TC642 Application Circuit (Switch Mode Fan Speed ​​Controller)

TC642 Application Circuit (Switch Mode Fan Speed ​​Controller)

The TC642 is a switch-mode fan speed controller for controlling the speed of brushless DC fans. The device uses pulse width modulation (PWM) to achieve a proportional relationship between fan speed and temperature. By connecting a thermistor (or other voltage output temperature sensor) to the VIN input pin, the required control voltage of a typical fan of 1.25V to 2.65V and a PWM duty cycle of 0% to 100% can be provided. The minimum speed of the fan can be set by a simple resistor divider at the VMIN input. The integrated startup timer ensures reliable start-up of the fan motor during power-up, shutdown mode recovery, and restart after transient faults. Applying a logic low level to VMIN (pin 3) puts the fan into shutdown mode.

Microchip Technology's patented FanSenseTM technology is used in the TC642 to improve system reliability. When the fan is operating normally, the pulse loss detector monitors the pulse train on the SENSE pin (pin 5). When the fan stalls, opens or is disconnected, the TC642 will trigger a start timer. If the fault persists, the FAULT output pin will go low and the device will be locked in shutdown mode. When the PWM output duty cycle reaches 100%, the FAULT output pin will also output a low level, indicating that thermal runaway may occur. At this time, the fan continues to run. For more information on the device and system design guidelines, see Section 5.0 "Typical Applications".

The TC642 is available in standard 8-pin plastic DIP, SOIC and MSOP packages and is offered in commercial, extended commercial and industrial grades.