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TPS55288: 20V to 5V fall time out of spec

Jeff YANG
Mastermind 7795 points
Part Number: TPS55288

Hi,

My customer meet an issue about TPS55288 fall time. Their product spec need limit 20V to 5V under 285ms.

But as below waveform, it over 600ms. Is there any way can improve?

And their TPS55288 output cap is less than EVM. Please also add me friend, I will pass schematic for review via privacy message. thanks!


Jeff

  • 0
    TI__Mastermind 34231 points

    Hi Jeff,

    For you case, it's suggested to configure TPS55288 working in FPWM mode to reduce the 20V to 5V transition time.

    Configure the MODE pin resistance to suitable value according to below table. 

  • 0 in reply to Zack Liu
    Mastermind 7795 points

    Hi Zack,

    thanks for suggestion, seems it work can reduce fall time.

    But have another question is we found ripple is bigger than PFM mode, now ~3.4V peak to peak ripple voltage on output side.

    Except increase output capacitor, any other way to improve ripple?

    We follow the EVM comp value now, adjust comp value can improve output ripple? thanks!

  • +1 in reply to Jeff YANG
    TI__Mastermind 34231 points

    Hi Jeff,

    The compensation parameters need to carefully designed according to your application Vin range, Vout, max Iout and external passive components, such as inductor L, output capacitance Cout.

    Could you let me know your application Vin range, Vout, max Iout information?

    So far I see the compensation parameter is not good, which will cause loop instability problem. You could probe switching node SW1, SW2 to verify that.

    You can adjust R551 to 20kohm first to see if that helps.

  • 0 in reply to Zack Liu
    Mastermind 7795 points

    Hi Zack,

    Thanks for your help, modify to FPWM is work, and ripple issue seems only one board meet this issue, should be single case, I will close this case.

    Jeff