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Original question:

LMG3410R050: Using UCC28070 interleaved CCM PFC

LMG3410R050: GaN FET + Flyback controller for AC-DC Adaptor

user4542981
Prodigy 40 points
Part Number: LMG3410R050
Other Parts Discussed in Thread: UCC28740, UCC28780

If I want to use UCC28740 as Flyback controller, and use the LMG3410R050 to replace the MOSFET, to make the solution smaller. Is it possible and anything that needs to be considered?

  • 0
    TI__Genius 16390 points

    Hello,

    As far as using the GaN for Flyback topology, I don't see problems. You may post this question to the controller part number and check with the controller expert to see if it is suitable.

    Some customers are using UCC28780 with LMG3410 device for Active Clamp Flyback topology.

    For designing with GaN, some guidelines for PCB layout are:

    To minimize the power loop for lowest parasitic inductance:

    • Place GaN device and bypass capacitor as close as possible.
    • Use multiple small ceramic bypass capacitors similar to our half-bridge EVM.
    • Reduce the trace length in the lateral power loop

    For better thermal performance it can also follow our general design rules as multi-layer board:

    • Larger area of thermal vias for heat dissipation
    • Reduce board thickness

    When the power loop is minimized, the voltage ringing can be reduced and GaN Fet will have a better slew rate, which allows applications to take advantage of GaN.

  • 0 in reply to Yichi Zhang.
    Prodigy 40 points

    Hi Yichi,

    Thanks for your support. 

    I will take UCC28780EVM as reference.

    After check the EVM schematic, there‘s an additional question:

    The Flyback controller and GaN are powered by the voltage Pre_bias, which is generated by the auxiliary winding.

    When AC power on, the auxiliary winding may not be able to provide the voltage Pre_bias. And I didn't see any resistor from VBULK to Pre_bias.

    So how the Flyback controller can be powered when AC power just on, can you kindly advise me, thanks.

  • 0 in reply to Yichi Zhang.
    Prodigy 40 points

    Hi Yichi,

    Can you help answer the question above, thanks.

  • 0 in reply to user4542981
    TI__Mastermind 31180 points

    Hello User4542981,

    Thank you for your interest in the UCC28780 Active-Clamp Flyback controller.

    The UCC28780 does not require a start-up resistor to Vbulk because this function is provided by the Vsw-sensing transistor Q2 through the SWS pin. This is explained in the UCC28780 datasheet, Section 7.3.3 (VDD Pin) and follow-on Sections 7.3.5 (HVG and SWS Pins) and 7.4.8 (Start-Up Sequence).

    Kindly read through the datasheet to understand how this controller works.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 40 points

    Hi Ulrich,

    Thanks for your support, I've read the datasheet and got the details.