General Description
The TC649 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. 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, auto-shutdown mode or following a transient fault.
In normal fan operation, a pulse train is present at SENSE (Pin 5). The TC649 features Microchip Technology’s proprietary FanSenseTM technology for increasing system reliability. 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 Section 5.0, “Typical Applications”, for more information and system design guidelines.
The TC649 is available in the 8-pin PDIP, SOIC and MSOP packages and is available in the industrial and extended commercial temperature ranges.

FEATUREs
• Temperature Proportional Fan Speed for Acoustic Control and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range:
   - Fan Voltage Independent of TC649 Supply Voltage
   - Supports any Fan Voltage
• FanSense™ Fault Detection Circuits Protect
   Against Fan Failure and Aid System Testing
• Automatic Shutdown Mode for “Green” Systems
• Supports Low Cost NTC/PTC Thermistors
• Space Saving 8-Pin MSOP Package

APPLICATIONs
• Power Supplies
• Computers
• File Servers
• Portable Computers
• Telecom Equipment
• UPSs, Power Amps
• General Purpose Fan Speed Control