It looks like you are observing the switching caused by the current limiting feature of the driver. Did you set the current limit for your stepper motor? You can find more information about how to do that in our video in this post on our blog.
If you already set the current limit, what did you set it to?
thanks for your advise and that helpful link. I adjusted the current level as it is said. Sadly, there is no change in function. (1V at V_Ref)
Now I disconnected the motor from the controller and the results on the oscilloscope are very good. So, there has to be something wrong between the motor and the controller, I guess.
I do not see anything wrong with those plots. The rapid switching on and off shown on the plot with the motor attached is exactly what we would expect for a current limiting driver controlling the motor current with PWM switching.
Setting the current limit to 2A (by setting vref to 1V) on this driver will probably result in the driver overheating and shutting itself off. We do not recommend setting the current limit above 1.5A without sufficient external cooling.
What benefit are you trying to achieve by using a 20V supply? It sounds like 11V was working well.
