TC646B/TC648B/TC649B Datasheet

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  TC646B/TC648B/TC649B Datasheet

The TC646B is a new version of the existing TC646 fan speed controller. This device is a switch mode fan speed controller, which incorporates 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. The auto-shutdown speed is set by a simple resistor divider on the VAS input. An integrated Start-Up Timer ensures reliable fan motor start-up at turn-on, coming out of shutdown mode, auto-shutdown mode, or following a transient fault. A logic low applied to VIN, pin 1, causes fan shutdown.
The TC646B also features Microchip Technology's proprietary FanSense™ technology for increasing system reliability. In normal fan operation, a pulse train is present at SENSE, pin 5. A missing-pulse detector monitors this pin during fan operation. A stalled, open, or unconnected fan causes the TC646B device to turn the VOUT output on full (100% duty cycle). If the fan fault persists (a fan current pulse is not detected within a 32/F period), the FAULT output goes low. Even with the FAULT output low, the VOUT output is on full during the fan fault condition in order to try and restart the fan. The FAULT signal is also asserted if the PWM reaches 100% duty cycle, indicating that maximum cooling capability has been reached and a possible thermal runaway condition exists.

Parameter Name  Value
Typical Accuracy (°C)  Depends on external thermistor
Over Temp Alert  yes
SM Bus  NO
Predictive Fan Fault  NO
Max. Supply Current (µA)  400
Max. Accuracy @ 25°C (°C)  Depends on external thermistor
Integrated Temp Sensor  No
Fan Sense  Yes
External Temp Input  Yes
Auto Shutdown  Yes
Device Description  Fan Manager
Temp Range (°C)  -40 to +85
Vcc Range (V)  +3.0 to +5.5

     Features
   Temperature Proportional Fan Speed for Acoustic Control and Longer Fan
    Life
  FanSense™ Protects Against Fan Failure
  Efficient PWM Drive
  Automatic Shutdown Mode for "Green" Systems
  3.0V to 5.5V Supply Range
  Fan Voltage Independent of Supply Voltage – Supports Any Fan Voltage
  Supports Low Cost NTC/PTC Thermistors
  Fan Auto-Restart
  Over-Temperature Indication


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