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UCC28950: Comp Pin

Brian Lu
Prodigy 10 points
Part Number: UCC28950

Tool/software:

Hi,

The error amplifier output Comp pin is 0.25~4.25Vdc per specs. In the application, I measured the voltage very unstable. Refer to attached slide 1 and 2, yellow trace is the measured Comp pin. The AC/DC power supply output voltage drops from nominal 36Vdc to ~16Vdc. I suspected the drops caused by the ripple because the Comp pin voltage is stable when the AC/DC power supply is loaded with Electronic load (slide 3).

Questions: Is it normal for Comp in to be unstable but within 0.25~4.25Vdc range? 

Thanks

Brian

UCC.pptx

  • 0
    TI__Guru* 86266 points

    Hello,

    Your inquiry has been received and is under review.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

    The comp pin seems very noisy in your waveform.   This pin is know to be noise sensitive if you probe it directly.

    It is recommended that you use a 1 k ohm resistor in series with the scope probe to ensure noise does not get injected in the pin.

    Did you sample the comp pin voltage this way?

    The following link will bring you to a step by step design process using the UCC28950 in a phase shifted full bridge.

    There is a link inside that can to excel design tool that uses the same equations in the application note.  You can use the application note and excel design tool to help check your design.

    https://www.ti.com/lit/an/slua560d/slua560d.pdf

    Regards,