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UCC28700-Q1: control law modulation

Dongbao Zhou
Expert 3960 points
Part Number: UCC28700-Q1
Other Parts Discussed in Thread: UCC28700

Hi team,

What are the factors that impact the control voltage Vcl? My customer found their design keep operating in frequency modulation mode across input and output current range， is that normal?

Regards,

Dongbao

  • 0
    TI__Expert 8210 points

    Dongbao

    VCL is the output of the error amplifier, which is an internal signal to UCC28700-Q1.  It is at its maximum value at minimum input full load, and it reduces as either the input voltage increases or the output power decreases.

    Depending on the specific design, such as the power stage design and range the load and input can vary, UCC28700-Q1 could stay in the FM operating mode.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    TI__Expert 3960 points

    HI Eric,

    Just double confirm with you, In customer's design, the input voltage is 150V-500V, the output voltage is 12V, load current from 0A-0.9A.  They don't find a operating point that makes UCC28700 works in amplitude modulation (AM) mode.

    Thanks

    Dongbao

  • 0 in reply to Dongbao Zhou
    TI__Expert 8210 points

    Dongbao

    There could be several reasons why your customer's design does not work in AM mode.  Depending on your design this could be expected behavior.

    If you or your customer is concerned about this please share details of your design, such as schematic and key waveforms at minimum and maximum input at full and no load.

    Best Regards,

    Eric