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UCC28740: Start Process

Francis Jiang
Intellectual 2680 points
Part Number: UCC28740

Tool/software:

Hi Team,

Do we have detailed documentation of the device startup process? Customers want to see how the duty cycle changes during the startup process. Thanks in advance.

BRs,

Francis

  • +1
    TI__Expert 8845 points

    Francis,

    Please see the start-up waveform. It is much larger than a single switching cycle so we don't have the zoom-in view to show the switching cycle change.

    The sequence is described in datasheet here. I hope it can clarify without the actual switching waveform.

    Best,

    Ning

  • 0 in reply to Ning Tan
    TI__Intellectual 2680 points

    Hi Ning,

    Seems another question is missed:

    "

    HV pin can withstand 700V voltage. Since the input is DC voltage at 400V, I don't see any issue."

    Yes, the relative voltage difference is only 400V, but the UCC28740 GND is a virtual GND. The absolute minimum voltage is at -400V bus, and Flyback output will supply the negative bus devices. There is no risk, right?

    Thanks.

    BRs,

    Francis

  • 0 in reply to Francis Jiang
    TI__Intellectual 2370 points

    Francis,

     Ning is out of office for a week.

    All the abs max voltages of IC are with respect to to its GND pin. The voltage stresses need to be measured accordingly.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    TI__Intellectual 2680 points

    Hi Hemanth,

    Sorry I don't understand it, for IC, I know the voltage stress definition, but for using in the system, and there is a negative bus, just use a position bus and the virtual GND, whether IC has failure risk? Thanks.

    BRs,

    Francis

  • +1 in reply to Francis Jiang
    TI__Intellectual 2370 points

    Hi Francis,

    Every pin on IC voltage stress only defined in the datasheet and that is what we guarantee. If the voltages on the mentioned pins w.r.to GND are within limits, we are good.

    However, if there is system with negative voltages or virtual ground - again, we need to see the differential voltage from each pin of the IC to its GND pin for the stress.

    If you need more help, please share a single line diagram of the system with IC along with voltages at the nodes of interest. I will just need to estimate the differential voltage between each pin of IC to GND as defined in the datasheet.

    Regards
    Hemanth