Dual SMBus? PWM Fan Speed Controllers With Fan Fault Detection

TC654 The TC654 and TC655 are PWM mode fan speed con- trollers with FanSense technology for use with brush- less DC fans. These devices implement temperature proportional fan speed control which lowers acoustic fan noise and increases fan life. The voltage at V IN (Pin 1) represents temperature and is typically pro- vided by an external thermistor or voltage output tem- perature Sensor The PWM output (V ) is adjusted OUT between 30% and 100%, based on the voltage at V . IN The PWM duty cycle CAN also be programmed via SMBus to allow fan speed control without the need for an external thermistor. If V is not connected, the IN TC654 TC655 will start driving the fan at a default duty cycle of 39.33%. See Section 4.3, "Fan Startup", for more details. By Microchip Technology Inc.