PWM Fan Speed Controllers With Auto-Shutdown, Fan Restart And FanSense? Technology For Fault Detection

TC649B The TC646B TC648B TC649B devices are new ver- sions of the existing TC646 TC648 TC649 fan speed controllers. These devices are switch-mode fan speed controllers that incorporate a new fan auto-restart func- tion. Temperature-proportional speed control is accom- plished using pulse width modulation. A thermistor (or other voltage output temperature sensor) connected to the V input supplies the required control voltage of IN 1.20V to 2.60V (typical) for 0% to 100% PWM duty cycle. The auto-shutdown threshold/temperature is set by a simple resistor divider on the V input. An inte- AS grated Start-Up Timer ensures reliable fan motor start- up at turn-on, coming out of shutdown mode, auto- shutdown mode or following a transient fault. A Logic low applied to V (pin 1) causes fan shutdown. IN By Microchip Technology Inc.