Rainbow Electronics LM77 - Manual

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
2 C ™ Serial Bus interface. The
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
HYST
, 10˚C T
LOW
, 64˚C T
HIGH
, 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
j Supply Voltage 3.0V to 5.5V
j Supply Current operating 250 µA (typ)
500 µA (max)
shutdown 5 µA (typ)
j Temperature
Accuracy
−10˚C to 65˚C ± 1.5˚C(max)
−25˚C to 100˚C ± 2˚C(max)
−55˚C to 125˚C ± 3˚C(max)
Applications
n System Thermal Management
n Personal Computers
n Office Electronics
n Electronic Test Equipment
n Automotive
n HVAC
I2C ® is a registered trademark of Philips Corporation.
July 2001
LM77
9-Bit
+
Sign
Digital
T
emperature
Sensor
and
Thermal
W
indow
Comparator
with
T
wo-W
ire
Interface
© 2001 National Semiconductor Corporation DS100136 www.national.com