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UCC28C44: Switching node goes from normal DCM operation to appears to be a quick pulse

Tom Herbert
Prodigy 30 points
Part Number: UCC28C44

The switching output of the UCC28C44 operates normally at a DC of 25% then it gets a small hiccup where it turns on briefly and off right away.  Appears to almost be like a protection mode or instability.  See attached image.

Fsw = ~300khz

Vin = 480V (L-L)

VBus = 680V

Vout = 24V

Power = 35W (designed for 50W)

Channel 1 = VDS of SiCFET

Channel 2 = Vout

Channel 3 = UCC28C44 COMP pin

Channel 4 = UCC28C44 VRef

Flyback.tif

  • 0
    TI__Guru 73085 points

    Hi,

    It looks like something is breakdown temporary. Can you check SiCFET? I think you may probe the Rcs (or something you do current sensing) and the OUT, if no OUT while you see high current from Rcs probe, it is an indicate your SiCFET is breakdown briefly.

    If you need further support, please provide your schematics so to facilitate the talk.

  • +1
    Prodigy 30 points

    The issues appears to have been related the filter on the current sensor input.  By increase the time constant the issue went away.