One of our design uses stepper motor driver TMC222.
The end product shall be subjected to lightning test per DO160G waveform4 level 3 => exponential pulse of 300V limited to 60Amps (6.4us to reach the peak, and 69us to decrease down to 50% of the peak), positive and negative polarity
The TMC222 motors outputs have been protected on the board by bipolar voltage transient supprossor (VTS) SMDJ22CA.
The following problem has been found during the test:
Test was OK. The VTS has been activated and blocked the voltage up to 37V. Current through the VTS was an exponential pulse up to 57Amps.
Test was FAILED. The VTS has been activated and blocked the voltage up to -37V. Current through the VTS was an exponential pulse up to -57Amps.
At the end of the test, the TMC222 motor outputs were “short-circuited” with the ground pin.
To understand why the transistors MOS of the TMC222 have been damaged, I need to understand how the H-Bridge driver has been designed inside (which protections implemented, characteristics of the MOS/diode).
For the negative pulse, I was expecting that the current did not go through the VTS but through body- diode of the low-side MOS. Apparently, I was wrong, since I measured the current peak through the VTS. It means that it is not the current peak that has damaged the MOS, but this is the -37V peak voltage.
Why does a negative voltage pulse not make the body-diode of the low side MOS turn on? Is there some protection inside the circuit to limit reverse current?
Can a negative pulse of -37V (during around 100us) on a motor output damage the circuit? What is the Vds maximum voltage of the MOS? The Vgs maximum voltage?
Thanks in advance for your help.
We need to qualify our design very quickly.