Hi,
We have a problem with a motor driver board. The application is a pump and the board has two DRV8711 that drives two stepper motors. The board has been out for a couple of years now and we are getting failure reports from our customers. It looks like the boards work (seemingly) without any problems for a while before the problem occurs. We do not know how much the pump has been used by the customers but we save some statistics in flash memory and it shows that the boards have been powered up for thousands of hours before the failure.
When analyzing returned boards the drivers report OCP fault. I have done some measurements and found some strange behaviors. I have set the oscilloscope to trigger at FAULT falling edge and measured gate voltages and Uds. Image below shows: Blue gate Q20, Red gate Q16, Green Uds Q19, yellow gate Q19, Trig FAULT negative edge (time 0us)
When the gate voltage to Q19 falls below 3,8V the Uds voltage starts to increase and when it goes above 1V OCP triggers. Why does the gate voltage make these strange steps?
When looking at the gate voltages in general I can see some other strange behaviors. Image below shows gate signals.
Blue gate Q20, Red gate Q16, Green gate Q15, yellow gate Q19
Edges of gate signal to Q15 and Q20 looks strange and gate voltages for Q16 and Q19 shows a bump. Voltage levels for bumps are 2V and 2.6V. This image is taken during motor hold current, OCP is not triggered.
What can cause this gate voltage levels?
Best Regards
Erik
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