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TPS54618 compensation issue

Patrick Chen
Mastermind 8875 points

Hello,

      Customer test transient fail. But if change PC214 from 0.1U to 1nF, the transient will be better but still fail. Has any suggest compensation value for this transient issue? Thank you. 

Schematics

https://drive.google.com/file/d/0B4htKR16pRs8c0U3NWVBUGEtV1k/view?usp=sharing 

BR

Patrick

  • 0
    TI__Guru**** 191445 points

    0.1 uF and 1 nF are both extremely large values for that capacitor.    I usually use PC212 / 100 for the value of PC214.  What is the transient specification?  Can you post waveforms of the transient response?

  • 0 in reply to JohnTucker
    Mastermind 8875 points

    Dear John,

                   Customer remove PC214 then transient test was pass. Has any problem to remove PC214? Thank you.

    BR

    Patrick 

  • 0 in reply to Patrick Chen
    TI__Guru**** 191445 points

    PC214 introduces a pole in the compensation network.  In your case the capacitance value was unreasonably high, causing a very low pole frequency and low closed loop BW.  That would certainly decrease transient performance.  While PC214 is not absolutely necessary, for true type 2 compensation you should include it.  Typically it will be a low vale to provide a high frequency roll off pole.  You could try 12 pF ro 22 pF.  I would not go any higher than that.  If you do nt see any noise sensitivity, you can leave it off.