LM77

9-Bit + Sign Digital Temperature Sensor and Thermal

Window Comparator with Two-Wire Interface

General Description

The LM77 is a digital temperature sensor and thermal win-

dow comparator with an I

window-comparator architecture of the LM77 eases the de-

sign of temperature control systems conforming to the ACPI

(Advanced Configuration and Power Interface) specification

for personal computers. The open-drain Interrupt (INT) out-

put becomes active whenever temperature goes outside a

programmable window, while a separate Critical Tempera-

ture Alarm (T_CRIT_A) output becomes active when the

temperature exceeds a programmable critical limit. The INT

output can operate in either a comparator or event mode,

while the T_CRIT_A output operates in comparator mode

only.

The host can program both the upper and lower limits of the

window as well as the critical temperature limit. Program-

mable hysterisis as well as a fault queue are available to

minimize false tripping. Two pins (A0, A1) are available for

address selection. The sensor powers up with default thresh-

olds of 2˚C T

10˚C T

64˚C T

and 80˚C

T_CRIT.

The LM77’s 3.0V to 5.5V supply voltage range, Serial Bus

interface, 9-bit + sign output, and full-scale range of over

128˚C make it ideal for a wide range of applications. These

include thermal management and protection applications in

personal computers, electronic test equipment, office elec-

tronics, automotive, and HVAC applications.

Features

n

Window comparison simplifies design of ACPI

compatible temperature monitoring and control.

n

Serial Bus interface

n

Separate open-drain outputs for Interrupt and Critical

Temperature shutdown

n

Shutdown mode to minimize power consumption

n

Up to 4 LM77s can be connected to a single bus

n

9-bit + sign output; full-scale reading of over 128˚C

n

SOP and MSOP 8-lead packages

Key Specifications

3.0V to 5.5V

operating

250 µA (typ)

500 µA (max)

shutdown

5 µA (typ)

Accuracy

−10˚C to 65˚C

−25˚C to 100˚C

−55˚C to 125˚C

Applications

n

System Thermal Management

n

Personal Computers

n

Office Electronics

n

Electronic Test Equipment

n

Automotive

n

HVAC

July 2001

© 2001 National Semiconductor Corporation

DS100136

www.national.com