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Original question:

UCC28950-Q1: more questions: Gate pulses occur when EA+ voltage is lower than EA- voltage

UCC28950-Q1: How to prevent the initial gate pulse output.

ryo umebori
Prodigy 30 points
Part Number: UCC28950-Q1

Tool/software:

Hello.

I asked about the initial gate pulse in the thread linked below.
ttps://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1421596/ucc28950-q1-more-questions-gate-pulses-occur-when-ea-voltage-is-lower-than-ea--voltage

And I understood as below.
* Initial pulse output must be within specifications.
* The purpose of the initial pulse is to charge the bootstrap capacitor.

Therefor I would like to know how to prevent the initial pulse output.

Thank you.

  • 0
    TI__Guru* 86286 points

    Hello,

    Your inquiry is under review and I will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86286 points

    Hello,

    This is part of the burst mode operation, so I don't believe there is an easy way to disable it.

    I do see from your waveform that switching does not really occur until the soft start has long timed out.

    There should be switching during soft start as the output voltage is coming up.

    Could you tell me what he cause of this delay is? 

    It almost looks like you are not using soft start and are using some other control to initiate soft start.

    If this is the case it might be beneficial for you to hold the SS pin with a FET until startup is needed.

    Regards, 

  • 0 in reply to Mike O'
    Prodigy 30 points

    Hello, thank you for reply.

    This circuit uses a microcontroller to control the EA+ voltage.
    Therefore, the rise of EA+ voltage is gradual.

    Also, a battery is connected to the output of the DCDC converter.
    Therefore, the EA- voltage at startup is referenced to the battery voltage.

    From the above, switching starts when the EA- voltage exceeds the EA+ voltage.

    The initial pulse is output before this timing.
    Therefore, what are the conditions under which the initial pulse is output?

    Thank you.

  • 0 in reply to ryo umebori
    TI__Guru* 86286 points

    Hello,

    Your inquiry is under review and I will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86286 points

    Hello,

    Since you are not using soft start if you bias the SS voltage with 4 V this should disable the soft start and remove those initial gate driver pulses.

    Thank you for interest in Texas Instruments (TI) products.  If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

    Regards,