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Original question:

UCC28951-Q1: PMP8740 - CC CV control circuit

UCC28951: Ref: PMP8740, does the CC loop gain change with load current value?

Nitish Agrawal
Expert 1595 points
Part Number: UCC28951
Other Parts Discussed in Thread: PMP8740,

Tool/software:

Hello Roberto,

Greetings!  I am looking to model the CC loop gain for the PMP8740 reference design.  A couple of questions:

(1) Do you have a formula for the CC loop gain (when charging a battery) that you can share?

(2) Would you mind also advising if the CC loop gain would change with respect to load current value?

Sincerely,

Nitish Agrawal

  • 0
    TI__Guru* 85926 points

    Hello,

     

    There is a high amount of e2e traffic and we will look into this in the order it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85926 points

    Hello,

     

    Are you trying to design a CC/CV for battery charging?

     

    Regards,

  • 0 in reply to Mike O'
    Expert 1595 points

    Hi Mike, the battery charger is already designed.  However, the measured CC loop gain does not match with simulations.  I am trying to figure out where the problem is and wanted to check the formulae I was using for operation in CCM and DCM mode.

    Sincerely,

    Nitish

  • 0 in reply to Nitish Agrawal
    TI__Guru* 85926 points

    Hello Nitish,

    I found this application information regarding this design.  One is an application note and the other is power point presentation.  Neither get into detailed information regarding the loops or how to model them.  It is possible that they use a network analyzer to compensate the current.

    https://www.ti.com/seclit/ml/slup348/slup348.pdf

    https://www.ti.com/seclit/ml/slup349/slup349.pdf

     

    I do not know of any information that is published in regards to CC/CV in regards to the UCC28951.  So, I do not have any information that I can share.

    I will ask Roberto the power supply designer of PMP8740 to see if he has any more detailed information on how to compensate the current loop for this design.

     

    Hello Roberto,

     

    Do you have any other information that you can share in regards to compensating the current loop in this design similar to the PMP8740 that you can share with Nitish?

     

    Regards and Thanks,

     

    Mike

  • 0 in reply to Mike O'
    TI__Expert 5875 points

    Hello Mike,

    I don't have other information about CC loop for phase shift full bridge; for PMP8740 I just fine tuned the loop with the help of a network analyzer (Venable) and simulating the battery with a very big output electrolytic capacitor (several tens of milli-Farad), while the real load was an electronic one, set into constant voltage (simulating the slowly change of battery voltage).

    Thanks,

    Roberto

  • 0 in reply to Roberto S.
    Expert 1595 points

    Hi Mike and Roberto,

    Thank you for your responses.  Roberto, did you mean to say that the large electrolytic cap was in parallel with the electronic load (during CC loop tuning)?

    Sincerely,

    Nitish Agrawal

  • +1 in reply to Nitish Agrawal
    TI__Expert 5875 points

    Hi Nitish,

    You are correct: the large electrolytic capacitor was connected in parallel with the electronic load (during CC loop tuning), simulating the equivalent "infinite" capacitance of a battery. I made this because in our labs, due to safety reasons, we are not allowed to charge big batteries.

    Regards,

    Roberto