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LMG3522R030-Q1: Questions Regarding LMG3522R030Q1 GaN Switch

Mahmoodreza Eskandarpour Azizkandi
Prodigy 10 points
Part Number: LMG3522R030-Q1
Other Parts Discussed in Thread: ISO7741

Tool/software:

Dear TI Experts,

I have some questions regarding the LMG3522R030Q1 GaN switch:

  1. When paralleling two LMG3522R030Q1 devices for higher current applications, what considerations should we take into account in our power supply, isolator section, or other components? Is there any application note available on this? Specifically, if I plan to use the UCC14130Q1 with 1.5W, 12V input, and 12V output, should I use two of these power modules for paralleling two LMG3522R030Q1 devices, or is one module sufficient? What other points should I consider?

  2. What is the total gate charge (Qg) of the LMG3522 GaN device? I noticed that this parameter is not provided in the datasheet.

  3. In this generation of the LMG3522R030Q1 GaN device, if we do not have adaptive dead time control and instead set our dead time for the worst-case scenario, does this device offer an ideal diode mode to improve third quadrant losses? The datasheet mentions that the ideal diode mode is only activated during overtemperature shutdown. If there is no overtemperature issue, can the device still operate in ideal diode mode?

Thank you for your assistance.

Best regards,

Mahmoodreza

  • 0
    TI__Expert 3415 points

    Hi Mahmoodreza, 

    1. What switching frequency are you planning for this design? Our devices' current consumption at the VDD pin (largely dominated by gate driver current consumption) is dependent on the switching frequency, as with any gate driver. You may refer to Figures  5-9 and 5-10 in the datasheet to estimate the total power consumption of each LMG3522 device at the targeted switching frequency. 

    2. Since the gate driver and GaN FET are integrated in the same package, the Qg is not published in the datasheet. For estimating power loss estimates due to the gate driver, it is best to refer to Figure 5-9 and 5-10. This current consumption includes current to charge the gate capacitance as well as current for internal OCP/UVLO/BB blocks.

    3. This device does not offer ideal-diode mode control outside of the overtemperature shutdown condition. The application's dead-time should be optimized to minimize time spent in conducting with third-quadrant operation. 

    Best Regards,

    John

  • 0 in reply to John Gomez
    Prodigy 10 points

    Dear John,
    Thank you for your detailed response. I have a few more questions regarding the paralleling of LMG3522R030Q1 GaN switches:

    1- If my switching frequency is 500 kHz, would one UCC14130Q1 power module be sufficient for paralleling two LMG3522R030Q1 devices?

    2- For the isolator section, should I use two separate isolators (e.g., two ISO7741) for each paralleled GaN switch, or would one isolator be sufficient for both?

    3- When paralleling two LMG3522R030Q1 devices, should I connect each pin of the switches together directly, or do I need to include some resistors? Could you provide specific guidance on how to handle the pins of the two GaN FETs during paralleling?

    4- Are there any application notes available for paralleling GaN switches from TI that you could recommend?

    5- Is there a TI GaN FET device that offers ideal diode mode outside of the overtemperature shutdown condition? If such a device exists, I would consider switching to it.

    6- Regarding the UCC14130 power module, which provides both 12V and 5V outputs: for the isolator supply (5V), I have two options. I could either use the 5V output from the UCC14130 module or use a GaN LDO 5V. Which option does TI recommend?

    Thank you for your continued assistance.

    Best regards,
    Mahmoodreza

  • +1 in reply to Mahmoodreza Eskandarpour Azizkandi
    TI__Expert 3415 points

    Hi Mahmoodreza, 

    1. Given that the current consumption at 500kHz for each GaN device is ~70mA, the total power consumption would be 2*70mA*12V = 1.68W, which would exceed the power rating of the UCC14130Q1. In this case, two of these devices would have to be used. 

    2. Each high-side device is recommended to use its own digital isolator. 

    3. For hard switching applications, a decoupling inductor is recommended to place atthe SW node for hard switching based topology toimprove the dynamic state performance. The recommended value of this inductor is 1uH. 

    4. We can send one over to your email. 

    5. Our GaN portfolio presently doesn't have any devices that operate with ideal diode mode outside of the overtemperature shutdown condition.

    6. We recommend to use the 5V output from the LDO5V pin on the GaN device.

    Best Regards,

    John

  • 0 in reply to John Gomez
    Prodigy 10 points

    Dear John,

    Thank you very much for your detailed and helpful answers. I truly appreciate the guidance you've provided.

    I would also appreciate it if you could send the relevant document regarding GaN in parallel with my email.

    Best regards,

    Mahmoodreza