LM40 Datasheet, PDF (1/27 Pages) National Semiconductor (TI) – Hardware Monitor with Dual Thermal Diodes and SensorPath Bus

May 2004
LM40
Hardware Monitor with Dual Thermal Diodes and
SensorPath^™ Bus
General Description
The LM40 is a hardware monitor that measures 3 tempera-
ture zones, 5 voltages and has a single-wire interface com-
patible with National Semiconductor’s SensorPath bus. Sen-
sorPath data is pulse width encoded, thereby allowing the
LM40 to be easily connected to many general purpose
micro-controllers. Several National Semiconductor Super I/O
products include a fully integrated SensorPath master, that
when connected to the LM40 can realize a hardware monitor
function that includes limit checking for measured values,
autonomous fan speed control and many other functions.
The LM40 measures the temperature of its own die as well
as two external devices such as a processor thermal diode
or a diode connected transistor. The LM40 can resolve tem-
peratures up to 255˚C and down to -256˚C. The operating
temperature range of the LM40 is 0˚C to +125˚C. Using Σ∆
ADC it measures +1.2V, +2.5V, +3.3V, +5V and +12V analog
input voltages with internal scaling resistors.The address
programming pin allows two LM40s to be placed on one
SensorPath bus.
Features
n SensorPath Interface
— 2 hardware programmable addresses
n Voltage Monitoring
— 9-bit Σ∆ ADC
— Internal scaling resistors for all inputs
— Monitors +1.2V, +2.5 V, +3.3 V, +5 V and +12 V
n Temperature Sensing
— 2 remote diode temperature sensor zones
— Internal local temperature zone
— 0.5 ˚C resolution
— Measures temperatures up to 140 ˚C
n 14-lead TSSOP package
Key Specifications
n Voltage Measurement Accuracy
n Temperature Sensor Accuracy
n Temperature Range:
— LM40 junction
— Remote Temp Accuracy
n Power Supply Voltage
n Average Power Supply Current
n Conversion Time (all Channels)
±2 % (max)
±3 ˚C (max)
0 ˚C to +85 ˚C
0 ˚C to +100 ˚C
+3.0 V to +3.6 V
0.5 mA (typ)
29.6ms to 1456ms
Applications
n Microprocessor based equipment
(Motherboards, Video Cards, Base-stations, Routers,
ATMs, Point of Sale, …)
n Power Supplies
Typical Application
SensorPath™ is a trademark of National Semiconductor Corporation
© 2004 National Semiconductor Corporation DS200684
20068401
www.national.com