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TPS5405: Pulse Skipping Mode High Ripple

Dennis Riester
Prodigy 20 points
Part Number: TPS5405
Other Parts Discussed in Thread: TPS62933P, TPS54308,

Hello,

I have designed a DC/DC converter (TPS5405DR) and used it on one of my boards.

At low load (<100mA) I now have a Pk-Pk voltage of 170mV with a frequency of 29k Hz.

At a load of about >400mA the Pk-Pk voltage suddenly drops below 20mV.
Attached is the schematic including the layout. On the two internal layers
there are two GND planes.

Schematic

How can i improve the ripple during low load conditions? 

  • 0
    TI__Expert 8100 points

    Hi Dennis,

    Due to longer time for output capacitor to discharge, output capacitor will release more energy and increasing peak-to-peak value of output voltage ripple.

    Two possible solutions are recommended: 1. increase the value of inductor 2. increase the value of output capacitor.

    Hope my advice will be helpful!

    BRs

    Zixu

  • 0
    TI__Genius 9280 points

    Hi Dennis,

    TPS5405 is a ECO mode part, which means that it will enter PFM with lower frequency at light load. This mode was for eff saving ,while brings larger ripple as Zixu said. You can try Zixu's suggestion to reduce the ripple. Another suggestion was to change to a FCCM part, like TPS54308, TPS62933P which are much newer than this part. 

    May I check with you if it is a new project ? What's the SOP time and TAM ? Pls let us know your concern. thanks.

    BRs.

    Young