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UCC25630-1EVM-291: How to built in LMG3410-HB-EVM

Part Number: UCC25630-1EVM-291
Other Parts Discussed in Thread: LMG3410-HB-EVM,

Hi all,

I have UCC25630-1EVM-291 and LMG3410-HB-EVM.

I want to change the LLC Mosfets Q1,Q2  from  two SPW20N60CFDs to two LMG3410s.

Use LMG3410-HB-EVM as is OK.   Primary 5V is from  another power supply unit.

I expect one or two percent efficiency up by this modification.

I want to know the best connection method.

Best regards,

H.DOI

  • Doi san,

    Thanks for your response. I will get back to you with our response.

    VA
  • What is the series resonant frequency that you are planning to run the LLC converter at? From the perspective of the GaN stage, Bluestone has built in drivers which generate 12V for MOSFETs. We use these as PWM for GaN gate and divide the driver voltage by a factor of 3, as GaN Abs Max IN voltage is 5.5V
  • I want to raise up the Minimum switching frequency to 300kHz.

    But UCC25630x Design calculator (Excel) does not meet.

    Japanese three big companys, which already use Fuji-elec LLC ,want new excel calculator for fsw(min) = 300kHz.

    Fuji-elec LLC IC is not good for many things, but the three maker already use it for their product without no problem.

    So their only one hope for UCC25630x is raise up frequency to make smaller transformer for cost and space reduction.

    Anyway you can't make that, so I only want to use LMG3410 now, no frequency change.

    Load and frequency are not changed so that UCC25630x RVCC 12V can be use for LMG3410 boot strap? enough current output?

    If yes, internal two iso. DCDC are no need. OK?

    For divide the voltage input, How about this,

    Change R3 and R11 from 49.9 to 470ohms.

    Change C2 and C17  from 68pF to 10pF

    Add on  330ohms onto C2 and C17

    GaN sw node, ISO_RET_H can be direct connect to UCC25630x  HS ?

  • Let me get back to you on these questions
  • Hello Doi-san,
    Let me try to help with the GaN related questions. First of all, we don't recommend running UCC25630x with LMG3410 at higher resonant frequencies (>300kHz) due to large start-up current. UCC25630x's maximum switching frequency is defined as 1MHz in the datasheet. If the circuit is designed to operate at resonant frequency of 300kHz, the start-up frequency will be limited and, start-up would still be rough because large start-up current can cause transformer to saturate.Larger resonant frequency designs does have a potential to not only saturate transformer but can trigger integrated over-current protection of LMG3410. We will have a reference design coming up soon. Please check back later for this design.

    The maximum current for UCC25630x is defined as 100mA, and LMG3410 supply current for 300kHz is around 15mA, so a total of 30mA for 2 FETs. However, during start-up, switching frequency will reach to 1MHz and two LMG3410s will draw 80mA current. I will get back to you on this.

    I would first remove digi ISO, short in and out pins to bypass digi ISO, then change R3 and R11 from 49.9 to 670ohms and replace C2 and C17 with 330ohms (1/3 ratio), bypass R4 and R12, replace C4 and C19 with 10pF.

    Yes, HS of UCC25630x can be connected to ISO_RET_H net of LMG3410 HB EVM, as UCC25630x has internal level shifter for gate driver.

    One more thing I have to mention is the 3rd quadrant operation of LMG3410 during dead-time. GaN FETs have large 3rd quadrant (reverse conduction) voltage drop, which needs to be minimized in order to have higher efficiency. However, UCC25630x has a minimum dead-time of 100ns. This would cause additional losses at high switching frequencies.

    I hope this answers your questions.
    Best,
    Serkan
  • Serkan-san,

    Thank you for your reply.

    I will wait for your new reference design.