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TPS568215: Cout(max) and Cff Larger Than Recommended Values

Shinichi Yokota
Genius 9715 points
Part Number: TPS568215

Hello,

I have two questions regarding COUT(max) and CFF capacitance values of TPS568215.

  • Is there any concern or care-about in selecting COUT(max) and CFF capacitance values larger than those recommended in Table 5 of the data sheet?
    • The purpose of using the larger values is to try to minimize overshoot and undershoot voltages of the output against fast load transient responses.
  • Are those capacitance values in the Table 5 the actual ones that take into account de-rating by DC bias voltage? Or, are they nominal capacitance values?

Best regards,
Shinichi Yokota

  • 0
    TI__Expert 4360 points

    Hi Shinichi

    My colleague will check it and get back to you next Monday.

  • +1
    TI__Expert 7320 points

    Hi Shinichi,

    Is there any concern or care-about in selecting COUT(max) and CFF capacitance values larger than those recommended in Table 5 of the data sheet?

        Yes, both Cout and Cff influence the stability of the loop. if the Cout capacitance is too large then the circuit may not have enough bandwidth and causes unstable loop. You can follow these two application notes for reference.

    Stability Analysis and Design of D-CAP2 and D-CAP3 Converter – Part 1: How to Select Output Capacitor

     https://www.ti.com/lit/an/slvaf11/slvaf11.pdf

    Stability Analysis and Design of D-CAP2 and D-CAP3 Converter – Part 2: How to Select Feedforward Capacitor

    https://www.ti.com/lit/an/slvaf45/slvaf45.pdf

    Are those capacitance values in the Table 5 the actual ones that take into account de-rating by DC bias voltage? Or, are they nominal capacitance values?

        The values in the table are nominal and do not account for derating.