LM89

Temperature Sensor with Two-Wire Interface

General Description

The LM89 is an 11-bit digital temperature sensor with a

2-wire System Management Bus (SMBus) serial interface.

The LM89 accurately measures its own temperature as well

as the temperature of an external device, such as processor

thermal diode or diode-connected transistor such as the

2N3904. The temperature of any ASIC can be accurately

determined using the LM89 as long as a dedicated diode

(semiconductor junction) is available on the target die. The

for the series resistance and 1.0021 typical non-ideality fac-

Processor-M thermal diode. The LM89 has an Offset

register

to

allow

measuring

other

diodes

without

requiring

continuous

software

management.

Contact

new processors.

The LM89 and the LM89-1 have the same functions but

different SMBus slave addresses. This allows for one of

each to be on the bus at the same time.

Activation of the ALERT output occurs when any tempera-

ture goes outside a preprogrammed window set by the HIGH

and LOW temperature limit registers or exceeds the T_CRIT

temperature limit. Activation of the T_CRIT_A occurs when

any temperature exceeds the T_CRIT programmed limit.

The LM89 is pin and register compatible with the LM86,

LM90, Analog Devices ADM1032 and Maxim MAX6657/8.

Features

n

Accurately senses die temperature of remote ICs or

diode junctions

n

Offset register allows sensing a variety of thermal

diodes accurately

n

On-board local temperature sensing

n

10 bit plus sign remote diode temperature data format,

0.125 ˚C resolution

n

T_CRIT_A output useful for system shutdown

n

ALERT output supports SMBus 2.0 protocol

n

SMBus 2.0 compatible interface, supports TIMEOUT

n

8-pin MSOP and SOIC packages

Key Specifications

3.0 V to 3.6 V

0.8 mA (typ)

T

error)

T

T

T

Applications

n

Processor/Computer System Thermal Management

(e.g. Laptop, Desktop, Workstations, Server)

n

Electronic Test Equipment

n

Office Electronics

Simplified Block Diagram

20041501

December 2004

© 2004 National Semiconductor Corporation

DS200415

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