The TC642B is a new version of the existing TC642 fan speed controller. This device is a switch mode fan speed controller, which incorporates a new fan auto restartfunction. Temperature proportional speed control is accomplished using pulse width modulation. A thermistor (or other voltage output temperature sensor) connected to the VIN input supplies the required control voltage of 1.2V to 2.6V (typical) for 0% to 100% PWM duty cycle. Minimum fan speed is set by a simple resistor divideron the VMIN input. An integrated Start-Up Timer ensures reliable fan motor start-up at turn-on, coming out of shutdown mode, or following a transient fault. A logic low applied to VIN, pin 1, causes fan shutdown.

The TC642B 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. A missing-pulse detector monitors this pin during fan operation. A stalled, open, or unconnected fan causes the TC642B device to turn the VOUT output on full (100% duty cycle). If the fan fault persists (a fan current pulse is not detected within a 32/F period), the FAULT output goes low. Even with the FAULT output low, the VOUT output is on full during the fan fault condition in order to try and restart the fan. The FAULT signal is also asserted if the PWM reaches 100% duty cycle, indicating that maximum cooling capability has been reached and a possible thermal runaway condition exists.

   Temperature Proportional Fan Speed for Acoustic Control and Longer Fan Life

  FanSense™ Protects Against Fan Failure

  Efficient PWM Drive

  Shutdown Mode for "Green" Systems

  3.0V to 5.5V Supply Range

  Fan Voltage Independent of Supply Voltage – Supports Any Fan Voltage

  Supports Low Cost NTC/PTC Thermistors

  Fan Auto-Restart

  Over-Temperature Indication