TC647B

• 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

Absolute Maximum Ratings †
Supply Voltage (V_DD) .....................................................6.0V
Input Voltage, Any Pin................(GND - 0.3V) to (V_DD +0.3V)
Operating Temperature Range ...............- 40°C to +125°C
Maximum Junction Temperature, T_J .........................+150°C
ESD Protection on all pins .......................................... > 3 kV

† Notice: Stresses above those listed under "Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operational listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may
affect device reliability.

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 V_MIN
input. An integrated Start-Up Timer of TC647B ensures reliable motor start-up at turn-on, coming out of shutdown
mode or following a transient fault. A logic-low applied to V_MIN (pin 3) causes fan shutdown.

The TC642B and TC647B also feature Microchip Technology's proprietary FanSense™ technology for increasing system reliability. In normal fan operation, a pulse train is present at SENSE (pin 5). A missingpulse detector monitors this pin during fan operation. A stalled, open or unconnected fan causes the TC642B/ TC647B device to turn the V_OUT output on full (100% duty cycle). If the fault persists (a fan current pulse is not detected within a 32/f period), theFAULT output goes low. Even with theFAULT output low, the V_OUT output is on full during the fan fault condition in order to attempt to restart the fan.FAULT is also asserted if the PWM reaches 100% duty cycle (TC642B only), indicating that maximum cooling capability has been reached and a possible overheating condition exists.

The TC642B and TC647B devices are available in 8-pin plastic MSOP, SOIC and PDIP packages. The specified temperature range of these devices is -40 to +85ºC.