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Original question:

LMG3410R070: H-bridge gets /FAULT interrupts

LMG3410R070: Isolated DC/DC powersupply clairification

Martin Belohorka47
Prodigy 60 points
Part Number: LMG3410R070

Hi

I have been struggeling with an H-bridge built with 4 LMG3410R070. Sometimes I get an fault indication signal and I always get it from the same FET. One of the top once. There is no reason to suspect too high temperature (max 65C seen with IR-camera) or too high current, no more than 4A. I therefore wonder if there could be something wrong with my powersupply.

I have used 1 RKZ-2512S for each LMG3410R070 due to layout situations. They are decoupled on the GAN side with 2*10uF + 100nF as well as decoupling close to the GAN fet in accordance with the datasheet.

I have not yet added a 18V zener protection. The components are ordered (what would by the way be a suitalble protection zener?)

I would also be interested if someone could shed some light to the following line from the LMG3410R070 datasheet

" Minimizing the inter-winding capacitance of the isolated power supply or transformer is necessary to reduce switching loss in hard-switched applications."

I don't believe i have high switching losses as i cant seen any high temperatures. but could this perhaps be the cause of the problem i am seeing and if so, can you point me toward a more suitable isolated DC/DC supply

Best regards

Martin

  • 0
    TI__Genius 16390 points

    Hi Martin,

    Thanks for contacting us. Are you providing 5V to the EVM? The EVM has both high and low side isolated power supply to generate 12V needed for the gate driver. Also the 16V zener diode should be there on the EVM as well.

    Is it always the same FET has fault? Have you tried to swap a EVM to see if you observe the same issue? Also it would be helpful if you can capture the high and low side PWM, and switch node waveform. It would help us better troubleshoot the issue.

    Thanks!

    Regards,

    Yichi Zhang

  • 0 in reply to Yichi Zhang.
    Prodigy 60 points

    Hi

    I am not using the EVM but rather a full H-bride on own board. Here is 1/4 (The top left part) of that H-bride

    As i said, it is powered by a RKZ-2512S and as i don't see any main reason for a overcurrent or overvoltage, i am now investigating the possibility of UVLO instead.

  • 0 in reply to Yichi Zhang.
    Prodigy 60 points

    I notice that I have no pull-up toward 5V on /LPM. Instead i pull it directly to 5V. That cant be the issue, right?

  • 0 in reply to Martin Belohorka47
    TI__Genius 16390 points

    Hi Marin,

    Sorry I just realized you are using a custom GaN card. I'm not familiar with RKZ-2512S. Is it an isolated power supply solution that's supplying power to both high and low side? 

    Right now UVLO or short circuit caused by shoot-through can be two suspects. Previously I mentioned to take a look at PWM signal and switch node waveform, and that can give a clue if shoot-through happened.

    Also if you could share the full schematics that would help as well (or a half bridge including a high and low side device together). Thanks!

    Regards,

    Yichi Zhang

  • 0 in reply to Martin Belohorka47
    TI__Genius 16390 points

    No the 5V on LPM should be okay.

    Regards,

    Yichi Zhang