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UCC256302: UCC256302 questions

Lin Zhao
Intellectual 1230 points
Part Number: UCC256302

Hi Expert,

1. In open loop control mode, what's the specific requirement for FB pin series resisitors, since during debug, if the resistor is small, IC can't work. is it ralated to burst mode?

2. could we turn off burst mode by external circuit? if so, how to achieve?

Thanks!

  • 0
    TI__Expert 6080 points

    Hello,

    1. Please share the schematic, I am not sure what resistor you are referring to, but in general, When FB pin is pulled to ground for over 200ms, the controller enters a fault state. When FB pin starts ramping the controller transitions to JFETON state. When VCC crosses the VCCStartSelf threshold the controller enters the soft start and starts switching.

    The startup process is open loop and controlled by the soft start ramp. Burst mode is not enabled during soft start phase.

    2.  One quick way is to remove the resistor connected from RVCC to LL/LL pin, this will put the burst mode threshold to its minimum. You cannot disable the burst mode completely. This will keep the controller out of burst mode if there is some minimum load on the output.

    I hope this answers your question.

    Regards,

    Sonal

  • 0 in reply to Sonal Singh
    TI__Expert 6080 points
    Hello Leo,

    I hope you are well.
    I am not sure if the previous reply has answered your question. Attached is a documentation that will enable them to set the burst mode properly.
    I hope this helps.
    www.ti.com/.../slua836a.pdf

    Regards,
    Sonal
  • 0 in reply to Sonal Singh
    TI__Intellectual 1230 points
    Hi Sonal,

    Thank you and it's useful.