FETs failing in 3-phase brushless motor H-bridge

GaN FETs and ICs in Applications Motor Drive
1

Hi,

I have designed a H-bridge using the LMG1205 as the driver and the EPC2022 as the low and high side FETs. We are using three pairs of circuits to drive a 3-phase brushless motor at about 40 kHz with a 100 ns deadtime. See circuit:

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It runs off a 48V supply and must produce currents up to 22A per phase. The circuit generally works very well however we have had a number of failures in two main instances:

  1. When the circuit is first turned on with a motor
  2. After the circuit completes all our inhouse testing and is installed in the final customer application.

We have monitored the temperature using a thermal camera and it only seems to be reaching about +45 degC.

We think the first instance may be due to poor soldering of either the FETs or the driver circuit, however are not completely sure.

An example of the second instance is shown below:

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Do you have any advice?

2

Hello,
we are sorry to hear about your troubles. Our FAE Pei-Cheng Huang will reach out to you for more detailed discussions and possible next steps.
In general, I would recommend taking a close look at your assembly process. X-rays can help determine if there are issues with the soldering. Optical pictures (at an angle) also help, and they can also help determine if there is any mechanical damage on the dies.
I also would like to mention that the EPC2022 is one of our largest devices and more critical in terms of assembly process. You might take a look at EPC2088: 100 V, 231 A Enhancement-Mode GaN Power Transistor (epc-co.com), same Rds(on) but smaller. (much cheaper too)