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About Cff of TPS54325

Satoshi
Guru 19645 points
Other Parts Discussed in Thread: TPS54325

Is Cff (feed forward Cap) have an influence Vout?

On TPS54325, Vout was different in Cff：open and Cff：220pF(customer mistake).

・Cff：Open→5.05V

・Cff：220pF→5.18V

Best regards,

Satoshoi

  • 0
    TI__Guru**** 191445 points
    That Cff is 10 times larger than recommended maximum value. TPS54325 uses hysteretic off time control based on VFB voltage with internal ripple injection. So the actual dc output voltage is off set slightly higher than the calculated set point. For small Cff or no Cff the delta voltage is negligible. For larger Cff I suppose you may see some additional off set. I have not personally tested and characterized it, but I think larger CFF can affect the output in that manner.