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ADM1021
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 1998
Low Cost Microprocessor
System Temperature Monitor
FUNCTIONAL BLOCK DIAGRAM
ON-CHIP TEMP.
SENSOR
ANALOG MUX
8-BIT 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
ADM1021
TEST V
DD
NC GND NC NC TEST
D+
D–
ALERT
STBY
SDATA SCLK ADD0 ADD1GND
FEATURES
Improved Replacement for MAX1617
On-Chip and Remote Temperature Sensing
No Calibration Necessary
18C Accuracy for On-Chip Sensor
38C Accuracy for Remote Sensor
Programmable Over/Under Temperature Limits
Programmable Conversion Rate
2-Wire SMBus Serial Interface
Supports System Management Bus (SMBus™) Alert
70 mA Max Operating Current
3 mA 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 ADM1021 is a two-channel digital thermometer and under/
over temperature alarm, intended for use in personal computers
and other systems requiring thermal monitoring and manage-
ment. The device can measure the temperature of a micropro-
cessor using a diode-connected PNP transistor, which may be
provided on-chip in the case of the Pentium
®
II or similar pro-
cessors, 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 ADM1021 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.
SMBus is a trademark and Pentium is a registered trademark of Intel Corporation.