The LM81 is a highly integrated data acquisition system for hardware monitoring of servers, Personal Computers, or virtually any microprocessor-based system. It can be used to monitor power supply voltages, temperatures, and fan speeds in a PC. 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™.
The LM81 is a highly integrated data acquisition system for hardware monitoring of servers, PCs and other microprocessor‑based systems. It provides voltage, temperature and fan‑speed monitoring, a programmable watchdog, and an SMBus‑compatible serial interface. The device includes an on‑chip digital temperature sensor, a 6‑channel 8‑bit ADC, an 8‑bit DAC, and fan tachometer inputs.
The handbook contains detailed pin descriptions, absolute maximum ratings, DC and AC electrical characteristics, serial‑bus timing, physical dimensions, and typical application circuits. It also lists ordering information, package options, and a life‑support policy disclaimer.
| Supply Voltage Range | 2.8 V to 3.8 V |
|---|---|
| Supply Current (typical) | 0.4 mA |
| ADC Resolution | 8 bits |
| Temperature Resolution (9‑bit mode) | 0.5 °C |
The LM81 uses a serial bus interface that is compatible with SMBus 1.0 and 1.1.
The LM81 provides six analog inputs for monitoring voltages such as +5 V, +12 V, +3.3 V, +2.5 V, Vecp and VID signals.
The LM81 includes programmable watchdog limits that can trigger an interrupt with two outputs (INT and T_CRIT_).