TC648B

• 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 TC646B/ TC648B/TC649B Supply Voltage
- Supports any Fan Voltage
• FanSense™ Fault Detection Circuit Protects Against Fan Failure and Aids System Testing (TC646B/TC649B)
• Automatic Shutdown Mode for "Green" Systems
• Supports Low Cost NTC/PTC Thermistors
• Over-Temperature Indication (TC646B/TC648B)
• 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 TC646B/TC648B/TC649B devices are new versions of the existing TC646/TC648/TC649 fan speed controllers. These devices are switch-mode fan speed controllers that incorporate a new fan auto-restart function. Temperature-proportional speed control of TC648B is accomplished using pulse width modulation. A thermistor (or other voltage output temperature sensor) connected to the V_IN input supplies the required control voltage of 1.20V to 2.60V (typical) for 0% to 100% PWM duty cycle. The auto-shutdown threshold/temperature of TC648B  is set by a simple resistor divider on the V_AS input. An integrated Start-Up Timer ensures reliable fan motor startup at turn-on, coming out of shutdown mode, autoshutdown mode or following a transient fault. A logic low applied to V_IN (pin 1) causes fan shutdown.

The TC648B 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 TC648B to turn the V_OUT output on full (100% duty cycle). If the fan 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 of TC648B is on full during the fan fault condition in order to attempt to restart the fan.FAULT (TC646B) orOTF (TC648B) is also asserted if the PWM reaches 100% duty cycle, indicating that maximum cooling capability has been reached and a possible overheating condition exists.

The TC648B devices are available in 8-pin plastic MSOP, SOIC and PDIP packages. The specified temperature range of these devices is -40 to +85ºC.