LM87 Datasheet | National Semiconductor

Description The LM87 is a highly integrated data acquisition system for hardware monitoring of servers, Personal puters, or virtually any microprocessor-based system. In a PC, the LM87 can be used to monitor power supply voltages, motherboard and processor temperatures, and fan speeds. Actual values for these inputs can be read at any time. Programmable WATCHDOG™ limits in the LM87 activate a fully programmable and maskable interrupt system with two outputs (INT# and THERM#). The LM87 has an on-chip digital output temperature sensor with 8-bit resolution as well as the capability of monitoring 2 external diode temperatures to 8-bit resolution, an 8 channel analog input ADC with 8-bit resolution and an 8-bit DAC. A channel on the ADC measures the supply voltage applied to the LM87, nominally 3.3 V. Two of the ADC inputs can be redirected to a counter that can measure the speed of up to 2 fans. A slow speed Σ∆ ADC architecture allows stable measurement of signals in an extremely noisy environment. The DAC, with a 0 to 2.5 V output voltage range, can be used for fan speed control. Additional inputs are provided for Chassis Intrusion detection circuits, and VID monitor inputs. The VID monitor inputs can also be used as IRQ inputs if VID monitoring is not required. The LM87 has a Serial Bus interface that is patible with SMBus™ and I2C™. n n n n n n n 2 inputs selectable for fan speed or voltage monitoring 8-bit DAC output for controlling fan speed Chassis Intrusion Detector input WATCHDOG™ parison of all monitored values SMBus or I2C Serial Bus interface patibility VID0-VID4 or IRQ0-IRQ4 monitoring inputs On chip temperature sensor Key Specifications n Voltage Monitoring Error n External Temperature Error n Internal Temperature Error - 40 ˚C to +125 ˚C n Supply Voltage Range n Supply Current n ADC and DAC Resolution n Temperature Resolution ± 2 % (max) ± 4 ˚C (max) ± 3 ˚C (typ) 2.8 to 3.8 V 0.7 m A (typ) 8 Bits 1.0 ˚C Applications n System Thermal and Hardware...