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UCC28064A: Disable burst mode

Mason Noh
Expert 2490 points
Part Number: UCC28064A

Hi TI,

My customer need to disable burst mode because of audible noise.

Does BRST pin need a pull down resistor? or Can it be connected to the ground directly?

And Is there no side-effect such as output regulation when no load?

  • 0
    TI__Mastermind 40580 points

    Hello Mason,

    The BRST pin may connected directly to GND to disable the burst mode.

    But please note that for very light-load conditions, the COMP voltage may fall below 250mV.  If that happens, switching will stop until COMP voltage rises above 250mV again.  Switching will start immediately after COMP > 250mV; it does not wait 210us for a restart pulse.

    This threshold behavior is not well documented but appears in Section 8.3.15.5 (page 33) and Section 9.2.2.11 (page 43) of the datasheet. It is likely that intervals of switching and non-switching will be not very periodic and at low frequencies.  There is still a possibility of audible noise.

    Hopefully, the low COMP voltage will drive very short on-times and peak current will be low.  But if there is significant turn-off delay (due to high Coss or other reason), peak inductor current may be higher than expected compared to the GDx drive duty cycle, especially at high line.

    No-load output regulation should be good, with less ripple than at full load.

    Regards,
    Ulrich