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UCC256402: Run UCC25640 at high frequencies

Part Number: UCC256402


I am considering designing an LLC at high frequencies using the UCC25640 device.
The purpose is to reduce the size of the circuit. The switching frequency is assumed to be 300kHz to 1MHz.
So I would like to ask you a question about transformer.

If the transformer is miniaturized, it will be difficult to make the leakage inductance with one transformer, and it will be necessary to make another inductor, so there is a concern that it may go against the miniaturization.
I would appreciate it if you could give me your opinion on the above.

I have one more question.
The UCC25640 has a high-side driver inside the IC, but is there any problem with the drive capability even if the frequency rises to 500kHz?

Best regards,

  • Kaji,

    The maximum switching frequency after soft start of UCC25640X is not recommended to be higher than 350kHz, because:

    1. the thermal of UCC25640X is critical because loss of high side low side driver inside the IC

    2. if the switching frequency is high, the resonant current at turn off event of HO/LO is small, which could trigger ZCS protection.

    We don't have suitable solution to support LLC upto 1MHz.


  • Thank you for your reply.
    I understand the switching frequency.
    Later, the first question is, is it possible for you to inform me about leakage inductance?
    The purpose of this question is to reduce the circuit size.

    Best regards,

  • Hi, Kaji

    I don't think external resonant inductor is must for high switching frequency LLC. I think planer transformer with leakage inductor is fine.