TC642B/TC647B PWM Fan Speed Controllers With Minimum Fan Speed, Fan Restart and FanSense Technology for Fault Detection Features Description Temperature-Proportional Fan Speed for Acoustic The TC642B/TC647B devices are new versions of the Noise Reduction and Longer Fan Life existing TC642/TC647 fan speed controllers. These devices are switch mode, fan speed controllers that Efficient PWM Fan Drive incorporate a new fan auto-restart function. Tempera- 3.0V to 5.5V Supply Range: ture-proportional speed control is accomplished using - Fan Voltage Independent of TC642B/TC647B pulse width modulation. A thermistor (or other voltage Supply Voltage input output temperature sensor) connected to the V IN - Supports any Fan Voltage supplies the required control voltage of 1.20V to 2.60V Fault Detection Circuit Protects FanSense (typical) for 0% to 100% PWM duty cycle. Minimum fan Against Fan Failure and Aids System Testing speed is set by a simple resistor divider on the V MIN Shutdown Mode forGree Systems input. An integrated Start-Up Timer ensures reliable motor start-up at turn-on, coming out of shutdown Supports Low Cost NTC/PTC Thermistors mode or following a transient fault. A logic-low applied Over-Temperature Indication (TC642B only) to V (pin 3) causes fan shutdown. MIN Fan Auto-Restart The TC642B and TC647B also feature Microchip Space-Saving 8-Pin MSOP Package Technology s proprietary FanSense technology for increasing system reliability. In normal fan operation, a Applications pulse train is present at SENSE (pin 5). A missing- Personal Computers & Servers pulse detector monitors this pin during fan operation. A stalled, open or unconnected fan causes the TC642B/ LCD Projectors TC647B device to turn the V output on full (100% OUT Datacom & Telecom Equipment duty cycle). If the fault persists (a fan current pulse is Fan Trays not detected within a 32/f period), the FAULT output File Servers goes low. Even with the FAULT output low, the V OUT General Purpose Fan Speed Control output is on full during the fan fault condition in order to attempt to restart the fan. FAULT is also asserted if the Package Types PWM reaches 100% duty cycle (TC642B only), indicat- ing that maximum cooling capability has been reached MSOP, PDIP, SOIC and a possible overheating condition exists. The TC642B and TC647B devices are available in 8-pin V 8 V plastic MSOP, SOIC and PDIP packages. The specified 1 IN DD temperature range of these devices is -40 to +85C. 2 C 7 V F OUT TC642B TC647B V 3 6 FAULT MIN GND 4 5 SENSE 2002-2013 Microchip Technology Inc. DS21756C-page 1TC642B/TC647B Functional Block Diagram TC642B/TC647B V OTF V V IN DD Note Note: The V comparator OTF is for the TC642B device only. Control Logic C F 3xT PWM V Timer OUT Clock Start-up Generator Timer V MIN FAULT Missing V SHDN Pulse Detect SENSE 10 k GND 70 mV (typ) DS21756C-page 2 2002-2013 Microchip Technology Inc.
