REV. A

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a

ADM1028

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

© Analog Devices, Inc., 2002

Remote Thermal Diode

Monitor with Linear Fan Control

FUNCTIONAL BLOCK DIAGRAM

2.5V

BANDGAP

REFERENCE

ANALOG

SIGNAL

CONDITIONING

ALERT

STATUS

REGISTER

ADC

ADM1028

R_OFF

R_RST

D+

D–

SDA

SCL

RST

10k

FAN_SPD/NTEST_IN

INT

FAN_OFF

SERIAL BUS

INTERFACE

LIMIT

COMPARATORS

INTERRUPT

STATUS

REGISTERS

MASK

GATING

CONFIGURATION

REGISTER

INT MASK

REGISTER

ANALOG O/P

REGISTER,

COUNTER

AND 8-BIT DAC

VALUE AND

LIMIT

REGISTERS

POWER-ON

RESET

FAN_SPD SHUTOFF

AND R_OFF RESET

10k

THERMA/NTEST_OUT

AUXRST

RESET

THERMB

GPI

GND

ADDRESS

POINTER

REGISTER

REMOTE

FUNCTION

REGISTER

FEATURES

On-Chip Temperature Sensor

External Temperature Measurement with Remote Diode

Interrupt and Over-Temperature Outputs

Fault-Tolerant Fan Control with Auto Hardware Trip Point

Remote Reset and Power-Down Functions

LDCM Support

System Management Bus (SMBus) Communications

Standby Mode to Minimize Power Consumption

Limit Comparison of all Monitored Values

DAC Output for Linear Fan Speed Control

Ramp Rate Register for Control of Rate of Change of

Fan Speed, Reduction of Fan Acoustics

APPLICATIONS

Network Servers and Personal Computers

Microprocessor-Based Office Equipment

Test Equipment and Measuring Instruments

GENERAL DESCRIPTION

The ADM1028 is a low-cost temperature monitor and fan

controller for microprocessor-based systems. The temperature

of a remote sensor diode may be measured, allowing monitoring

of processor temperature in single processor systems. An on-chip

temperature sensor monitors ambient system temperature.

Measured values can be read out via the System Management

Bus, and values for limit comparisons can be programmed in

over the same serial bus.

The ADM1028 also contains a DAC for fan speed control. An

automatic hardware temperature trip point is provided and the fan

will be driven to full speed if it is exceeded. A Ramp Rate Register

is provided to control the rate with which fan speed is increased or

decreased. This is to eliminate sudden changes in fan speed,

thereby reducing fan acoustics and prolonging the fan’s life.

Finally, the chip has remote reset and power-down functionality,

allowing it to be remotely shut down via the SMBus.

The ADM1028’s 3.0 V to 5.5 V supply voltage range, low

supply current, and SMBus make it ideal for a wide range of

applications. These include hardware monitoring applications

in PCs, electronic test equipment, and office electronics.