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TPS55340-Q1: Vout waveform difference between Cout value

Takao Yamamoto
Genius 4135 points
Part Number: TPS55340-Q1


Dear all,

Could you teach me about the reason why Vout waveform change like following PDF file?

Vout waveform.pdf

Best regards,

  • 0
    TI__Guru* 78675 points
    Hi Yamamoto-san,

    Your 1uF capacitor is not an adequate and effective filter capacitor because of its esr and esl. The later causes the voltage distortion. Usually larger capacitors of the same type has lower esr.

    Best Regards,
    Youhao Xi, System and Applications Engineering, APP-BMC-BCS, TI
  • 0 in reply to Youhao Xi
    Genius 4135 points
    Dear Xi,

    Thank you for your answer.
    Could you explain about 'voltage distortion' in more detail?
    What is the mechanism that causes the voltage distortion?

    I thought that Vout voltage ripple will just be larger (not be square form) because of esr and esl.
    In other words, I tought that Vout waveform will maintain like triangle wave, not square wave.

    Could you explain what is the matter?
    Best regards,
  • 0 in reply to Takao Yamamoto
    TI__Guru* 78675 points
    when the current flows into the capacitor, it also flows through the ESR and ESL. The capacitor is actually an R-L-C circuit, not a pure C circuit, and these ESR and ESL will cause the waveform distortion. If C is very large and the ESR and ESL's effects will be come negligible and you can see a sinusoidal type of ripple voltage.