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TPS56C215: Questions about Cff range

Cage Chen
Prodigy 490 points
Part Number: TPS56C215

Hi, 

    In the TPS56C215 datasheet, table 5. It mentions recommended component values.

    One of the items is Cff, how does the value define or calculate?

    In what kind of condition, we may need to put 220pF on Cff? 

    What if we put 330pF?

    Thanks a lot for your great help always.

Best regards, Cage.

ps, this is a 12V input, and 5V output with load transient 5A ~ 10A.

Cff=220pF, you can see ring back.

Cff=330pF, ring back is improved.

  • 0
    TI__Expert 8245 points

    Hi

    TPS56C215 has D-CAP3 control mode and its phase margin and bandwith will decrease as Vout increases. So a Cff could be introduced which can bring about 20~40° phase shift and 5~10dB shift at the frequency f0 = [√(Vout/Vref)] / (2π*Rfbt*Cff), due to a zero and a pole. In actual application, you can just use the recommended range and choose one from it which brings the best performance you want.

  • 0 in reply to Iven Su
    TI__Prodigy 490 points

    Hi Iven,

         Got your point.

         Thanks a lot for your help.

    Best regards, Cage.