Description
The TC642B/TC647B devices are new versions of the existing TC642/TC647 fan speed controllers. These devices are switch mode, fan speed controllers that incorporate a new fan auto-restart function. Temperature-proportional speed control is accomplished using pulse width modulation. A thermistor (or other voltage output temperature sensor) connected to the VIN input supplies the required control voltage of 1.20V to 2.60V (typical) for 0% to 100% PWM duty cycle. Minimum fan speed is set by a simple resistor divider on the VMIN input. An integrated Start-Up Timer ensures reliable motor start-up at turn-on, coming out of shutdown mode or following a transient fault. A logic-low applied to VMIN (pin 3) causes fan shutdown.

Features
• Temperature-Proportional Fan Speed for Acoustic Noise Reduction and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range:
    - Fan Voltage Independent of TC642B/TC647B Supply Voltage
    - Supports any Fan Voltage
• FanSense™ Fault Detection Circuit Protects Against Fan Failure and Aids System Testing
• Shutdown Mode for "Green" Systems
• Supports Low Cost NTC/PTC Thermistors
• Over-Temperature Indication (TC642B only)
• Fan Auto-Restart
• Space-Saving 8-Pin MSOP Package

Applications
• Personal Computers & Servers
• LCD Projectors
• Datacom & Telecom Equipment
• Fan Trays
• File Servers
• General Purpose Fan Speed Control