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UCC256301: UCC25630X question

Masazumi Ishii
Genius 3945 points
Part Number: UCC256301

Hello.

I have a question about UCC25630X.
We are evaluating using UCC25630 XEVM (Board received before release).
When entering the burst mode, the tone sounds from the transformer.

Please let me know how to take measures.

thank you.

  • 0
    TI__Mastermind 26215 points

    Hi Masazumi-san,

    Thanks for your interest in UCC256301. I would suggest taking a look at the low side gate on an oscilloscope and determine the burst segment frequency you are currently operating at. One option is to tune the controller to enter burst mode at a lower power level by adjusting the values of R14 and R15. This will lower audible noise but will result in lower light load efficiency.

    Also in the upper right hand corner there should be a silkscreen marking which says SV601296xx. Could you tell me what the last two digits are? It is possible your prototype EVM has a different transformer than the released EVM.

    Best Regards,
    Ben Lough

  • 0 in reply to Benjamin Lough
    Genius 3945 points

    Hello.

    Ben-san

    Silkscreen marking for evaluation:SV601291E3-001.
    Attach photos of transformers.

    Thanking you.

    Microsoft PowerPoint - UCC25630Board.pdf

  • 0 in reply to Masazumi Ishii
    TI__Mastermind 26215 points
    Hi Masazumi-san,

    Could you request a new EVM? The transformer on the released version of UCC25630 EVM is much quieter.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Genius 3945 points

    Hello.

    Thank you for your answer.
    UCC 25630-1 EVM - 291 confirmed that the sound is getting smaller.
    There are additional questions.

    There was an application note on the audible noise at burst.
    SLUA836–August 2017
    UCC25630x Practical Design Guidelines.
    page7
    6.2 Soft Burst On Circuit

    Furthermore, I will consider this circuit and think about reducing the audible noise.
    Please tell me how to determine the constants of this circuit?
    Is there a calculation formula?

    Thank you.

  • 0 in reply to Masazumi Ishii
    TI__Mastermind 26215 points

    Hi Masazumi-san,

    I would suggest adding the following circuit:

    This circuit will provide a certain soft-on/soft-off when in burst mode. 

    I would start with R1=150kΩ, R2=150kΩ, R3=50kΩ and C1=10nF. Increasing C1 slows the rate at which the PNP turns on, which slows the rate at which you pull current out of the FB pin. This also extends the period of time VCOMP is above the burst threshold.

    Ultimately, this results in more burst packets delivered during each burst period and less frequent burst periods. This helps to avoid the audible noise region but with higher output ripple.

    Best Regards,


    Ben Lough