I have the following Driver IC for a stepper motor:
When the motor is running, I cannot hear the switching from the current chopping in the motor windings, but when I stop the motor (no more STEP inputs are coming in the driver), i can hear the switching frequency at a random, audible frequency. The Driver should provide 30khz constant switching frequency.
I tried also to switch from mixed decay to slow decay and fast decay, the problem remains the same. I use 1/4 Step Mode.
Can anyone suggest me, what I could do against it? The only thing that works so far is to disable the motor, but then there is no holding torque and that can lead to a drift over time.
I measured with the oscilloscope the switching behaviour when the motor stops, different cases can occur at random:
There are alot of other audible and non-audible cases aswell, where always the audible cases have a constant switching frequency.