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UCC28730: HV pin sags the node it's connected to each power cycle until UUT no longer powers on.

Kyle Haston1
Prodigy 10 points
Part Number: UCC28730

I noticed that after repeated power cycles my device no longer powers on and traced it back to the voltage on the HV pin decreasing with each power cycle.

Below is an oscilloscope capture showing the sagging of the DC bus 2/3 and 1/3 nodes over time (HV pin connected to DC bus 2/3). Any ideas what could be causing this?

And here's the schematic:

 

  • 0
    TI__Guru* 85896 points

    Hello,

    After power the UCC28730 should be getting power from the aux winding.  After trickle charge startup there should not be any current going through the HV pin.  So this actually is not making sense.  Unless your UCC28730 or input bulk capacitors are being electrically overstressed.

    I would suggest studding the HV pin, VDD pin, CS pin and VOUT during power up. 

    I have seen if capacitors are over voltage their impedance will decrease overtime evidently becoming a short.  You might want to study your input bulk capacitors to make sure they are dividing the voltage correctly as well.

    Regards,