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About input bulk cap on the buck converter

GARAM AN
Intellectual 1990 points

Hello all,

I have very simple and basic question about the input bulk cap.

I know that low capacitance(22uF) is enough for the input side cap to reduce the voltage ripple generally, but I sometimes can find 150uF or 220uF on the input side.

Why tantal or aluminum bulk cap is designed in the input side, even the ESR is higher than MLCC?

is this reason, MLCC has low capacitance?

Thank you

  • 0
    TI__Guru**** 191445 points

    Garam,

    Typically you will need one or more high quality ceramic MLCC directly across the input voltage and GND pins of your converter.  You may also add some electrolytic capacitors.  This is particularly useful with the input supply uses long inductive leads or if an input filter inductor is used.  The higher ESR can damp out any resonances the inductance introduces.