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TPS53355: Input Bulk capacitor concern

Ann_Lien
Genius 14430 points

Hi expert,

My customer wants to apply 1*0.1uF MLCC+1*10uF MLCC+9*15uF POSCAP in their application. Condition is shown below. Do we have concern in our control loop based on this input capacitance combination? Thank you so much!!

Condition:

Vin=12V, Vout=3.3V, Imax=23.7A, TDC=16.594A, fsw=500kHz

Best regards,

Ann Lien

  • 0
    TI__Guru**** 191445 points
    Ann,

    The input capacitance does not directly affect the loop stability. 9 pieces of 15 uF POSCAP will require some board space. Capacitance far from the input pins is not very effective as a filter though. Can you tell me about the ESR of the capacitors?
  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    There are three main points to consider with input capacitance.
    1. You need to make sure they can handle the RMS ripple current. Worst case it is Iout/2.
    2. You need to insure the input voltage ripple is acceptable.
    3. You need to get the input capacitors as close as possible to the IC.
    I would use 1*0.1uF MLCC+5*10uF MLCC+5*15uF POSCAP, or if you cab replace the 10 uF with 22 uF, that would be better.
  • 0 in reply to JohnTucker
    TI__Genius 14430 points
    Hi John,

    Thanks for your detail description.
    I will let customer know it, thanks!

    Best regards,
    Ann Lien