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Failed electronics from customer
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mattko:
Hello all,

In our company we just had a returned electronics from our customer. It is a three phase inverter for motor control. The problem is that high and low side MOSFET are in short circuit, which means 0,5 Ohm between VDC and GND input connections. Gate resistor is 10 Ohms and driven from internal driver in the MCU. Due to company policy, I can't give every information there is.

We allready performed CT scan, thermal picture, potential root cause testing etc. But we did not found the problem.

Any suggestions on how to find the root cause would be greatly appreciated.

Best regards!
Siwastaja:
Look at a working unit instead.

Test and verify that your overcurrent protection kicks in properly.

Measure switch node ringing (peak voltage) using high bandwidth (at least 100MHz?) oscilloscope with full load. Is it close to the MOSFET ratings?

Measure gate voltages with full load. Does it approach the limits, even for very short times? How much negative does it go? Some gate drivers die at slightly negative gate voltages, say, just -5V will kill some.
moffy:
You might not find out, if it was say an overvoltage event/spike(externally induced). Just repair it. If you get multiple similar failures then you have a problem.
MagicSmoker:

--- Quote from: mattko on October 07, 2019, 06:45:42 am ---In our company we just had a returned electronics from our customer. It is a three phase inverter for motor control. The problem is that high and low side MOSFET are in short circuit...

--- End quote ---

I bet you are using one of those shitty level-shifting driver ICs that require a bootstrap charge pump for the upper MOSFET, aren't you? Those things are notoriously sensitive to high dV/dt leading to all sorts of mysterious failures at frustratingly random times.

Psi:

--- Quote from: mattko on October 07, 2019, 06:45:42 am ---Gate resistor is 10 Ohms and driven from internal driver in the MCU.

--- End quote ---

Is this a specific "gate driver" built into the mcu designed to drive mosfets? or just a GPIO ?

Do you have TVS/Zener diodes between the gates and sources to prevent Vgs spikes from exceeding the max and damaging the mosfets?
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