LM80 Serial Interface ACPI-Compatible Microprocessor System Hardware Monitor
June 1999
LM80
Serial Interface ACPI-Compatible Microprocessor System
Hardware Monitor
General Description
The LM80 provides 7 positive voltage inputs, temperature
measurement, fan speed measurement, and hardware
monitoring on an I
2
C
™
interface. The LM80 performs
WATCHDOG
™
comparisons of all measured values and an
open-drain interrupt output becomes active when any values
exceed programmed limits. A Chassis Intrusion input is pro-
vided to monitor and reset an external circuit designed to
latch a chassis intrusion event.
The LM80 is especially suited to interface to both linear and
digital temperature sensors. The 10 mV LSB and 2.56 volt
input range is ideal for accepting inputs from a linear sensor
such as the LM50. The BTI is used as an input from either
digital or thermostat sensors such as LM75 and LM56.
The LM80’s 2.8V to 5.75V supply voltage range, low supply
current, and I
2
C interface make it ideal for a wide range of
applications. These include hardware monitoring and protec-
tion applications in personal computers, electronic test
equipment, and office electronics.
n
WATCHDOG comparison of all monitored values
n
Separate input to show status in Interrupt Status
Register of additional external temperature sensors such
as the LM56 or LM75
n
I
2
C Serial Bus interface compatibility
n
Shutdown mode to minimize power consumption
n
Programmable RST_OUT/OS pin: RST_OUT provides a
Reset output; OS provides an Interrupt Output activated
by an Overtemperature Shutdown event
Key Specifications
n
Voltage monitoring Error
n
Temperature Error
−25˚C to +125˚C
n
Supply Voltage Range
n
Supply Current
n
ADC Resolution
n
Temperature Resolution
Operating:
Shutdown:
±
1% (max)
±
3˚C (max)
2.8V to
5.75V
0.2 mA typ
15 µA typ
8 Bits
0.5˚C
Features
Temperature sensing
7 positive voltage inputs
2 programmable fan speed monitoring inputs
10 mV LSB and 2.56V input range accepts outputs from
linear temperature sensors such as the LM50
n
Chassis Intrusion Detector input
n
n
n
n
Applications
n
System Thermal and Hardware Monitoring for Servers
and PCs
n
Office Electronics
n
Electronic Test Equipment and Instrumentation
Typical Application
DS100040-1
#
Indicates Active Low (“Not”)
TRI-STATE
®
is a registered trademark of National Semiconductor Corporation.
WATCHDOG
™
is a trademark of National Semiconductor Corporation.
I2C
®
is a registered trademark of the Philips Corporation.
© 1999 National Semiconductor Corporation
DS100040
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
