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About capacitor selection of TPS5430

watanabe
Expert 1740 points
Other Parts Discussed in Thread: TPS5430

Hi,

I have a question about formula of fco and Cout(SLVS632G 8.2.1.2.3.2 Capacitor Selection (7)and(8)).

Did you come out from where the figure of 85?

Likewise,Could you tell me about the source of the 3357?

I 'm looking for your reply.

Best regards,

Watanabe

  • 0
    TI__Guru**** 191445 points
    Those equations are simplifications. I rolled all of the numeric values ( 2, pi, etc) together into a single constant for simplicity. The equations only hold for the specific conditions as outlined in the text. I did that work over 10 years ago and do not remember all the exact details. I can look for my old notes, but I doubt that I have retained anything that old. I would recommend that you just use webench for capacitor selection. I'll let you know If I can locate the old notes, but I very much doubt that I still have them.
  • 0 in reply to JohnTucker
    Expert 1740 points

    John Tucker-san,

    Thank you for quick reply.

    I understand about equations are simplifications.

    The reason why was asked a question,

    these were different  crossover frequency between datasheet(SLVS632G equation(7)) and webench opvals.

    Do you have excellent selection capacitor more of webench than datasheet?

    Best regards,

    Watanabe

  • 0 in reply to watanabe
    TI__Guru**** 191445 points

    let me know your webench inputs, or share your webench designs with me.  I will take a look at them and let you know my thoughts about them.

  • 0 in reply to JohnTucker
    Expert 1740 points

    Tucker-san,

    I appriciate for your support.

    WEBENCH Design: webench.ti.com/.../SDP.cgi

    Becoming crossoverfrequency of WEBENCH OpVals is 19.2kHz .

    But,crossoverfrequency of datasheet is 27.1kHz.

    Why the difference is born?

    Which one should I trust webench or datasheet?

    Best regards,

    Watanabe

  • 0 in reply to watanabe
    TI__Guru**** 191445 points
    Those datasheet equations only hold under certain conditions as outlined in the text. For your case they will not work as your ESR is too low. TPS5430 will not work with ceramic capacitors unless you add a feed forward capacitor (which webench does not support).
  • 0 in reply to JohnTucker
    Expert 1740 points
    Tucker-san,

    Sorry for my late reply.
    I was understand EST is too low.
    I recommend Electrolytic capacitor for my customer.
    Thank you very much for your help.

    Best regards,
    Watanabe