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UCC28C44: UCC28C44 has Jitter come out, is it normal?

Bob Lee62837
Mastermind 7230 points
Part Number: UCC28C44

Dear support member

My customer used UCC28C44.

Specification condition
Vin:50V～140V （DC）
Vout:100V （DC）
Iout:45mA

fsw：118kHz


Jitter has appeared in the OUT output waveform and switching waveform when the input voltage is 50 V, 80 V, 110 V, 120 V.

Q1.
Is it normal behavior for jitter to come out?


Q2.
Is the cause of jitter related to the duty cycle?


Best regard.
Bob Lee.

  • 0
    TI__Genius 9130 points
    Bob,

    Can you provide more details please, a schematic, and waveforms?

    Are you saying that the jitter only appears at those exact input voltages, and is not there in between? Or are you saying that the jitter is always there, at these sample voltage levels, and also in between?

    Are they using the IC in current-mode or voltage-mode? What is the power topology (Flyback?).


    If we get more details, we will be in a better position to make comments and suggestions.

    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Mastermind 7230 points

    Dear Bernard Keogh,

    Thank you very much for reply.

    I want to send you a schematic and waveform.
    Could you teach your e-mail adress?

    Jitter occurs only with input voltages of 50 V, 80 V, 110 V, and 120 V, but not with other input voltages.

    Topology is flyback and current-mode.


    Best regard.
    Bob Lee.

  • 0 in reply to Bernard Keogh
    TI__Expert 7395 points
    Bob,
    Out may show some jitter due to noise on the control loops feedback, or if the load or input is varying in anyway or have ripple. If you have further questions please feel free to comment but i'll consider this thread closed for now.
    Regards,
    John
  • 0 in reply to John Stevens
    TI__Genius 9130 points
    Bob,

    It sounds like the issue may be related to control loop or noise.

    If there is jitter on the PWM output, then it is either coming from noise or jitter on the CS signal, or noise/oscillation on the COMP signal. These are the 2 inputs to the internal PWM comparator.


    Following an offline review of your schematic, the problem has since been resolved by increasing the cap C3 on the COMP pin (in series with 1 k), then it may be a loop stability issue, or possibly noise on the COMP pin (probably less likely).

    I would recommend that you measure the control loop gain/phase to verify the stability of your design.


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Mastermind 7230 points

    Dear Bernard Keogh,


    Thank you very much for reply.

    I reply my customer and I feedback it.


    If there is some question from my customer,
    Also, I will question.


    ​Best regard.
    Bob Lee.