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TPS2378EVM-105: Role of Q1 FET connected to RTN pin

Kaji@PAN
Mastermind 7350 points
Part Number: TPS2378EVM-105
Other Parts Discussed in Thread: TPS2378

Hi,

I would like to ask you about the circuit of the TPS2378EVM-105.
The circuit diagram is excerpted below.
What is the role of the Q1 FET connected to the RTN pin?

Best regards,

  • 0
    Mastermind 7350 points
    It seems that Q1 is required when using dual PD, but is Q1 unnecessary when using single PD?
    Best regards,
  • 0
    TI__Mastermind 21320 points

    Hello, 

    Per page 3 of the User's Guide, 

    "To the right of the TPS2378 (U1) is the switched side of the PD controller. The TPS2378 RTN pin provides inrush limited turn on and charge of the bulk capacitor, C4. During inrush, the TPS2378 CDB pin is pulled low (with respect to the RTN pin). Since the CDB pin is connected to the GATE of Q1, Q1 is off during inrush and J6 pin 1 is not connected to the RTN pin. This allows the output load to remain connected during EVM testing."

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments