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UCC28782: Regarding selection of secondary side synchronous rectification controller

Kaji@PAN
Mastermind 7420 points
Part Number: UCC28782
Other Parts Discussed in Thread: UCC24612, UCC28780, LMG3616, LMG3622

Hello,

I asked a question in the thread below about the secondary side synchronous rectification controller used with UCC28782 and got an answer.
I would like to ask you a similar question as I would also like to get an opinion from the UCC28782 perspective.

I am using Infineon's IR11662S as the secondary side synchronous rectification controller in the UCC28782 circuit.
However, when evaluating the manufactured board, abnormal oscillation-like behavior was observed in the switching waveform.
Therefore, I am considering using UCC24612 instead of IR11662S.
(Question 1)
IR11662S has similar characteristics to UCC24612-2, but is it better to use UCC24612-1?
(Question 2)
UCC28780 recommends the use of UCC24612, but UCC28782 does not seem to recommend its use.
The EVM of UCC28782 also uses MPS's MP6908.
Please let me know if there is a reason.
(Question 3)
Does the selection of secondary-side synchronous rectification controller affect the switching behavior of the UCC28782?
For reference, I have attached the UCC28782 calculation tool that I set up.
The main FET of UCC28782 is LMG3622, and the one for active clamp is LMG3616.

Best regards,

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1361841/ucc24612-regarding-selection-of-secondary-side-synchronous-rectification-controller

8585.UCC28782 Excel Design Calculator RevC 20240515.xlsx

  • +1
    TI__Mastermind 24365 points

    Hi Kaji-San,

    Thank you for reaching out.

    Q1. UCC24612-1 has an inherently short turn-on propagation delay (80 ns typical) and can be used with the converters that need shorter delay, such as standard Flyback converters or Active Clamp Flyback converters using GaN MOSFETs as main switches. UCC24612-2 has a longer 170-ns turn-on delay, to further ignore the leading edge spike and can be used with Active Clamp Flyback using Si-based super-junction MOSFETs as the main switch or LLC converters.  Due to the longer turn-on delay, UCC24612-2 also increases its minimum on time-to 540ns to allow further enhancement on dealing with resonant-shape current, which makes a better choice for Si-based super-junction MOSFETs as the main switch or LLC converters. So I think you should use UCC24612-1.

    Q2. We found that during burst-mode of the ACF controller, there are some aspects of the DCM ringing between bursts that confuses the UCC24612 operation and inconsistent pulse widths and pulse skipping would result.
    We found that the MP6908 does not react that way and and provides better burst-mode performance in this case, so we used that SR controller for the EVM. You could try UCC24612 as we have many customers who have successfully used this.

    Q3. I do not think it should have a big impact as these are standalone and should be able to operate similar.

    Regards,

    Harish