Rainbow Electronics LM85 - Manual

LM85
Hardware Monitor with Integrated Fan Control
General Description
The LM85, hardware monitor, has a two wire digital interface
compatible with SMBus 2.0. Using an 8-bit
Σ∆ ADC, the
LM85 measures:
– the temperature of two remote diode connected transis-
tors as well as its own die
– the V
CCP
, 2.5V, 3.3VSBY, 5.0V, and 12V supplies (inter-
nal scaling resistors).
To set fan speed, the LM85 has three PWM outputs that are
each controlled by one of three temperature zones. The
LM85 includes a digital filter that can be invoked to smooth
temperature readings for better control of fan speed. The
LM85 has four tachometer inputs to measure fan speed.
Limit and status registers for all measured values are in-
cluded.
Features
n 2-wire, SMBus 2.0 compliant, serial digital interface
n 8-bit Σ∆ ADC
n Monitors V
CCP
, 2.5V, 3.3 VSBY, 5.0V, and 12V
motherboard/processor supplies
n Monitors 2 remote thermal diodes
n Programmable autonomous fan control based on
temperature readings
n Noise filtering of temperature reading for fan control
n 1.0˚C digital temperature sensor resolution
n 3 PWM fan speed control outputs
n 4 fan tachometer inputs
n Monitors 5 VID control lines
n 24-pin QSOP package
n XOR-tree test mode
Key Specifications
n Voltage Measurement Accuracy ± 2% FS (max)
n Resolution 8-bits, 1˚C
n Temperature Sensor Accuracy ± 3˚C (max)
n Temperature Range
— LM85 Operational 0˚C to +85˚C
— Remote Temp Accuracy 0˚C to +125˚C
n Power Supply Voltage +3.0V to +3.6V
n Power Supply Current 0.53 mA
Applications
n Desktop PC
n Microprocessor based equipment
(e.g. Base-stations, Routers, ATMs, Point of Sales)
Block Diagram
20035301
March 2003
LM85
Hardware
Monitor
with
Integrated
Fan
Control
© 2003 National Semiconductor Corporation DS200353 www.national.com