Rainbow Electronics LM81 - Manual

LM81
Serial Interface ACPI-Compatible Microprocessor System
Hardware Monitor
General Description
The LM81 is a highly integrated data acquisition system for
hardware monitoring of servers, Personal Computers, or
virtually any microprocessor-based system. In a PC, the
LM81 can be used to monitor power supply voltages, tem-
peratures, and fan speeds. Actual values for these inputs
can be read at any time. Programmable WATCHDOG limits
in the LM81 activate a fully programmable and maskable
interrupt system with two outputs (INT and T_CRIT_).
The LM81 has an on-chip digital output temperature sensor
with 9-bit or 12-bit resolution, a 6 analog input ADC with 8-bit
resolution and an 8-bit DAC. Two fan tachometer outputs
can be measured with the LM81’s FAN1 and FAN2 inputs.
The DAC, with a 0 to 1.25V output voltage range, can be
used for fan speed control. Additional inputs are provided for
Chassis Intrusion detection circuits, and VID monitor inputs.
The LM81 has a Serial Bus interface that is compatible with
SMBus
™ .
Features
n Temperature sensing
n 6 positive voltage inputs with scaling resistors to monitor
+5V, +12V, +3.3V, +2.5V, Vccp power supplies directly
n 8-bit DAC output for controlling fan speed
n 2 fan speed monitoring inputs
n Chassis Intrusion detector input
n WATCHDOG comparison of all monitored values
n SMBus 1.0 (LM81C) and 1.1 (LM81B) Serial Bus
interface compatibility
n LM81B has improved voltage monitoring accuracy
n VID0-VID4 monitoring inputs
Key Specifications
j Voltage Monitoring Error +2% or ± 1.2% (max)
j Temperature Error
−40˚C to +125˚C ± 3˚C (max)
j Supply Voltage Range 2.8V to 3.8V
j Supply Current 0.4 mA (typ)
j ADC and DAC Resolution 8 Bits
j Temperature Resolution 0.5˚C
Applications
n System Thermal and Hardware Monitoring for Servers
and PCs
n Office Electronics
n Electronic Test Equipment and Instrumentation
Typical Application
DS100072-1
# Indicates Active Low (“Not”)
February 2002
LM81
Serial
Interface
ACPI-Compatible
Microprocessor
System
Hardware
Monitor
© 2002 National Semiconductor Corporation DS100072 www.national.com