Rainbow Electronics LM76 - Manual

LM76
± 0.5˚C, ± 1˚C, 12-Bit + Sign Digital Temperature Sensor
and Thermal Window Comparator with Two-Wire
Interface
General Description
The LM76 is a digital temperature sensor and thermal win-
dow comparator with an I
2 C ™ Serial Bus interface with an
accuracy of ± 1˚C. This accuracy for the LM76CHM is speci-
fied for a −10˚C to 45˚C temperature range, while for the
LM76CNM the temperature range is 70˚C to 100˚C. The
LM76CHM is specified with an accuracy
± 0.5˚C at 25˚C. The
window-comparator architecture of the LM76 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 LM76’s 3.3V and 5.0V supply voltage, Serial Bus inter-
face, 12-bit + sign output, and full-scale range of over 127˚C
make it ideal for a wide range of applications. These include
thermal management and protection applications in personal
computers, electronic test equipment, office electronics and
bio-medical 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 LM76s can be connected to a single bus
n 12-bit + sign output; full-scale reading of over 127˚C
Key Specifications
j Supply Voltage 3.3V or 5.0V
j Supply Current operating 250 µA (typ)
450 µA (max)
shutdown 8 µA (max)
j Temperature
Accuracy
+25˚C ± 0.5˚C(max)
−10˚C to +45˚C ± 1.0˚C(max)
70˚C to 100˚C ± 1.0˚C(max)
j Resolution 0.0625˚C
Applications
n System Thermal Management
n Personal Computers
n Office Electronics
n HVAC
I2C ® is a registered trademark of Philips Corporation.
January 2000
LM76
±
0.5˚C,
±
1˚C,
12-Bit
+
Sign
Digital
T
emperature
Sensor
and
Thermal
W
indow
Comparator
with
T
wo-W
ire
Interface
© 2001 National Semiconductor Corporation DS101015 www.national.com