DRV8825: NFAULT pulled down and fail to run

Hi  team,

My customer is using DRV8825 for step motor driving. Days ago they discovered 5 failure parts out of 1000. The failure is that the NFAULT node is pulled down after there comes STEP signal, and no output current, as shown in below Fig.1 and Fig.2.

Fig.1

Fig.2

They have conducted cross experiments: put a failure part into a new board, still failure; put a new part into the original board, failure disappears, which indicates that the failure goes with the device.

Below are the schematic, the data sheet of the motor they are using and the normal part test results.

Fig.3 schematic

Fig.4 motor spec

Fig.5 normal part

Fig.6 normal part

I wonder do this part have such problem before? Or what may be the cause for this problem?

Looking forward to your reply! Thanks!

George Zhao