The TC642 is a switch mode fan speed controller for use with brushless DC motors. Temperature proportional speed control is accomplished using pulse width modulation. A thermistor (or other voltage output temperature sensor) connected to the VIN input furnishes the required control voltage of 1.25Vto 2.65V (typical) for 0% to 100% PWM duty cycle. Minimum fan speed is set by a simple resistor divider on the VMIN input. An integrated Start-Up Timer ensures reliable motor start-up at turn-on, coming out of Shutdown Mode, or following a transient fault.A logic low applied to VMIN, pin 3, causes fan shutdown.The TC642 also features Microchip Technology's proprietary FanSense? technology for increasing system reliability.In normal fan operation, a pulse train is present at SENSE, pin 5, indicating normal operation. A missing-pulse detector monitors this pin during normal fan operation. A stalled, open, or unconnected fan causes the TC642 to trigger its start-up timer once. If the fault persists, the FAULT output goes low, and the device is latched in its Shutdown Mode. FAULT is also asserted if the PWM reaches 100%

  Temperature Proportional

  Fan Speed for Acoustic Control and Longer Fan Life

  Efficient PWM Fan Drive

  3.0V 5.5V Supply Range

  Fan Voltage Independent of TC642 Supply Voltage

  Supports Any Fan Voltage!

  FanSense? Fault Detection Circuits Protect Against Fan Failure and Aid

  System Testing

  Shutdown Mode for "Green" Systems

  Supports Low Cost NTC/PTC Thermistors