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LMG3522R030-Q1: PWM Inverter design

Part Number: LMG3522R030-Q1
Other Parts Discussed in Thread: ISO7721, ISO7741

HI, we are working on a inverter design with the LMG3522R030-Q1 to be used with Li-on batteries. We have made a rough board with just the H-bridge to test the GAN-FET devices out but we are running into problems when running the inverter. On very extremely low frequencies it seems to work ok, the GAN-FETs can give out the 400VDC we input. But as we start the switching with the desired frequency to generate the VAC the circuit breaks down and both the digital isolators and the GAN-FETs break.

Pherhaps we have made some mistake with the grounding/isolation but I can not for the life of me find the issue. I have attached the schematic and I have gerber files as well if you want. I would really appreciate some assitance here, thank you in advance.

/Anton LindströmInverter Prototype_2022-01-12.pdf

  • Hi Anton,

    Thank you for the question. One concern is with the isolator selection. The MAX14935BAWE you are using only has 25kV/us CMTI rating and our suggested isolator ISO7721 has capability to go to 100kV/us. So if you are operating at slew rate higher than 25kV/us, the isolation can have some risk.

    Additionally, would you happen to know the PG of this device?



  • Hi Noah, thank you for your quick reply!

    Ok I see I completely missed this, the only reason the MAX1493 IC is there was because I could not buy the ISO7741 chips due to the global shortage. I will change it to IL 717E from NVE Corp, really the only chip I can order that fulfills the requirements.

    But this should be the reason it does not work when switching starts, I am a bit confused as to why this would damage the GAN-FETs however, should this not simply cause errors on the control/PWM pin?

    I will order new ICs and test and mark this as resolved if it works,

    thanks again / Anton

  • Hi Anton,

    It could be coming from the layout related signal integrity, but it's hard to know where exactly with the given information. This should help eliminate some variables. Please let me know if this works.



  • Hello Noah apologies for the late reply. I could not get a hold of another isolator that worked well so I ordered 2 of your EV-board for the GAN-FETs and borrowed the isolators from them, and that did indeed solve the problem!

    So thank you for your help, I´m new to this type of FET so I´m sure i will have more questions to post about.

    Regards Anton