LMG3411R050: Is there a way to Reset FAULT pin?

Hi Zach,

The board was powered off overnight, but the FAULT is still there. The FAULT LED lights up as soon as the board is powered again.

We have used the same design as TI has used for LMG3411EVM-018.

For now, as you suggested, I will try to set the IN pin Low and see if the FAULT is RESET.

If during startup the fault pin is triggered for any reason, it will remain low unless reset. From your message, it seems like there might be an issue with your start-up sequence.

For now though, as you mentioned, I would attempt to reset the fault pin using the IN pin and see if that resolves the issue.

Hello Arvind,

Could you let me know what hardware you are using? We offer the LMG3411EVM-018 as you mentioned and the LMG34XX-BB-EVM motherboard which are compatible with one another. Are you using either system directly or have you made your own?

I may be able to offer you more technical help if I can get some more information about your hardware setup.

Regards,

Zach

Hi Zach,

We have our own board but we are using the same design of LMG3411EVM-018 for our purpose. LMG34XX-BB-EVM is a buck converter while our design is for a Full Bridge Inverter.

I see, earlier you mentioned a FAULT LED being triggered, are you referring to a physical LED lighting up or just a pin name? The LMG34XX-BB-EVM mother board has multiple LEDs, one of which used as the fault indicator, but the LMG3411EVM-018 daughter card does not. You clarified that you made your own full bridge motherboard so I am wondering if you included LEDs there as well.

I am referring to a physical LED which I have placed for Fault indication. I have used the complementary PWM circuit generating 50ns deadband from LMG34XX-BB-EVM motherboard. The Fault LED is connected exactly at the same place as it is on LMG34XX-BB-EVM motherboard. I can see complementary PWM with deadband at the end of this circuit which then goes to the digital isolator IC.

Understood, have you been able to manually reset the FAULT pin of the device after startup by setting the IN pin low as mentioned earlier? If so, did this fix any issues, or does the FAULT pin immediately move back to a triggered state?

Hi Zach,

I am not able to Reset the FAULT pin by setting IN pin low. The FAULT pin immediately move back to triggered state.

Are you able to provide your schematics and/or test procedure for this case? That would help very much.

Regards,

Zach

Hi Zach,

Here is the half bridge schematic.  Its replicated for the other half bridge of the inverter.

The first thing to do is check the VDD, LDO5V, FAULT, and VNEG pins to verify if they are reporting properly. After powering the system on, measure the voltage across C123 and C140 to verify VDD is within proper operating specifications (between 9.5 and 18V). Then measure across C125 and C141 to see if each LDO5V pin is outputting 5V, do the same for C136 and C145 on the VNEG pin which should output -14V. Last, try and measure each fault signal individually before reaching the AND gate U21A. This will tell us if the problem is related to external fault circuitry or within the devices themselves.

Thanks Zach, I will test the board as you suggested and get back to you.

Hello Zach,

I did the test as you suggested. The VDD voltage across all the GaN switches is within the operating specification (Approx. 12.5 V). However, some switches doesn't have the LDO5V output across the capacitor and other doesn't have VNEG voltage.

Can you provide me with more schematic details for the motherboard you have made including power supplies for each of the devices? I feel that this could be part of your issue and would like to investigate further.