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Original question:

TPS65131-Q1: TPS65131-Q1 suggestion Vref Cap value

TPS65131-Q1: TPS65131-Q1 suggestion Vref Cap value

Lawrence He
Genius 3280 points
Part Number: TPS65131-Q1

Dear,

IF Vref cap was remove, or change cap vaule from 22pf to 2pf, have any side effect ?

beacuse we find the reduce cap vaule will improve VNEG ripple and voltage level.

Vref Cap =22pf waveform

Vref Cap =2pf waveform


if any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence.

  • 0
    TI__Guru 58225 points
    Hello Lawrence,

    I expect that the measurements above are taken with no load on the output. If this is the case, the ripple with the 22pF cap is coming from the power save mode.

    We do not recommend to use a 2pF capacitor as feed-forward capacitor parallel to the top resistor of the feedback divider. Please follow the recommendation given in the datasheet for this capacitor.

    If the ripple in PFM is too high for your application, you need to pull the pin PSN low to disable this feature.

    Best regards,
    Brigitte
  • 0 in reply to Brigitte
    Genius 3280 points

    Hi, Brigitte


    We will try PSN pin short to GND  and Could you explain why Vref cap need 22pF, it`s about reference point of the feedback?


    If any suggestion, Please advise me.


    Thanks,


    Best regards,


    Lawrence.

  • 0 in reply to Lawrence He
    TI__Guru 58225 points
    Hello Lawrence,

    The capacitor that is marked with a black circle above has nothing to do with the VREF. This capacitor is called feed-forward capacitor and has an influence on the stability of the converter. Please review chapter 9.2.1.2.6.1 in the datasheet for more details about this capacitor. I did not check if 22pF is the recommended value from the calculation in the datasheet.

    Best regards,
    Brigitte