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UCC24624: About light load operation

ACGUY
Guru 11170 points

Part Number: UCC24624

Helo E2E,

Our customer is using the UCC24624 with LLC.
The UCC24624 has pulses two time output from one VGx at 1-cycle. It happen on light load.

Question;
1: Please let me know the reason or cause for it.
2: Is it normal operation?
3: Could TI advice about it for resolve?

Regards,
ACGUY

  • 0
    TI__Genius 9790 points

    Hi, ACGUY

    1. The reason is the current duration is very narrow and let VGX has output, but the minimum turn on time is 450ns, so there is negative current.

    2. It is not normal operation but has no risk. it is better to  fix it.

    3. it is recommended to add RC filter on VDx pin, 1kohm+100pF.

    Yunsheng  

  • 0 in reply to Yunsheng Qu
    Guru 11170 points

    Hello Yunsheng,

    1
    : Customer connected 1.8k-ohm and 100-pF RC-filter on Vgx, FETs are had switching serge.
    2
    : They changed the value of RC-filter
    from 1.8k-ohm and 100-pF
    to 1.0k-ohm and 100-pF.
    The switching serge alleviated.
    3
    : They changed further the value of RC-filter
    from 1.0k-ohm and 100-pF.
    to 1.0k-ohm and Open.
    The switching serge disappeared. But Vgx outputs 2-pulses under light load.

    I understand that there is a trade-off between 2-pulse output and switching surge.

    ACGUY

  • 0 in reply to ACGUY
    TI__Guru**** 189401 points

    Hi, ACGUY,

    Yunsheng is off for the New Year holiday.  He will respond next week when he's back.

  • 0 in reply to ACGUY
    TI__Genius 9790 points

    Hi, ACGUY

    You are right about the trade-off.

    I suggest you to verify the reliability with 2-pulse output. 

    Yunsheng