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  • TI Thinks Resolved

UCC28780: Behavior Is Latch When Output OVP.

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Replies: 1

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Part Number: UCC28780

Hi TI experts,

I want to design UCC28780 output OV fault protection that behavior is latch.

1. Which pin is suitable? 

2. Would you provide reference circuit for me? 

  • Hello Che,

    Thank you for your interest in the UCC28780 ACF controller.

    This controller will require an external circuit to achieve latch-up after detecting an output over-voltage condition.  At this time, we do not have a reference circuit design readily available, however, I can list some of the design requirements:

    1.  Use a micro-power comparator on the primary side of the converter powered by VDD.

    2.  Use REF as reference for comparison.

    3.  Add strong latching hysteresis such that only power down will unlatch.  Add sufficient filtering and delay to prevent nuisance tripping by noise.

    4.  Output of comparator should do two things: a) pull NTC pin below 1V and b) prevent VDD from increasing above 15V.  
    (a) will trigger a fault condition that will start a UVLO cycle and (b) will prevent the VDD from completing the UVLO cycle. Micro-power circuit will prevent overloading of start-up circuit.

    5.  Set VS resistor-divider for OVP level much higher than required.  Set another resistor-divider from AUX winding to the comparator programmed to the desired OVP level.  Since the AUX signal is pulsing, it will detect OV only during the demagnetization portion of the switching cycle, so the comparator must be fast enough even for the shortest demag times but not trip on noise or switching spikes. 

    I hope this can get you started.

    Regards,
    Ulrich

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