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LM3431 DLY Pin capacitor

Lucifer
Expert 2600 points
Other Parts Discussed in Thread: LM3431

Dear Sir,

we are encountering a LM3431 power on issue, when we power on the power supply, LM3431 output voltage will shutdown after 10ms. once we increase the capacitor value of DLY to 1uF ( from 0.1uF to 1uF) then it does work very well without any problems.
may I have your comment that the effect of DLY 0.1uF to 1uF  ?

Thanks.

  • 0
    TI__Intellectual 1010 points
    Hi Eason,

    The capacitance on DLY pin programs the delay time for shutdown.

    During powering on, your circuit triggered a fault (Should be Current limit ) and DLY pin start to source 57 uA (typical) current, the DLY voltage ramps up.
    If the fault holds and DLY voltage reaches its threshold, LM3431 will shutdown. ------- for 0.1uF case
    The DLY pin will discharge ( sinking 1.8 uA ) when the fault is removed before shutdown occurs. ------ for 1uF case

    You may need to take a look at the waves at DLY pin.

    Best Regards,
    Jason