• Temperature Proportional
• Fan Speed for Acoustic Control and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range
• Supports Any Fan Voltage!
• Fault Detection Circuits Protect Against Fan Failure and Aid System Testing
• Automatic Shutdown Mode for "Green" Systems
• Supports Low Cost NTC/PTC Thermistors

The TC649 is a switch mode 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 1.25V to 2.65V (typical) for 0% to 100% PWM duty cycle. The TC649 automatically suspends fan operation when measured temperature (VIN) is below a user-programmed minimum setting (VAS). An integrated Start-Up Timer ensures reliable 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 TC649 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. See the Applications section for more information and system design guidelines. The TC649 is packaged in a space-saving 8-Pin PDIP, MSOP or a SOIC package and is available in the industrial temperature range.