The LM81 is a highly integrated data acquisition system for hardware monitoring of servers, Personal Computers, 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 compatible with SMBus. Serial Bus Timing Diagram

• Temperature Sensing
• 6 Positive Voltage Inputs with Scaling Resistors to Monitor +5V, +12V, +3.3V, +2.5V, Vccp Power Supplies Directly
• 8-Bit DAC Output for Controlling Fan Speed
• 2 Fan Speed Monitoring Inputs
• Chassis Intrusion Detector Input
• WATCHDOG Comparison of all Monitored Values
• SMBus 1.0 (LM81C) and 1.1 (LM81B) Serial Bus Interface Compatibility
• LM81B has Improved Voltage Monitoring Accuracy
• VID0-VID4 Monitoring Inputs

Key Specifications

• Voltage Monitoring Error: +2% or ±1.2% (max)
• Temperature Error
  • −40?C to +125?C ± 3?C (max)
• Supply Voltage Range: 2.8V to 3.8V
• Supply Current: 0.4 mA (typ)
• ADC and DAC Resolution: 8 Bits
• Temperature Resolution: 0.5°C

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