
Intelligent Temperature Monitor
and Dual PWM Fan Controller
ADM1031
Rev. B
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FEATURES
Optimized for Pentium III
Reduced guardbanding software
Automatic fan speed control, independent of CPU
intervention after initial setup
Control loop to minimal acoustic noise and battery
consumption
Remote temperature measurement accurate to 1°C using
remote diode (two channels)
0.125°C resolution on external temperature channels
Local sensor with 0.25°C resolution
Pulse width modulation (PWM) fan control for two fans
Programmable PWM frequency and PWM duty cycle
Tach fan speed measurement (two channels)
Analog input to measure fan speed of 2-wire fans (using
sense resistor)
2-wire system management Bus (SMBus) with ARA
support
Overtemperature THERM output pin for CPU throttling
Programmable INT output pin
Configurable offsets for temperature channels 3 V to
5.5 V supply range
Shutdown mode to minimize power consumption
Limit comparison of all monitored values
APPLICATIONS
Notebook PCs, network servers, and personal computers
Telecommunications equipment
GENERAL DESCRIPTION
The ADM1031 is an ACPI-compliant, three-channel digital
thermometer and under/over temperature alarm for use in
personal computers and thermal management systems.
Optimized for the Pentium III, the part offers a 1°C higher
accuracy, which allows system designers to safely reduce
temperature guardbanding and increase system performance.
Two PWM fan control outputs control the speed of two cooling
fans by varying output duty cycle. Duty cycle values between
33% and 100% allow smooth control of the fans. The speed of
each fan can be monitored via TACH inputs, which can be
reprogrammed as analog inputs to allow speeds for 2-wire fans
to be measured via sense resistors. The device also detects a
stalled fan. A dedicated fan speed control loop provides control
without the intervention of CPU software. It also ensures that if
the CPU or system locks up, each fan can still be controlled
based on temperature measurements, and the fan speed is
adjusted to correct any changes in system temperature. Fan
speed can also be controlled using existing ACPI software.
Two inputs (four pins) are dedicated to remote temperature-
sensing diodes with an accuracy of ±1°C, and an on-chip
temperature sensor allows ambient temperature to be monitored.
The device has a programmable INT output to indicate error
conditions, and a dedicated FAN_FAULT output to signal fan
failure. The THERM pin is a fail-safe output for overtemperature
conditions that can be used to throttle a CPU clock.
FUNCTIONAL BLOCK DIAGRAM
SLAVE
ADDRESS
REGISTER
SERIAL BUS
INTERFACE
ADDRESS
POINTER
REGISTER
INTERRUPT
STATUS
REGISTERS
VALUE AND LIMIT
REGISTERS
OFFSET
REGISTERS
CONFIGURATION
REGISTERS
LIMIT
COMPARATOR
FAN FILTER
REGISTER
FAN
CHARACTERISTICS
REGISTER
ADD
SDA
SCL
GND
ADM1031
INT (SMBALERT)
THERM
FAN_FAULT
PWM_OUT1
D1+
D1–
VCC
ADC
FAN SPEED
CONFIG
REGISTER
FAN SPEED
COUNTER
ANALOG
MULTIPLEXER
PWM
CONTROLLERS
TACH SIGNAL
CONDITIONING
BANDGAP
TEMPERATURE
SENSOR
2.5V
BANDGAP
REFERENCE
TACH2/AIN2
TACH1/AIN1
PWM_OUT2
D2+
D2–
1
3
4
2
9
10
12
11
6
13
15
16
14
7
8
5
02402-001
Figure 1.
m
Fax: 781.461.3113
2005 Analog Devices, Inc. All rights reserved