LM81 Datasheet | National Semiconductor

Description The LM81 is a highly integrated data acquisition system for hardware monitoring of servers, Personal puters, or virtually any microprocessor-based system. In a PC, the LM81 can be used to monitor power supply voltages, temperatures, 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 patible with SMBus™. n n n n n 2 fan speed monitoring inputs Chassis Intrusion Detector input WATCHDOG™ parison of all monitored values SMBus Serial Bus interface patibility VID0-VID4 monitoring inputs Key Specifications n Voltage monitoring Error n Temperature Error - 40˚C to +125˚C n Supply Voltage Range n Supply Current n ADC and DAC Resolution n Temperature Resolution Operating: +2% (max) ± 3˚C (max) 2.8V to 3.8V 0.4 m A (typ) 8 Bits 0.5˚C Features n Temperature sensing n 6 positive voltage inputs with scaling resistors for monitoring +5V, +12V, +3.3V, +2.5V, Vccp power supplies directly n 8-bit DAC output for controlling fan speed 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”) TRI-STATE ® is a registered trademark of National Semiconductor Corporation. WATCHDOG™ is a trademark of National Semiconductor Corporation. SMBus™ is a trademark of the Intel Corporation. © 1999 National Semiconductor...