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LP2985-N: output capacitor selection

Balazs Kim47
Prodigy 20 points
Part Number: LP2985-N

I would like to ask you to review the attached schematic,
regading the output capacitor selection and stability.
Recommend better type if I'm wrong.
I need this becouse I'm facing with the following problem:
At the EMC laboratory, during the design review, I got the istruction to
put a WE 742792040 (EMI suppression ferrite bead 600R @ 100MHz ) between C23 and C20 against oscillation.
I'm not sure this helps.

LDO: LP2985AIM-3.6/NOPB
output capacitor: CL32A226KOJNNNE


 

  • 0
    TI__Mastermind 25546 points
    hi,

    actually you have already C23 on the output for the HF component, the rest is done by the LDO itself...
    better would be to put a little inductance at the input of the LDO: indeed the CMRR of LDOs tend to be worse at HF, but the inductor/ferrite at the input avoids the input noise propagates further on...
    layout also play a big role in EMI compliance, and here probably you can improve it a bit...

    PS: what is the need of having R4?

    KR
    Vincenzo
  • 0 in reply to Vincenzo Pizzolante
    Prodigy 20 points
    Hi,

    Thank you for the answer. R4 is for fully discharge the output capacitor.
    There is a ground plane on other layer what is not shown on the PCB.

    Balazs