The ADM1031 is an ACPI-compliant three-channel digital thermometer and under/over temperature alarm, for use in personal computers and thermal management systems. Optimized for the Pentium III, the higher 1C accuracy offered allows systems designers to safely reduce temperature guardbanding and increase system performance. Two Pulsewidth Modulated (PWM) Fan Control outputs control the speed of two cooling fans by varying output duty cycle. Duty cycle values between 33%-100% allow smooth control of the fans. The speed of each fan can be monitored via TACH inputs. The TACH inputs may be reprogrammed as analog inputs, allowing fan speeds for 2-wire fans to be measured via sense resistors. The device will also detect a stalled fan. A dedicated Fan Speed Control Loop provides control even without the intervention of CPU software. It also ensures that if the CPU or system locks up, each fan can still be controlled based on temperature measurements, and the fan speed adjusted to correct any changes in system temperature. Fan speed may also be controlled using
existing ACPI software. Two inputs (four pins) are dedicated to remote temperature-sensing diodes with an accuracy of +-1C, and an on-chip temperature sensor allows ambient temperature to be monitored. The device has a programmable INT output to indicate error conditions. There is a dedicated FAN_FAULT output to signal fan failure. The THERM pin is a fail-safe output for overtemperature conditions that can be used to throttle a CPU clock.