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TPS54561: PWM switched feedback resistors

Andres Curiel
Prodigy 20 points
Part Number: TPS54561

Hi,

I am wondering whether this arrangement to switch the lower side feedback resistor value using a PWM signal and a FET might work OK as a way to dynamically adjust the output voltage on the TPS54561?

Thanks.

  • +1
    TI__Guru 59185 points

    Hello

    I don't think that would work, since you can not combine the filtering in the feedback.

    The large capacitor will add a low frequency pole to the loop.

    You will need to filter your PWM first, then apply it as a "DAC" voltage to the FB pin through a resistor.

    Then you don't need the FET.

    I have attached a spreadsheet that you may find helpful with this type of application.

    You will need to test it carefully on an EVM before going into production.

    Thanks

    DAC_calc4.xlsx

  • 0 in reply to Frank De Stasi
    Prodigy 20 points

    Hi Frank,

    I feared that might be the case. Thanks so much for your reply, I couldn't have asked for any more Slight smile

    All the best,

    Andres