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UCC256302: after the burst operation

ACGUY
Guru 11170 points
Part Number: UCC256302

Hello E2E,

In an individual, on the board using UCC256302, when the burst operation is exited, high side FET become to on at ISNS during fall down.

Please ket me know, is it normally? or malfunction?

e2e.ti.com/.../TI_5F00_Inquiry.xlsx

Regards,
ACGUY

  • 0
    TI__Guru 72115 points

    We have received your inquiry and are looking into it.

    Regards, 

  • 0 in reply to Mike O'
    TI__Guru 72115 points

    Hello,

    I believe what your are observing is the converter detecting zero current switching when it comes out of burst mode. The controller will adjust the gate drive signals and frequency until the converter is not zero current switching on the primary.  I believe this is normal and should not cause any issues with the design. 

    Please refer section 6.13.14 ZCS Region prevention and figure 29, 39, 40 and 42.  When ZCS switching is detected the SS voltage is pulled down through Rdischarge.  This resistor should have been labeled RSSdown and is roughly 447 ohms.

    If you relook at HO, LO, and Isns you will observe this is what is occurring.  If this is not causing an issue with output voltage ripple, I would not make any adjustments to the design.

    Regards,

  • 0 in reply to Mike O'
    Guru 11170 points

    Hello,

    Please let me know that why did not happen that operation on other device? I want to know reason that what different each device operation.

    Regards,

    ACGUY

  • 0 in reply to ACGUY
    TI__Guru 72115 points

    Hello,

    The difference may be due to resistor and capacitor tolerances on the VCR, LLC and ISNS pins.

    Regards,

  • 0 in reply to Mike O'
    Guru 11170 points

    Hello,

    Thank you for reply.

    I will suggest device swap between each boards to customer.

    BR,

    ACGUY