AD ADM1027

dB COOL™ Remote Thermal
Controller and Voltage Monitor
ADM1027*
FEATURES
Monitors up to 5 Supply Voltages
Controls and Monitors up to 4 Fan Speeds
1 On-Chip and 2 Remote Temperature Sensors
Monitors up to 5 Processor VID Bits
Automatic Fan Speed Control Mode Controls System
Cooling Based on Measured Temperature
Enhanced Acoustic Mode Dramatically Reduces User
Perception of Changing Fan Speeds
2-Wire and 3-Wire Fan Speed Measurement
Limit Comparison of All Monitored Values
Meets SMBus 2.0 Electrical Specifications
(Fully SMBus 1.1 Compliant)
GENERAL DESCRIPTION
The ADM1027 dBCOOL controller is a complete systems
monitor and multiple PWM fan controller for noise sensitive
applications requiring active system cooling. It can monitor
12 V, 5 V, 2.5 V CPU supply voltage, plus its own supply voltage. It can monitor the temperature of up to two remote sensor
diodes, plus its own internal temperature. It can 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. Once the control loop parameters are programmed,
the ADM1027 can vary fan speed without CPU intervention.
APPLICATIONS
Low Acoustic Noise PCs
Networking and Telecommunications Equipment
FUNCTIONAL BLOCK DIAGRAM
ADDR
SELECT ADDR EN SCL SDA SMBALERT
VID4
VID3
VID
REGISTER
VID2
SMBUS
ADDRESS
SELECTION
SERIAL BUS
INTERFACE
VID1
ADDRESS
POINTER
REGISTER
VID0
PWM1
PWM2
PWM3
PWM
REGISTERS
AND
CONTROLLERS
AUTOMATIC
FAN SPEED
CONTROL
ACOUSTIC
ENHANCEMENT
CONTROL
PWM
CONFIGURATION
REGISTERS
TACH1
TACH2
FAN SPEED
COUNTER
TACH3
INTERRUPT
MASKING
TACH4
VCC
VCC TO ADM1027
D1+
D1–
D2+
D2–
+5VIN
ADM1027
INPUT
SIGNAL
CONDITIONING
AND
ANALOG
MULTIPLEXER
+12VIN
+2.5VIN
10-BIT
ADC
BAND GAP
REFERENCE
VCCP
BAND GAP
TEMP. SENSOR
INTERRUPT
STATUS
REGISTERS
LIMIT
COMPARATORS
VALUE AND
LIMIT
REGISTERS
GND
*Protected by U.S. Patent Nos. 6,188,189; 6,169,442; 6,097,239; 5,982,221;
and 5,867,012. Other patents pending.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2003 Analog Devices, Inc. All rights reserved.
to T (0ⴗC to 105ⴗC), V
ADM1027–SPECIFICATIONS1, 2, 3, 4 (Tunless= T otherwise
noted.)
A
MIN
MAX
CC
= VMIN to VMAX (3 V to 5.5 V),
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
POWER SUPPLY
Supply Voltage
Supply Current, ICC
3.0
3.3
1.4
5.5
3
V
mA
Interface Inactive, ADC Active
±3
±2
o
TEMP-TO-DIGITAL CONVERTER
Local Sensor Accuracy
±1
0.25
Resolution
Remote Diode Sensor Accuracy
±1
Resolution
Remote Sensor Source Current
0.25
200
12
ANALOG-TO-DIGITAL CONVERTER
(INCLUDING MUX AND ATTENUATORS)
Total Unadjusted Error, TUE
Differential Nonlinearity, DNL
Power Supply Sensitivity
Conversion Time (Voltage Input)
Conversion Time (Local Temperature)
Conversion Time (Remote Temperature)
Total Monitoring Cycle Time
Total Monitoring Cycle Time
Input Resistance
± 0.5
80
± 0.1
11.38
12.09
25.59
120.17
13.51
140
FAN RPM-TO-DIGITAL CONVERTER
Accuracy
OPEN-DRAIN DIGITAL OUTPUTS,
PWM1–PWM3, XTO
Current Sink, IOL
Output Low Voltage, VOL
High Level Output Current, IOH
±1
± 1.5
±1
12.29
13.05
27.64
129.78
14.59
250
±6
±8
65,535
Full-Scale Count
Nominal Input RPM
Internal Clock Frequency
±3
± 1.5
82.8
C
C
o
C
o
C
o
C
o
C
o
C
o
C
o
C
mA
mA
0oC TA 105oC
0oC TA 70oC
TA = 40oC
%
%
LSB
%/V
ms
ms
ms
ms
ms
k
All ADC Inputs except 12 V
12 V Input
8 Bits
o
High Level
Low Level
Averaging Enabled
Averaging Enabled
Averaging Enabled
Averaging Enabled
Averaging Disabled
%
%
0oC TA 70oC
3.0 V VCC 3.6 V
Fan Count = 0xBFFF
Fan Count = 0x3FFF
Fan Count = 0x0438
Fan Count = 0x021C
109
329
5,000
10,000
90
97.2
RPM
RPM
RPM
RPM
kHz
0.1
8.0
0.4
1
mA
V
mA
–2–
0oC TD 120oC
0oC TD 120oC; 0oC TA 70oC
TA = 40oC
0oC TD 120oC; TA = 40oC
IOUT = –8.0 mA, VCC = 3.3 V
VOUT = VCC
REV. A
ADM1027
Parameter
Min
OPEN-DRAIN SERIAL DATA BUS
OUTPUT (SDA)
Output Low Voltage, VOL
High Level Output Current, IOH
SMBUS DIGITAL INPUTS
(SCL, SDA)
Input High Voltage, VIH
Input Low Voltage, VIL
Hysteresis
DIGITAL INPUT LOGIC LEVELS
(VID0–4)
Input High Voltage, VIH
Input Low Voltage, VIL
DIGITAL INPUT LOGIC LEVELS
(TACH INPUTS)
Input High Voltage, VIH
Typ
Max
Unit
Test Conditions/Comment
0.1
0.4
1
V
mA
IOUT = –4.0 mA, VCC = 3.3 V
VOUT = VCC
0.4
V
V
mV
2.0
500
1.7
0.8
2.0
5.5
0.8
Input Low Voltage, VIL
–0.3
Hysteresis
DIGITAL INPUT CURRENT
Input High Current, IIH
Input Low Current, IIL
Input Capacitance, CIN
SERIAL BUS TIMING
Clock Frequency, fSCLK
Glitch Immunity, tSW
Bus Free Time, tBUF
Start Setup Time, tSU;STA
Start Hold Time, tHD;STA
SCL Low Time, tLOW
SCL High Time, tHIGH
SCL, SDA Rise Time, tr
SCL, SDA Fall Time, tf
Data Setup Time, tSU;DAT
Data Hold Time, tHD;DAT
Detect Clock Low Timeout, tTIMEOUT
0.5
–1
1
5
10
100
50
4.7
4.7
4.0
4.7
4.0
50
1000
300
250
300
15
35
V
V
V
V
V
V
V p-p
REV. A
–3–
Minimum Input Voltage
mA
mA
pF
VIN = VCC
VIN = 0
kHz
ns
ms
ms
ms
ms
ms
ns
ms
ns
ns
ms
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
Can Be Optionally Disabled
NOTES
1
All voltages are measured with respect to GND, unless otherwise specified.
2
Typicals are at TA = 40∞C and represent the most likely parametric norm.
3
Logic inputs will accept input high voltages up to V MAX even when the device is operating down to V MIN.
4
Timing specifications are tested at logic levels of V IL = 0.8 V for a falling edge and V IH = 2.0 V for a rising edge.
Specifications subject to change without notice.
Maximum Input Voltage
ADM1027
ABSOLUTE MAXIMUM RATINGS*
PIN CONFIGURATION
Positive Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . 6.5 V
Voltage on 12 VIN Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 V
Voltage on Any Other Input or Output Pin . . . . –0.3 V to +6.5 V
Input Current at Any Pin . . . . . . . . . . . . . . . . . . . . . . . . ± 5 mA
Package Input Current . . . . . . . . . . . . . . . . . . . . . . . . ± 20 mA
Maximum Junction Temperature (TJ MAX) . . . . . . . . . . 150∞C
Storage Temperature Range . . . . . . . . . . . . . –65∞C to +150∞C
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215∞C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200∞C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000 V
SDA 1
24 PWM1/XTO
SCL 2
23 VCCP
GND 3
22 2.5VIN
VCC 4
21 12VIN
VID0 5
ADM1027
20 5V
IN
19 VID4
VID1
6
VID2
7 (Not to Scale) 18 D1+
VID3
8
17 D1–
TACH3
9
16 D2+
PWM2/SMBALERT 10
15 D2–
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
TOP VIEW
TACH1 11
14 TACH4/ADDRESS SELECT
TACH2 12
13 PWM3/ADDRESS ENABLE
THERMAL CHARACTERISTICS
24-Lead QSOP Package:
qJA = 123∞C/W, qJC = 27∞C/W
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
ADM1027
0ºC to 105ºC
24-Lead QSOP
RQ-24
tLOW
tR
tHD; STA
tF
SCL
tHD; STA
tHD; DAT
tHIGH
tSU; STA
tSU; DAT
tSU; STO
SDA
tBUF
P
S
P
S
Figure 1. Diagram for Serial Bus Timing
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
ADM1027 features proprietary ESD protection circuitry, permanent damage may occur on devices
subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended
to avoid performance degradation or loss of functionality.
–4–
WARNING!
ESD SENSITIVE DEVICE
REV. A
ADM1027
PIN FUNCTION DESCRIPTIONS
Pin
Mnemonic
Description
1
SDA
Digital I/O (Open-Drain). SMBus bidirectional serial data. Requires SMBus pull-up.
2
SCL
Digital Input (Open-Drain). SMBus serial clock input. Requires SMBus pull-up.
3
GND
Ground Pin for the ADM1027.
4
VCC
Power Supply. Can be powered by 3.3 V standby if monitoring in low power states is required.
VCC is also monitored through this pin. The ADM1027 can also be powered from a 5 V supply.
Setting Bit 7 of Configuration Register 1 (Reg. 0x40) rescales the VCC input attenuators to
correctly measure a 5 V supply.
5
VID0
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
6
VID1
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
7
VID2
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
8
VID3
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
9
TACH3
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 3. Can be
reconfigured as an analog input (AIN3) to measure the speed of 2-wire fans.
10
PWM2/SMBALERT
Digital Output (Open-Drain). Requires 10 kW typical pull-up. Pulsewidth modulated output
to control Fan 2 speed. This pin may be reconfigured as an SMBALERT interrupt output to
signal out-of-limit conditions.
11
TACH1
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 1. Can be
reconfigured as an analog input (AIN1) to measure the speed of 2-wire fans.
12
TACH2
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 2. Can be
reconfigured as an analog input (AIN2) to measure the speed of 2-wire fans.
13
PWM3/ADDRESS ENABLE
Digital I/O (Open-Drain). Pulsewidth modulated output to control Fan 3 speed. Requires
10 kW typical pull-up. If pulled low on power-up, this places the ADM1027 into address
select mode, and the state of Pin 14 will determine the ADM1027’s slave address.
14
TACH4/ADDRESS SELECT
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 4. Can be reconfigured
as an analog input (AIN4) to measure the speed of 2-wire fans. If in address select mode,
this pin determines the SMBus device address.
15
D2–
Cathode Connection to Second Thermal Diode.
16
D2+
Anode Connection to Second Thermal Diode.
17
D1–
Cathode Connection to First Thermal Diode.
18
D1+
Anode Connection to First Thermal Diode.
19
VID4
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
20
5VIN
Analog Input. Monitors 5 V power supply.
21
12VIN
Analog Input. Monitors 12 V power supply.
22
2.5VIN
Analog Input. Monitors 2.5 V supply, typically a chipset voltage.
23
VCCP
Analog Input. Monitors processor core voltage (0 V to 3 V).
24
PWM1/XTO
Digital Output (Open-Drain). Pulsewidth modulated output to control Fan 1 speed. Requires
10 kW typical pull-up. Also functions as the output from the XOR tree in XOR test mode.
REV. A
–5–
ADM1027
FUNCTIONAL DESCRIPTION
General Description
Internal Registers of the ADM1027
A brief description of the ADM1027’s principal internal registers follows. More detailed information on the function of each
register is given in Tables IV to XXXVI.
The ADM1027 is a complete systems monitor and multiple fan
controller for any system requiring monitoring and cooling. The
device communicates with the system via a serial system
management bus. The serial bus controller has an optional
address line for device selection (Pin 14), a serial data line
for reading and writing addresses and data (Pin 1), and an input
line for the serial clock (Pin 2). All control and programming
functions of the ADM1027 are performed over the serial bus. In
addition, one of the pins can be reconfigured as an SMBALERT
output to indicate out-of-limit conditions.
Configuration Registers
Provide control and configuration of the ADM1027, including
alternate pinout functionality.
Address Pointer Register
Contains the address that selects one of the other internal registers.
When writing to the ADM1027, the first byte of data is always a
register address, which is written to the Address Pointer Register.
Status Registers
Measurement Inputs
The device has six measurement inputs, four for voltage and
two for temperature. It can also measure its own supply voltage
and can measure ambient temperature with its on-chip temperature sensor.
Provide the status of each limit comparison and are used to
signal out-of-limit conditions on the temperature, voltage, or
fan speed channels. If Pin 10 is configured as SMBALERT,
then this pin will assert low whenever a status bit gets set.
Pins 20 to 23 are analog inputs with on-chip attenuators,
configured to monitor 5 V, 12 V, 2.5 V, and the processor core
voltage (2.25 V input), respectively.
Interrupt Mask Registers
Allow each interrupt status event to be masked when Pin 10 is
configured as an SMBALERT output. This affects only the
SMBALERT output and not the bits in the status register.
Power is supplied to the chip via Pin 4, which the system also
uses to monitor VCC. In PCs, this pin is normally connected to a
3.3 V standby supply. This pin can, however, be connected to a
5 V supply and monitor it without overranging.
VID Register
The status of the VID0 to VID4 pins of the processor can be
read from this register.
Remote temperature sensing is provided by the D1+/– and
D2+/– inputs, to which diode-connected, external temperaturesensing transistors such as a 2N3906 or CPU thermal diode
may be connected.
Value and Limit Registers
The ADC also accepts input from an on-chip band gap temperature sensor that monitors system ambient temperature.
Offset Registers
The results of analog voltage inputs, temperature, and fan speed
measurements are stored in these registers, along with their limit
values.
Allow each temperature channel reading to be offset by a twos
complement value written to these registers.
Sequential Measurement
TMIN Registers
When the ADM1027 monitoring sequence is started, it cycles
sequentially through the measurement of analog inputs and the
temperature sensors. Measured values from these inputs are
stored in value registers. These can be read out over the serial
bus, or can be compared with programmed limits stored in the
limit registers. The results of out-of-limit comparisons are stored
in the status registers, which can be read over the serial bus to
flag out-of-limit conditions.
Program the starting temperature for each fan under automatic
fan speed control.
TRANGE Registers
Program the temperature-to-fan speed control slope in automatic
Fan Speed Control Mode for each PWM output.
Enhance Acoustics Registers
Allow each PWM output controlling fan to be tweaked to enhance
the system’s acoustics.
Processor Voltage ID
Five digital inputs (VID0 to VID4 — Pins 5 to 8 and 19) read
the processor Voltage ID code and store it in the VID register,
from which it can be read out by the management system over
the serial bus. The VID code monitoring function is compatible
with both VRM9.x and future VRM10 solutions. The VID code
monitoring function is compatible with VRM9.x.
ADM1027 Address Selection
Pin 13 is the dual function PWM3/ADDRESS ENABLE pin.
If Pin 13 is pulled low on power-up, the ADM1027 will read the
state of Pin 14 (TACH4/ADDRESS SELECT pin) to determine
the ADM1027 slave address. If Pin 13 is high on power-up, then
the ADM1027 will default to SMBus slave address 0x5C. This
function is described later in more detail.
–6–
REV. A
Typical Performance Characteristics–ADM1027
10
DXP TO GND
0
–5
DXP TO VCC (3.3V)
–10
–15
–20
1.0
10.0
30.0
3.3
LEAKAGE RESISTANCE (M⍀)
LOCAL TEMPERATURE ERROR (ⴗC)
REMOTE TEMPERATURE ERROR (ⴗC)
8.0
250mV
4.0
2.0
100mV
5M
550k
FREQUENCY (Hz)
REMOTE TEMPERATURE ERROR (ⴗC)
REMOTE TEMPERATURE ERROR (ⴗC)
20mV
10.0
8.0
10mV
4.0
2.0
0
1M
10M
FREQUENCY (Hz)
50M
TPC 7. Remote Temperature Error
vs. Differential Mode Noise
Frequency
REV. A
–27
–30
–33
2.2
3.3
4.7
10.0 22.0
DXP – DXN CAPACITANCE (nF)
2
1
+3 SIGMA
0
–1
–3 SIGMA
–2
–3
–40
47.0
0
40
80
TEMPERATURE (ⴗC)
120
TPC 3. Remote Temperature Error
vs. Actual Temperature
1.90
1.85
10.0
7.5
250mV
5.0
2.5
0
100mV
1.80
1.75
1.70
1.65
1.60
1.55
1.50
–2.5
1.45
5M
550k
FREQUENCY (Hz)
50M
40.0
12.0
–2.0
60k 110k
–24
TPC 5. Local Temperature Error vs.
Power Supply Noise Frequency
16.0
6.0
–21
–5.0
100k
50M
TPC 4. Remote Temperature Error
vs. Power Supply Noise Frequency
14.0
–18
12.5
10.0
–2.0
100k
–15
TPC 2. Remote Temperature Error
vs. Capacitance between D+ and D–
12.0
0
–9
–12
1
14.0
6.0
REMOTE TEMPERATURE
ERROR (ⴗC)
–6
–36
100.0
TPC 1. Remote Temperature
Error vs. Leakage Resistance
–3
SUPPLY CURRENT (mA)
5
3
3
0
REMOTE TEMPERATURE ERROR (ⴗC)
REMOTE TEMPERATURE ERROR (ⴗC)
REMOTE TEMPERATURE ERROR (ⴗC)
15
35.0
100mV
30.0
25.0
20.0
15.0
10.0
40mV
5.0
20mV
0
–5.0
–10.0
10k
100k
1M
10M
FREQUENCY (Hz)
TPC 8. Remote Temperature Error
vs. Common Mode Noise Frequency
–7–
1.40
2.60 3.00 3.40 3.80 4.20 4.60 5.00 5.40
2.50
5.50
TPC 6. Supply Current vs.
Supply Voltage
ADM1027
SERIAL BUS INTERFACE
VCC
Control of the ADM1027 is carried out using the serial System
Management Bus (SMBus). The ADM1027 is connected to this
bus as a slave device, under the control of a master controller.
ADM1027
ADDR_SEL
The ADM1027 has a 7-bit serial bus address. When the device
is powered up with Pin 13 (PWM3/ADDRESS ENABLE) high,
the ADM1027 will have a default SMBus address of 0101110
or 0x5C. If more than one ADM1027 is to be used in a system,
then each ADM1027 should be placed in address select mode
by strapping Pin 13 low on power-up. The logic state of Pin 14
then determines the device’s SMBus address.
13
PWM3/ADDR_EN
Pin 14 State
0
0
1
Low (10 kW to GND)
High (10 kW pull-up)
Don’t Care
Figure 5. Unpredictable SMBus Address if Pin 13
is Unconnected
Care should be taken to ensure that Pin 13 (PWM3/
ADDR_EN) is either tied high or low. Leaving Pin 13
floating could cause the ADM1027 to power up with an
unexpected address.
Address
0101100 (0x58)
0101101 (0x5A)
0101110 (0x5C)
(default)
Note that if the ADM1027 is placed into address select mode,
Pins 13 and 14 can be used as their alternate functions once
address assignment has taken place (PWM3, TACH4). Care
should be taken using muxes to connect in the appropriate circuit
at the appropriate time.
VCC
ADM1027
ADDR_SEL
The serial bus protocol operates as follows:
14
10k⍀
1. The master initiates data transfer by establishing a start
condition, defined as a high to low transition on the serial
data line SDA while the serial clock line SCL remains high.
This indicates that an address/data stream will follow. All
slave peripherals connected to the serial bus respond to the
start condition and shift in the next eight bits, consisting
of a 7-bit address (MSB first) plus the R/W bit, which determines the direction of the data transfer, i.e., whether data
will be written to or read from the slave device.
13
PWM3/ADDR_EN
ADDRESS = 0x5C
Figure 2. Default SMBus Address = 0x5C
ADM1027
ADDR_SEL
10k⍀
14
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the acknowledge
bit. All other devices on the bus now remain idle while the
selected device waits for data to be read from or written to
it. If the R/W bit is a 0, the master will write to the slave
device. If the R/W bit is a 1, the master will read from the
slave device.
13
PWM3/ADDR_EN
ADDRESS = 0x58
Figure 3. SMBus Address = 0x58 (Pin 14 = 0)
The device address is sampled and latched on the first valid
SMBus transaction, so any attempted addressing changes made
thereafter will have no immediate effect.
2. Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, as 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.
The facility to make hardwired changes to the SMBus slave
address allows the user to avoid conflicts with other devices
sharing the same serial bus (for example, if more than one
ADM1027 is used in a system).
Once the SMBus address has been assigned, these pins return
to their original function. However, since the circuits required
to set up the SMBus address are unworkable with the PWM
and TACH circuits, it would require the use of muxes to switch
in and out the correct circuit at the correct time.
3. When all data bytes have been read or written, stop conditions
are established. In write mode, the master will pull the
data line high during the 10th clock pulse to assert a
stop condition. In read mode, the master device will
override 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 will then take the
data line low during the low period before the 10th clock
pulse, then high during the 10th clock pulse to assert a
stop condition.
VCC
ADM1027
ADDR_SEL
PWM3/ADDR_EN
NC
DO NOT LEAVE ADDR_EN
UNCONNECTED! CAN
CAUSE UNPREDICTABLE
ADDRESSES
Table I. ADM1027 Address Select Mode
Pin 13 State
10k⍀
14
10k⍀
14
13
ADDRESS = 0x5A
Figure 4. SMBus Address = 0x5A (Pin 14 = 1)
–8–
REV. A
ADM1027
register to be written to, which is stored in the address pointer
register. The second data byte is the data to be written to the
internal data register.
Any number of bytes of data can be transferred over the serial
bus in one operation. However, it is not possible to mix read
and write in one operation because the type of operation is
determined at the beginning and subsequently cannot be changed
without starting a new operation.
When reading data from a register, there are two possibilities:
1. If the ADM1027 address pointer register value is unknown or
not the desired value, it is first necessary to set it to the correct
value before data can be read from the desired data register.
This is done by performing a write to the ADM1027 as before,
but only sending the data byte containing the register address,
as data is not to be written to the register. This is shown in
Figure 7.
In the case of the ADM1027, write operations contain either
one or two bytes, and read operations contain one byte and
perform the following functions:
To write data to one of the device data registers or read data
from it, the address pointer register must be set so the correct
data register is addressed, then data can be written into that
register or read from it. The first byte of a write operation always
contains an address that is stored in the address pointer register.
If data is to be written to the device, then the write operation
contains a second data byte that is written to the register selected
by the address pointer register.
A read operation is then performed consisting of the serial
bus address, R/W bit set to 1, followed by the data byte read
from the data register. This is shown in Figure 8.
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,
so Figure 7 can be omitted.
This is illustrated in Figure 6. The device address is sent over
the bus followed by R/W being set to 0. This is followed by two
data bytes. The first data byte is the address of the internal data
1
9
9
1
SCL
0
SDA
1
0
1
1
A0
A1
D6
D7
R/W
START BY
MASTER
D4
D5
D2
D3
D1
D0
ACK. BY
ADM1027
ACK. BY
ADM1027
FRAME 1
SERIAL BUS ADDRESS
BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
SCL (CONTINUED)
D7
SDA (CONTINUED)
D4
D5
D6
D2
D3
D1
D0
ACK. BY
ADM1027
FRAME 3
DATA
BYTE
STOP BY
MASTER
Figure 6. Writing a Register Address to the Address Pointer Register, Then Writing Data to the Selected Register
1
9
9
1
SCL
SDA
0
1
START BY
MASTER
0
1
1
A1
A0
D7
R/W
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1027
FRAME 1
SERIAL BUS ADDRESS
BYTE
ACK. BY
ADM1027
STOP BY
MASTER
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 7. Writing to the Address Pointer Register Only
1
9
9
1
SCL
SDA
START BY
MASTER
0
1
0
1
1
A1
FRAME 1
SERIAL BUS ADDRESS
BYTE
A0
D7
R/W
D6
D5
D4
D3
D2
FRAME 2
DATA BYTE FROM ADM1027
–9–
D0
NO ACK. BY STOP BY
MASTER
MASTER
Figure 8. Reading Data from a Previously Selected Register
REV. A
D1
ACK. BY
ADM1027
ADM1027
3.
4.
5.
6.
7.
8.
Notes
1. 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.
2. In Figures 6 to 8, the serial bus address is shown as the default
value 01011(A1)(A0), where A1 and A0 are set by the address
select mode function previously defined.
The addressed slave device asserts ACK on SDA.
The master sends a command code.
The slave asserts ACK on SDA.
The master sends a data byte.
The slave asserts ACK on SDA.
The master asserts a stop condition on SDA to end the
transaction.
This is illustrated in Figure 10.
1
3. In addition to supporting the send byte and receive byte
protocols, the ADM1027 also supports the read byte protocol
(see System Management Bus specifications Rev. 2.0 for
more information).
S
2
3
SLAVE W A
ADDRESS
4
5
REGISTER
ADDRESS
6
7 8
A DATA A P
Figure 10. Single Byte Write to a Register
4. If it is required to perform several read or write operations in
succession, the master can send a repeat start condition instead
of a stop condition to begin a new operation.
ADM1027 READ OPERATIONS
ADM1027 WRITE OPERATIONS
This is useful when repeatedly reading a single register. The
register address needs to have been 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.
The ADM1027 uses the following SMBus read protocols:
Receive Byte
The SMBus specification defines several protocols for different
types of read and write operations. The ones used in the
ADM1027 are discussed below. The following abbreviations are
used in the diagrams:
S – START
P – STOP
R – READ
W – WRITE
A – ACKNOWLEDGE
A – NO ACKNOWLEDGE
The ADM1027 uses the following SMBus write protocols:
In the ADM1027, 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.
Send Byte
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.
1
S
2
3
SLAVE
S
W A
ADDRESS
4
REGISTER
ADDRESS
5
6
A P
The SMBALERT output can be used as an interrupt output or
can be used as an SMBALERT. One or more outputs can be
connected to a common SMBALERT line connected to the
master. If a device’s SMBALERT line goes low, the following
procedure occurs:
Figure 9. Setting a Register Address for Subsequent Read
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).
SLAVE
R A DATA
ADDRESS
5
Alert Response Address (ARA) is a feature of SMBus devices,
which allows an interrupting device to identify itself to the host
when multiple devices exist on the same bus.
A P
Write Byte
4
Alert Response Address
6
If it is required to read data from the register immediately after
setting up the address, the master can assert a repeat start condition immediately after the final ACK and carry out a single
byte read without asserting an intermediate stop condition.
3
Figure 11. Single Byte Read from a Register
For the ADM1027, the send byte protocol is used to write a
register address to RAM for a subsequent single byte read from
the same address. This is illustrated in Figure 9.
1
2
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the alert response
address (ARA = 0001 100). This is a general call address that
must not be used as a specific device address.
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 it 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 will have priority, in accordance
with normal SMBus arbitration.
–10–
REV. A
ADM1027
5. Once the ADM1027 has responded to the alert response
address, the master must read the status registers and the
SMBALERT will only be cleared if the error condition has
gone away.
VOLTAGE MEASUREMENT LIMIT REGISTERS
Associated with each voltage 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.
SMBus Timeout
The ADM1027 includes an SMBus timeout feature. If there is
no SMBus activity for a minimum of 15 ms and a maximum of
35 ms, the ADM1027 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.
CONFIGURATION REGISTER 1 – Register 0x40
Reg. 0x44 2.5 V Low Limit = 0x00 default
Reg. 0x45 2.5 V High Limit = 0xFF default
Reg. 0x46 VCCP Low Limit = 0x00 default
Reg. 0x47 VCCP High Limit = 0xFF default
Reg. 0x48 VCC Low Limit = 0x00 default
Reg. 0x49 VCC High Limit = 0xFF default
<6> TODIS = 0; SMBus timeout enabled (default)
<6> TODIS = 1; SMBus timeout disabled
Reg. 0x4A 5 V Low Limit = 0x00 default
Reg. 0x4B 5 V High Limit = 0xFF default
VOLTAGE MEASUREMENT INPUTS
Reg. 0x4C 12 V Low Limit = 0x00 default
The ADM1027 has four external voltage measurement channels.
It can also measure its own supply voltage, VCC.
Reg. 0x4D 12 V High Limit = 0xFF default
Pins 20 to 23 are dedicated to measuring 5 V, 12 V, 2.5 V supplies
and the processor core voltage VCCP (0 V to 3 V input). The
VCC supply voltage measurement is carried out through the VCC
pin (Pin 4). Setting Bit 7 of Configuration Register 1 (Reg. 0x40)
allows a 5 V supply to power the ADM1027 and be measured
without overranging the VCC measurement channel. The 2.5 V
input can be used to monitor a chipset supply voltage in computer systems.
12VIN
120k⍀
20k⍀
5VIN
30pF
93k⍀
47k⍀
30pF
68k⍀
ANALOG-TO-DIGITAL CONVERTER
3.3VIN
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
inputs have built-in attenuators to allow measurement of 2.5 V,
3.3 V, 5 V, 12 V and the processor core voltage VCCP, without
any external components. To allow for the tolerance of these
supply voltages, the ADC produces an output of 3/4 full scale
(768 decimal or 300 hex) for the nominal input voltage, and so
has adequate headroom to cope with overvoltages.
71k⍀
2.5VIN
30pF
MUX
45k⍀
94k⍀
30pF
35k⍀
VCCPIN
105k⍀
35pF
INPUT CIRCUITRY
The internal structure for the analog inputs is shown in Figure 12.
Each 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.
VOLTAGE MEASUREMENT REGISTERS
Reg. 0x20 2.5 V Reading = 0x00 default
Reg. 0x21 VCCP Reading = 0x00 default
Figure 12. Structure of Analog Inputs
Table II shows the input ranges of the analog inputs and output
codes of the 10-bit A/D converter.
When the ADC is running, it samples and converts a voltage
input in 711 ms, and averages 16 conversions to reduce noise.
Therefore a measurement on any input takes nominally 11.38 ms.
Reg. 0x22 VCC Reading = 0x00 default
Reg. 0x23 5 V Reading = 0x00 default
Reg. 0x24 12 V Reading = 0x00 default
REV. A
–11–
ADM1027
Table II. 10-Bit A/D Output Code vs. V IN
Input Voltage
A/D Output
12 VIN
5 VIN
VCC (3.3 VIN)*
2.5 VIN
VCCPIN
Decimal
Binary (10 Bits)
<0.0156
0.0156 – 0.0312
0.0312 – 0.0469
0.0469 – 0.0625
0.0625 – 0.0781
0.0781 – 0.0937
0.0937 – 0.1093
0.1093 – 0.1250
0.1250 – 0.1406
<0.0065
0.0065 – 0.0130
0.0130 – 0.0195
0.0195 – 0.0260
0.0260 – 0.0325
0.0325 – 0.0390
0.0390 – 0.0455
0.0455 – 0.0521
0.0521 – 0.0586
<0.0042
0.0042 – 0.0085
0.0085 – 0.0128
0.0128 – 0.0171
0.0171 – 0.0214
0.0214 – 0.0257
0.0257 – 0.0300
0.0300 – 0.0343
0.0343 – 0.0386
<0.0032
0.0032 – 0.0065
0.0065 – 0.0097
0.0097 – 0.0130
0.0130 – 0.0162
0.0162 – 0.0195
0.0195 – 0.0227
0.0227 – 0.0260
0.0260 – 0.0292
<0.00293
0.0293 – 0.0058
0.0058 – 0.0087
0.0087 – 0.0117
0.0117 – 0.0146
0.0146 – 0.0175
0.0175 – 0.0205
0.0205 – 0.0234
0.0234 – 0.0263
0
1
2
3
4
5
6
7
8
00000000 00
00000000 01
00000000 10
00000000 11
00000001 00
00000001 01
00000001 10
00000001 11
00000010 00
4.0000 – 4.0156
1.6675 – 1.6740
1.1000 – 1.1042
0.8325 – 0.8357
0.7500 – 0.7529
256 (1/4 scale)
01000000 00
8.0000 – 8.0156
3.3300 – 3.3415
2.2000 – 2.2042
1.6650 – 1.6682
1.5000 – 1.5029
512 (1/2 scale)
10000000 00
12.0000 – 12.0156
5.0025 – 5.0090
3.3000 – 3.3042
2.4975 – 2.5007
2.2500 – 2.2529
768 (3/4 scale)
11000000 00
15.8281 – 15.8437
15.8437 – 15.8593
15.8593 – 15.8750
15.8750 – 15.8906
15.8906 – 15.9062
15.9062 – 15.9218
15.9218 – 15.9375
15.9375 – 15.9531
15.9531 – 15.9687
15.9687 – 15.9843
>15.9843
6.5983 – 6.6048
6.6048 – 6.6113
6.6113 – 6.6178
6.6178 – 6.6244
6.6244 – 6.6309
6.6309 – 6.6374
6.6374 – 6.4390
6.6439 – 6.6504
6.6504 – 6.6569
6.6569 – 6.6634
>6.6634
4.3527 – 4.3570
4.3570 – 4.3613
4.3613 – 4.3656
4.3656 – 4.3699
4.3699 – 4.3742
4.3742 – 4.3785
4.3785 – 4.3828
4.3828 – 4.3871
4.3871 – 4.3914
4.3914 – 4.3957
>4.3957
3.2942 – 3.2974
3.2974 – 3.3007
3.3007 – 3.3039
3.3039 – 3.3072
3.3072 – 3.3104
3.3104 – 3.3137
3.3137 – 3.3169
3.3169 – 3.3202
3.3202 – 3.3234
3.3234 – 3.3267
>3.3267
2.9677 – 2.9707
2.9707 – 2.9736
2.9736 – 2.9765
2.9765 – 2.9794
2.9794 – 2.9824
2.9824 – 2.9853
2.9853 – 2.9882
2.9882 – 2.9912
2.9912 – 2.9941
2.9941 – 2.9970
>2.9970
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
11111101 01
11111101 10
11111101 11
11111110 00
11111110 01
11111110 10
11111110 11
11111111 00
11111111 01
11111111 10
11111111 11
*The VCC output codes listed assume that V CC is 3.3 V. If V CC input is reconfigured for 5 V operation (by setting Bit 7 of Configuration Register 1), then the V CC
output codes are the same as for the 5 V IN column.
–12–
REV. A
ADM1027
VID CODE MONITORING
Single-Channel ADC Conversions
The ADM1027 has five dedicated voltage ID (VID code) inputs.
These are digital inputs that can be read back through the
VID register (Reg. 0x43) to determine the processor voltage
required/being used in the system. Five VID code inputs
support VRM9.x solutions.
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADM1027 into single-channel ADC conversion mode. In this
mode, the ADM1027 can be made to read a single voltage channel
only. If the internal ADM1027 clock is used, the selected input
will be read every 711 ms. The appropriate ADC channel is
selected by writing to Bits <7:5> of TACH1 minimum high
byte register (0x55).
VID CODE REGISTER – Register 0x43
<0> = VID0 (reflects logic state of Pin 5)
Bits <7:5> Reg. 0x55
000
001
010
011
100
<1> = VID1 (reflects logic state of Pin 6)
<2> = VID2 (reflects logic state of Pin 7)
<3> = VID3 (reflects logic state of Pin 8)
<4> = VID4 (reflects logic state of Pin 19)
Channel Selected
2.5 V
VCCP
VCC
5V
12 V
Configuration Register 2 (Reg. 0x73)
ADDITIONAL ADC FUNCTIONS
<4> = 1 Averaging off
<5> = 1 Bypass input attenuators
<6> = 1 Single-channel convert mode
A number of other functions are available on the ADM1027 to
offer the systems designer increased flexibility:
Turn Off Averaging
For each voltage measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. There may
be an instance where the user would like to speed up conversions.
Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns
averaging off. This effectively gives a reading 16¥ faster than
711 ms, but the reading may be noisier.
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> Selects ADC channel for single-channel convert mode
Bypass Voltage Input Attenuators
Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes
the attenuation circuitry from the 2.5 V, VCCP, VCC, 5 V, and
12 V inputs. This allows the user to directly connect external
sensors or 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.
REV. A
–13–
ADM1027
TEMPERATURE MEASUREMENT SYSTEM
Local Temperature Measurement
The ADM1027 contains an on-chip band gap temperature
sensor whose output is digitized by the on-chip 10-bit ADC.
The 8-bit MSB temperature data is stored in the local temp
register (Address 0x26). As both positive and negative temperatures can be measured, the temperature data is stored in twos
complement format, as shown in Table III. Theoretically, the
temperature sensor and ADC can measure temperatures from
–128oC to +127oC with a resolution of 0.25oC. However, this
exceeds the operating temperature range of the device (0oC to
105oC), so local temperature measurements outside this range
are not possible. Temperature measurement from –127oC to
+127oC is possible using a remote sensor.
The forward voltage of a diode or diode-connected transistor,
operated at a constant current, exhibits a negative temperature
coefficient of about –2 mV/oC. Unfortunately, the absolute
value of Vbe varies from device to device, and individual calibration is required to null this out, so the technique is unsuitable
for mass production. The technique used in the ADM1027 is to
measure the change in Vbe when the device is operated at two
different currents. This is given by
where:
DVbe = KT q ¥ ln ( N )
K is Boltzmann’s constant.
q is charge on the carrier.
T is absolute temperature in kelvins.
Remote Temperature Measurement
N is the ratio of the two currents.
The ADM1027 can measure the temperature of two remote
diode sensors or diode-connected transistors connected to
Pins 15 and 16, or 17 and 18.
Figure 13 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 equally well be a
discrete transistor such as a 2N3904/06.
VDD
I
NⴛI
IBIAS
CPU
REMOTE
SENSING
TRANSISTOR
THERMDA
D+
VOUT+
THERMDC
D–
VOUT–
TO ADC
BIAS
DIODE
LOW-PASS
FILTER
fC = 65kHz
Figure 13. Signal Conditioning for Remote Diode Temperature Sensors
–14–
REV. A
ADM1027
If a discrete transistor is used, the collector will not be 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 14 shows
how to connect the ADM1027 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.
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 25.5 ms. The results of remote temperature
measurements are stored in 10-bit, twos complement format,
as illustrated in Table III. The extra resolution for the temperature
measurements is held in the Extended Resolution Register 2
(Reg. 0x77). This gives temperature readings with a resolution
of 0.25oC.
Table III. Temperature Data Format*
Temperature
Digital Output (10-Bit)
–128∞C
–125∞C
–100∞C
–75∞C
–50∞C
–25∞C
–10oC
0∞C
+10.25∞C
+25.5∞C
+50.75∞C
+75∞C
+100∞C
+125∞C
+127∞C
1000 0000 00
1000 0011 00
1001 1100 00
1011 0101 00
1100 1110 00
1110 0111 00
1111 0110 00
0000 0000 00
0000 1010 01
0001 1001 10
0011 0010 11
0100 1011 00
0110 0100 00
0111 1101 00
0111 1111 00
ADM1027
2N3904
NPN
D–
Figure 14a. Measuring Temperature Using an
NPN Transistor
ADM1027
D+
2N3906
PNP
D–
Figure 14b. Measuring Temperature Using a
PNP Transistor
NULLING OUT TEMPERATURE ERRORS
As CPUs run faster, it is getting more difficult to avoid high
frequency clocks when routing the D–/D+ traces around a system
board. Even when recommended layout guidelines are followed,
there may still be temperature errors attributed to noise being
coupled onto the D+/D– lines. High frequency noise generally
has the effect of giving temperature measurements that are too
high by a constant amount. The ADM1027 has temperature
offset registers at addresses 0x70, 0x71, and 0x72 for the Remote 1,
Local, and Remote 2 temperature channels. By doing a one-time
calibration of the system, you can determine the offset caused
by system board noise and null it out using the offset registers.
The offset registers automatically add a twos complement 8-bit
reading to every temperature measurement. The LSB adds a 1∞C
offset to the temperature reading so the 8-bit register effectively
allows temperature offsets of up to ⫾127∞C with a resolution of
1∞C. This ensures that the readings in the temperature measurement registers are as accurate as possible.
TEMPERATURE OFFSET REGISTERS
Reg. 0x70 Remote 1 Temperature Offset = 0x00 (0∞C default)
Reg. 0x71 Local Temperature Offset = 0x00 (0∞C default)
Reg. 0x72 Remote 2 Temperature Offset = 0x00 (0∞C default)
*Bold denotes 2 LSBs of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25 oC resolution.
REV. A
D+
–15–
ADM1027
TEMPERATURE MEASUREMENT REGISTERS
Single-Channel ADC Conversions
Reg. 0x25 Remote 1 Temperature = 0x80 default
Reg. 0x26 Local Temperature = 0x80 default
Reg. 0x27 Remote 2 Temperature = 0x80 default
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADM1027 into single-channel ADC conversion mode. In this
mode, the ADM1027 can be made to read a single temperature
channel only. If the internal ADM1027 clock is used, the selected
input will be read every 1.4 ms. The appropriate ADC channel
is selected by writing to Bits <7:5> of TACH1 minimum high
byte register (Reg. 0x55).
Reg. 0x77 Extended Resolution 2 = 0x00 default
<7:6> TDM2 = Remote 2 Temperature LSBs
<5:4> LTMP = Local Temperature LSBs
<3:2> TDM1 = Remote 1 Temperature LSBs
Bits <7:5> Reg 0x55
101
110
111
TEMPERATURE MEASUREMENT LIMIT REGISTERS
Associated with each temperature measurement channel are
high and low limit registers. Exceeding the programmed high or
low limit causes the appropriate status bit to be set. Exceeding
either limit can also generate SMBALERT interrupts.
Channel Selected
Remote 1 Temp
Local Temp
Remote 2 Temp
Configuration Register 2 (Reg. 0x73)
<4> = 1 Averaging off
<6> = 1 Single-channel convert mode
Reg. 0x4E Remote 1 Temperature Low Limit = 0x81 default
Reg. 0x4F Remote 1 Temperature High Limit = 0x7F default
Reg. 0x50 Local Temperature Low Limit = 0x81 default
Reg. 0x51 Local Temperature High Limit = 0x7F default
Reg. 0x52 Remote 2 Temperature Low Limit = 0x81 default
Reg. 0x53 Remote 2 Temperature High Limit = 0x7F default
READING TEMPERATURE FROM THE ADM1027
It is important to note that temperature can be read from the
ADM1027 as an 8-bit value (with 1∞C resolution), or as a 10bit 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.
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> Selects ADC channel for single-channel convert mode
OVERTEMPERATURE EVENTS
Overtemperature events on any of the temperature channels can
be detected and dealt with automatically. Registers 0x6A to
0x6C are the THERM limits. When a temperature exceeds its
THERM limit, all fans will run at 100% duty cycle. The fans
will stay running at 100% until the temperature drops below
THERM – 4∞C.
THERM LIMIT
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution register
(Reg. 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.
HYSTERESIS = 4ⴗC
TEMP
FANS
100%
Figure 15. THERM Limit Operation
ADDITIONAL ADC FUNCTIONS
A number of other functions are available on the ADM1027 to
offer the systems 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. There may
be an instance where the user would like to take a very fast
measurement, e.g., of CPU temperature. Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off. This takes
a reading every 13 ms. The measurement itself takes 4 ms.
–16–
REV. A
ADM1027
SMBALERT, STATUS, AND MASK REGISTERS
SMBALERT CONFIGURATION
Pin 10 of the ADM1027 can be configured as either PWM2 or
as an SMBALERT output. The SMBALERT output may be
used to signal out-of-limit conditions as explained below. The
default state of Pin 10 is PWM2. To configure Pin 10 as
SMBALERT:
Configuration Reg. 3 (Addr = 0x78), Bit 0 = 1 = SMBALERT
Configuration Reg. 3 (Addr = 0x78), Bit 0 = 0 = PWM2 =
default
LIMIT VALUES
Associated with each measurement channel on the ADM1027
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 a processor or
microcontroller of out-of-limit conditions.
8-BIT LIMITS
The following is a list of 8-bit limits on the ADM1027:
Voltage Limit Registers
16-Bit Limits
The fan TACH measurements are 16-bit results. The fan TACH
limits are also 16 bits, consisting of a high byte and low byte.
Since fans running underspeed or stalled are normally the only
conditions of interest, only high limits exist for fan TACHs.
Since fan TACH period is actually being measured, exceeding
the limit indicates a slow or stalled fan.
Fan Limit Registers
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF default
Reg. 0x55 TACH1 Minimum High Byte = 0xFF default
Reg. 0x56 TACH2 Minimum Low Byte = 0xFF default
Reg. 0x57 TACH2 Minimum High Byte = 0xFF default
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default
Reg. 0x59 TACH3 Minimum High Byte = 0xFF default
Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default
Reg. 0x5B TACH4 Minimum High Byte = 0xFF default
OUT-OF-LIMIT COMPARISONS
The ADM1027 will measure all parameters in round-robin format
and set the appropriate status bit for out-of-limit conditions.
Comparisons are done differently depending on whether the
measured value is being compared to a high or low limit.
Reg. 0x44 2.5 V Low Limit = 0x00 default
Reg. 0x45 2.5 V High Limit = 0xFF default
Reg. 0x46 VCCP Low Limit = 0x00 default
Reg. 0x47 VCCP High Limit = 0xFF default
Reg. 0x48 VCC Low Limit = 0x00 default
Reg. 0x49 VCC High Limit = 0xFF default
Reg. 0x4A 5 V Low Limit = 0x00 default
Reg. 0x4B 5 V High Limit = 0xFF default
Reg. 0x4C 12 V Low Limit = 0x00 default
Reg. 0x4D 12 V High Limit = 0xFF default
HIGH LIMIT: > COMPARISON PERFORMED
LOW LIMIT: < OR = COMPARISON PERFORMED
Temperature Limit Registers
Reg. 0x4E Remote 1 Temp Low Limit = 0x81 default
Reg. 0x4F Remote 1 Temp High Limit = 0x7F default
Reg. 0x6A Remote 1 THERM Limit = 0x64 default
Reg. 0x50 Local Temp Low Limit = 0x81 default
Reg. 0x51 Local Temp High Limit = 0x7F default
Reg. 0x6B Local THERM Limit = 0x64 default
Reg. 0x52 Remote 2 Temp Low Limit = 0x81 default
Reg. 0x53 Remote 2 Temp High Limit = 0x7F default
Reg. 0x6C Remote 2 THERM Limit = 0x64 default
REV. A
–17–
ADM1027
ANALOG MONITORING CYCLE TIME
STATUS REGISTER 1 (REG. 0x41)
The analog monitoring cycle begins when a 1 is written to the
start bit (Bit 0) of Configuration Register 1(Reg. 0x40). 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.
Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and
Status Register 2 should be read.
Bit 6 (R2T) = 1, Remote 2 temp high or low limit has been
exceeded.
Bit 5 (LT) = 1, Local temp high or low limit has been exceeded.
Since the ADC will normally be left to free-run in this manner,
the time taken to monitor all the analog inputs will normally not
be of interest as the most recently measured value of any input
can be read out at any time.
Bit 4 (R1T) = 1, Remote 1 temp high or low limit has been
exceeded.
Bit 3 (5 V) = 1, 5 V high or low limit has been exceeded.
Bit 2 (VCC) = 1, VCC high or low limit has been exceeded.
Bit 1 (VCCP) = 1, VCCP high or low limit has been exceeded.
For applications where the monitoring cycle time is important,
it can easily be calculated.
Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.
The total number of channels measured is
∑ Four dedicated supply voltage inputs
∑ 3.3 VSTBY or 5 V supply (VCC pin)
∑ Local temperature
∑ Two remote temperatures
STATUS REGISTER 2 (REG. 0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2– inputs.
Bit 6 (D1) = 1, indicates an open or short on D2+/D2– inputs.
Bit 5 (FAN4) = 1, indicates Fan 4 has dropped below minimum speed.
As mentioned previously, the ADC performs round-robin conversions and takes 11.38 ms for each voltage measurement,
12 ms for a local temperature reading, and 25.5 ms for a remote
temperature reading.
The total monitoring cycle time for averaged voltage and temperature monitoring is therefore nominally
Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below minimum speed.
Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below minimum speed.
Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below minimum speed.
(5 11.38) + 12 + (2 25.5) = 120 ms
Bit 1 (OVT) = 1, indicates that a THERM overtemperature
limit has been exceeded.
Fan TACH measurements are made in parallel and are not
synchronized with the analog measurements in any way.
Bit 0 (12 V) = 1, 12 V high or low limit has been exceeded.
STATUS REGISTERS
The results of limit comparisons are stored in Status Registers 1
and 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 will be cleared to 0. If the measurement is out-of-limits,
the corresponding status register bit will be set to 1.
The state of the various measurement channels may be polled by
reading the status registers over the serial bus. When 1, Bit 7
(OOL) of Status Register 1 (Reg. 0x41) means that an out-oflimit event has been flagged in Status Register 2. This means that
the user need read only Status Register 2 when this bit is set.
Alternatively, Pin 10 can be configured as an SMBALERT output.
This will automatically notify 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 gets set, indicating an out-of-limit
condition, it will remain 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 (Reg. 0x74, 0x75) allow individual interrupt sources to be masked from causing an SMBALERT.
However, if one of these masked interrupt sources goes outof-limit, its associated status bit will get set in the interrupt
status registers.
–18–
REV. A
ADM1027
SMBALERT INTERRUPT BEHAVIOR
HIGH LIMIT
The ADM1027 can be polled for status, or an SMBALERT
interrupt can be generated for out-of-limit conditions. It is
important to note how the SMBALERT output and status bits
behave when writing interrupt handler software.
TEMPERATURE
CLEARED ON READ
(TEMP BELOW LIMIT)
HIGH LIMIT
STICKY
STATUS
BIT
SMBALERT
TEMPERATURE
CLEARED ON READ
(TEMP BELOW LIMIT)
STICKY
STATUS
BIT
SMBALERT
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
INTERRUPT
MASK BIT SET
INTERRUPT MASK
BIT CLEARED
(SMBALERT REARMED)
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
Figure 17. How Masking the Interrupt Source
Affects SMBALERT Output
Figure 16. SMBALERT and Status Bit Behavior
MASKING INTERRUPT SOURCES
Interrupt Mask Registers 1 and 2 are located at Addresses 0x74
and 0x75. These 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 will be set as normal.
Figure 16 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 since 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 status register has been read. This has
implications on how software handles the interrupt.
INTERRUPT MASK REGISTER 1 (REG. 0x74)
Bit 7 (OOL) = 1, set this bit to 1 to allow masking of interrupts
by Status Register 2. If this bit = 0, then setting a bit in Mask
Register 2 to 1 will have no effect.
Bit 6 (R2T) = 1, masks SMBALERT for Remote 2 temperature.
HANDLING SMBALERT INTERRUPTS
Bit 5 (LT) = 1, masks SMBALERT for local temperature.
To prevent the system from being tied up servicing interrupts,
it is recommend to handle the SMBALERT interrupt as follows:
Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature.
1. Detect the SMBALERT assertion.
Bit 3 (5 V) = 1, masks SMBALERT for 5 V channel.
2. Enter the interrupt handler.
Bit 2 (VCC) = 1, masks SMBALERT for VCC channel.
3. Read the status registers to identify the interrupt source.
Bit 1 (VCCP) = 1, masks SMBALERT for VCCP channel.
4. Mask the interrupt source by setting the appropriate mask bit
in the interrupt mask registers (Reg. 0x74, 0x75).
Bit 0 (2.5 V) = 1, masks SMBALERT for 2.5 V channel.
INTERRUPT MASK REGISTER 2 (REG. 0x75)
5. Take the appropriate action for a given interrupt source.
Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors.
6. Exit the interrupt handler.
Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors.
7. Periodically poll the status registers. If the interrupt status bit
has cleared, reset the corresponding interrupt mask bit to 0.
This will cause the SMBALERT output and status bits to
behave as shown in Figure 17.
Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4.
Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3.
Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2.
Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1.
Bit 1 (OVT) = 1, masks SMBALERT for overtemperature
(exceeding THERM limits).
Bit 0 (12 V) = 1, masks SMBALERT for 12 V channel.
REV. A
–19–
ADM1027
FAN DRIVE CIRCUITRY
Fan Drive Using PWM Control
The ADM1027 uses Pulsewidth 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. A single NMOSFET 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 you drive several fans
in parallel from a single PWM output or drive larger server fans,
the MOSFET will need to 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_OUT pin. VGS can be greater than 3.3 V as long as
the pull-up on the gate is tied to 5 V. The MOSFET should
also have a low on resistance to ensure that there is not significant voltage drop across the FET. This would reduce the
voltage applied across the fan and thus the maximum operating
speed of the fan.
Figure 18 uses a 10 kW pull-up resistor for the TACH signal.
This assumes that the TACH signal is open-collector from the
fan. In all cases, the TACH signal from the fan must be kept
below 5 V maximum to prevent damaging the ADM1027. 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 19 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 such that the transistor is saturated when the
fan is powered on.
12V
10k⍀
10k⍀
TACH/AIN
12V
FAN
4.7k⍀
ADM1027
Figure 18 shows how a 3-wire fan may be driven using PWM
control.
12V
12V
3.3V
10k⍀
PWM
12V
Q1
MMBT2222
10k⍀
10k⍀
TACH/AIN
12V
FAN
Figure 19. Driving a 3-Wire Fan Using an NPN Transistor
4.7k⍀
ADM1027
3.3V
10k⍀
PWM
Q1
NDT3055L
Figure 18. Driving a 3-Wire Fan Using an
N-Channel MOSFET
–20–
REV. A
ADM1027
NDT3055L MOSFET. Note that since the MOSFET can
handle up to 3.5 A, it is simply a matter of connecting another
fan directly in parallel with the first.
Driving 2 Fans From PWM3
Note that the ADM1027 has four TACH inputs available for
fan speed measurement, but only three PWM drive outputs. If a
fourth fan is being used in the system, it should be driven from
the PWM3 output in parallel with the third fan. Figure 20
shows how to drive two fans in parallel using low cost NPN
transistors. Figure 21 is the equivalent circuit using the
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 max current specified on the data sheet.
12V
3.3V
3.3V
ADM1027
TACH3
TACH4
10k⍀
PWM3
2.2k⍀
Q1
MMBT3904
Q2
MMBT2222
10⍀
10⍀
Q3
MMBT2222
Figure 20. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
3.3V
10k⍀
TYPICAL
TACH4
+V
3.3V
ADM1027
10k⍀
TYPICAL
TACH3
+V
TACH
5V OR 12V
FAN
TACH
5V OR 12V
FAN
3.3V
10k⍀
TYPICAL
PWM3
Q1
NDT3055L
Figure 21. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
REV. A
–21–
ADM1027
Driving 2-Wire Fans
Tek PreVu
[
]
T
T
Figure 22 shows how a 2-wire fan may be connected to the
ADM1027. This circuit allows the speed of a 2-wire fan to be
measured even though the fan has no dedicated TACH signal.
A series resistor, RSENSE, in the fan circuit converts the fan
commutation pulses into a voltage. This is ac-coupled into the
ADM1027 through the 0.01 F capacitor. On-chip signal conditioning allows accurate monitoring of fan speed. For fans
drawing approximately 200 mA, a 2 W RSENSE value is suitable.
For fans that draw more current, such as larger desktop or
server fans, RSENSE may be reduced. The smaller RSENSE is the
better, since more voltage will be developed across the fan, and
the fan will spin faster. Figure 23 shows a typical plot of the
sensing waveform at a TACH/AIN pin. The most important
thing is that the negative going spikes are more than 250 mV in
amplitude. This allows fan speed to be reliably determined.
⌬: +250mV
@: –258mV
1
4
Ch1 100mV
Ch3 50.0mV
Ch2 5.00mV
Ch4 50.0mV
M 4.00ms A Ch1
T
–2.00mV
–1.00000ms
Figure 23. Fan Speed Sensing Waveform at
TACH/AIN Pin
+V
Laying Out for 2-Wire and 3-Wire Fans
ADM1027
5V OR 12V
FAN
3.3V
10k⍀
TYPICAL
Figure 24 shows how to lay out a common circuit arrangement
for 2-wire and 3-wire fans. Some components will not be populated depending on whether a 2-wire or 3-wire fan is being used.
Q1
NDT3055L
PWM
12V OR 5V
0.01␮F
TACH/AIN
R1
RSENSE
2⍀
TYPICAL
3.3V OR 5V
R2
R5
Figure 22. Driving a 2-Wire Fan
PWM
Q1
MMBT2222
C1
TACH/AIN
R3
R4
FOR 3-WIRE FANS:
POPULATE R1, R2, R3
R4 = 0⍀
C1 = UNPOPULATED
FOR 2-WIRE FANS:
POPULATE R4, C1
R1, R2, R3 UNPOPULATED
Figure 24. Planning for 2-Wire or 3-Wire Fans on a PCB
–22–
REV. A
ADM1027
With a pull-up voltage of 12 V and pull-up resistor less than
1 kW, suitable values for R1 and R2 would be 100 kW and
47 kW. This will give a high input voltage of 3.83 V.
FAN SPEED MEASUREMENTS
TACH Inputs
Pins 11, 12, 9, and 14 are open-drain TACH inputs intended
for fan speed measurement.
5V OR 12V
Signal conditioning in the ADM1027 accommodates the slow
rise and fall times typical of fan tachometer outputs. The maximum input signal range is 0 V to 5 V, even where VCC is less
than 5 V. In the event that these inputs are supplied from fan
outputs that exceed 0 V to 5 V, either resistive attenuation of
the fan signal or diode clamping must be included to keep
inputs within an acceptable range.
VCC
FAN
PULL-UP TYP
<1k⍀
OR
TOTEM POLE
ADM1027
R1
10k⍀
TACHO
OUTPUT
Figures 25a to 25d show circuits for most common fan TACH
outputs. If the fan TACH output has a resistive pull-up to VCC, it
can be connected directly to the fan input, as shown in Figure 25a.
TACH X
FAN SPEED
COUNTER
ZD1*
*CHOOSE ZD1 VOLTAGE APPROX 0.8 ⴛ VCC
Figure 25c. Fan with Strong TACH Pull-Up to > VCC or
Totem-Pole Output, Clamped with Zener and Resistor
VCC
5V OR 12V
5V OR 12V
FAN
VCC
FAN
PULL-UP
4.7k⍀
TYP
ADM1027
TACHO
OUTPUT
TACH X
FAN SPEED
COUNTER
ADM1027
PULL-UP TYP
<1k⍀
R1*
TACHO
OUTPUT
Figure 25a. Fan With TACH Pull-Up to +VCC
VCC
FAN
PULL-UP
4.7k⍀
TYP
ADM1027
TACHO
OUTPUT
TACH X
FAN SPEED
COUNTER
FAN SPEED
COUNTER
R2*
*SEE TEXT
If the fan output has a resistive pull-up to 12 V (or other voltage
greater than 5 V), then the fan output can be clamped with a
Zener diode, as shown in Figure 25b. The Zener diode voltage
should be chosen so that it is greater than VIH of the TACH
input but less than 5 V, allowing for the voltage tolerance of the
Zener. A value of between 3 V and 5 V is suitable.
5V OR 12V
TACH X
Figure 25d. Fan with Strong TACH Pull-Up to > VCC
or Totem-Pole Output, Attenuated with R1/R2
Fan Speed Measurement
The fan counter does not count the fan TACH output pulses
directly because the fan speed may be less than 1000 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 TACHO output
(Figure 26), so the accumulated count is actually proportional
to the fan tachometer period and inversely proportional to the
fan speed.
ZD1*
CLOCK
*CHOOSE ZD1 VOLTAGE APPROX 0.8 ⴛ VCC
PWM
Figure 25b. Fan with TACH Pull-Up to Voltage
> 5 V (e.g., 12 V) Clamped with Zener Diode
TACH
If the fan has a strong pull-up (less than 1 k⍀) to 12 V, or a
totem-pole output, then a series resistor can be added to limit
the Zener current, as shown in Figure 25c. Alternatively, a
resistive attenuator may be used, as shown in Figure 25d.
1
2
3
4
R1 and R2 should be chosen such that
2 V < VPULLUP ¥ R2 ( RPULLUP + R1 + R2) > 5 V
The fan inputs have an input resistance of nominally 160 kW to
ground; this should be taken into account when calculating
resistor values.
REV. A
Figure 26. Fan Speed Measurement
N, the number of pulses counted, is determined by the settings
of Register 0x7B (fan pulses per revolution register). This register
contains two bits for each fan, allowing 1, 2 (default), 3, or 4
TACH pulses to be counted.
–23–
ADM1027
Fan Speed Measurement Registers
Fan Speed Measurement Rate
The fan tachometer readings are 16-bit values consisting of a
2-byte read from the ADM1027.
The fan TACH readings are normally updated once every second.
Reg. 0x28 TACH1 Low Byte = 0x00 default
Reg. 0x29 TACH1 High Byte = 0x00 default
The fast bit (Bit 3) of Configuration Register 3 (Reg. 0x78),
when set, updates the fan TACH readings every 250 ms.
Reg. 0x2C TACH3 Low Byte = 0x00 default
If any of the fans are not being driven by a PWM channel but
are powered directly from 5 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.
Reg. 0x2D TACH3 High Byte = 0x00 default
Calculating Fan Speed
Reg. 0x2A TACH2 Low Byte = 0x00 default
Reg. 0x2B TACH2 High Byte = 0x00 default
Reg. 0x2E TACH4 Low Byte = 0x00 default
Reg. 0x2F TACH4 High Byte = 0x00 default
Reading Fan Speed From the ADM1027
If fan speeds are being measured, this 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 from. This prevents erroneous TACH
readings.
The fan tachometer reading registers report back the number of
11.11 s 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). Since 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
Since actual fan TACH period is being measured, exceeding a
fan TACH limit by 1 will set the appropriate status bit and can
be used to generate an SMBALERT.
Fan Tach Limit Registers
The fan TACH limit registers are 16-bit values consisting of
two bytes.
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF default
Reg. 0x55 TACH1 Minimum High Byte = 0xFF default
Reg. 0x56 TACH2 Minimum Low Byte = 0xFF default
Assuming a fan with 2 pulses/revolution (and 2 pulses/rev being
measured), fan speed is calculated by:
Fan Speed ( RPM ) = (90, 000 ¥ 60) Fan Tach Reading
where Fan Tach Reading = 16-bit fan tachometer reading.
Example:
TACH1 high byte (Reg. 0x29) = 0x17
TACH1 low byte (Reg. 0x28) = 0xFF
What is Fan 1 speed in RPM?
Fan 1 TACH reading = 0x17FF = 6143 decimal
RPM = (f ¥ 60)/fan 1 TACH reading
RPM = (90000 ¥ 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 fan pulses
per revolution register (Reg. 0x7B) for each fan. Alternatively,
this register can be used to determine the number or pulses/
revolution output by a given fan. By plotting fan speed measurements at 100% speed with different pulses/rev setting, the
smoothest graph with the lowest ripple determines the correct
pulses/rev value.
Fan Pulses Per Revolution Register
<1:0> FAN1 default = 2 pulses/rev
<3:2> FAN2 default = 2 pulses/rev
<5:4> FAN3 default = 2 pulses/rev
<7:6> FAN4 default = 2 pulses/rev
Reg. 0x57 TACH2 Minimum High Byte = 0xFF default
00 = 1 pulse/rev
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default
01 = 2 pulses/rev
Reg. 0x59 TACH3 Minimum High Byte = 0xFF default
10 = 3 pulses/rev
Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default
11 = 4 pulses/rev
Reg. 0x5B TACH4 Minimum High Byte = 0xFF default
–24–
REV. A
ADM1027
2-Wire Fan Speed Measurements
PWM1 CONFIGURATION (REG. 0x5C)
The ADM1027 is capable of measuring the speed of 2-wire
fans, i.e., fans without TACH outputs. To do this, the fan must
be interfaced as shown in the Fan Drive Circuitry section of the
data sheet. In this case, the TACH inputs need to be reprogrammed as analog inputs, AIN.
<2:0> SPIN
CONFIGURATION REGISTER 2 (REG. 0x73)
Bit 3 (AIN4) = 1, Pin 14 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
Bit 2 (AIN3) = 1, Pin 9 is reconfigured to measure the speed of
a 2-wire fan using an external sensing resistor and coupling
capacitor.
These bits control the start-up timeout for
PWM1.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
PWM2 CONFIGURATION (REG. 0x5D)
<2:0> SPIN
Bit 1 (AIN2) = 1, Pin 12 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
Bit 0 (AIN1) = 1, Pin 11 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
These bits control the start-up timeout for
PWM2.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
FAN SPIN-UP
PWM3 CONFIGURATION (REG. 0x5E)
The ADM1027 has a unique fan spin-up function. It will spin
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. Once two pulses have been
detected, the PWM duty cycle will go to the expected running
value, e.g., 33%. The advantage of this is that fans have different spin-up characteristics and will take different times to
overcome inertia. The ADM1027 just runs the fans fast enough
to overcome inertia and will be quieter on spin-up than fans
programmed to spin up for a given spin-up time.
<2:0> SPIN
These bits control the start-up timeout for
PWM3.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
Disabling Fan Start-Up Timeout
FAN START-UP TIMEOUT
To prevent false interrupts being generated as a fan spins up
(since it is below running speed), the ADM1027 includes a fan
start-up timeout function. This is the time limit allowed for two
TACH pulses to be detected on spin-up. For example, if 2
seconds fan start-up timeout is chosen, and no TACH pulses
occur within 2 seconds of the start of spin-up, a fan fault is
detected and flagged in the interrupt status registers.
REV. A
Although fan start-up makes fan spin-ups much quieter than
fixed-time spin-ups, the option is there to use fixed spin-up times.
Bit 5 (FSPDIS) = 1 in Configuration Register 1 (Reg. 0x40)
disables the spin-up for two TACH pulses. Instead, the fan will
spin up for the fixed time as selected in registers 0x5C to 0x5E.
–25–
ADM1027
MANUAL FAN SPEED CONTROL MODE
PWM CONFIGURATION (REG. 0x5C to 0x5E)
PWM Logic State
<7:5> BHVR 111 = Manual Mode
The PWM outputs can be programmed to be high for 100%
duty cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (Reg. 0x5C)
Once under manual control, each PWM output may be manually
updated by writing to Registers 0x30 to 0x32 (PWMx current
duty cycle registers).
<4> INV
Programming the PWM Current Duty Cycle Registers
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM2 Configuration (Reg. 0x5D)
<4> INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM3 Configuration (Reg. 0x5E)
<4> INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM Drive Frequency
The PWM drive frequency can be adjusted for the application.
Registers 0x5F to 0x61 configure the PWM frequency for
PWM1 to PWM3, respectively.
PWM1 FREQUENCY REGISTERS (REG. 0x5F to 0x61)
<2:0> FREQ
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
Manual Fan Speed Control
The ADM1027 allows the duty cycle of any PWM output to be
manually adjusted. This can be useful if you want to change fan
speed in software or want to adjust PWM duty cycle output for
test purposes. Bits <7:5> of Registers 0x5C to 0x5E (PWM
configuration) control the behavior of each PWM output.
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%. This allows the 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 ) = PWM MIN 0.39
Example 1: for a PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex.
Example 2: for a PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex.
PWM Duty Cycle Registers
Reg. 0x30 PWM1 Duty Cycle = 0xFF (100% default)
Reg. 0x31 PWM2 Duty Cycle = 0xFF (100% default)
Reg. 0x32 PWM3 Duty Cycle = 0xFF (100% default)
By reading the PWMx current duty cycle registers, you can keep
track of the current duty cycle on each PWM output, even when
the fans are running in automatic fan speed control mode or
acoustic enhancement mode.
–26–
REV. A
ADM1027
AUTOMATIC FAN SPEED CONTROL MODE
The ADM1027 has a local temperature sensor and two remote
temperature channels that may be connected to an on-chip
diode-connected transistor on a CPU. These three temperature
channels may be used as the basis for automatic fan speed control
to drive fans using pulsewidth modulation (PWM). In general,
the greater the number of fans in a system, the better the cooling,
but to the detriment of system acoustics. Automatic fan speed
control reduces acoustic noise by optimizing fan speed according
to 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, including TMIN and TRANGE, as discussed in detail later.
The TMIN and TRANGE values chosen for a given fan are critical,
since these define the thermal characteristics of the system. The
thermal validation of the system is one of the most important
steps of the design process, so these values should be carefully
selected.
The aim of this section is not only to provide the system designer
with an understanding of the automatic fan control loop, but also
to provide step-by-step guidance as to how to most effectively
evaluate and select the critical system parameters. To optimize
the system characteristics, the designer needs to give some forethought to how the system will be configured, e.g., 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 actual system evaluation should
also be involved at the beginning of the process.
Automatic Fan Control Overview
Figure 27 gives a top-level overview of the automatic fan control
circuitry on the ADM1027. 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 ADM1027 allows the speed
of four fans to be monitored. The right side of the block diagram
shows controls that are fan-specific. The designer has control
over individual parameters such as minimum PWM duty cycle,
fan speed failure thresholds, and even ramp control of the PWM
outputs. This ultimately allows graceful fan speed changes that
are less perceptible to the system user.
THERMAL CALIBRATION
⌺
REMOTE 1
TEMP
TMIN
TRANGE
0%
MUX
TRANGE
⌺
0%
⌺
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 3
AND 4
MEASUREMENT
0%
Figure 27. Automatic Fan Control Block Diagram
REV. A
PWM
GENERATOR
PWM2
PWM
CONFIG
PWM
MIN
100%
TMIN
PWM1
TACHOMETER 2
MEASUREMENT
THERMAL CALIBRATION
REMOTE 2
TEMP
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
100%
TMIN
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL
TEMP
PWM
CONFIG
PWM
MIN
100%
–27–
PWM
GENERATOR
PWM3
ADM1027
3. Use wide tracks to minimize inductance and reduce noise
pickup. A 10 mil track minimum width and spacing is
recommended.
Step 1
Determine the Hardware Configuration
Essentially this means choosing whether to use Pin 10 as a PWM2
output or as an SMBALERT output and deciding which SMBus
address is to be used. To set Pin 10 as SMBALERT, set Bit 0
of Configuration Register 3 (Addr = 0x78) equal to 1. The
default state is PWM2, where this bit equals 0.
4. Try to minimize the number of copper/solder joints, which
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D–
path and at the same temperature. Avoid routing D+/D–
on multiple layers or through vias if possible. These increase
series resistance that will cause temperature error.
It also refers to the layout recommendations of the ADM1027
on a motherboard, for example.
5. Place a 0.1 mF supply bypass capacitor close to the ADM1027.
ADM1027 Placement Considerations
Motherboards are electrically noisy environments, and care must
be taken to protect the analog inputs from noise, particularly the
D+/D– lines of a remote diode sensor. The following precautions
should be taken:
1. Place the ADM1027 as close as possible to the remote sensing
diode. Provided that the worst noise sources such as clocks
and data/address buses are avoided, this distance can be
4 inches to 8 inches.
2. Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible. Do NOT run the D+/D– lines in
different directions.
6. If the distance to the remote sensor is more than 8 inches,
the use of shielded twisted pair cable is recommended. This
will work up to 100 feet. Connect the twisted pair to D+/D–
and the shield to GND close to the ADM1027. Leave the
remote end of the shield unconnected to avoid ground loops.
Because the measurement technique uses switched current
sources, excessive cable (adds resistance) and/or filter capacitance
can affect the measurement. A 1 W series resistance introduces
about 0.8oC error.
–28–
REV. A
ADM1027
Step 2
Automatic Fan Control Mux Options
Configuring the Mux: Which Temperature Controls Which Fan?
<7:5> (BHVR) REGISTERS 0x5C, 0x5D, 0x5E
Having decided on the system hardware configuration, the fans
can be assigned to particular temperature channels. Not only
can fans be assigned to individual channels, but how a fan
behaves is configurable. For example, fans can run under
automatic fan control, manually (software control), or can run
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 bits) of Registers 0x5C, 0x5D, and 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.
000 = Remote 1 temp controls PWMx
001 = Local temp controls PWMx
010 = Remote 2 temp controls PWMx
101 = Fastest speed calculated by local and remote 2 temp
controls PWMx
110 = Fastest speed calculated by all three temperature channels
controls PWMx
The fastest speed calculated options refer to the ability to control one PWM output based on multiple temperature channels.
While the thermal characteristics of the three temperature zones
can be set up differently, they can drive a single fan. An example
would be if the fan turns on when Remote 1 temp exceeds 60∞C
or local temp exceeds 45∞C.
Other Mux Options
<7:5> (BHVR) REGISTERS 0x5C, 0x5D, 0x5E
011 = PWMx runs full-speed (default).
100 = PWMx disabled.
111 = Manual Mode. PWMx is run under software control. In
this mode, PWM duty cycle registers (Reg. 0x30 to 0x32) are
writable and control the PWM outputs.
MUX
PWM
MIN
THERMAL CALIBRATION
100%
⌺
REMOTE 1 =
AMBIENT TEMP
TMIN
TRANGE
0%
PWM
MIN
100%
⌺
MUX
TMIN
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACH1
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
MIN
PWM
GENERATOR
–29–
FRONT
CHASSIS
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
Figure 28. Assigning Temperature Channels to Fan Channels
REV. A
PWM2
TACH2
TACHOMETERS 3
AND 4
MEASUREMENT
0%
PWM1
CPU
FANSINK
TACHOMETER 2
MEASUREMENT
⌺
REMOTE 2 =
CPU TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
PWM3
TACH3
REAR
CHASSIS
ADM1027
Step 3
TMIN Registers
Determine TMIN Setting for Each Thermal Channel
Reg. 0x67 Remote 1 Temperature TMIN = 0x5A (90∞C default)
TMIN is the temperature at which the fans will start to turn on
under automatic fan control. The speed at which the fan runs
at TMIN is programmed later. The TMIN values chosen will be
temperature channel specific, e.g., 25∞C for ambient channel,
30∞C for VRM temperature, and 40∞C for processor temperature.
Reg. 0x68 Local Temperature TMIN = 0x5A (90∞C default)
TMIN is an 8-bit twos complement value 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 Temp. Once the TMIN value is exceeded, the fan
turns on and runs at minimum PWM duty cycle. The fan will
turn off once temperature has dropped below TMIN – THYST
(detailed later).
To overcome fan inertia, the fan is spun up until two valid TACH
rising edges are counted. See the Fan Start-Up Timeout section
for more details. In some cases, primarily for psycho-acoustic
reasons, it is desirable that the fan never switches off below TMIN.
Bits <7:5> of Enhance Acoustics Register 1 (Reg. 0x62), when
set, keep the fans running at PWM minimum duty cycle should
the temperature be below TMIN.
Reg. 0x69 Remote 2 Temperature TMIN = 0x5A (90∞C default)
Enhance Acoustics Reg 1 (Reg. 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.
PWM DUTY CYCLE
100%
0%
TMIN
PWM
MIN
THERMAL CALIBRATION
100%
⌺
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
0%
⌺
MUX
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
TACH1
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
PWM2
FRONT
CHASSIS
TACH2
PWM
MIN
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
TACHOMETERS 3
AND 4
MEASUREMENT
0%
PWM1
CPU
FANSINK
TACHOMETER 2
MEASUREMENT
⌺
REMOTE 1 =
AMBIENT TEMP
PWM
GENERATOR
PWM
MIN
100%
TMIN
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
PWM3
TACH3
REAR
CHASSIS
Figure 29. Understanding TMIN Parameter
–30–
REV. A
ADM1027
Step 4
Programming the PWMMIN Registers
Determine PWMMIN for Each PWM (Fan) Output
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 minimum PWM duty cycle to be
set in steps of 0.39%.
PWMMIN is the minimum PWM duty cycle that each fan in the
system will run at. 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. Starting the fans at higher speeds than necessary
will merely make the system louder than needed. Depending on
the fan used, the PWMMIN setting should be in the range 20%
to 33% duty cycle. This value can be found through
fan validation.
The value to be programmed into the PWMMIN register is
given by
Value (decimal ) = PWM MIN 0.39
Example 1: For a minimum PWM Duty Cycle of 50%,
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex
100%
PWM DUTY CYCLE
Example 2: For a minimum PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex
PWMMIN Registers
PWMMIN
Reg. 0x64 PWM1 Minimum Duty Cycle = 0x80 (50% default)
0%
Reg. 0x65 PWM2 Minimum Duty Cycle = 0x80 (50% default)
TMIN
Reg. 0x66 PWM3 Minimum Duty Cycle = 0x80 (50% default)
TEMPERATURE
Figure 30. PWMMIN Determines Minimum PWM Duty Cycle
It is important to note that 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,
then the fan characteristics can be set up differently. So Fan 1
driven by PWM1 can have a different PWMMIN value than
that of Fan 2 connected to PWM2. Figure 31 illustrates this as
PWM1MIN (front fan) is turned on at a minimum duty cycle of
20%, whereas PWM2MIN (rear fan) turns on at a minimum of
40% duty cycle. Note however, that both fans turn on at the
exact same temperature, defined by TMIN.
Fan Speed and PWM Duty Cycle
Note that 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 relates to the square
root of PWM duty cycle. Given a PWM square wave as the
drive signal, fan speed in RPM equates to
PWM DUTY CYCLE
100%
M2
PW
M1
PW
PWM2MIN
PWM1MIN
0%
TMIN
TEMPERATURE
Figure 31. Operating Two Different Fans from a
Single-Temperature Channel
REV. A
–31–
% fan speed = PWM duty cycle ¥ 10
ADM1027
Determine TRANGE for Each Temperature Channel
TRANGE is the range of temperature over which automatic fan
control occurs once the programmed TMIN temperature has
been exceeded. TRANGE is actually a temperature slope and not
an arbitrary value, i.e., a TRANGE of 40∞C only holds true for
PWMMIN = 33%. If PWMMIN is increased or decreased, the
effective TRANGE is changed, as described later.
TRANGE is implemented as a slope, which means as PWMMIN is
changed, TRANGE changes, but the actual slope remains the
same. The higher the PWMMIN value, the smaller the effective
TRANGE will be, i.e., the fan will reach full speed (100%) at a
lower temperature.
100%
PWM DUTY CYCLE
Step 5
TRANGE
PWM DUTY CYCLE
100%
50%
33%
25%
10%
0%
30ⴗC
40ⴗC
45ⴗC
54ⴗC
PWMMIN
0%
TMIN
TMIN
TEMPERATURE
Figure 34. Increasing PWMMIN Changes Effective TRANGE
Figure 32. TRANGE Parameter Affects Cooling Slope
The TRANGE or fan control slope is determined by the following
procedure:
For a given TRANGE value, the temperature at which the fan
will run full-speed for different PWMMIN values can easily be
calculated:
1. Determine the maximum operating temperature for that
channel, e.g., 70∞C.
where:
2. Determine experimentally the fan speed (PWM duty cycle
value) will not exceed that temperature at the worst-case
operating points, e.g., 70∞C is reached when the fans are
running at 50% PWM duty cycle.
TMAX = TMIN + ( MaxD.C. - MinD.C.) ¥ TRANGE 170
TMAX = Temperature at which the fan runs full-speed
TMIN = Temperature at which the fan will turn on
MaxD.C. = Maximum duty cycle (100%) = 255 decimal
3. Determine the slope of the required control loop to meet
these requirements.
MinD.C. = PWMMIN
4. Use best fit approximation to determine the most suitable
TRANGE value. There is ADM1027 evaluation software available to calculate the best fit value; ask your local Analog
Devices representative for more details.
Example: Calculate TMAX, given TMIN = 30∞C, TRANGE = 40∞C,
and PWMMIN = 10% duty cycle = 26 decimal
TMAX = TMIN + ( MaxD.C . - MinD.C .) ¥ TRANGE 170
TMAX = 30∞C + (100% - 10%) ¥ 40∞C 170
TMAX = 30∞C + (255 - 26) ¥ 40∞C 170
100%
PWM DUTY CYCLE
TRANGE = PWM duty cycle versus temperature slope
TMAX = 84∞C (effective TRANGE = 54∞C)
Example: Calculate TMAX, given TMIN = 30∞C, TRANGE = 40∞C
and PWMMIN = 25% duty cycle = 64 decimal
50%
TMAX = TMIN + ( MaxD.C . - MinD.C .) ¥ TRANGE 170
33%
TMAX = 30∞C + (100% - 25%) ¥ 40∞C 170
0%
30ⴗC
40ⴗC
TMAX = 30∞C + (255 - 64) ¥ 40∞C 170
TMAX = 75∞C (effective TRANGE = 45∞C)
TMIN
Figure 33. Adjusting PWMMIN Affects TRANGE
–32–
REV. A
ADM1027
Example: Calculate TMAX, given TMIN = 30∞C, TRANGE = 40∞C,
and PWMMIN = 33% duty cycle = 85 decimal
TMAX = TMIN + ( MaxD.C . - MinD.C .) ¥ TRANGE 170
TMAX = 30∞C + (100% - 33%) ¥ 40∞C 170
TMAX = 30∞C + (255 - 85) ¥ 40∞C 170
TMAX = 70∞C (effective TRANGE = 40∞C)
Example: Calculate TMAX, given TMIN = 30∞C, TRANGE = 40∞C,
and PWMMIN = 50% duty cycle = 128 decimal
TMAX = TMIN + ( MaxD.C . - MinD.C .) ¥ TRANGE 170
TMAX = 30∞C + (100% - 50%) ¥ 40∞C 170
TMAX = 30∞C + (255 - 128) ¥ 40∞C 170
TMAX = 60∞C (effective TRANGE = 30∞C)
Selecting a TRANGE Slope
The TRANGE value can be selected for each temperature channel:
Remote 1, Local and Remote 2 Temp. Bits <7:4> (TRANGE)
of Registers 0x5F to 0x61 define the TRANGE value for each
temperature channel.
REV. A
Bits <7:4>*
TRANGE (∞C)
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
2
2.5
3.33
4
5
6.67
8
10
13.33
16
20
26.67
32 (default)
40
53.33
80
* Register 0x5F configures remote 1 T RANGE.
Register 0x60 configures local T RANGE.
Register 0x61 configures remote 2 T RANGE.
–33–
ADM1027
Step 6
Determine TTHERM for Each Temperature Channel
TTHERM is the absolute maximum temperature allowed on a
temperature channel. Above this temperature, a component such
as the CPU or VRM may be operating beyond its safe operating
limit. When the measured temperature exceeds TTHERM, all fans
are driven at 100% PWM duty cycle (full speed) to provide
critical system cooling. The fans remain running at 100% until
the temperature drops below TTHERM – hysteresis. The hysteresis
value is 4∞C.
The TTHERM limit should be considered the maximum worstcase operating temperature of the system. Since 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 user should ensure that it is not exceeded under normal
system operating conditions.
Note that the TTHERM limits are nonmaskable and affect the fan
speed no matter what automatic fan control settings are configured. This allows some flexibility since a TRANGE value can be
selected based on its slope, while a hard limit, e.g., 70∞C, can be
programmed as TMAX (the temperature at which the fan reaches
full speed) by setting TTHERM to 70∞C.
THERM hysteresis is 4∞C.
THERM Registers
Reg. 0x6A Remote 1 THERM Limit = 0x64 (100∞C default)
Reg. 0x6B Local Temperature THERM Limit = 0x64
(100∞C default)
Reg. 0x6C Remote 2 THERM Limit = 0x64 (100∞C default)
TRANGE
PWM DUTY CYCLE
100%
0%
TTHERM
TMIN
PWM
MIN
THERMAL CALIBRATION
100%
⌺
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
0%
PWM
MIN
100%
⌺
MUX
TMIN
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACH1
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
MIN
PWM
GENERATOR
PWM2
FRONT
CHASSIS
TACH2
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
0%
PWM1
CPU
FANSINK
TACHOMETER 2
MEASUREMENT
⌺
REMOTE 1 =
AMBIENT TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
PWM
GENERATOR
PWM3
TACH3
REAR
CHASSIS
Figure 35. Understanding How TTHERM Relates to Automatic Fan Control
–34–
REV. A
ADM1027
Step 7
Determine THYST for Each Temperature Channel
THYST is the amount of extra cooling a fan provides after the
measured temperature 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 about the
TMIN setting.
The THYST value chosen will determine the amount of time
needed for the system to cool down or heat up, as the fan is
turning on and off. Values of hysteresis are programmable in
the range 1∞C to 15∞C. Larger values of THYST prevent the fans
chattering on and off as previously described. The THYST default
value is 4∞C.
Hysteresis Registers
Note that in some applications it is required that the fans not
turn off below TMIN, but remain running at PWMMIN. Bits <7:5>
of Enhance Acoustics Register 1 (Reg. 0x62) allow the fans to
be turned off or 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.
Enhance Acoustics Register 1 (Reg. 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.
Reg. 0x6D Remote 1, Local Hysteresis Register
<7:4> = Remote 1 temperature hysteresis (default = 4∞C)
<3:0> = Local temperature hysteresis (default = 4∞C)
Reg. 0x6E Remote 2 Temperature Hysteresis Register
<7:4> = Remote 2 temperature hysteresis (default = 4∞C)
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.
TRANGE
PWM DUTY CYCLE
100%
THYST
0%
TMIN
TTHERM
PWM
MIN
THERMAL CALIBRATION
100%
⌺
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
0%
PWM
MIN
100%
⌺
MUX
TMIN
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACH1
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
MIN
PWM
GENERATOR
PWM2
FRONT
CHASSIS
TACH2
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
0%
PWM1
CPU
FANSINK
TACHOMETER 2
MEASUREMENT
⌺
REMOTE 1 =
AMBIENT TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
PWM
GENERATOR
PWM3
TACH3
Figure 36. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
REV. A
–35–
REAR
CHASSIS
ADM1027
this approach causes an inherent delay in updating fan speed
and causes the thermal characteristics of the system to change.
It also causes the system fans to stay on longer than necessary,
since the fan reaction is merely delayed. The user also has no
control over noise from different fans driven by the same temperature source. Consider controlling a CPU cooler fan (on PWM1)
and a chassis fan (on PWM2) using Remote 1 temperature.
Because the Remote 1 temperature is smoothed, both fans will
be updated at exactly the same rate. If the chassis fan is much
louder than the CPU fan, there is no way to improve its acoustics
without changing the thermal solution of the CPU cooling fan.
ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to
changes in temperature, i.e., the PWM duty cycle will respond
immediately to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psycho-acoustic
reasons, the ADM1027 can prevent the PWM output from
reacting instantaneously to temperature changes. Enhanced
acoustic mode will control the maximum change in PWM duty
cycle in a given time. The objective is to prevent the fan cycling
up and down and annoying the system user.
Acoustic Enhancement Mode Overview
Figure 37 gives a top-level overview of the automatic fan
control circuitry on the ADM1027 and where acoustic
enhancement fits in. Acoustic enhancement is intended as a
post-design tweak when a system or mechanical engineer is
evaluating best settings for the system. Having determined the
optimal settings for the thermal solution, the engineer can adjust
the system acoustics. The goal is to implement a system that is
acoustically pleasing without causing the user annoyance due to
fan cycling. It is important to realize that although a system may
pass an acoustic noise requirement specification, e.g., 36 dB,
if the fan is annoying, it will fail the consumer test.
The Approach
There are two different approaches to implementing system
acoustic enhancement. The first method is temperature-centric.
This involves smoothing transient temperatures as they are measured by a temperature source, e.g., Remote 1 temperature.
The temperature values used to calculate PWM duty cycle
values would be smoothed, reducing fan speed variation. However,
The second approach is fan-centric. The idea is to control the
PWM duty cycle driving the fan at a fixed rate, e.g., 6%. Each
time the PWM duty cycle is updated, it is incremented by a
fixed 6%. So the fan ramps smoothly to its newly calculated
speed. If the temperature starts to drop, the PWM duty cycle
immediately decreases by 6% every update. So the fan ramps
smoothly up or down without inherent system delay. Consider
controlling the same CPU cooler fan (on PWM1) and chassis
fan (on PWM2) using Remote 1 temperature. The TMIN and
TRANGE settings have already been defined in automatic fan
speed control mode, i.e., thermal characterization of the control
loop has been optimized. Now the chassis fan is noisier than the
CPU cooling fan. So PWM2 can be placed into acoustic
enhancement mode independent of PWM1. The acoustics of
the chassis fan can therefore be adjusted without affecting the
acoustic behavior of the CPU cooling fan, even though both
fans are being controlled by Remote 1 temperature. This is
exactly how acoustic enhancement works on the ADM1027.
ACOUSTIC
ENHANCEMENT
PWM
MIN
THERMAL CALIBRATION
100%
⌺
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
0%
PWM
MIN
100%
⌺
MUX
TMIN
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACH1
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
MIN
PWM
GENERATOR
PWM2
FRONT
CHASSIS
TACH2
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
0%
PWM1
CPU
FANSINK
TACHOMETER 2
MEASUREMENT
⌺
REMOTE 1 =
AMBIENT TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
PWM
GENERATOR
PWM3
TACH3
REAR
CHASSIS
Figure 37. Acoustic Enhancement Smooths Fan Speed Variations Under Automatic Fan Speed Control
–36–
REV. A
ADM1027
Enabling Acoustic Enhancement for Each PWM Output
READ
TEMPERATURE
ENHANCED ACOUSTICS REGISTER 1 (Reg. 0x62)
<3> = 1 enables acoustic enhancement on PWM1 output.
CALCULATE
NEW PWM
DUTY CYCLE
ENHANCED ACOUSTICS REGISTER 2 (Reg. 0x63)
<7> = 1 enables acoustic enhancement on PWM2 output.
<3> = 1 enables acoustic enhancement on PWM3 output.
IS NEW PWM
VALUE >
PREVIOUS
VALUE?
Effect of Ramp Rate on Enhanced Acoustics Mode
The PWM signal driving the fan will have a period, T, given by
the PWM drive frequency, f, since T = 1/f. For a given PWM
period, T, the PWM period is subdivided into 255 equal time
slots. One time slot corresponds to the smallest possible increment in PWM duty cycle. A PWM signal of 33% duty cycle will
thus be high for 1/3 255 time slots and low for 2/3 255
time slots. Therefore, 33% PWM duty cycle corresponds to a
signal that is high for 85 time slots and low for 170 time slots.
PWM_OUT
33% DUTY
CYCLE
85
TIME SLOTS
170
TIME SLOTS
PWM OUTPUT
(ONE PERIOD)
= 255 TIME SLOTS
Figure 38. 33% PWM Duty Cycle Represented in Time Slots
The ramp rates in enhanced acoustics mode are selectable
between 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are actually discrete time slots. For example, if the ramp rate = 8, then
eight time slots will be added to the PWM high duty cycle each
time the PWM duty cycle needs to be increased. If the PWM
duty cycle value needs to be decreased, it will be decreased by
eight time slots. Figure 39 shows how the enhanced acoustics
mode algorithm operates.
REV. A
NO
DECREMENT
PREVIOUS
PWM VALUE
BY RAMP
RATE
YES
INCREMENT
PREVIOUS
PWM VALUE
BY RAMP
RATE
Figure 39. Enhanced Acoustics Algorithm
The enhanced acoustics mode algorithm calculates a new PWM
duty cycle based on the temperature measured. If the new
PWM duty cycle value is greater than the previous PWM value,
then the previous PWM duty cycle value is incremented by
either 1, 2, 3, 5, 8, 12, 24, or 48 time slots (depending on the
settings of the enhanced acoustics registers). If the new PWM
duty cycle value is less than the previous PWM value, then the
previous PWM duty cycle is decremented by 1, 2, 3, 5, 8, 12, 24,
or 48 time slots. Each time the PWM duty cycle is incremented
or decremented, it is stored as the previous PWM duty cycle for
the next comparison.
A ramp rate of 1 corresponds to one time slot, which is 1/255 of
the PWM period. In enhanced acoustics mode, incrementing or
decrementing by 1 changes the PWM output by 1/255 100%.
It is important to note that when using the enhanced acoustics
mode, the fan spin-up should be disabled.
–37–
ADM1027
Figure 40 shows remote temperature plotted against PWM duty
cycle for enhanced acoustics mode. The ramp rate is set to 48,
which corresponds to the fastest ramp rate. Assume that a new
temperature reading is available every 115 ms. With these settings, it took approximately 0.76 seconds to go from 33% duty
cycle to 100% duty cycle (full speed). It can be seen that even
though the temperature increased very rapidly, the fan ramps up
to full speed gradually.
CHOOSING RAMP RATE FOR ACOUSTIC
ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found
through system characterization after the thermal optimization
has been finished. Each ramp rate’s effects should be logged, if
possible, to determine the best setting for a given solution.
Enhanced Acoustics Register 1 (Reg. 0x62)
<2:0> ACOU Select the ramp rate for PWM1.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Figure 41 shows how changing the ramp rate from 48 to 8
affects the control loop. The overall response of the fan is
slower. Since the ramp rate is reduced, it takes longer for the
fan to achieve full running speed. In this case, it took approximately 4.4 sec for the fan to reach full speed.
120
140
120
100
Enhanced Acoustics Register 2 (Reg. 0x63)
100
<2:0> ACOU3 Select the ramp rate for PWM3.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
80
80
60
60
40
40
20
20
0
0
<6:4> ACOU2 Select the ramp rate for PWM2.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Figure 41. Enhanced Acoustics Mode with Ramp Rate = 8
120
Figure 42 shows the behavior of the PWM output as temperature
varies. As the temperature rises, the fan speed ramps up. Small
drops in temperature will not affect the ramp-up function since
the newly calculated fan speed will still be higher than the previous
PWM value. The enhanced acoustics mode allows the PWM
output to be made less sensitive to temperature variations. This
will be dependent on the ramp rate selected and programmed
into the enhanced acoustics.
90
120
0
4.4
As can be seen from the preceding examples, the rate at which
the fan will react to temperature change is dependent on the
ramp rate selected in the enhance acoustics registers. The higher
the ramp rate, the faster the fan will reach the newly calculated
fan speed.
Another way to view the ramp rates is as the time it takes for the
PWM output to ramp from 0% to 100% duty cycle for an instantaneous change in temperature. This can be tested by putting
the ADM1027 into manual mode and changing the PWM output
from 0% to 100% PWM duty cycle. The PWM output takes
35 sec to reach 100% with a ramp rate of 1 time slot selected.
140
TIME – sec
90
100
RTEMP (ⴗC)
80
100
80
70
80
60
60
60
POWER DUTY CYCLE (%)
PWM DUTY CYCLE
40
80
70
RTEMP
60
50
50
40
40
30
30
20
20
10
10
40
20
20
0
0
TIME – sec
0
0.76
0
0
Figure 40. Enhanced Acoustics Mode with Ramp Rate = 48
Figure 42. How Fan Reacts to Temperature
Variation in Enhanced Acoustics Mode
–38–
REV. A
ADM1027
OPERATING FROM 3.3 V STANDBY
VID0
The ADM1027 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 will be lowered in these states.
VID1
VID2
Note that since other voltages can drop or be turned off during
a low power state, these voltage channels will set status bits or
generate SMBALERTs. It is still necessary to mask out these
channels prior to entering a low power state by using the interrupt
mask registers. When exiting the low power state, the mask bits
can be cleared. This prevents the device from generating unwanted
SMBALERTs during the low power state.
XOR TREE TEST MODE
VID3
VID4
TACH1
TACH2
The ADM1027 includes an XOR 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 XOR tree, it is
possible to detect opens or shorts on the system board. Figure 43
shows the signals that are exercised in the XOR tree test mode.
TACH3
TACH4
The XOR tree test is invoked by setting Bit 0 (XEN) of the
XOR tree test enable register (Reg. 0x6F).
PWM2
PWM3
PWM1/XTO
Figure 43. XOR Tree Test
REV. A
–39–
ADM1027
Table IV. ADM1027 Registers
Address
R/W
Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
0x20
0x21
0x22
0x23
0x24
0x25
0x26
0x27
0x28
0x29
0x2A
0x2B
0x2C
0x2D
0x2E
0x2F
0x30
0x31
0x32
0x3D
0x3E
0x3F
0x40
0x41
0x42
0x43
0x44
0x45
0x46
0x47
0x48
0x49
0x4A
0x4B
0x4C
0x4D
0x4E
0x4F
0x50
0x51
0x52
0x53
0x54
0x55
0x56
0x57
0x58
0x59
0x5A
0x5B
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R/W
R/W
R/W
R
R
R
R/W
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
2.5 V Reading
VCCP Reading
VCC Reading
5 V Reading
12 V Reading
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
TACH1 Low Byte
TACH1 High Byte
TACH2 Low Byte
TACH2 High Byte
TACH3 Low Byte
TACH3 High Byte
TACH4 Low Byte
TACH4 High Byte
PWM1 Current Duty Cycle
PWM2 Current Duty Cycle
PWM3 Current Duty Cycle
Device ID Register
Company ID Number
Revision Number
Configuration Register 1
Interrupt Status Register 1
Interrupt Status Register 2
VID Register
2.5 V Low Limit
2.5 V High Limit
VCCP Low Limit
VCCP High Limit
VCC Low Limit
VCC High Limit
5 V Low Limit
5 V High Limit
12 V Low Limit
12 V High Limit
Remote 1 Temp Low Limit
Remote 1 Temp High Limit
Local Temp Low Limit
Local Temp High Limit
Remote 2 Temp Low Limit
Remote 2 Temp High Limit
TACH1 Minimum Low Byte
TACH1 Minimum High Byte
TACH2 Minimum Low Byte
TACH2 Minimum High Byte
TACH3 Minimum Low Byte
TACH3 Minimum High Byte
TACH4 Minimum Low Byte
TACH4 Minimum High Byte
9
9
9
9
9
9
9
9
7
15
7
15
7
15
7
15
7
7
7
7
7
VER
VCC
OOL
D2
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
15
7
15
7
15
7
15
8
8
8
8
8
8
8
8
6
14
6
14
6
14
6
14
6
6
6
6
6
VER
TODIS
R2T
D1
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
14
6
14
6
14
6
14
7
7
7
7
7
7
7
7
5
13
5
13
5
13
5
13
5
5
5
5
5
VER
FSPDIS
LT
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
13
5
13
5
13
5
13
6
6
6
6
6
6
6
6
4
12
4
12
4
12
4
12
4
4
4
4
4
VER
V¥I
R1T
FAN3
VID4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
12
4
12
4
12
4
12
5
5
5
5
5
5
5
5
3
11
3
11
3
11
3
11
3
3
3
3
3
STP
FSPD
5V
FAN2
VID3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
11
3
11
3
11
3
11
4
4
4
4
4
4
4
4
2
10
2
10
2
10
2
10
2
2
2
2
2
STP
RDY
VCC
FAN1
VID2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
10
2
10
2
10
2
10
3
3
3
3
3
3
3
3
1
9
1
9
1
9
1
9
1
1
1
1
1
STP
LOCK
VCCP
OVT
VID1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
1
9
1
9
1
9
2
2
2
2
2
2
2
2
0
8
0
8
0
8
0
8
0
0
0
0
0
STP
STRT
2.5 V
12 V
VID0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
8
0
8
0
8
0
8
0x00
0x00
0x00
0x00
0x00
0x80
0x80
0x80
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0xFF
0xFF
0xFF
0x27
0x41
0x60
0x00
0x00
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x81
0x7F
0x81
0x7F
0x81
0x7F
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
–40–
Lockable?
Yes
REV. A
ADM1027
Table IV. ADM1027 Registers (continued)
Address
R/W Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable?
0x5C
0x5D
0x5E
0x5F
0x60
0x61
0x62
0x63
0x64
0x65
0x66
0x67
0x68
0x69
0x6A
0x6B
0x6C
0x6D
0x6E
0x6F
0x70
0x71
0x72
0x73
0x74
0x75
0x76
0x77
0x78
0x7B
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
BHVR
BHVR
BHVR
RANGE
RANGE
RANGE
MIN3
EN2
7
7
7
7
7
7
7
7
7
HYSR1
HYSR2
RES
7
7
7
7
OOL
D2
5V
TDM2
DC4
FAN4
BHVR
BHVR
BHVR
RANGE
RANGE
RANGE
MIN2
ACOU2
6
6
6
6
6
6
6
6
6
HYSR1
HYSR2
RES
6
6
6
CONV
R2T
D1
5V
TDM2
DC3
FAN4
BHVR
BHVR
BHVR
RANGE
RANGE
RANGE
MIN1
ACOU2
5
5
5
5
5
5
5
5
5
HYSR1
HYSR2
RES
5
5
5
ATTN
LT
5
VCC
LTMP
DC2
FAN3
INV
INV
INV
RANGE
RANGE
RANGE
4
ACOU2
4
4
4
4
4
4
4
4
4
HYSR1
HYSR2
RES
4
4
4
AVG
R1T
FAN3
VCC
LTMP
DC1
FAN3
3
3
3
3
3
3
EN1
EN3
3
3
3
3
3
3
3
3
3
HYSL
RES
RES
3
3
3
AIN4
5V
FAN2
VCCP
TDM1
FAST
FAN2
SPIN
SPIN
SPIN
FREQ
FREQ
FREQ
ACOU
ACOU3
2
2
2
2
2
2
2
2
2
HYSL
RES
RES
2
2
2
AIN3
VCC
FAN1
VCCP
TDM1
BOOST
FAN2
SPIN
SPIN
SPIN
FREQ
FREQ
FREQ
ACOU
ACOU3
1
1
1
1
1
1
1
1
1
HYSL
RES
RES
1
1
1
AIN2
VCCP
OVT
2.5 V
12 V
1
FAN1
SPIN
SPIN
SPIN
FREQ
FREQ
FREQ
ACOU
ACOU3
0
0
0
0
0
0
0
0
0
HYSL
RES
XEN
0
0
0
AIN1
2.5 V
12 V
2.5 V
12 V
ALERT
FAN1
0x62
0x62
0x62
0xC4
0xC4
0xC4
0x00
0x00
0x80
0x80
0x80
0x5A
0x5A
0x5A
0x64
0x64
0x64
0x44
0x40
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x55
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
REV. A
PWM1 Configuration Register
PWM2 Configuration Register
PWM3 Configuration Register
Remote 1 TRANGE/PWM 1 Freq
Local TRANGE/PWM 2 Freq
Remote 2 TRANGE/PWM 3 Freq
Enhance Acoustics Reg 1
Enhance Acoustics Reg 2
PWM1 Min Duty Cycle
PWM2 Min Duty Cycle
PWM3 Min Duty Cycle
Remote 1 Temp TMIN
Local Temp TMIN
Remote 2 Temp TMIN
Remote 1 THERM Limit
Local THERM Limit
Remote 2 THERM Limit
Remote 1, Local Hysteresis
Remote 2 Temp Hysteresis
XOR Tree Test Enable
Remote 1 Temperature Offset
Local Temperature Offset
Remote 2 Temperature Offset
Configuration Register 2
Interrupt Mask 1 Register
Interrupt Mask 2 Register
Extended Resolution 1
Extended Resolution 2
Configuration Register 3
Fan Pulses per Revolution
–41–
Yes
ADM1027
Table V. Voltage Reading Registers (Power-On Default = 0x00)
Register Address
R/W
Description
0x20
0x21
0x22
0x23
0x24
Read-Only
Read-Only
Read-Only
Read-Only
Read-Only
2.5 V Reading (8 MSBs of reading).
VCCP Reading. Holds processor core voltage measurement (8 MSBs of reading).
VCC Reading. Measures VCC through the VCC pin (8 MSBs of reading).
5 V Reading (8 MSBs of reading).
12 V Reading (8 MSBs of reading).
If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read
first. Once the extended resolution register is read, the associated MSB reading registers are frozen until read. Both the extended
resolution register and the MSB registers are frozen.
Table VI. Temperature Reading Registers (Power-On Default = 0x80)
Register Address
R/W
Description
0x25
0x26
0x27
Read-Only
Read-Only
Read-Only
Remote 1 Temperature Reading* (8 MSBs of reading).
Local Temperature Reading (8 MSBs of reading).
Remote 2 Temperature Reading* (8 MSBs of reading).
These temperature readings are in twos complement format.
*Note that a reading of 0x80 in a temperature reading register indicates a diode fault (open or short) on that channel. If the extended resolution bits of these readings
are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read first. Once the extended resolution register is read, all associated MSB reading
registers are frozen until read. Both the extended resolution register and the MSB registers are frozen.
Table VII. Fan Tachometer Reading Registers (Power-On Default = 0x00)
Register Address
R/W
Description
0x28
0x29
0x2A
0x2B
0x2C
0x2D
0x2E
0x2F
Read-Only
Read-Only
Read-Only
Read-Only
Read-Only
Read-Only
Read-Only
Read-Only
TACH1 Low Byte
TACH1 High Byte
TACH2 Low Byte
TACH2 High Byte
TACH3 Low Byte
TACH3 High Byte
TACH4 Low Byte
TACH4 High Byte
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 fan pulses per revolution register
(Reg. 0x7B). This allows the fan speed to be accurately measured. Since a valid fan tachometer reading requires that two bytes are
read; the low byte MUST be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain
0x0000 until such time as the first valid fan tach measurement is read in to these registers. This prevents false interrupts from occurring
while the fans are spinning up.
A count of 0xFFFF indicates that a fan is:
1. Stalled or Blocked (object jamming the fan)
2. Failed (internal circuitry destroyed)
3. Not Populated (The ADM1027 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.)
4. 2-Wire Instead of 3-Wire Fan
–42–
REV. A
ADM1027
Table VIII. Current PWM Duty Cycle Registers (Power-On Default = 0xFF)
Register Address
R/W
Description
0x30
0x31
0x32
Read/Write
Read/Write
Read/Write
PWM1 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
PWM2 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
PWM3 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADM1027
reports the PWM duty cycles back through these registers. The PWM duty cycle values will 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 IX. Register 0x40 – Configuration Register 1 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<0>
STRT
Read/Write
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 power-up
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 becomes read-only and
cannot be changed once Bit 1 (lock bit) has been written. All limit registers should be
programmed by BIOS before setting this bit to 1 (lockable).
<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 ADM1027 is powered down
and powered up again. This prevents rogue programs such as viruses from modifying
critical system limit settings (lockable).
<2>
RDY
Read-Only
This bit gets set to 1 by the ADM1027 to indicate that the device is fully powered up
and ready to begin systems monitoring.
<3>
FSPD
Read/Write
When set to 1, this runs all fans at full speed. Power-on default = 0. This bit does not get
locked at any time.
<4>
V¥I
Read/Write
BIOS should set this bit to 1 when the ADM1027 is configured to measure current
from an ADI ADOPT® VRM controller and measure the CPU’s core voltage. This will
allow monitoring software to display CPU watts usage (lockable).
<5>
FSPDIS
Read/Write
Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs will go
high for the entire fan spin-up timeout selected.
<6>
TODIS
Read/Write
When this bit is set to 1, the SMBus timeout feature is disabled. This allows the ADM1027
to be used with SMBus controllers that cannot handle SMBus timeouts (lockable).
<7>
VCC
Read/Write
When this bit is set to 1, the ADM1027 rescales its VCC pin to measure a 5 V supply.
If this bit is 0, the ADM1027 measures VCC as a 3.3 V supply (lockable).
REV. A
–43–
ADM1027
Table X. Register 0x41 – Interrupt Status Register 1 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<0>
2.5 V
Read-Only
A 1 indicates the 2.5 V 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.
<1>
VCCP
Read-Only
A 1 indicates the VCCP high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<2>
VCC
Read-Only
A 1 indicates the VCC high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<3>
5V
Read-Only
A 1 indicates the 5 V 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
A 1 indicates the Remote 1 low or high temp limit 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
A 1 indicates the local low or high temp limit 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
A 1 indicates the Remote 2 low or high temperature limit 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
A 1 indicates that an out-of-limit event has been latched in Status Register 2. This bit is
a logical OR of all status bits in Status Register 2. Software can test this bit in isolation to
determine whether any of the voltage, temperature, or fan speed readings represented by
Status Register 2 are out-of-limit. This saves the need to read Status Register 2 every
interrupt or polling cycle.
Table XI. Register 0x42 – Interrupt Status Register 2 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<0>
12 V
Read-Only
A 1 indicates the 12 V 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.
<1>
OVT
Read-Only
A 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 – 4∞C
<2>
FAN1
Read-Only
A 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 1 output is off.
<3>
FAN2
Read-Only
A 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 2 output is off.
<4>
FAN3
Read-Only
A 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 3 output is off.
<5>
FAN4
Read-Only
A 1 indicates that Fan 4 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 3 output is off.
<6>
D1
Read-Only
A 1 indicates either an open or short circuit on the Thermal Diode 1 inputs.
<7>
D2
Read-Only
A 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
–44–
REV. A
ADM1027
Table XII. Register 0x43 – VID Register (Power-On Default = 0x00 )
Bit
Name
R/W
Description
<4:0>
VID[4:0]
Read-Only
The VID[4:0] inputs from the CPU to indicate the expected processor core voltage. On
power-up, these bits reflect the state of the VID pins, even if monitoring is not enabled.
<7:5>
Reserved
Read-Only
Reserved for future use.
Table XIII. Voltage Limit Registers
Register Address
R/W
Description
Power-On Default
0x44
0x45
0x46
0x47
0x48
0x49
0x4A
0x4B
0x4C
0x4D
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
2.5 V Low Limit
2.5 V High Limit
VCCP Low Limit
VCCP High Limit
VCC Low Limit
VCC High Limit
5 V Low Limit
5 V High Limit
12 V Low Limit
12 V High Limit
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
Setting the Configuration Register 1 lock bit has no effect on these registers.
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 XIV. Temperature Limit Registers
Register Address
R/W
Description
Power-On Default
0x4E
0x4F
0x50
0x51
0x52
0x53
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Remote 1 Temperature Low Limit
Remote 1 Temperature High Limit
Local Temperature Low Limit
Local Temperature High Limit
Remote 2 Temperature Low Limit
Remote 2 Temperature High Limit
0x81
0x7F
0x81
0x7F
0x81
0x7F
Exceeding any of these temperature limits by 1oC will cause 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.
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).
REV. A
–45–
ADM1027
Table XV. Fan Tachometer Limit Registers
Register Address
R/W
Description
Power-On Default
0x54
0x55
0x56
0x57
0x58
0x59
0x5A
0x5B
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
TACH 1 Minimum Low Byte
TACH 1 Minimum High Byte
TACH 2 Minimum Low Byte
TACH 2 Minimum High Byte
TACH 3 Minimum Low Byte
TACH 3 Minimum High Byte
TACH 4 Minimum Low Byte
TACH 4 Minimum High Byte
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit
will be 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 XVI. PWM Configuration Registers
Register Address
R/W
Description
Power-On Default
0x5C
0x5D
0x5E
Read/Write
Read/Write
Read/Write
PWM1 Configuration
PWM2 Configuration
PWM3 Configuration
0x62
0x62
0x62
Read/Write
Description
<2:0>
SPIN
(Fan Startup
Timeout)
Read/Write
These bits control the startup timeout for PWMx. The PWM output stays high until two
valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during
the fan TACH measurement directly after the fan startup timeout period, then the TACH
measurement will read 0xFFFF and Status Register 2 will reflect the fan fault. If the
TACH minimum high and low byte contains 0xFFFF or 0x0000, then the Status Register
2 bit will not be set, even if the fan has not started.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
Note: Do not program 100.
<3>
Reserved
Read-Only
Reserved for future use.
<4>
INV
Read/Write
This bit inverts the PWM output. The default is 0, which corresponds to a logic high
output for 100% duty cycle. Setting this bit to 1, inverts the PWM output, so 100% duty
cycle corresponds to a logic low output.
<7:5>
BHVR
Read/Write
These bits assign each fan to a particular temperature sensor for localized cooling.
000 = Remote 1 temperature controls PWMx (automatic fan control mode).
001 = Local temperature controls PWMx (automatic fan control mode).
010 = Remote 2 temperature controls PWMx (automatic fan control mode).
011 = PWMx runs full speed (default).
100 = PWMx disabled.
101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx.
110 = Fastest speed calculated by all three temperatures controls PWMx.
111 = Manual mode. PWM duty cycle registers (Reg. 0x30 to 0x32) become writable.
Bit
Name
These registers become read-only when the configuration register 1 lock bit is set to 1. Any subsequent attempts to write to these
registers will fail.
–46–
REV. A
ADM1027
Table XVII. TEMP TRANGE/PWM Frequency Registers
Register Address
R/W
Description
Power-On Default
0x5F
0x60
0x61
Read/Write
Read/Write
Read/Write
Remote 1 TRANGE/PWM 1 Frequency
Local Temperature TRANGE/PWM 2 Frequency
Remote 2 TRANGE/PWM 3 Frequency
0xC4
0xC4
0xC4
Bit
Name
Read/Write
Description
<2:0>
FREQ
Read/Write
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>
Reserved
Read/Write
Reserved for future use.
<7:4>
RANGE
Read/Write
These bits determine the PWM duty cycle versus temperature slope for automatic
fan control.
0000 = 2oC
0001 = 2.5oC
0010 = 3.33oC
0011 = 4oC
0100 = 5oC
0101 = 6.67oC
0110 = 8oC
0111 = 10oC
1000 = 13.33oC
1001 = 16oC
1010 = 20oC
1011 = 26.67oC
1100 = 32oC (default)
1101 = 40oC
1110 = 53.33oC
1111 = 80oC
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers
will have no effect.
REV. A
–47–
ADM1027
Table XVIII. Register 0x62 – Enhance Acoustics Register 1 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<2:0>
ACOU
Read-Only
These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 will ramp gracefully at the rate
determined by these bits. This feature enhances the acoustics of the fan being driven by
the PWM1 output.
Time slot increase
000 = 1
001 = 2
010 = 3
011 = 5
100 = 8
101 = 12
110 = 24
111 = 48
Time for 33% to 100%
35 sec
17.6 sec
1.8 sec
7 sec
4.4 sec
3 sec
1.6 sec
0.8 sec
<3>
EN1
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM1 output. When
acoustic enhancement is enabled, fan spin-up time should be disabled.
<4>
Reserved
Read-Only
Reserved for future use.
<5>
MIN1
Read/Write
When the ADM1027 is in automatic fan control mode, this bit defines whether PWM 1
is off (0% duty cycle) or at PWM 1 minimum duty cycle when the controlling temperature
is below its TMIN – hysteresis value.
0 = 0% duty cycle below TMIN – hysteresis
1 = PWM 1 minimum duty cycle below TMIN – hysteresis
<6>
MIN2
Read/Write
When the ADM1027 is in automatic fan speed control mode, this bit defines whether
PWM 2 is off (0% duty cycle) or at PWM 2 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
Read/Write
When the ADM1027 is in automatic fan speed control mode, this bit defines whether
PWM 3 is off (0% duty cycle) or at PWM 3 minimum duty cycle when the controlling
temperature is below its TMIN – hysteresis value.
0 = 0% duty cycle below TMIN – hysteresis
1 = PWM 3 minimum duty cycle below TMIN – hysteresis
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
–48–
REV. A
ADM1027
Table XIX. Register 0x63 – Enhance Acoustics Register 2 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<2:0>
ACOU3
Read/Write
These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping
instantaneously to its newly calculated speed, PWM3 will ramp gracefully at the rate
determined by these bits. This effect enhances the acoustics of the fan being driven by the
PWM3 output.
Time slot increase
Time for 33% to 100%
000 = 1
35 sec
001 = 2
17.6 sec
010 = 3
11.8 sec
011 = 5
7 sec
100 = 8
4.4 sec
101 = 12
3 sec
110 = 24
1.6 sec
111 = 48
0.8 sec
<3>
EN3
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM3 output. When acoustic
enhancement is enabled, fan spin-up time should be disabled.
<6:4>
ACOU2
Read/Write
These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping
instantaneously to its newly calculated speed, PWM2 will ramp gracefully at the rate
determined by these bits. This effect enhances the acoustics of the fans being driven by
the PWM2 output.
Time slot increase
Time for 33% to 100%
000 = 1
35 sec
001 = 2
17.6 sec
010 = 3
11.8 sec
011 = 5
7 sec
100 = 8
4.4 sec
101 = 12
3 sec
110 = 24
1.6 sec
111 = 48
0.8 sec
<7>
EN2
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM2 output. When acoustic
enhancement is enabled, fan spin-up time should be disabled.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
–49–
ADM1027
Table XX. PWM Minimum Duty Cycle Registers
Register Address
R/W
Description
Power-On Default
0x64
0x65
0x66
Read/Write
Read/Write
Read/Write
PWM1 Minimum Duty Cycle
PWM2 Minimum Duty Cycle
PWM3 Minimum Duty Cycle
0x80 (50% duty cycle)
0x80 (50% duty cycle)
0x80 (50% duty cycle)
Bit
Name
Read/Write
Description
<7:0>
PWM Duty
Read/Write
These bits define the PWMMIN duty cycle for the PWMx output.
0x00 = 0% duty cycle (fan off)
0x40 = 25% duty cycle
0x80 = 50% duty cycle
0xFF = 100% duty cycle (fan full speed)
These registers become read-only when the ADM1027 is in automatic fan control mode.
Table XXI. TMIN Registers
Register Address
R/W
Description
Power-On Default
0x67
0x68
0x69
Read/Write
Read/Write
Read/Write
Remote 1 Temperature TMIN
Local Temperature TMIN
Remote 2 Temperature TMIN
0x5A (90oC)
0x5A (90oC)
0x5A (90oC)
These are the TMIN registers for each temperature channel. When the temperature measured exceeds TMIN, the appropriate fan will
run at minimum speed and increase with temperature according to TRANGE.
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers
will have no effect.
Table XXII. Therm Limit Registers
Register Address
R/W
Description
Power-On Default
0x6A
0x6B
0x6C
Read/Write
Read/Write
Read/Write
Remote 1 THERM Limit
Local THERM Limit
Remote 2 THERM Limit
0x64 (100oC)
0x64 (100oC)
0x64 (100oC)
If any temperature measured exceeds its THERM limit, all PWM outputs will 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 will remain at 100% until the
temperature drops below THERM limit – 4∞C .
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers
will have no effect.
Table XXIII. Temperature Hysteresis Registers
Register Address
R/W
Description
Power-On Default
0x6D
0x6E
Read/Write
Read/Write
Remote 1, Local Temperature Hysteresis
Remote 2 Temperature Hysteresis
0x44
0x40
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 will remain running at PWMMIN duty cycle until the temperature = TMIN – hysteresis.
Up to 15oC of hysteresis may be assigned to any temperature channel. Setting the hysteresis value lower than 4oC will cause the fan
to switch on and off regularly when the temperature is close to TMIN.
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers
will have no effect.
–50–
REV. A
ADM1027
Table XXIV. XOR Tree Test Enable
Register Address
R/W
Description
Power-On Default
0x6F
Read/Write
XOR Tree Test Enable Register
0x00
<0>
XEN
If the XEN bit is set to 1, the device enters the XOR tree test mode. Clearing the bit
removes the device from the XOR tree test mode.
<7:1>
Reserved
Unused. Do not write to these bits.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXV. Remote 1 Temperature Offset
Register Address
R/W
Description
Power-On Default
0x70
Read/Write
Remote 1 Temperature Offset
0x00
<7:0>
Read/Write
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 = 1oC.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXVI. Local Temperature Offset
Register Address
R/W
Description
Power-On Default
0x71
Read/Write
Local Temperature Offset
0x00
<7:0>
Read/Write
Allows a twos complement offset value to be automatically added to or subtracted from
the local temperature reading. LSB value = 1oC.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXVII. Remote 2 Temperature Offset
Register Address
R/W
Description
Power-On Default
0x72
Read/Write
Remote 2 Temperature Offset
0x00
<7:0>
Read/Write
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 = 1oC.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
–51–
ADM1027
Table XXVIII. Register 0x73 – Configuration Register 2 (Power-On Default = 0x00)
Bit
Name
R/W
Description
0
AIN1
Read/Write
1
AIN2
Read/Write
2
AIN3
Read/Write
3
AIN4
Read/Write
4
AVG
Read/Write
5
ATTN
Read/Write
6
CONV
Read/Write
AIN1 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN1 = 1, Pin 11 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
AIN2 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN2 = 1, Pin 12 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
AIN3 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN3 = 1, Pin 9 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
AIN4 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN4 = 1, Pin 14 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
AVG = 1, averaging on the temperature and voltage measurements is turned off. This
allows measurements on each channel to be made much faster.
ATTN = 1, the ADM1027 removes the attenuators from the 2.5 V, VCCP, 5 V, and
12 V inputs. The inputs can be used for other functions such as connecting up external
sensors.
CONV = 1, the ADM1027 is put into a single-channel ADC conversion mode.
In this mode, the ADM1027 can be made to read continuously from one input only,
e.g., Remote 1 temperature. It is also possible to start ADC conversions using an
external clock on Pin 11 by setting Bit 2 of Test Register 2 (Reg. 0x7F). This mode
could be useful if, for example, the user wanted to characterize/profile CPU temperature
quickly. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1
minimum high byte register (0x55).
Bits <7:5> Reg. 0x55
Channel Selected
000
2.5 V
001
VCCP
010
VCC (3.3 V)
011
5V
100
12 V
101
Remote 1 Temp
110
Local Temp
111
Remote 2 Temp
Reserved for future use
`
7
Reserved
Read/Write
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
–52–
REV. A
ADM1027
Table XXIX. Register 0x74 – Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00)
Bit
Name
R/W
Description
0
1
2
3
4
5
6
7
2.5 V
VCCP
VCC
5V
R1T
LT
R2T
OOL
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
A 1 masks SMBALERT for out-of-limit conditions on the 2.5 V channel.
A 1 masks SMBALERT for out-of-limit conditions on the VCCP channel.
A 1 masks SMBALERT for out-of-limit conditions on the VCC channel.
A 1 masks SMBALERT for out-of-limit conditions on the 5 V channel.
A 1 masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel.
A 1 masks SMBALERT for out-of-limit conditions on the local temperature channel.
A 1 masks SMBALERT for out-of-limit conditions on the Remote 2 temperature channel.
This bit needs to be set to 1 to allow masking in the Interrupt Mask Register 2. If this bit
is not set to 1, then setting a bit in Mask Register 2 will have no effect.
Table XXX. Register 0x75 – Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)
Bit
Name
R/W
Description
0
1
2
3
4
5
6
7
12 V
OVT
FAN1
FAN2
FAN3
FAN4
D1
D2
Read/Write
Read-Only
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
A 1 masks SMBALERT for out-of-limit conditions on the 12 V channel.
A 1 masks SMBALERT for overtemperature THERM conditions.
A 1 masks SMBALERT for a Fan 1 fault.
A 1 masks SMBALERT for a Fan 2 fault.
A 1 masks SMBALERT for a Fan 3 fault.
A 1 masks SMBALERT for a Fan 4 fault.
A 1 masks SMBALERT for a diode open or short on Remote 1 channel.
A 1 masks SMBALERT for a diode open or short on Remote 2 channel.
Table XXXI. Register 0x76 – Extended Resolution Register 1
Bit
Name
R/W
Description
<1:0>
<3:2>
<5:4>
<7:6>
2.5 V
VCCP
VCC
5V
Read-Only
Read-Only
Read-Only
Read-Only
2.5 V LSBs. Holds the 2 LSBs of the 10-bit 2.5 V measurement.
VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP measurement.
VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement.
5 V LSBs. Holds the 2 LSBs of the 10-bit 5 V measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table XXXII. Register 0x77 – Extended Resolution Register 2
Bit
Name
R/W
Description
<1:0>
<3:2>
12 V
TDM1
Read-Only
Read-Only
<5:4>
<7:6>
LTMP
TDM2
Read-Only
Read-Only
12 V LSBs. Holds the 2 LSBs of the 10-bit 12 V measurement.
Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature
measurement.
Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement.
Remote 2 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature
measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
REV. A
–53–
ADM1027
Table XXXIII. Register 0x78 – Configuration Register 3 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<0>
ALERT
Read/Write
<1>
<2>
<3>
Reserved
Reserved
FAST
Read/Write
Read/Write
Read/Write
<4>
<5>
<6>
<7>
DC1
DC2
DC3
DC4
Read/Write
Read/Write
Read/Write
Read/Write
ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an SMBALERT interrupt
output to indicate out-of-limit error conditions. Default = 0 = PWM2.
Reserved for future use.
Reserved for future use.
FAST = 1 enables fast TACH measurements on all channels. This increases the
TACH measurement rate from once per second, to once per 250 ms (4).
DC1 = 1 enables TACH measurements to be continuously made on TACH1.
DC2 = 2 enables TACH measurements to be continuously made on TACH2.
DC3 = 1 enables TACH measurements to be continuously made on TACH3.
DC4 = 1 enables TACH measurements to be continuously made on TACH4.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXXIV. Register 0x7B – Fan Pulses Per Revolution Register (Power On Default = 0x55)
Bit
Name
R/W
Description
<1:0>
FAN1
Read/Write
Sets number of pulses to be counted when measuring FAN1 speed. Can be used to
determine fan’s pulses per revolution number for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<3:2>
FAN2
Read/Write
Sets number of pulses to be counted when measuring FAN2 speed. Can be used to
determine fan’s pulses per revolution number for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<5:4>
FAN3
Read/Write
Sets number of pulses to be counted when measuring FAN3 speed. Can be used to
determine fan’s pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<7:6>
FAN4
Read/Write
Sets number of pulses to be counted when measuring FAN4 speed. Can be used to
determine fan’s pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
–54–
REV. A
ADM1027
Table XXXV. Register 0x7E – Manufacturer’s Test Register 1 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<7:0>
Reserved
Read-Only
Manufacturer’s Test Register. These bits are reserved for the manufacturer’s test
purposes and should NOT be written to under normal operation.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXXVI. Register 0x7F – Manufacturer’s Test Register 2 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<7:0>
Reserved
Read-Only
Manufacturer’s Test Register. These bits are reserved for the manufacturer’s test
purposes and should NOT be written to under normal operation.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
–55–
ADM1027
OUTLINE DIMENSIONS
24-Lead Shrink Small Outline Package [QSOP]
(RQ-24)
C02928–0–3/03(A)
Dimensions shown in millimeters and (inches)
0.341
BSC
24
13
0.154
BSC
1
0.236
BSC
12
PIN 1
0.069
0.053
0.065
0.049
0.010
0.004
0.025
BSC
COPLANARITY
0.004
0.012
0.008
SEATING
PLANE
0.010
0.006
8ⴗ
0ⴗ
0.050
0.016
COMPLIANT TO JEDEC STANDARDS MO-137AE
Revision History
Location
Page
3/03—Data Sheet changed from REV. 0 to REV. A.
Changes to Nulling Out Temperature Errors section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Changes to Tables XXV–XXVII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
–56–
REV. A