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Original question:

UCC28780: ucc28780-CONFLICTING RESULTS FROM sluc666REV c

UCC28780: ucc28780- HVG LEVEL

robin gangopadhya18
Mastermind 6050 points
Part Number: UCC28780

Jaden:

 Any explanation you can offer why HVG pin does not go to 11V? It stays at 9.85 V.

Between pad HVG and depletion mode FET, there is nothing else other than 22V zener, 2200pF cap. 

So it would seem something is not turning ON 11V regulator in the controller.

We had a failure in the controller chip. HVG & VSW won't go to proper levels.  Although VDD did go up to 17.5V initially.

Any help in the understanding of this will be highly appreciated.

-robin

  • 0
    TI__Genius 9790 points

    Hi, Robin

    Jaden didn't cover E2E today, I've assign your post to Jaden, please expect a reply by day of Wednesday.

    Yunsheng

  • 0 in reply to Yunsheng Qu
    TI__Expert 7080 points

    Hi Robin,

    As you said , the controller had a failure , So did you have replaced it with a new controller and checked it's surrounding components , such as the Zener and cap.  if HVG is out of regulation , the internal regulator or external components already failed.

    Thanks.

  • 0 in reply to Jaden Ning
    Mastermind 6050 points

    Hello Jaden

    Thanks for checking in on this.

    We will put a new controller but first, we check all parts connecting to all 16 pins of the device BEFORE  a new part goes in.

    We know multimeter reading from REF pin to pin 16 is much lower impedance than a new one....the depletion MOSFET BSS126 is damaged(!) but nothing else has been damaged.

    We are going to change something- otherwise, it would be insane to do the same thing and expect a different outcome.

    This time, I am going to add 10 Ohm from pin 14 to its cap(.1uF). I do think REF output cannot handle charging/discharging .1uF even at 50ms rate.

    #2 change: Although the Eval kit works fine with 2200 pF, 0402 X7R cap at HVG node, we are going to replace it with NPO  of the same value 0805 size. The theory being 0402 sizes have poor Q and  high dC with voltage(dV being approx 17V- that is large for X7R)..maybe a factor in our board, who knows.....NPO has no such behavior. Very stable.

    Can I send you our special Test method in your email?...The ppt file has results of testing as well.

    Yeah, 28782  is identical for startup- which is where we are stuck. Won't go there yet.

    -robin

  • 0 in reply to robin gangopadhya18
    TI__Guru**** 189399 points

    Hi, Robin,

    Please send Jaden a friend request, and then you can send him a DM with your file.