Hello Luis,
I completed the respin and have tested the new Rev C board with the same results as Rev B. I still see serious irregularities in the PWM output and the motion of the stepper motor is erratic. I attached a zip file containing the Rev C gerbers and schematic to this post using the Rich Text drag & drop method but I can't tell if it really was attached. If it was not then let me know how to get it to you.
There are three DRV8825 devices on this board and they are all behaving similarly so it has to be something in my design but so far I have been unable to figure out the issue. I simplified the test case somewhat by setting the device under test to single step mode and then observing the output in each of the four step positions. In each position there is distortion in the A output but not in the B output. This occurs on all three devices on the board. However, if I then start stepping at 40Hz, the distortion is intermittently on both A and B outputs.
If I switch to slow or mixed decay, the problem goes away, but then I have the issue when microstepping where the steps are not uniform. There is one big step followed by several smaller ones and I must have consistent steps for my application.
The scope traces below show the output of the device. From the step position and the polarity of the output it looks like the problem is occuring in fast decay during the time it is allowing the current to flow in reverse. Has anyone seen anything like this? Any help will be appreciated.
Thanks,
John
(Please visit the site to view this file)