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TPS22922: Recommended capacitance of the output capacitor

Dice-K
Mastermind 6330 points
Part Number: TPS22922

Hi support team,

When the input capacitor is 1μF, is the recommended value of the output capacitor 0.1μF?

Or when the output capacitor is 4.7μF, should the input capacitor be 47μF?

Regards,
Dice-K

  • +1
    TI__Genius 14225 points

    Hi Dice-K, 

    Yes the 10:1 ratio of input capacitance to output capacitance is the standard we recommend to start with and the convention we use in the TPS22922 EVM. This is because if the output capacitance is larger than the input capacitance, then if the input drops very suddenly, the output voltage will drop slower than the input and reverse current may flow through the device. However, this has more to do with your systems power capability than anything else. 

    If your supply has a sufficient power capability, this large ratio might not be needed and with QOD implemented in the device, reverse current flow should not be an issue. If your input to the system is a battery, something to consider is whether the large input capacitance will cause the battery to be overdrawn instead of slowly being drawn as the device intends. 

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    Mastermind 6330 points

    Hi Elizabeth,
    Thank you for your reply.

    Is it a correct way to determine the capacitance by first setting the input capacitor to 1μF and the output capacitor to 0.1μF and adjusting as appropriate?

    Best regards,
    Dice-K

  • +1 in reply to Dice-K
    TI__Genius 14225 points

    Hi Dice-K, 

    Yes that would be appropriate.

    A larger output capacitance will increase the possible inrush current and a larger input capacitance could possibly overdraw your supply. 

    So the smallest capacitance which still holds your voltage up for transient cases would be preferable. 

    Best Regards, 

    Elizabeth