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LMG2650: Using LMG2650 in parallel

Francis Jiang
Expert 3260 points
Part Number: LMG2650

Tool/software:

Hi Team,

Can this device be used in parallel? Such as 6pcs. Customer would like to use this device to replace LMG3426 to save size.

Would like to know any risk here in such design. Such as the internal gate drivers are also in parallel, maybe cause circulating current issue due to propagation delay time differences?

BRs,

Francis

  • 0
    TI__Expert 4520 points

    Hello Francis,

    The risk with paralleling our integrated GaN devices can be mitigated with proper design, but some considerations need to be evaluated and depend on hard or soft switching conditions.
    Can you give me more information about the application and switching conditions?

    Thanks,
    Zach Soviero

  • 0 in reply to Zachary Soviero
    TI__Expert 3260 points

    Hi Zach,

    Customer is developing Server PSU, about 10kW. Previously, they use TI LG3426R030 as the PFC+LLC power FET, but they think the Rdson and size is too larger. Need 8pcs in parallel(one bridge) to achieve the target Rdson.

    So they would like to try the half-bridge GaN LMG2650. Need 6pcs in parallel to achieve the target Rdson, but the size is half. That's the background.

    PFC frequency is ~300kHz, LLC is ~100kHz.

    Could you please help explain your below comments in detail? Thanks in advance.

    Zachary Soviero said:
    some considerations need to be evaluated and depend on hard or soft switching conditions.

    BRs,

    Francis

  • +1 in reply to Francis Jiang
    TI__Expert 4520 points

    Hello Francis,

    Our integrated gate drivers require some attention when trying to parallel devices.
    In hard switching conditions, current may be shared unequally between devices if one turns on before the other (2 FET parallel example). The large inrush of current can damage the turned-on device and must be prevented.
    To mitigate this issue, we recommend placing a decoupling inductor between the two FETs so that the inrush current speed is reduced to a point where both FETs have time to turn on and share current equally

    In soft switching applications this is not an issue since there is no large inrush current to worry about.

    Thanks,
    Zach Soviero

  • 0 in reply to Zachary Soviero
    TI__Expert 3260 points

    Hi Zach,

    Got it, thanks for your reply, I have provide it to customer, but customer is curious about why the soft switching don't need to consider the inrush current issue, or whether the soft switching will also happen the current shared unequally between devices?

    BRs,

    Francis

  • +1 in reply to Francis Jiang
    TI__Expert 4520 points

    For soft switching, the stress on device is very low, and switching loss are also very low, so there is no concern about SOA curve or thermals.
    In soft switching, either voltage or current will be at or near 0, so the total power passing through device will be small and therefore decoupling inductor is not needed.

    Thanks,
    Zach