Other Parts Discussed in Thread: CSD19532Q5B,
Over-Current Latched Failures:
I'm seeing what appears to be random behavior on the first run command (post a reset or a pwr up) issued to a motor (most boards OK, small percentage fail). If the first run command works, then subsequent run commands work OK without failure, even on a bad board. I found setting the OC behavior of the 8301 to Over-current Latch mode produces the OC error on bad boards, however, changing the behavior to Current Limiting seems to fix the bad board with no errors on the first (or subsequent) runs. Wonder what is different about the first Run (actually a Ramp command) command that might setoff the bad boards. Also increasing the OC threshold from 0.138V to 0.155V seems to fix the problem as well. Lowering the Threshold a few notches and the bad board continues to work most of the time, indicating the rare OC is not real perhaps.
Also, monitoring the 48V current supply, I don't see an over current. My normal Ramp produces a peak current during acceleration of about 140mA and when I get the OC latch error the scope doesn't trigger. If this were a real OC I would think I would see something. I don't see any punch through current when looking across the sense resistors either so I think the dead-band is sufficient.
I had a great deal of trouble trying to pass emissions testing. Tried setting the drive current down to 0.25A but no help (little to no effect). I adjusted the gate resistors to 70 Ohms, going above 150 Ohms caused the DRV to stop working and I don't know why. Next, I had to add RC snubbers (C=3300pf, R = 1 Ohm across each MOSFET, CSD19532Q5B) which finally fixed the bad emissions. Not sure if any of this is causing the internal workings of the DRV to work inconsistently on a few boards or not. I also have dead-band dialed into the Piccolo, but don't remember how much.
We tested many boards in OC limiting mode in development and never saw this and perhaps was masking some other underlying issue. These boards also work in OC latched mode and these older boards still work OK but it seems like the new batch are failing? Is it possible we have either bad parts (ESD damaged perhaps, given the supply chain issues) or something else.
Any suggestions appreciated.
Thanks.