The TC642 is a switch mode fan speed controller for use with brushless DC fans. Temperature proportional speed control is accomplished using pulse width modulation (PWM). A thermistor (or other voltage output temperature sensor) connected to the VIN input furnishes the required control voltage of 1.25V to 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 FanSenseTM 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 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% duty cycle, indicating a possible thermal runaway situation, although the fan continues to run. See Section 5.0, "Typical Applications", for more information and system design guidelines. The TC642 is available in the standard 8-pin plastic DIP, SOIC and MSOP packages and is available in the commercial, extended commercial and industrial temperature ranges.