The TC647B is a new version of the existing TC647 fan speed controller. This device is a switch mode fan speed controller, which incorporates a new fan auto restart function. 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 1.20V to 2.60V (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 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 TC647B also features Microchip Technology's proprietary FanSense™ technology for increasing system reliability. In normal fan operation, a pulsetrain is present at SENSE, pin 5. A missing-pulse detector monitors this pin during fan operation. A stalled, open, or unconnected fan causes the TC647B 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.

   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