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UCC25600: About off-resonant of UCC25600

Shuji Ishiwata
Mastermind 7825 points
Part Number: UCC25600
Other Parts Discussed in Thread: UCC256301

Hi Team

I have a question about UCC25600
Please check my question.

1)If the voltage of PFC drops due to instantaneous power failure, we are concerned that off-resonant will occur.
  Please tell me about the concerns and behavior of the IC by off-resonant (device and other destruction etc.).

2)The maximum and minimum frequencies can be set with the RT pin,
  I understand that it can protect off-resonant by being clamped at minimum frequency.
  Is my understanding correct?

Best Regards,
Ishiwata

  • 0
    TI__Expert 8210 points
    Ishiwata-san

    The following PSDS papers explain operation for LLC
    Designing an LLC Resonant Half-Bridge Power Converter: www.ti.com/.../slup263.pdf
    Design and Optimization of a High-Performance LLC Converter: www.ti.com/.../slup306.pdf

    When the high voltage DC input from the PFC stage drops, the LLC converter will reduce the switching frequency to maintain a constant voltage regulation. Since the input voltage drops the gain of the LLC stage needs to increase to maintain regulation on the output. By properly setting the minimum frequency for UCC25600 you can guarantee that it will stay in inductive region and not enter the undesired capacitive region. Figure 9 in Designing an LLC Resonant Half-Bridge Power Converter illustrates this.

    We do have a newer LLC controller UCC256301/2/3/4 that has improved features over UCC25600. It integrates a high voltage half bridge gate driver, integrates x-capacitor discharge (optional) and has improved transient response from the hybrid hysisteretic control (more details available here www.ti.com/.../slua834.pdf). This new control scheme also includes improved capacitive region avoidance scheme. Details on this are in the datasheet section 7.3.14.1 (page 29).

    Differences between the 4 variants are available here www.ti.com/.../slyt728.pdf

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    Mastermind 7825 points
    Hi Eric-san

    Thank you your response.
    I could not check your document about this (www.ti.com/.../slua834.pdf).
    Please, you can modify to check document for me .

    Best Regards,
    Ishiwata
  • 0 in reply to Shuji Ishiwata
    TI__Expert 8210 points
    Ishiwata-san

    Sorry about that. Here is the correct link for hybrid hysisteretic control
    www.ti.com/.../slua834.pdf

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    Mastermind 7825 points

    Eric-san

    Thank you.
    I appreciate your support.
    Thank you in the future.

    Best Regards,
    Ishiwata