Microchip TC649 switchmode fan speed controller

The TC649 is a switchmode fan speed controller for use with brushless DC motors. Temperature-proportional speed control is accomplished using pulse width modulation (PWM). A thermistor (or other voltage output temperature sensor) connected to VIN furnishes the required control voltage of 1.25 to 2.65 V (typical) for 0% to 100% PWM duty cycle.

The product automatically suspends fan operation when measured temperature (VIN) is below a user-programmed minimum setting (VAS). An integrated start-up timer ensures motor start-up at turn-on, coming out of shutdown mode or following a transient fault.

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 product 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.

The controller is packaged in a space-saving 8-pin PDIP, MSOP or an SOIC package and is available in the industrial temperature range.