <7:5> of Configuration Register 5 (0x7C).
THERM can also be disabled by:
• In Offset 64 mode, writing −64°C to the appropriate
THERM Temperature Limit.
• In twos complement mode, writing −128°C to the
appropriate THERM Temperature Limit.
Setting Bit 6 of Configuration Register 2 (0x73) places
the ADT7475 into single-channel ADC conversion mode. In
this mode, the ADT7475 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).
Limits, Status Registers, and Interrupts
Limit Values
Table 19. PROGRAMMING SINGLE-CHANNEL ADC
MODE FOR TEMPERATURES
Associated with each measurement channel on the
ADT7475 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 detected by polling the device.
Alternatively, SMBALERT interrupts can be generated to flag
out-of-limit conditions to a processor or microcontroller.
Channel Selected
101
Remote 1 Temperature
110
Local Temperature
111
Remote 2 Temperature
100%
Figure 23. THERM Temperature Limit Operation
Single-channel ADC Conversions
Register 0x55, Bits <7:5>
HYSTERESIS (°C)
8-bit Limits
Configuration Register 2 (0x73)
The following is a list of 8-bit limits on the ADT7475.
Bit <4> = 1, Averaging off
Bit <6> = 1, Single-channel Convert Mode
Table 20. VOLTAGE LIMIT REGISTERS
Register
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
automatic fan speed control mode. Register 0x6A to
Register 0x6C are the THERM temperature limit registers.
When a temperature exceeds its THERM temperature limit,
all PWM outputs run at the maximum PWM duty cycle
(Register 0x38, Register 0x39, and Register 0x3A).
This effectively runs the fans at the fastest allowed speed.
The fans run 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 the THERM temperature
limit is the value programmed into Register 0x6D and
Register 0x6E (hysteresis registers). The default hysteresis
value is 4°C.
Description
Default
0x46
VCCP Low Limit
0x00
0x47
VCCP High Limit
0xFF
0x48
VCC Low Limit
0x00
0x49
VCC High Limit
0xFF
Table 21. TEMPERATURE LIMIT REGISTERS
Register
Description
Default
0x4E
Remote 1 Temperature Low Limit
0x81
0x4F
Remote 1 Temperature High Limit
0x7F
0x6A
Remote 1 THERM Temp. Limit
0x64
0x50
Local Temperature Low Limit
0x81
0x51
Local Temperature High Limit
0x7F
0x6B
Local THERM Temperature Limit
0x64
0x52
Remote 2 Temperature Low Limit
0x81
0x53
Remote 2 Temperature High Limit
0x7F
0x6C
Remote 2 THERM Temp. Limit
0x64
Table 22. THERM LIMIT REGISTERS
Register
0x7A
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16
Description
THERM Timer Limit
Default
0x00
ADT7475
16-bit Limits
of interest, because the most recently measured value of any
input can be read out at any time.
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 Pin)
• Supply Voltage (VCC Pin)
• Local Temperature
• Two Remote Temperatures
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.
Table 23. FAN 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
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
ADT7475 is a derivative of the ADT7467. As a result, the
total conversion time in the ADT7475 is the same as the total
conversion time of the ADT7467.
Fan TACH measurements are made in parallel and are not
synchronized with the analog measurements in any way.
Out-of-Limit Comparisons
Interrupt Status Registers
Once all limits have been programmed, the ADT7475 can
be enabled for monitoring. The ADT7475 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 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 (0x41), 1 means
that an out-of-limit event has been flagged in Interrupt
Status Register 2. This means that the user needs only to read
Interrupt Status Register 2 when this bit is set. Alternatively,
Pin 5 or Pin 9 can be configured as an SMBALERT output.
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 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 status mask registers (0x74
and 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.
High Limit > Comparison Performed
Low Limit ≤ Comparison Performed
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
The analog monitoring cycle begins when a 1 is written to
the start bit (Bit 0) of Configuration Register 1 (0x40).
By default, the ADT7475 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
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ADT7475
Figure 24 shows how the SMBALERT output and sticky
status bits behave. Once a limit is exceeded, the
corresponding status bit is set to 1. The status bit remains set
until the error condition subsides and the 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 for how software handles the
interrupt.
Table 24. INTERRUPT STATUS REGISTER 1
(REG. 0X41)
Bit
Mnemonic
Description
7
OOL
1 denotes that a bit in Status Register 2
is set and that 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 Remote 1
Temperature High or Low Limit has
been exceeded.
2
VCC
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.
1 indicates that the Local Temperature
High or Low Limit has been exceeded.
Handling SMBALERT Interrupts
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
(0x74 and 0x75).
5. Take the appropriate action for a given interrupt
source.
6. Exit the interrupt handler.
7. 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 25.
Table 25. INTERRUPT STATUS REGISTER 2
(REG. 0X42)
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 minimum speed. Alternatively,
indicates that THERM timer limit has
been exceeded, if the THERM function
is used.
4
FAN3
1 indicates that Fan 3 has dropped
below minimum speed.
3
FAN2
1 indicates that Fan 2 has dropped
below minimum speed.
2
FAN1
1 indicates that Fan 1 has dropped
below minimum speed.
1
OVT
1 indicates that a THERM
overtemperature limit has been
exceeded.
HIGH LIMIT
TEMPERATURE
“STICKY”
STATUS BIT
SMBALERT Interrupt Behavior
The ADT7475 can be polled for status, or an SMBALERT
interrupt can be generated for out-of-limit conditions. Note
how the SMBALERT output and status bits behave when
writing interrupt handler software.
SMBALERT
CLEARED ON READ
(TEMP BELOW LIMIT)
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
INTERRUPT
MASK BIT SET
INTERRUPT MASK BIT
CLEARED
(SMBALERT RE-ARMED)
HIGH LIMIT
TEMPERATURE
Figure 25. How Masking the Interrupt Source Affects
SMBALERT Output
“STICKY”
STATUS BIT
Masking Interrupt Sources
CLEARED ON READ
Interrupt Mask Register 1 (0x74) and Interrupt Mask
Register 2 (0x75) allow individual interrupt sources to be
masked out to prevent SMBALERT interrupts. Note that
masking an interrupt source prevents only the SMBALERT
output from being asserted; the appropriate status bit is set
normally.
(TEMP BELOW LIMIT)
TEMP BACK IN LIMIT
SMBALERT
(STATUS BIT STAYS SET)
Figure 24. SMBALERT and Status Bit Behavior
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ADT7475
Once Pin 9 is configured as THERM, it must be enabled
(Bit 1, Configuration Register 3 (0x78)).
Table 26. INTERRUPT MASK REGISTER 1
(REG. 0X74)
Bit
Mnemonic
Description
7
OOL
1 masks SMBALERT for any alert
condition flagged in Interrupt Status
Register 2.
6
R2T
1 masks SMBALERT for Remote 2
temperature.
5
LT
4
R1T
1 masks SMBALERT for Remote 1
temperature.
2
VCC
1 masks SMBALERT for the VCC
channel.
0
VCCP
1 masks SMBALERT for the VCCP
channel.
THERM as an Input
When THERM is configured as an input, the user can time
assertions on the THERM pin. This can be useful for
connecting to the PROCHOT output of a CPU to gauge
system performance.
The user can also set up the ADT7475 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 that 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, pulling the THERM low
externally has no effect. See Figure 26 for more information.
1 masks SMBALERT for Local
temperature.
Table 27. 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).
TMIN
THERM
THERM ASSERTED TO LOW AS
AN INPUT: FANS DO NOT GO
TO 100% BECAUSE TEMPERATURE
IS BELOW TMIN
Enabling the SMBALERT Interrupt Output
Figure 26. Asserting THERM Low as an Input in
Automatic Fan Speed Control Mode
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.
THERM Timer
The ADT7475 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 ADT7475’s
THERM input and stopped when THERM is un-asserted.
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 the Bit 0 is set to 1 on the first THERM assertion. Once
the cumulative THERM assertion time has exceeded
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 27.
Table 28. CONFIGURING PIN 5 AS SMBALERT
OUTPUT
Register
Bit Setting
Configuration Register 3
(Reg. 0x78)
<0> ALERT Enable = 1
Assigning THERM Functionality to a Pin
Pin 9 on the ADT7475 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 29. PIN 9 CONFIGURATION
Bit 1
Bit 0
0
0
TACH4
0
1
THERM
1
0
SMBALERT
1
1
GPIO
THERM ASSERTED TO LOW AS
AN INPUT: FANS DO NOT GO TO
100% BECAUSE TEMPERATURE
IS ABOVE TMIN AND FANS ARE
ALREADY RUNNING.
Function
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ADT7475
When using the THERM timer, be aware of the following.
After a THERM timer read (Register 0x79), the following
happens:
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
THERM
TIMER
(REG. 0x79)
0 0 0 0 0 0 0 1
7 6 5 4 3 2 1 0
THERM ASSERTED
≤22.76 ms
If the THERM timer is read during a THERM assertion,
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 zero.
4. If the THERM timer limit (Register 0x7A) = 0x00,
the F4P bit is set.
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
Generating SMBALERT Interrupts from A THERM
Timer Events
THERM
The ADT7475 can generate SMBALERTs when a
programmable THERM timer limit has been exceeded. This
allows the system designer to ignore brief, infrequent
THERM assertions, while capturing longer THERM timer
events. Register 0x7A is the THERM timer limit register.
This 8-bit register allows a limit from 0 seconds (first
THERM assertion) to 5.825 seconds to be set before an
SMBALERT is generated. The THERM timer value is
compared with the contents of the THERM timer limit
register.
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 27. Understanding the THERM Timer
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 28. Functional Diagram of the ADT7475 THERM Monitoring Circuitry
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ADT7475
If the THERM timer value exceeds the THERM timer
limit value, then the F4P bit (Bit 5) of Interrupt Status
Register 2 is set, and an SMBALERT is generated. Note that
the F4P bit (Bit 5) of Interrupt Mask Register 2 (0x75)
masks out SMBALERTs if this bit is set to 1, although the
F4P bit of Interrupt Status Register 2 is still set if the
THERM timer limit is exceeded.
Figure 28 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
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.
Alternatively, OS- or BIOS-level software can
time-stamp when the system is powered on. If an
SMBALERT is generated due to the THERM timer
limit being exceeded, another time-stamp 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.
Configuring the THERM Pin as an Output
In addition to monitoring THERM as an input, the
ADT7475 can optionally drive THERM low as an output. In
cases where PROCHOT is bidirectional, THERM can be
used to throttle the processor by asserting PROCHOT. The
user can pre-program 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 limit is
exceeded by 0.25°C. The THERM temperature limit
registers are at Register 0x6A, Register 0x6B, and
Register 0x6C. Setting
Bit 3 of Register 0x5F,
Register 0x60, and Register 0x61 enables the THERM
output feature for the Remote 1, local, and Remote 2
temperature channels, respectively. Figure 29 shows how
the THERM pin asserts low as an output in the event of a
critical over temperature.
Configuring the THERM Behavior
1. Configure the relevant pin as the THERM timer
input. Setting Bit 1 (THERM) 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,
THERM, of Configuration Register 3, must also
be set). Pin 9 can also be used as TACH4.
2. Select the desired fan behavior for THERM timer
events.
Assuming that the fans are running, setting Bit 2
(BOOST bit) 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 to 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 SMBALERTs when the
THERM timer limit value is exceeded. This bit
should be cleared if SMBALERTs based on
THERM events are required.
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
>2.914 s in Hour 3, this can indicate that system
performance is degrading significantly because
THERM is asserting more frequently on an hourly
basis.
THERM LIMIT
0.255C
THERM LIMIT
TEMP
THERM
MONITORING
CYCLE
Figure 29. Asserting THERM as an Output, Based on
Tripping THERM Limits
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 64°C or 128°C,
respectively, THERM is disabled.
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ADT7475
Enabling and Disabling THERM on Individual
Channels
voltage applied across the fan and, therefore, the maximum
operating speed of the fan.
Figure 30 shows how to drive a 3-wire fan using PWM
control.
THERM can be enabled/disabled for individual or
combinations of temperature channels using Bits <7:5> of
Configuration Register 5 (0x7C).
12 V
12 V
Setting Bit 0 of Configuration Register 7 (0x11) disables
THERM hysteresis.
If THERM hysteresis is enabled and THERM is disabled
(Bit 2 of Configuration Register 4, 0x7D), the THERM pin
does not assert low when a THERM event occurs. If
THERM hysteresis is disabled and THERM is disabled
(Bit 2 of Configuration Register 4, 0x7D, and assuming the
appropriate pin is configured as THERM), the THERM pin
asserts low when a THERM event occurs.
If THERM and THERM hysteresis are both enabled, the
THERM output asserts as expected.
TACH
10 kW
10 kW
12 V
FAN
4.7 kW
ADT7475
1N4148
THERM Hysteresis
3.3 V
10 kW
Q1
NDT3055L
PWM
Figure 30. Driving a 3-wire Fan Using an N-channel
MOSFET
THERM Operation in Manual Mode
Figure 30 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 ADT7475. If in doubt 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 31 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.
Fan Drive Using PWM Control
The ADT7475 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 may need only a pullup resistor. In many cases,
the 4-wire fan PWM input has a built-in pullup resistor.
The ADT7475 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.
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, so
SOT devices can be used where board space is a concern. In
desktops, fans can typically draw 250 mA to 300 mA each.
If several fans are driven 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 should
have a gate voltage drive, VGS < 3.3 V, for direct interfacing
to the PWM output pin. 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
12 V
TACH
10 kW
10 kW
TACH
4.7 kW
ADT7475
12 V
12 V
FAN
1N4148
In manual mode, THERM events do not cause fans to go
to full speed, unless Bit 3 of Configuration Register 6
(0x10) is set to 1.
Additionally, Bit 3 of Configuration Register 4 (0x7D)
can be used to select PWM speed on THERM event (100%
or maximum PWM).
Bit 2 in Configuration Register 4 (0x7D) can be set to
disable THERM events from affecting the fans.
3.3 V
665 W
PWM
Q1
MMBT2222
Figure 31. 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 32 shows a typical drive circuit for 4-wire fans.
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ADT7475
12 V
10 kW
TACH
ADT7475
12 V, 4-WIRE FAN
10 kW
VCC
TACH
PWM
TACH
4.7 kW
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 that 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
3.3 V
Driving up to Three Fans from PWM3
2 kW
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 36 and
Figure 37. The SYNC bit in Register 0x62 enables this
function.
Synchronization is not required in high frequency mode
when used with 4-wire fans.
PWM
Figure 32. Driving a 4-wire Fan
Driving Two Fans from PWM3
The ADT7475 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 33 shows
how to drive two fans in parallel using low cost NPN
transistors. Figure 34 shows the equivalent circuit using a
MOSFET.
Table 30. SYNC: ENHANCE ACOUSTICS REGISTER 1
(REG. 0X62)
12 V
3.3 V
1N4148
3.3 V
ADT7475
TACH3
1 kW
PWM3
2.2 kW
TACH4
Q1
MMBT3904
Figure 33. Interfacing Two Fans in Parallel to the
PWM3 Output Using Low Cost NPN Transistors
3.3 V
10 kW
TYP
3.3 V
ADT7475
TACH3
10 kW
TYP
TACH
3.3 V
10 kW
TYP
PWM3
+V
+V
5V
or
12 V
FAN
1N4148
TACH4
<4>
SYNC
Description
1, Synchronizes TACH2, TACH3, and
TACH4 to PWM3.
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 ADT7475 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 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 35 to Figure 38 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 35.
Q3
MMBT2222
10 W
Mnemonic
TACH Inputs
Q2
MMBT2222
10 W
Bit
TACH
VCC
12 V
5V
or
12 V
FAN
PULLUP
4.7 kW
TYP
TACH
OUTPUT
TACH
Q1
NDT3055L
FAN SPEED
COUNTER
ADT7475
Figure 35. Fan with TACH Pullup to VCC
Figure 34. Interfacing Two Fans in Parallel to the
PWM3 Output Using a Single N-channel MOSFET
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 36. The Zener diode voltage
should be chosen so that it is greater than VIH of the TACH
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ADT7475
Fan Speed Measurement
input but less than 3.6 V, allowing for the voltage tolerance of
the Zener. A value between 3.0 V and 3.6 V is suitable.
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 39), 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 Register 0x7B (TACH Pulses per Revolution
register). 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
ZD1*
FAN SPEED
COUNTER
ADT7475
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × VCC
Figure 36. Fan with TACH Pullup to Voltage > 3.6 V
(Example, 12 V) Clamped with Zener Diode
If the fan has a strong pullup (less than 1 kW) to 12 V or
a totem-pole output, then a series resistor can be added to
limit the Zener current, as shown in Figure 37.
5 V OR12 V
Measuring Fan TACH
When the ADT7475 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.
VCC
FAN
R1
10 kW
PULLUP
TYP < 1 kW
TACH
OUTPUT
TACH
ZD1*
ZENER
OR TOTEM-POLE
FAN SPEED
COUNTER
ADT7475
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × VCC
CLOCK
Figure 37. Fan with Strong TACH. Pullup to > VCC or
Totem-Pole Output, Clamped with Zener and Resistor
PWM
Alternatively, a resistive attenuator can be used, as shown
in Figure 38. R1 and R2 should be chosen such that:
TACH
2 V t V PULLUP
1
R2ńǒR PULLUP ) R1 ) R2Ǔ t 3.6 V (eq. 3)
2
3
The fan inputs can have an input resistance of 160 kW to
5.1 kW to ground, which should be taken into account when
calculating resistor values.
With a pullup voltage of 12 V and pullup resistor less than
1 kW, suitable values for R1 and R2 would be 100 kW and
33 kW, respectively. This gives a high input voltage of
2.95 V.
12 V
4
Figure 39. Fan Speed Measurement
Fan Speed Measurement Registers
The fan tachometer readings are 16-bit values consisting
of a 2-byte read from the ADT7475.
Table 31. FAN SPEED MEASUREMENT REGISTERS
VCC
Register
< 1 kW
TACH
OUTPUT
R1*
TACH
R2*
FAN SPEED
COUNTER
ADT7475
*SEE TEXT
Figure 38. Fan with Strong TACH. Pullup to > VCC or
Totem-Pole Output, Attenuated with R1/R2
Default
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
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Description
0x28
ADT7475
Reading Fan Speed from the ADT7475
Example
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
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 that the fan either has stalled or is running
very slowly (<100 RPM).
High Limit > Comparison Performed
Because the actual fan TACH period is being measured,
falling below a fan TACH limit by 1 sets the appropriate
status bit and can be used to generate an SMBALERT.
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 × 60)/Fan 1 TACH Reading
RPM = (90,000 × 60)/6143
Fan Speed = 879 RPM
Fan Pulses per Revolution
Different fan models can output either 1, 2, 3, or 4 TACH
pulses per revolution. Once the number of fan TACH pulses
has been determined, it can be programmed into the TACH
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 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 33. TACH PULSES/REVOLUTION REGISTER
(REG. 0X7B)
Table 32. 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
Description
<1:0>
FAN1 Default
2 Pulses per Revolution
<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 34. 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 ADT7475 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 have
been 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 ADT7475 runs the fans just
fast enough to overcome inertia and is quieter on spin-up
than fans programmed to spin up for a given spin-up time.
Calculating Fan Speed
Fan Startup Timeout
Assuming a fan with a two pulses per revolution (and two
pulses per revolution being measured), fan speed is
calculated by the following:
Fan Speed (RPM) = (90,000 × 60)/Fan TACH Reading
To prevent the generation of false interrupts as a fan spins
up (because it is below running speed), the ADT7475
includes a fan startup timeout function. During this time, the
ADT7475 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
where Fan TACH Reading is the 16-bit fan tachometer
reading.
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ADT7475
Fan Speed Control
functionality can be changed (see the Disabling Fan Startup
Timeout section).
The ADT7475 controls fan speed using automatic mode
and manual mode as follows:
• 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, if the system hangs, the user is
guaranteed that the system is protected from overheating.
For more information about how to program
the automatic fan speed control loop, see the
Programming the Automatic Fan Speed Control Loop
section.
• In manual fan speed control mode, the ADT7475 allows
the duty cycle of any PWM output to be manually
adjusted. This can be useful if the user wants to change
fan speed at the software level or adjust PWM duty
cycle output for test purposes. Bits <7:5> of
Register 0x5C to Register 0x5E (PWM configuration)
control the behavior of each PWM output.
Table 35. PWM1 TO PWM3 CONFIGURATION
(REG. 0X5C TO 0X5E)
Bit
Mnemonic
<2:0>
SPIN
Description
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
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.
Table 38. PWM CONFIGURATION
(REG. 0X5C TO 0X5E) BITS
PWM Logic State
The PWM outputs can be programmed high for 100%
duty cycle (non-inverted) or low for 100% duty cycle
(inverted).
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 (PWMx current duty cycle registers).
Table 36. PWM1 TO PWM3 CONFIGURATION
(REG. 0X5C TO 0X5E) BITS
Programming the PWM Current Duty Cycle Registers
Bit
Mnemonic
Description
<4>
INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
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:
Value (decimal) = PWMMIN /0.39
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.
Example 1:
For a PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 0x80 (hex)
High Frequency Mode PWM Drive
Example 2:
Setting Bit 3 of Register 0x5F, Register 0x60, and
Register 0x61 enables high frequency mode for Fan 1,
Fan 2, and Fan 3, respectively.
For a PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 0x54 (hex)
Table 39. PWM CURRENT DUTY CYCLE REGISTERS
Table 37. PWM FREQUENCY REGISTERS
(REG. 0X5F TO 0X61)
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
Register
Description
Default
0x30
PWM1 Current Duty Cycle
0x00 (0%)
0x31
PWM2 Current Duty Cycle
0x00 (0%)
0x32
PWM3 Current Duty Cycle
0x00 (0%)
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
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ADT7475
of the default registers after the ADT7475 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
ADT7475 is not addressed by any valid SMBus transactions
before the fail-safe timeout (4.6 seconds) lapses, the
ADT7475 drives the fans to full speed. If the ADT7475 is
addressed by a valid SMBus transaction after this point, the
fans stop, and the ADT7475 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 ADT7475 is addressed by a valid SMBus transaction
before the fail-safe timeout (4.6 seconds) lapses, then the
ADT7475 operates normally, assuming the functionality of
all the default registers. See the flow chart in Figure 41.
speed control mode or acoustic enhancement mode. See the
Programming the Automatic Fan Speed Control Loop
section for details.
Operating from 3.3 V Standby
The ADT7475 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. When monitoring THERM, the THERM timer
should be disabled during these states.
Standby Mode
The ADT7475 has been specifically designed to respond to
the STBY supply. In computers that support S3 and S5 states,
the core voltage of the processor is lowered in these states.
When monitoring THERM, the THERM timer should be
disabled during these states.
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.
ADT7475 IS POWERED UP
Y
HAS THE ADT7475 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
Once the core voltage, VCCP, goes above the VCCP low
limit, everything is re-enabled and the system resumes
normal operation.
IS VCCP ABOVE 0.75 V?
N
CHECK VCCP
Y
START FAIL-SAFE TIMER
XNOR Tree Test Mode
The ADT7475 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 40 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).
Y
HAS THE ADT7475 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
FAIL-SAFE TIMER
ELAPSES AFTER THE
FAIL-SAFE TIMEOUT
TACH1
TACH2
HAS THE ADT7475 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
TACH3
Y
TACH4
N
RUNS THE FANS
TO FULL SPEED
HAS THE ADT7475 BEEN
ACCESSED BY A VALID
SMBus TRANSACTION?
N
Y
PWM2
PWM3
START UP THE ADT7475
NORMALLY
PWM1/XTO
SWITCH OFF FANS
Figure 41. Power-on Flow Chart
Figure 40. XNOR Tree Test
Programming the Automatic Fan Speed Control Loop
To more efficiently understand the automatic fan speed
control loop, it is strongly recommended to use the ADT7475
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
Power-On Default
When the ADT7475 is powered up, it polls the VCCP
input.
If VCCP stays below 0.75 V (the system CPU power rail
is not powered up), the ADT7475 assumes the functionality
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ADT7475
and selecting critical system parameters. To optimize the
system characteristics, the designer needs to give some
thought to system configuration, including the number of
fans, where they are located, and what temperatures are
being 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 this process.
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 select these
values carefully.
Figure 42 gives a top-level overview of the automatic fan
control circuitry on the ADT7475. 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
ADT7475 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, the 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 42 shows controls that are fan-specific. The
designer has individual control over parameters such as
minimum PWM duty cycle, fan 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.
Automatic Fan Control Overview
The ADT7475 can automatically control the speed of fans
based upon the measured temperature. This is done
independently of CPU intervention once initial parameters
are set up.
The ADT7475 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
and other CPUs). These three temperature channels can be
used as the basis for automatic fan speed control to drive fans
using pulse-width modulation (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
owing to the number of programmable parameters,
THERMAL CALIBRATION
PWM
MIN
100%
S
REMOTE1
TEMP
TMIN
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
MUX
LOCAL
TEMP
TMIN
TRANGE
S
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
REMOTE2
TEMP
TMIN
TRANGE
PWM
CONFIG
PWM
GENERATOR
TACHOMETER 1
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM
GENERATOR
Figure 42. Automatic Fan Control Block Diagram
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PWM1
TACH1
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
TACHOMETER 3
AND 4
MEASUREMENT
0%
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM3
TACH3
ADT7475
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
ADT7475 or will it run at full speed 100% of the
time?
If run at 100%, this frees up a PWM output, but
the system is louder.
4. Where will the ADT7475 be physically located in
the system?
This influences the assignment of the temperature
measurement channels to particular system
thermal zones. For example, locating the
ADT7475 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.
Ask the following questions:
1. What ADT7475 functionality will be used?
• PWM2 or SMBALERT?
• TACH4 fan speed measurement or
overtemperature THERM function?
The ADT7475 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?
THERMAL CALIBRATION
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
REMOTE2 =
CPU TEMP
TRANGE
PWM
CONFIG
PWM
CONFIG
CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
TACH1
TACHOMETER2
MEASUREMENT
PWM
GENERATOR
S
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
GENERATOR
S
MUX
PWM
CONFIG
Figure 43. Hardware Configuration Example
FRONT CHASSIS
PWM3
TACH3
REAR CHASSIS
• CPU temperature measured using the Remote 1
Recommended Implementation 1
Configuring the ADT7475 as in Figure 44 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 3.
• CPU core voltage measurement (VCORE).
• VRM temperature using local temperature sensor.
temperature channel.
• Ambient temperature measured through the Remote 2
•
•
temperature channel.
Bidirectional THERM pin, which 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.
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ADT7475
FRONT
CHASSIS
FAN
ADT7475
PWM1
TACH1
TACH2
CPU FAN
REAR
CHASSIS
FAN
PWM3
D2+
TACH3
D2−
THERM
PROCHOT
CPU
D1+
AMBIENT
TEMPERATURE
SDA
SCL
SMBALERT
D1−
ICH
GND
Figure 44. Recommended Implementation 1
• CPU temperature measured using the Remote 1
Recommended Implementation 2
Configuring the ADT7475 as in Figure 45 provides the
system designer with the following features:
• Three PWM outputs for fan control of up to three fan
(All three fans can be individually controlled).
• Three TACH fan speed measurement inputs.
• VCC measured internally through Pin 3.
• CPU core voltage measurement (VCORE).
FRONT
CHASSIS
FAN
temperature channel.
• Ambient temperature measured through the Remote 2
temperature channel.
• Bidirectional THERM pin that allows the monitoring of
PROCHOT output from an Intel® Pentium® 4
processor, for example, or can be used as an
overtemperature THERM output.
ADT7475
PWM1
TACH1
TACH2
PWM2
CPU FAN
REAR
CHASSIS
FAN
D2+
PWM3
TACH3
D2−
THERM
PROCHOT
CPU
D1+
AMBIENT
TEMPERATURE
D1−
SDA
SCL
GND
ICH
Figure 45. Recommended Implementation 2
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ADT7475
Step 2: Configuring the Mux
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
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
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.
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 when the
local temperature exceeds 45°C.
Other Mux Options
Bits <7:5> (BHVR), Register 0x5C, Register 0x5D, and
Register 0x5E.
011 = PWMx runs full speed
100 = PWMx disabled (default)
111 = manual mode. PWMx is running under
software control. In this mode, PWM current
duty cycle registers (0x30 to 0x32) are writable
and control the PWM outputs
Automatic Fan Control Mux Options
Bits <7:5> (BHVR), Register 0x5C, Register 0x5D, and
Register 0x5E.
000 = Remote 1 temperature controls PWMx
001 = Local temperature controls PWMx
MUX
THERMAL CALIBRATION
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE1 =
AMBIENT TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
REMOTE2 =
CPU TEMP
TRANGE
PWM
CONFIG
PWM
CONFIG
CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
TACH1
TACHOMETER2
MEASUREMENT
PWM
GENERATOR
S
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
GENERATOR
S
MUX
PWM
CONFIG
Figure 46. Assigning Temperature Channels to Fan Channels
FRONT CHASSIS
PWM3
TACH3
REAR CHASSIS
• PWM1 (CPU fan sink) is controlled by the fastest speed
Mux Configuration Example
This is an example of how to configure the mux in a
system using the ADT7475 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 behavior:
•
calculated by the local (VRM temperature) and
Remote 2 (processor) Temperatures. 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).
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ADT7475
• PWM3 (rear chassis fan) is controlled by the Remote 1
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
Temperature (ambient).
Example Mux Settings
Bits <7:5> (BHVR), PWM1 Configuration Register (0x5C)
101 = Fastest speed calculated by local and Remote 2
temperature controls PWM1
THERMAL CALIBRATION
These settings configure the mux, as shown in Figure 47.
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
0%
MUX
THERMAL CALIBRATION
100%
PWM
MIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
S
TMIN
PWM
CONFIG
TACH1 CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
PWM2
TACH2
FRONT CHASSIS
PWM
CONFIG
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
REAR CHASSIS
Figure 47. Mux Configuration Example
Step 3: TMIN Settings for Thermal Calibration Channels
Table 40. TMIN REGISTERS
TMIN is the temperature at which the fans turn on under
automatic fan control. The speed at which the fan runs at
TMIN is programmed later in the process. 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. There
is a TMIN register associated with each temperature
measurement channel: Remote 1, local, and Remote 2
temperatures. Once the TMIN value is exceeded, the fan turns
on and runs at the minimum PWM duty cycle. The fan turns
off once the temperature has dropped 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
switch off below TMIN. Bits <7:5> of Enhanced Acoustics
Register 1 (0x62), when set, keep the fans running at the
PWM minimum duty cycle, if the temperature should fall
below TMIN.
Register
Description
Default
0x67
Remote 1 Temperature TMIN
0x5A (90°C)
0x68
Local Temperature TMIN
0x5A (90°C)
0x69
Remote 2 Temperature TMIN
0x5A (90°C)
Enhanced Acoustics Register 1 (0x62)
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.
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.
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ADT7475
PWM DUTY CYCLE
100%
0%
TMIN
THERMAL CALIBRATION
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM1
TACHOMETER1
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
S
MUX
PWM
CONFIG
TACH1
CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM2
TACHOMETER2
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
TACH2
FRONT CHASSIS
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM3
TACHOMETER3
AND 4
MEASUREMENT
0%
TACH3
REMOTE1 =
AMBIENT TEMP
REAR CHASSIS
Figure 48. Understanding the TMIN Parameter
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. For maximum system acoustic benefit,
PWMMIN should be 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%
PWM2
PWM1MIN
0%
TMIN
100%
PWM DUTY CYCLE
PWM1
PWM2MIN
TEMPERATURE
Figure 50. Operating Two Different Fans from a
Single Temperature Channel
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 Fan 2 connected to PWM2. Figure 50 illustrates this as
PWM1MIN (front fan) turns on at a minimum duty cycle of
20%, while PWM2MIN (rear fan) turns on at a minimum of
PWMMIN
0%
TMIN
TEMPERATURE
Figure 49. PWMMIN Determines Minimum
PWM Duty Cycle
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ADT7475
40% duty cycle. Note that both fans turn on at exactly the
same temperature, defined by TMIN.
PWM DUTY CYCLE
100%
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
TMIN
Programming the PWMMAX Registers
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)
Table 41. PWMMIN REGISTERS
Default
0x64
PWM1 Minimum Duty Cycle
0x80 (50%)
0x65
PWM2 Minimum Duty Cycle
0x80 (50%)
0x66
PWM3 Minimum Duty Cycle
0x80 (50%)
Example 1
For a maximum PWM duty cycle of 50%,
Value (decimal) − 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Note on Fan Speed and PWM Duty Cycle
Example 2
The PWM duty cycle does not directly correlate to fan
speed in RPM. Running a fan at 33% PWM duty cycle does
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 the PWM duty cycle.
Given a PWM square wave as the drive signal, fan speed in
RPM approximates to:
% fanspeed + ǸPWM duty cycle
10
TEMPERATURE
Figure 51. PWMMAX Determines Maximum PWM Duty
Cycle Below the THERM Temperature Limit
For a minimum PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Description
PWMMIN
0%
Example 1
Register
PWMMAX
For a minimum PWM duty cycle of 75%,
Value (decimal) = 75/0.39 = 192 (decimal)
Value = 192 (decimal) or C0 (hex)
Table 42. PWMMAX REGISTERS
(eq. 4)
Step 5: PWMMAX for PWM (Fan) Outputs
Register
Description
Default
0x38
PWM1 Maximum Duty Cycle
0xFF (100%)
0x39
PWM2 Maximum Duty Cycle
0xFF (100%)
0x3A
PWM3 Maximum Duty Cycle
0xFF (100%)
Step 6: TRANGE for Temperature Channels
PWMMAX is the maximum duty cycle that each fan in the
system runs at 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.
There is a PWMMAX limit for each fan channel. The
default value of all PWMMAX registers is 0xFF.
TRANGE is the range of temperature over which automatic
fan control occurs once the programmed TMIN temperature
has been exceeded. TRANGE is the temperature range
between PWMMIN and 100% PWM where the fan speed
changes linearly. Otherwise stated, it is the line drawn
between the TMIN/PWMMIN and the (TMIN + TRANGE)
/PWM 100% intersection points.
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ADT7475
TRANGE
100%
PWM DUTY CYCLE
PWM DUTY CYCLE
100%
PWMMIN
0%
TMIN
10%
0%
TMIN−HYST
TEMPERATURE
Figure 52. TRANGE Parameter Affects Cooling Slope
TMIN
The TRANGE 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.
4. Using the ADT7475 evaluation software,
graphically program and visualize this
functionality.
Figure 54. Increasing TRANGE Changes the AFC Slope
PWM DUTY CYCLE
100%
MAX
PWM
10%
0%
TMIN−HYST
As PWMMIN is changed, the automatic fan control slope
also changes.
TRANGE
Figure 55. Changing PWMMAX Does Not Change the
AFC Slope
100%
PWM DUTY CYCLE
30°C
40°C
45°C
54°C
Selecting TRANGE
The TRANGE value can be selected for each temperature
channel: Remote 1, local, and Remote 2 temperatures.
Bits <7:4> (RANGE) of Register 0x5F to Register 0x61
define the TRANGE value for each temperature channel.
50%
Table 43. SELECTING A TRANGE VALUE
33%
Bits <7:4> (Note 1)
0%
30°C
TMIN
Figure 53. Adjusting PWMMIN Changes the Automatic
Fan Control Slope
As TRANGE is changed, the slope also changes. As
TRANGE gets smaller, the fans reach 100% speed with a
smaller temperature change.
TRANGE (5C)
0000
2
0001
2.5
0010
3.33
0011
4
0100
5
0101
6.67
0110
8
0111
10
1000
13.33
1001
16
1010
20
1011
26.67
1100
32 (Default)
1101
40
1110
53.33
1111
80
1. Register 0x5F configures Remote 1 TRANGE; Register 0x60
configures local TRANGE; Register 0x61 configures Remote 2
TRANGE.
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Actual Changes in PWM Output
(Advanced Acoustics Settings)
PWM DUTY CYCLE (%)
PWM DUTY CYCLE (%)
55C
6.675C
105C
165C
205C
30
26.65C
325C
20
405C
53.35C
0
325C
405C
20
40
60
80
100
120
805C
TEMPERATURE ABOVE TMIN
25C
100
2.55C
90
3.335C
45C
80
55C
70
85C
105C
50
165C
205C
30
26.65C
20
325C
405C
10
53.35C
0
20
40
60
80
100
120
120
805C
2.55C
3.335C
45C
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
20
325C
405C
53.35C
0
20
40
60
80
100
120
805C
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 = 53.33°C for CPU temperature
TRANGE = 40°C for VRM temperature
13.35C
40
100
Example: Determining TRANGE for Each Temperature
Channel
6.675C
60
80
The graphs in Figure 56 assume that 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 57 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.
53.35C
0
60
Figure 57. TRANGE and % Fan Speed Slopes with
PWMMIN = 20%
26.65C
20
40
TEMPERATURE ABOVE TMIN
205C
30
20
25C
165C
10
FAN SPEED (% OF MAX)
13.35C
40
0
13.35C
40
0
105C
10
85C
50
85C
50
90
45C
60
6.675C
60
100
3.335C
70
55C
TEMPERATURE ABOVE TMIN
2.55C
80
45C
70
0
25C
90
3.335C
80
10
FAN SPEED (% OF MAX)
100
2.55C
90
While the automatic fan control algorithm describes the
general response of the PWM output, the enhanced acoustics
registers (0x62 and 0x63) can be used to set/clamp the
maximum rate of change of PWM output for a given
temperature zone. This means if TRANGE is programmed
with a steep AFC slope, a relatively small change in
temperature can cause a large change in PWM output and an
audible change in fan speed, which may be noticeable/
annoying to users. Decreasing the PWM output’s maximum
rate of change, by programming the smoothing on the
appropriate temperature channels (Register 0x62 and
Register 0x63), clamps the fan speed’s maximum rate of
change in the event of a temperature spike. The PWM duty
cycle increases slowly until the PWM duty cycle reaches the
appropriate duty cycle as defined by the AFC curve.
Figure 56 shows PWM duty cycle versus temperature for
each TRANGE setting. The lower graph shows how each
TRANGE setting affects fan speed vs. temperature. As can be
seen from the graph, the effect on fan speed is non-linear.
0
25C
100
805C
This example uses the mux configuration described in
Step 2: Configuring the Mux, with the ADT7475 connected
as shown in Figure 47. Both CPU temperature and VRM
TEMPERATURE ABOVE TMIN
Figure 56. TRANGE vs. Actual Fan Speed (not PWM
Drive) Profile
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ADT7475
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 that 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% or less. In extreme
cases, some 3-wire fans do not run unless a PWM drive of
60% or more is applied.
100
VRM TEMP.
90
PWM DUTY CYCLE (%)
number programmed into the hysteresis registers (0x6D and
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 the designer should ensure that
it is not exceeded under normal system operating conditions.
Note that TTHERM limits are non-maskable and affect the
fan speed no matter how automatic fan control settings are
configured. This allows some flexibility because a TRANGE
value can be selected based on its slope, while a 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).
80
70
Table 44. THERM REGISTERS
CPU TEMPERATURE
60
Register
50
AMBIENT TEMPERATURE
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
FAN SPEED (% MAX RPM)
90
80
CPU TEMPERATURE
60
30
20
10
0
10
20
30
40
50
60
70
80
0x64 (100°C)
0x6B
Local THERM Temperature
Limit
0x64 (100°C)
0x6C
Remote 2 THERM
Temperature Limit
0x64 (100°C)
Register 0x6D, Remote 1 and Local Temperature/TMIN
Hysteresis Register
Bits <7:4> (HYSR1), Remote 1 Temperature Hysteresis
(4°C default)
Bits <3:0> (HYSL), Local Temperature Hysteresis
(4°C default)
Register 0x6E, Remote 2 Temperature TMIN Hysteresis
Register
Bits <7:4> (HYSR2), Remote 2 Temperature Hysteresis
(4°C default)
40
0
Remote 1 THERM
Temperature Limit
Hysteresis Registers
AMBIENT TEMPERATURE
50
0x6A
THERM hysteresis on a particular channel is configured
via the hysteresis settings in Register 0x6D and
Register 0x6E. For example, setting hysteresis on the
Remote 1 channel also sets the hysteresis on Remote 1
THERM.
VRM TEMP.
70
Default
THERM Hysteresis
TEMPERATURE ABOVE TMIN
100
Description
90
100
TEMPERATURE ABOVE TMIN
Figure 58. TRANGE and % Fan Speed Slopes for VRM,
Ambient, and CPU Temperature Channels
Step 7: TTHERM for Temperature Channels
Because each hysteresis setting is four bits, hysteresis
values are programmable from 1°C to 15°C. It is not
recommended that hysteresis values ever be programmed to
0°C because this disables hysteresis. In effect, this causes the
fans to cycle (during a THERM event) between normal
speed and 100% speed or, while operating close to TMIN,
between normal speed and off, creating unsettling acoustic
noise.
TTHERM is the absolute maximum temperature allowed
on a temperature channel. Above this temperature, a
component such as the CPU or VRM might be operating
beyond its safe operating limit. When the temperature
measured exceeds TTHERM, all fans drive 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
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TRANGE
PWM DUTY CYCLE
100%
0%
TMIN
TTHERM
THERMAL CALIBRATION
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
S
MUX
PWM
CONFIG
TACH1
CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
FRONT CHASSIS
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
Figure 59. How TTHERM Relates to Automatic Fan Control
Step 8: THYST for Temperature Channels
REAR CHASSIS
TTHERM hysteresis value, described in Step 6: TRANGE for
Temperature
Channels.
Therefore,
programming
Register 0x6D and Register 0x6E sets the hysteresis for both
fan on/off and the THERM function.
In some applications, it is required that fans not turn off
below TMIN but remain running at PWMMIN. Bits<7:5> of
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.
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 the
temperature is hovering at about the TMIN setting.
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.
The THYST setting applies not only to the temperature
hysteresis for fan on/off, but the same setting is used for the
THERM Hysteresis
Any hysteresis programmed via Register 0x6D and
Register 0x6E also applies to hysteresis on the appropriate
THERM channel.
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ADT7475
TRANGE
PWM DUTY CYCLE
100%
0%
TMIN
TTHERM
THERMAL CALIBRATION
PWM
MIN
100%
PWM
GENERATOR
S
TMIN
REMOTE2 =
CPU TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
0%
PWM
MIN
THERMAL CALIBRATION
100%
S
TMIN
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
S
MUX
PWM
CONFIG
TACH1
CPU FAN SINK
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
0%
PWM1
FRONT CHASSIS
PWM3
TACH3
REMOTE1 =
AMBIENT TEMP
REAR CHASSIS
Figure 60. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
Enhanced Acoustics Register 1 (0x62)
Configuration Register 6 (0x10)
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.
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 0 (SLOW Remote 1), 1 slows the ramp rate for PWM
changes associated with the Remote 1 temperature channel
by 4.
Bit 1 (SLOW Local), 1 slows the ramp rate for PWM
changes associated with the Local temperature channel by 4.
Bit 2 (SLOW Remote 2), 1 slows the ramp rate for PWM
changes associated with the Remote 2 temperature channel
by 4.
Bit 7 (ExtraSlow), 1 slows the ramp rate for all fans by a
factor of 39.2%.
The following sections list the ramp-up times when the
SLOW bit is set for each temperature monitoring channel.
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Enhanced Acoustics Register 1 (0x62)
Bits <6:4> (ACOU2), select the ramp rate for PWM outputs
associated with the Remote 2 temperature input.
000 = 37.5 sec
001 = 18.8 sec
010 = 12.5 sec
011 = 7.5 sec
100 = 4.7 sec
101 = 3.1 sec
110 = 1.6 sec
111 = 0.8 sec
When Bit 7 of Configuration Register 6 (0x10) = 1, the ramp
rates change to the following values:
000 = 52.2 sec
001 = 26.1 sec
010 = 17.4 sec
011 = 10.4 sec
100 = 6.5 sec
101 = 4.4 sec
110 = 2.2 sec
111 = 1.1 sec
Bits <2:0> (ACOU1), select the ramp rate for PWM outputs
associated with the Remote 1 temperature input.
000 = 37.5 sec
001 = 18.8 sec
010 = 12.5 sec
011 = 7.5 sec
100 = 4.7 sec
101 = 3.1 sec
110 = 1.6 sec
111 = 0.8 sec
Enhanced Acoustics Register 2 (0x63)
Bits <2:0> (ACOU3), select the ramp rate for PWM outputs
associated with the local temperature channel.
000 = 37.5 sec
001 = 18.8 sec
010 = 12.5 sec
011 = 7.5 sec
100 = 4.7 sec
101 = 3.1 sec
110 = 1.6 sec
111 = 0.8 sec
Setting the appropriate SLOW bits <2:0> of
Configuration Register 6 (0x10) slows the ramp rate further
by a factor of 4.
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Register Tables
Table 45. ADT7475 REGISTERS
Default
Lockable
SLOW
Remote 1
0x00
−
RES
Dis
THERM
Hys
0x00
−
4
3
2
0x00
−
5
4
3
2
0x00
−
5
4
3
2
0x80
−
6
5
4
3
2
0x80
−
6
5
4
3
2
0x80
−
5
4
3
2
1
0
0x00
−
14
13
12
11
10
9
8
0x00
−
7
6
5
4
3
2
1
0
0x00
−
TACH2 High
Byte
15
14
13
12
11
10
9
8
0x00
−
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
−
0x31
R/W
PWM2
Current Duty
Cycle
7
6
5
4
3
2
1
0
0x00
−
0x32
R/W
PWM3
Current Duty
Cycle
7
6
5
4
3
2
1
0
0x00
−
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
−
0x3D
R
Device ID
Reg
7
6
5
4
3
2
1
0
0x75
−
0x3E
R
Company ID
Number
7
6
5
4
3
2
1
0
0x41
−
0x40
R/W
Config Reg 1
RES
TODIS
FSPDIS
Vx1
FSPD
RDY
LOCK
STRT
0x04
Yes
0x41
R
Interrupt
Status Reg 1
OOL
R2T
LT
R1T
RES
VCC
VCCP
RES
0x00
−
0x42
R
Interrupt
Status Reg 2
D2
D1
F4P
FAN3
FAN2
FAN1
OVT
RES
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
−
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x10
R/W
Configuration
Register 6
Extra
Slow
VCCP
Low
RES
RES
THERM
in Manual
SLOW
Remote 2
SLOW
Local
0x11
R
Configuration
Register 7
RES
RES
RES
RES
RES
RES
0x21
R
VCCP
Reading
9
8
7
6
5
0x22
R
VCC Reading
9
8
7
6
0x25
R
Remote 1
Temp
9
8
7
6
0x26
R
Local Temp
9
8
7
0x27
R
Remote 2
Temp
9
8
7
0x28
R
TACH1 Low
Byte
7
6
0x29
R
TACH1 High
Byte
15
0x2A
R
TACH2 Low
Byte
0x2B
R
0x2C
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ADT7475
Table 45. ADT7475 REGISTERS (continued)
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
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
0x81
−
0x4F
R/W
Remote 1
Temp High
Limit
7
6
5
4
3
2
1
0
0x7F
−
0x50
R/W
Local Temp
Low Limit
7
6
5
4
3
2
1
0
0x81
−
0x51
R/W
Local Temp
High Limit
7
6
5
4
3
2
1
0
0x7F
−
0x52
R/W
Remote 2
Temp Low
Limit
7
6
5
4
3
2
1
0
0x81
−
0x53
R/W
Remote 2
Temp High
Limit
7
6
5
4
3
2
1
0
0x7F
−
0x54
R/W
TACH1
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x55
R/W
TACH1 Min
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 Min
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 Min
High Byte
15
14
13
12
11
10
9
8
0xFF
−
0x5A
R/W
TACH4
Minimum
Low Byte
7
6
5
4
3
2
1
0
0xFF
−
0x5B
R/W
TACH4 Min
High Byte
15
14
13
12
11
10
9
8
0xFF
−
0x5C
R/W
PWM1
Configuration
Register
BHVR
BHVR
BHVR
INV
RES
SPIN
SPIN
SPIN
0x62
Yes
0x5D
R/W
PWM2
Configuration
Register
BHVR
BHVR
BHVR
INV
RES
SPIN
SPIN
SPIN
0x62
Yes
0x5E
R/W
PWM3
Config
Register
BHVR
BHVR
BHVR
INV
RES
SPIN
SPIN
SPIN
0x62
Yes
0x5F
R/W
Remote 1
TRANGE/
PWM1 Freq
RANGE
RANGE
RANGE
RANGE
HF/LF
FREQ
FREQ
FREQ
0xC4
Yes
0x60
R/W
Local
TRANGE/
PWM2 Freq
RANGE
RANGE
RANGE
RANGE
HF/LF
FREQ
FREQ
FREQ
0xC4
Yes
0x61
R/W
Remote 2
TRANGE/
PWM3 Freq
RANGE
RANGE
RANGE
RANGE
HF/LF
FREQ
FREQ
FREQ
0xC4
Yes
0x62
R/W
Enhanced
Acoustics
Reg 1
MIN3
MIN2
MIN1
SYNC
EN1
ACOU1
ACOU1
ACOU1
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
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ADT7475
Table 45. ADT7475 REGISTERS (continued)
Addr
R/W
Desc
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable
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
0x5A
Yes
0x68
R/W
Local Temp
TMIN
7
6
5
4
3
2
1
0
0x5A
Yes
0x69
R/W
Remote 2
Temp TMIN
7
6
5
4
3
2
1
0
0x5A
Yes
0x6A
R/W
Remote 1
THERM
Temp Limit
7
6
5
4
3
2
1
0
0x64
Yes
0x6B
R/W
Local
THERM
Temp Limit
7
6
5
4
3
2
1
0
0x64
Yes
0x6C
R/W
Remote 2
THERM
Temp Limit
7
6
5
4
3
2
1
0
0x64
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
HYSR2
RES
RES
RES
RES
0x40
Yes
0x6F
R/W
XNOR Tree
Test Enable
RES
RES
RES
RES
RES
RES
RES
XEN
0x00
Yes
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 Reg 2
SHDN
CONV
ATTN
AVG
RES
RES
RES
RES
0x00
Yes
0x74
R/W
Interrupt
Mask Reg 1
OOL
R2T
LT
R1T
RES
VCC
VCCP
RES
0x00
−
0x75
R/W
Interrupt
Mask Reg 2
D2
D1
F4P
FAN3
FAN2
FAN1
OVT
RES
0x00
−
0x76
R/W
Extended
Res 1
RES
RES
VCC
VCC
VCCP
VCCP
RES
RES
0x00
−
0x77
R/W
Extended
Res 2
TDM2
TDM2
LTMP
LTMP
TDM1
TDM1
RES
RES
0x00
−
0x78
R/W
Configuration
Reg 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
Configuration
Reg 5
R2
THERM
O/P
Only
Local
THERM
O/P
Only
R1
THERM
O/P
Only
RES
GPIOP
GPIOD
Temp
Offset
TWOS
COMPL
0x01
Yes
0x7D
R/W
Configuration
Reg 4
RES
RES
BpAtt
VCCP
RES
Max/
Full on
THERM
THERM
Disable
PIN9
FUNC
PIN9
FUNC
0x00
Yes
0x7E
R
Test Reg 1
DO NOT WRITE TO THESE REGISTERS
0x00
Yes
0x7F
R
Test Reg 2
DO NOT WRITE TO THESE REGISTERS
0x00
Yes
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ADT7475
Table 46. REGISTER 0X10 − CONFIGURATION REGISTER 6 (POWER-ON DEFAULT = 0X00) (Notes 1 and 2)
Bit No.
Mnemonic
R/W
Description
<0>
SLOW
Remote 1
R/W
When this bit is set, Fan 1 smoothing times are multiplied x4 for Remote 1 temperature channel
(as defined in Register 0x62).
<1>
SLOW
Local
R/W
When this bit is set, Fan 2 smoothing times are multiplied x4 for local temperature channel
(as defined in Register 0x63).
<2>
SLOW
Remote 2
R/W
When this bit is set, Fan 3 smoothing times are multiplied x4 for Remote 2 temperature channel
(as defined in Register 0x63).
<3>
THERM in
Manual
R/W
When this bit is set, THERM is enabled in manual mode. (Note 1)
<5:4>
Reserved
N/A
Reserved. Do not write to these bits.
<6>
VCCPLow
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:
Bit 1 in Interrupt Status Register 1 is set.
SMBALERT is generated, if enabled.
PROCHOT monitoring is disabled.
Everything is re-enabled once VCCP increases above the VCCP low limit.
When VCCP increases above the low limit:
PROCHOT monitoring is enabled.
Fans return to their programmed state after a spin-up cycle.
<7>
ExtraSlow
R/W
When this bit is set, all fan smoothing times are increased by a further 39.2%.
1. A THERM event always overrides any fan setting (even when fans are disabled).
2. 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 47. REGISTER 0X11 − CONFIGURATION REGISTER 7 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
<0>
Dis
THERM
Hys
R/W
Setting This Bit to 1 Disables THERM Hysteresis
Description
<7:1>
Reserved
N/A
Reserved. Do Not Write to These Bits
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 48. VOLTAGE READING REGISTERS (POWER-ON DEFAULT = 0X00) (Notes 1 and 2)
Register Address
R/W
Description
0x21
Read-only
Reflects the Voltage Measurement at the VCCP Input on Pin 14 (8 MSBs of Reading)
0x22
Read-only
Reflects the Voltage Measurement at the VCC Input on Pin 3 (8 MSBs of Reading)
1. If the extended resolution bits of these readings are also read, the extended resolution registers (Reg. 0x76, Reg. 0x77) must be read first.
Once the extended resolution registers are read, the associated MSB reading registers are frozen until read. Both the extended resolution
registers and the MSB registers are frozen.
2. VCC (Pin 3) is the supply voltage for the ADT7475.
Table 49. TEMPERATURE READING REGISTERS (POWER-ON DEFAULT = 0X80) (Notes 1 and 2)
Register Address
R/W
Description
ReadingPP
0x25
Read-only
Remote 1 Temperature
0x26
Read-only
Local Temperature Reading (8 MSBs of Reading)
0x27
Read-only
Remote 2 Temperature Reading (8 MSBs of Reading)
(8 MSBs of Reading) (Notes 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 read, the extended resolution registers (0x76 and 0x77) must be read first. Once
the extended resolution registers are 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.
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ADT7475
Table 50. 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 (0x7B). This
allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes be 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 that a fan is one of the following:
• Stalled or blocked (object jamming the fan).
• Failed (internal circuitry destroyed).
• Not populated. (The ADT7475 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 a THERM pin.).
Table 51. CURRENT PWM DUTY CYCLE REGISTERS (POWER-ON DEFAULT = 0X00) (Note 1)
Register Address
R/W
Description
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)
1. These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7475
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 52. MAXIMUM PWM DUTY CYCLE REGISTERS (POWER-ON DEFAULT = 0XFF) (Notes 1 and 2)
Register Address
R/W
0x38
R/W
Maximum Duty Cycle for PWM1 Output, Default = 100% (0xFF)
Description
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. 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.
2. These registers set the maximum PWM duty cycle of the PWM output.
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ADT7475
Table 53. REGISTER 0X40 − CONFIGURATION REGISTER 1 (POWER-ON DEFAULT = 0X04)
Bit No.
Mnemonic
R/W
Description
<0>
STRT
(Notes 1, 2)
R/W
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.
Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the
default settings are enabled. This bit does not become locked once Bit 1 (LOCK) has been set.
<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 ADT7475 is powered down and powered up
again. This prevents rogue programs such as viruses from modifying critical system limit
settings. This bit is lockable.
<2>
RDY
Read-only
This bit is set to 1 by the ADT7475 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 max speed as programmed in the PWM current duty
cycle registers (0x30 to 0x32). 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 ADT7475 is configured to measure current from the
controller and to measure the CPU’s core voltage. This bit allows monitoring software to display
CPU watts usage. This bit is lockable.
<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 disabled. This allows the ADT7475 to be
used with SMBus controllers that cannot handle SMBus timeouts. This bit is lockable.
<7>
RES
Reserved.
1. Bit 0 (STRT) of Configuration Register 1 (0x40) remains writable after the lock bit is set.
2. When monitoring is disabled, PWM outputs always go to 100% for thermal protection.
Table 54. REGISTER 0X41 − INTERRUPT STATUS REGISTER 1 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<1>
VCCP
Read-only
VCCP = 1 indicates that 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 that 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 that 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 that 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 that 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 that an out-of-limit event has been latched in Interrupt Status Register 2.
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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ADT7475
Table 55. REGISTER 0X42 − INTERRUPT STATUS REGISTER 2 (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<1>
OVT
Read-only
OVT = 1 indicates that one of the THERM overtemperature limits has been 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 that 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 that 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 that 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 that 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, this bit is set when the
THERM assertion time exceeds the limit programmed in the THERM timer limit register (0x7A).
R/W
Read-only
<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 56. VOLTAGE LIMIT REGISTERS (Note 1)
Register Address
R/W
0x46
R/W
VCCP Low Limit
0x00
0x47
R/W
VCCP High Limit
0xFF
0x48
R/W
VCC Low Limit
0x00
0x49
R/W
VCC High Limit
0xFF
Description (Note 2)
Power-On Default
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 57. TEMPERATURE LIMIT REGISTERS (Note 1)
Register Address
R/W
0x4E
R/W
Remote 1 Temperature Low Limit
0x81
0x4F
R/W
Remote 1 Temperature High Limit
0x7F
0x50
R/W
Local Temperature Low Limit
0x81
0x51
R/W
Local Temperature High Limit
0x7F
0x52
R/W
Remote 2 Temperature Low Limit
0x81
0x53
R/W
Remote 2 Temperature High Limit
0x7F
Description (Note 2)
Power-On Default
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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ADT7475
Table 58. 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 too 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 59. 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 register.
<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 register.
Table 60. PWM CONFIGURATION REGISTERS (Note 1)
Register Address
R/W
Description
Power-On Default
0x5C
R/W
PWM1 Configuration
0x62
0x5D
R/W
PWM2 Configuration
0x62
0x5E
R/W
PWM3 Configuration
0x62
1. 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.
Table 61. REGISTER 0X05C, REGISTER 0X5D, AND REGISTER 0X5E − PWM CONFIGURATION REGISTERS
(POWER-ON DEFAULT = 0X62)
Bit No.
Mnemonic
R/W
Description
<2:0>
SPIN
R/W
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, 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, the Interrupt Status Register 2 bit is not set, even if the fan
has not started.
000 = No Startup Timeout
001 = 100 ms
010 = 250 ms (Default)
011 = 400 ms
100 = 667 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
<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 that 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.
100 = PWMx disabled (default).
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 (0x30 to 0x32) become writable.
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Table 62. TEMP TRANGE/PWM FREQUENCY REGISTERS (Note 1)
Register Address
R/W
0x5F
R/W
Remote 1 TRANGE/PWM1 Frequency
Description
Power-On Default
0xC4
0x60
R/W
Local TRANGE/PWM2 Frequency
0xC4
0x61
R/W
Remote 2 TRANGE/PWM3 Frequency
0xC4
1. These registers become read-only when the Configuration Register 1 Lock bit is set. Any subsequent attempts to write to these registers fail.
Table 63. REGISTER 0X05F, REGISTER 0X60, AND REGISTER 0X61 − TEMP TRANGE/PWM FREQUENCY
REGISTERS (POWER-ON DEFAULT = 0XC4)
Bit No.
Mnemonic
R/W
Description
<2:0>
FREQ
R/W
These bits control the PWMx frequency.
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
<3>
HF/LF
R/W
HF/LF = 1, enables high frequency PWM output for 4-wire fans. Once enabled, 3-wire fan
specific settings have no effect (this means, pulse stretching).
<7:4>
RANGE
R/W
These bits determine the PWM duty cycle vs. the temperature slope for automatic fan control.
0000 = 2°C
0001 = 2.5°C
0010 = 3.33°C
0011 = 4°C
0100 = 5°C
0101 = 6.67°C
0110 = 8°C
0111 = 10°C
1000 = 13.33°C
1001 = 16°C
1010 = 20°C
1011 = 26.67°C
1100 = 32°C (Default)
1101 = 40°C
1110 = 53.33°C
1111 = 80°C
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Table 64. REGISTER 0X62 − ENHANCED ACOUSTICS REGISTER 1 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
<2:0>
ACOU1
R/W
Description
Assuming that PWMx is associated with the Remote 1 temperature channel, these bits define
the maximum rate of change of the PWMx output for Remote 1 temperature related changes.
Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps
gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics
of the fan.
When Bit 7 of Configuration Register 6 (0x10) is 0
Time Slot Increase
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
Time for 0% to 100%
37.5 sec
18.8 sec
12.5 sec
7.5 sec
4.7 sec
3.1 sec
1.6 sec
0.8 sec
When Bit 7 of Configuration Register 6 (0x10) is 1
Time Slot Increase
Time for 0% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
52.2 sec
26.1 sec
17.4 sec
10.4 sec
6.5 sec
4.4 sec
2.2 sec
1.1 sec
<3>
EN1
R/W
When this bit is 1, smoothing is enabled on the Remote 1 temperature channel.
<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 ADT7475 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 ADT7475 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 ADT7475 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 subsequent attempts to write to this register fail.
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ADT7475
Table 65. REGISTER 0X63 − ENHANCED ACOUSTICS REGISTER 2 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<2:0>
ACOU3
R/W
Assuming that PWMx is associated with the local temperature channel, these bits define the
maximum rate of change of the PWMx output for local temperature related changes. Instead of
the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the
rate determined by these bits. This feature ultimately enhances the acoustics of the fan.
When Bit 7 of Configuration Register 6 (0x10) is 0
Time Slot Increase
Time for 0% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
37.5 sec
18.8 sec
12.5 sec
7.5 sec
4.7 sec
3.1 sec
1.6 sec
0.8 sec
When Bit 7 of Configuration Register 6 (0x10) is 1
Time Slot Increase
Time for 0% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
52.2 sec
26.1 sec
17.4 sec
10.4 sec
6.5 sec
4.4 sec
2.2 sec
1.1 sec
<3>
EN3
R/W
When this bit is 1, smoothing is enabled on the Local temperature channel.
<6:4>
ACOU2
R/W
Assuming that PWMx is associated with the Remote 2 temperature channel, these bits define
the maximum rate of change of the PWMx output for Remote 2 temperature related changes.
Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps
gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics
of the fan.
When Bit 7 of Configuration Register 6 (0x10) is 0
Time Slot Increase
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
Time for 0% to 100%
37.5 sec
18.8 sec
12.5 sec
7.5 sec
4.7 sec
3.1 sec
1.6 sec
0.8 sec
When Bit 7 of Configuration Register 6 (0x10) is 1
<7>
EN2
R/W
Time Slot Increase
Time for 0% to 100%
000 = 1
001 = 2
010 = 3
011 = 4
100 = 8
101 = 12
110 = 24
111 = 48
52.2 sec
26.1 sec
17.4 sec
10.4 sec
6.5 sec
4.4 sec
2.2 sec
1.1 sec
When this bit is 1, smoothing is enabled on the Remote 2 temperature channel.
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 66. PWM MINIMUM DUTY CYCLE REGISTERS (Note 1)
Register Address
R/W
Description
0x64
R/W
PWM1 Minimum Duty Cycle
0x80 (50% Duty Cycle)
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 ADT7475 is in automatic fan control mode.
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Power-On Default
ADT7475
Table 67. REGISTER 0X64, REGISTER 0X65, 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 68. TMIN REGISTERS (Note 1 and 2)
Register Address
R/W
0x67
R/W
Remote 1 Temperature TMIN
Description
Power-On Default
0x5A (90°C)
0x68
R/W
Local Temperature TMIN
0x5A (90°C)
0x69
R/W
Remote 2 Temperature TMIN
0x5A (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 subsequent attempts to write to these registers fail.
Table 69. THERM TEMPERATURE LIMIT REGISTERS (Note 1)
Register Address
R/W
(Note 2)
0x6A
R/W
Remote 1 THERM Temperature Limit
0x64 (100°C)
0x6B
R/W
Local THERM Temperature Limit
0x64 (100°C)
0x6C
R/W
Remote 2 THERM Temperature Limit
0x64 (100°C)
Description
Power-On Default
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 a 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 subsequent attempts to write to these registers fail.
Table 70. TEMPERATURE/TMIN HYSTERESIS REGISTERS (Note 1)
Register Address
R/W
(Note 2)
0x6D
R/W
Bit Name
Description
Power-On Default
Remote 1 and local temperature hysteresis.
Local temperature hysteresis. 0°C to 15°C of hysteresis
can be applied to the local temperature and AFC loops.
0x44
HYSL
<3:0>
HYSR1
<7:4>
0x6E
R/W
HYSR2
<7:4>
Remote 1 temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the Remote 1 temperature
and AFC loops.
Remote 2 temperature hysteresis.
Local temperature hysteresis. 0°C to 15°C of hysteresis
can be applied to the local temperature and AFC loops.
0x40
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 to 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 subsequent attempts to write to these registers fail.
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Table 71. XNOR TREE TEST ENABLE REGISTER (Note 1)
Register Address
R/W
0x6F
R/W
Bit Name
Description
Power-On Default
0x00
XEN <0>
XNOR tree test enable register.
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.
1. 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.
Table 72. REMOTE 1 TEMPERATURE OFFSET REGISTER (Note 1)
Register Address
R/W
Bit Name
Description
Power-On Default
0x70
R/W
<7:0>
Remote 1 temperature offset.
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.
0x00
1. 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.
Table 73. LOCAL TEMPERATURE OFFSET REGISTER (Note 1)
Register Address
R/W
Bit Name
0x71
R/W
<7:0>
Description
Local temperature offset.
Allows a twos complement offset value to be
automatically added to or subtracted from the local
temperature reading. LSB value = 0.5°C.
Power-On Default
0x00
1. 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.
Table 74. REMOTE 2 TEMPERATURE OFFSET REGISTER (Note 1)
Register Address
R/W
Bit Name
Description
Power-On Default
0x72
R/W
<7:0>
Remote 2 temperature offset.
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. 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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ADT7475
Table 75. REGISTER 0X73 − CONFIGURATION REGISTER 2 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
<0:3>
RES
R/W
Description
<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 ADT7475 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 ADT7475 is put into a single-channel ADC conversion mode. In this mode, the
ADT7475 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).
Reserved.
Register 0x55, Bits <7:5>
000
Reserved
001
VCCP
010
VCC (3.3 V)
011
Reserved
100
Reserved
101
Remote 1 Temperature
110
Local Temperature
111
Remote 2 Temperature
<7>
SHDN
R/W
SHDN = 1, ADT7475 goes into shutdown mode. All PWM outputs assert low (or high depending
on state of the INV bit) to switch off all fans. The PWM current duty cycle registers read 0x00 to
indicate that the fans are not being driven.
1. 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.
Table 76. REGISTER 0X74 − INTERRUPT MASK REGISTER 1 (POWER-ON DEFAULT <7:0> = 0X00)
Bit No.
Mnemonic
R/W
Description
<1>
VCCP
R/W
VCCP = 1, masks SMBALERT for out-of-limit conditions on the VCCP channel.
<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, when one or more alerts are generated in Interrupt Status Register 2, assuming that
all the mask bits in the Interrupt Mask Register 2 (0x75) = 1, SMBALERT is still asserted.
OOL = 1, when one or more alerts are generated in Interrupt Status Register 2, assuming that
all the mask bits in the Interrupt Mask Register 2 (0x75) = 1, SMBALERT is not asserted.
Table 77. REGISTER 0X75 − INTERRUPT MASK REGISTER 2 (POWER-ON DEFAULT <7:0> = 0X00)
Bit No.
Mnemonic
R/W
<1>
OVT
Read-only
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.
OVT = 1, masks SMBALERT for overtemperature THERM conditions.
Table 78. REGISTER 0X76 − EXTENDED RESOLUTION REGISTER 1 (Note 1)
Bit No.
Mnemonic
R/W
Description
<3:2>
VCCP
R/W
VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP measurement.
<5:4>
VCC
R/W
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.
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ADT7475
Table 79. REGISTER 0X77 − EXTENDED RESOLUTION REGISTER 2 (Note 1)
Bit No.
Mnemonic
R/W
<3:2>
TDM1
R/W
Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature measurement.
Description
<5:4>
LTMP
R/W
Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement.
<7:6>
TDM2
R/W
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 80. REGISTER 0X78 − CONFIGURATION REGISTER 3 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<0>
ALERT
Enable
R/W
ALERT = 1, Pin 5 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to
indicate out-of-limit error conditions.
<1>
THERM
R/W
THERM Enable = 1 enables THERM timer monitoring functionality on Pin 9. Also determined by
Bit 0 and Bit 1 (PIN9FUNC) of Configuration Register 4. When THERM is asserted, if the fans
are running and the boost bit is set, the fans run at full speed. Alternatively, THERM can be
programmed so that a timer is triggered to time how long 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. 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.
Table 81. REGISTER 0X79 − THERM TIMER STATUS REGISTER (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<0>
ASRT/
TMR0
Read-only
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.
<7:1>
TMR
Read-only
Times how long THERM input is asserted. These seven bits read zero until the THERM
assertion time exceeds 45.52 ms.
Table 82. THERM TIMER LIMIT REGISTER (POWER-ON DEFAULT = 0X00)
Bit No.
Mnemonic
R/W
Description
<7:0>
LIMT
R/W
Sets the 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 sec
to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt
Status Register 2 (0x42) is set. If the limit value is 0x00, an interrupt is generated immediately
on the assertion of the THERM input.
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ADT7475
Table 83. REGISTER 0X7B − TACH PULSES PER REVOLUTION REGISTER (POWER-ON DEFAULT = 0X55)
Bit No.
Mnemonic
R/W
<1:0>
FAN1
R/W
Sets the number of pulses to be counted when measuring Fan 1 speed. Can be used to
determine fan pulses per revolution for an unknown fan type.
Pulses Counted
00 = 1
01 = 2 (Default)
10 = 3
11 = 4
Description
<3:2>
FAN2
R/W
Sets the number of pulses to be counted when measuring Fan 2 speed. Can be used to
determine fan pulses per revolution for an unknown fan type.
Pulses Counted
00 = 1
01 = 2 (Default)
10 = 3
11 = 4
<5:4>
FAN3
R/W
Sets the number of pulses to be counted when measuring Fan 3 speed. Can be used to
determine fan pulses per revolution for an unknown fan type.
Pulses Counted
00 = 1
01 = 2 (Default)
10 = 3
11 = 4
<7:6>
FAN4
R/W
Sets the number of pulses to be counted when measuring Fan 4 speed. Can be used to
determine fan pulses per revolution for an unknown fan type.
Pulses Counted
00 = 1
01 = 2 (Default)
10 = 3
11 = 4
Table 84. REGISTER 0X7C − CONFIGURATION REGISTER 5 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
Description
<0>
TWOS
COMPL
R/W
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 ADT7475 interprets all relevant temperature register values as defined by this bit.
<1>
TempOffset
R/W
TempOffset = 0, sets offset range to −63°C to +64°C with 0.5°C resolution.
TempOffset = 1, sets offset range to −63°C to +127°C with 1°C resolution.
These settings apply to the 0x70, 0x71, and 0x72 registers (Remote 1, local, and Remote 2
temperature offset registers).
<2>
GPIOD
R/W
GPIO direction. When the GPIO function is enabled, this determines whether the GPIO is an
input (0) or an output (1).
<3>
GPIOP
R/W
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
<5>
R1 THERM
R/W
Reserved.
R1 THERM = 0, THERM temperature limit functionality is enabled for the Remote 1
temperature channel.
THERM can also be disabled on any channel by the following:
In offset 64 mode, writing −64°C to the appropriate THERM temperature limit.
In twos complement mode, writing −128°C to the appropriate THERM temperature limit.
<6>
Local
THERM
R/W
Local THERM = 0, THERM temperature limit functionality enabled for local temperature
channel.
THERM can also be disabled on any channel by the following:
In Offset 64 mode, writing −64°C to the appropriate THERM temperature limit.
In twos complement mode, writing −128°C to the appropriate THERM temperature limit.
<7>
R2 THERM
R/W
R2 THERM = 0, THERM temperature limit functionality enabled for Remote 2 temperature
channel.
THERM can also be disabled on any channel by the following:
In offset 64 mode, writing 64°C to the appropriate THERM temperature limit.
In twos complement mode, writing 128°C to the appropriate THERM temperature limit.
1. 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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ADT7475
Table 85. REGISTER 0X7D − CONFIGURATION REGISTER 4 (POWER-ON DEFAULT = 0X00) (Note 1)
Bit No.
Mnemonic
R/W
<1:0>
PIN9FUNC
R/W
These bits set the functionality of Pin 9:
00 = TACH4 (Default)
01 = Bidirectional THERM
10 = SMBALERT
11 = GPIO
Description
<2>
THERM
Disable
R/W
THERM Disable = 0, THERM overtemperature output is enabled assuming THERM is correctly
configured (Register 0x78, Register 0x7C, and Register 0x7D).
THERM Disable = 1, THERM overtemperature output is disabled on all channels.
THERM can also be disabled on any channel by the following:
In Offset 64 mode, writing −64°C to the appropriate THERM temperature limit.
In twos complement mode, writing −128°C to the appropriate THERM temperature limit.
<3>
Max/Full
on THERM
R/W
Max/Full on THERM = 0. When THERM limit is exceeded, fans go to full speed.
Max/Full on THERM = 1. When THERM limit is exceeded, fans go to maximum speed as
defined in Register 0x38, Register 0x39, and Register 0x3A.
<4:7>
RES
<5>
BpAttVCCP
<6:7>
RES
Unused.
R/W
Bypass VCCP attenuator. When set, the measurement scale for this channel changes from 0 V
(0x00) to 2.2965 V (0xFF).
Unused.
1. 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.
Table 86. 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 87. 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 88. ORDERING INFORMATION
Device Number*
Temperature Range
Package Type
Package Option
Shipping†
ADT7475ARQZ−REEL
−40°C to +125°C
16-lead QSOP
RQ−16
2,500 Tape & Reel
†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.
*The “Z’’ suffix indicates Pb-Free part.
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ADT7475
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
EXCEED 0.005 PER SIDE. DIMENSION E1 DOES NOT
INCLUDE INTERLEAD FLASH OR PROTRUSION.
INTERLEAD FLASH OR PROTRUSION SHALL NOT
EXCEED 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
L
C
DETAIL A
2X
2X 10 TIPS
0.20 C D
1
8
16X
e
B
A2
0.10 C
0.10 C
16X
b
0.25
A1
C
DIM
A
A1
A2
b
c
D
E
E1
e
h
L
L2
M
0.25 C D
M
C A-B D
h x 45 _
H
A
SEATING
PLANE
DETAIL A
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.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC
reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without
limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC
does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for
surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where
personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and
its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly,
any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture
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PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
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Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
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ON Semiconductor Website: www.onsemi.com
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For additional information, please contact your local
Sales Representative
ADT7475/D
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