REV.A
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a
ADM1021A
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., 2001
FUNCTIONAL BLOCK DIAGRAM
ON-CHIP TEMP.
SENSOR
ANALOG MUX
A-TO-D
CONVERTER
LOCAL TEMPERATURE
VALUE REGISTER
REMOTE TEMPERATURE
VALUE REGISTER
BUSY RUN/STANDBY
LOCAL TEMPERATURE
LOW LIMIT COMPARATOR
STATUS REGISTER
REMOTE TEMPERATURE
LOW LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH LIMIT COMPARATOR
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERSION RATE
REGISTER
LOCAL TEMPERATURE
LOW LIMIT REGISTER
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
REMOTE TEMPERATURE
LOW LIMIT REGISTER
LOCAL TEMPERATURE
HIGH LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH LIMIT REGISTER
CONFIGURATION
REGISTER
INTERRUPT
MASKING
EXTERNAL DIODE OPEN-CIRCUIT
SMBUS INTERFACE
ADM1021A
NC V
DD
NC GND NC NC NC
D+
D–
ALERT
STBY
SDATA SCLK ADD0 ADD1GND NC = NO CONNECT
Low-Cost Microprocessor
System Temperature Monitor*
FEATURES
Alternative to the ADM1021
On-Chip and Remote Temperature Sensing
No Calibration Necessary
1H11543C Accuracy for On-Chip Sensor
3H11543C Accuracy for Remote Sensor
Programmable Over/Under Temperature Limits
Programmable Conversion Rate
2-Wire SMBus Serial Interface
Supports System Management Bus (SMBus) Alert
200 H9262A Max Operating Current
1 H9262A Standby Current
3 V to 5.5 V Supply
Small 16-Lead QSOP Package
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecomms Equipment
Instrumentation
PRODUCT DESCRIPTION
The ADM1021A is a two-channel digital thermometer and under/
over temperature alarm, intended for use in personal computers
and other systems requiring thermal monitoring and management.
The device can measure the temperature of a microprocessor
using a diode-connected PNP transistor, which may be provided
on-chip in the case of the Pentium
®
III or similar processors,
or can be a low-cost discrete NPN/PNP device such as the
2N3904/2N3906. A novel measurement technique cancels out
the absolute value of the transistor’s base emitter voltage, so
that no calibration is required. The second measurement chan-
nel measures the output of an on-chip temperature sensor, to
monitor the temperature of the device and its environment.
The ADM1021A communicates over a two-wire serial interface
compatible with SMBus

standards. Under and over temperature
limits can be programmed into the devices over the serial bus,
and an ALERT output signals when the on-chip or remote
temperature is out of range. This output can be used as an inter-
rupt, or as an SMBus alert.
*Patents Pending.
Pentium is a registered trademark of Intel Corporation.