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UCC28C42: PMP10783 Rev A problem

lorenzo fagnani6
Prodigy 80 points
Part Number: UCC28C42
Other Parts Discussed in Thread: PMP10783

Good morning,
I replied to my board the application note PMP10783 Rev A.
When I turned on the board, the power supply works, it stays at 15.5V, but if it loads, it starts to whistle and the output voltage has dropped to 13V. I thought it was a inductor saturation problem (330uH 1,4A as inserted in appnote PMP10783 Rev A) so I replaced it with one larger and in fact the output voltage stays stable on the 15V (consistent with the application's value Notes PMP10783) but the whistle remains.
The heated MOSFET arrives at 110 Celsius degrees with an output current equal to 250mA.
I have verified the gate of the mosfet and there are riarms, what is it for? Did you have the same problems?

King regard

Lorenzo

  • 0
    TI__Mastermind 31580 points
    Hi Lorenzo

    Let me get one of our applications team to respond to your post, you should see a response soon.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Expert 4015 points

    Hi Lorenzo, do you mean that you built a board according to the BOM of the PMP10783.

    Whistling is generally either heard when something in the unit is switching in the audible range. Either the switching frequency of the IC is in this range, (20Hz - 20kHz) or the unit is in some kind of burst mode.

    If the inductor is saturating this can also lead to audible noise. If you can capture scope plots of the waveform on the gate of the MosFET and the voltage of R11 and post them, it might help us to see what is going on.

    If you can capture plots with timescales of 10us/div, 100us/div and 2ms/div it would be good. Also, can you confirm the part numbers for the inductors which you are using.

    Thanks

    Billy

    Peter Meaney said:
    Hi Lorenzo

    Let me get one of our applications team to respond to your post, you should see a response soon.

    Regards

    Peter

  • 0 in reply to Billy Long
    Prodigy 80 points

    Hi Peter,

    thank you for the reply.

    I see my bom and i find the problem (in theory). It is possible that my diode is too slow and generate this whistle? My diode has a Trr (Typical reverse recovery time) of 2.5us (datasheet http://www.vishay.com/docs/88931/s5a.pdf. the switching works on 900ns. I think this is a problem.

    For you? Now i buy a new diode and when arrived, i will try the power supply. I buy a diode that has a 20ns of recovery time.(datasheet https://www.power.com/sites/default/files/product-docs/qspeed/lxa04t600_%20lxa04b600.pdf

    Thank you

    Have a nice day

    Lorenzo