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UCC256404: UCC256404

Stuart Linzer
Intellectual 260 points
Part Number: UCC256404
Other Parts Discussed in Thread: UCC25640EVM-020

Hi Engineering Support, 

Application note SLUP263, Designing an LLC Resonant Converter page 24 gives the following values; Vcr and Vcr-rms.  

Vcr is less than Vcr-rms.  

Please explain details about the value Vcr and compare to Vcr-rms.

Regards, 

Stuart

  • 0
    TI__Genius 12865 points

    Hi Stuart,

    You can find the the Resonant capacitor voltage in half bridge LLC during different operating modes as shown below:

    At Resonance:

    Below Resonance:

    Above Resonance:

    Here You can see that resonant capacitor voltage is a combination of DC voltage and a AC voltage on top of it.

    In the app note, the AC voltage magnitude (Vcr) is found out by the Fundamental harmonic analysis.

    For total RMS calculation, you need to consider both AC as well as DC voltage (which is Vin/2).

    Let me know if you have any further questions.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Intellectual 260 points

    Hi Manikanta,

    Thank for the explanation.  While waiting for our custom board and transformer to arrive started working with UCC25640EVM-020 evaluation board to test different transformer configurations.  First tried to wind transformer to duplicated the evaluation board specification but with using separate resonant inductor.  Used same turns ratio and matched primary inductance.  Board did not operate correctly.  I was hoping you can assist me to better understand what went wrong.  Waveform for TP-5 (center-point of Mosfets) is attached. 

    Stuart   

  • 0 in reply to Stuart Linzer
    Intellectual 260 points

    Second image may not have uploaded.  Switch freq is 430Khz.  

  • 0 in reply to Stuart Linzer
    TI__Genius 12865 points

    Hi Stuart,

    Could you share the waveforms at RVCC, VCR, ISNS, LO pins.

    Also, you need to make sure the tank has sufficient gain for a given load and input voltages. 

    Could you share the design calculator with the new tank parameters.

    Regards

    Manikanta P