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UCC28780: Questions about SLUC664 spreadsheet

Gerrit Barrere
Expert 1245 points
Part Number: UCC28780

I don't understand a couple of the data inputs in the SLUC664 design calculator spreadsheet for this IC:

  • What should I use for "Input Voltage BUR, VINPUT_BUR"?  The data sheet in section 7.3.1 doesn't say what the BUR voltage should be, it only says 50% - 60% load at "high line" for entering ABM.
  • How does "Low Line Input Voltage VIN_LOW" differ from the brown-in/out voltages?  What should I use for VIN_LOW relative to the brown-in/out voltages?
  • Is "Transformer Parasitic Capacitance" the capacitance across the primary, or the interwinding capacitance between pri and sec?

Thanks for any help,

Gerrit

  • 0
    TI__Guru 73005 points

    Input Voltage BUR, that is "high line" in your design - you need to define it. In 85Vac to 265Vac input, we define high line as 230Vac.

    For burst starting point, the datasheet suggests to start with 60% of full load at high line. You can use 60% as well. This percentage will be adjusted in bench test to get better performance in terme of efficiency across load and line range.

    In this calculator, input voltage range is 90Vac to 265Vac, to guanrantee the converter operation at 90Vac, the startup input should be slight lower, which is called brown-in point, this calculator uses 75Vac for this brown-in.

    CTr is an estimated parasitic capacitance in the transformer all reflected to spot between the switch node and the GND.

  • 0 in reply to Hong Huang
    Expert 1245 points

    Thank you for the response.

    So should VINPUT_BUR be about 85% of VINPUT_max?  You have quoted the data sheet on BUR, which says to start with 60% load current.  That doesn't say anything about what the "Input Voltage BUR" should be.

    And VIN_LOW is the lowest operating line voltage (at full output power?), and the brown-in and -out voltages are somewhat less than that?

    Gerrit

  • 0 in reply to Gerrit Barrere
    TI__Guru 73005 points
    60% of rated current at high line (you need to define it - in the calculator high line is 230Vac).

    Please read through my last reply which answers all your question. If something you think still not clear please cite my reply and indicate which are still not clear.
  • 0 in reply to Hong Huang
    Expert 1245 points
    I did read your original reply, many times. I found it obscure and indirect, so I asked a couple followup questions. Would it kill you to just reply yes or no to them?
  • 0 in reply to Gerrit Barrere
    TI__Guru 73005 points
    So should VINPUT_BUR be about 85% of VINPUT_max?

    [reply] No, we do not define with 85% and in general no percentage for this definition. We define it as 230Vac, because 230Vac is an often seen or nearby value from line to neutral such as in Europe or US two single phase.

    You have quoted the data sheet on BUR, which says to start with 60% load current. That doesn't say anything about what the "Input Voltage BUR" should be.

    [reply] At high line, burst starting point is 60% of the rated load. "Input Voltage BUR" is input voltage at high line that you need to define.

    And VIN_LOW is the lowest operating line voltage (at full output power?)
    [reply] VIN-LOW is input voltage at lower end of your input range, at any output power.

    and the brown-in and -out voltages are somewhat less than that?
    [reply] Brown-in is a voltage lower than VIN-LOW if you want your converter can operate for sure at VIN-LOW. Brown-OUT is a voltage you want your converter not get back and forth between brown-in and -out.