General Description

The TC646 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 TC646

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.

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 TC646 Supply Voltage

- Supports any Fan Voltage

• FanSense™Fault Detection Circuits Protect Against Fan Failure and Aid System Testing

• Shutdown Mode for "Green" Systems

• Supports Low Cost NTC/PTC Thermistors

• Space Saving 8-Pin MSOP Package

• Over-temperature Indication

Applications

• Power Supplies

• Computers

• File Servers

• Portable Computers

• Telecom Equipment

• UPS, Power Amps

• General Purpose Fan Speed Control