Hi,
We are trying to use DRV8962EVM and its 4 current sense signals as feedback signals in closing the current loop in a stepper motor control project.
We had some issues applying a PI current loop. To check the validity of these 4 current feedback signals, we applied 50Hz Sine Voltages to 4 motor lines according to commutation via a 20kHz PWM voltage signal, and monitored the open loop response of the 4 current sense signals. Please see the oscilloscope image attached.
With current prob, we confirm that there is a nice and complete sinusoidal current occurring in both windings of the stepper motor. Please see the oscilloscope image attached. So we expect the 2 current sense on 2 motor lines of each coil to pickup the sinusoidal current happening in the coil, each of signal covering a half sine wave when the current is passing through the high side of the bridge for that coil. we also expect the other 2 signals for the 2nd coil to also represent a full sine current confirmed to happen in the 2nd coil.
However, we encounter the problem of all 4 current sense signals not generating their corresponding full half-cycle of the sine wave. All 4 sense signals show a cut off towards the end of their half sine wave, and this (cut-off / zero / no-value section) on the signals dominate in higher frequencies (>50Hz) and erases the whole half sign wave current feedback which we need to use to close the current loop.
Whether it is the problem with our chip (it is malfunctioning or half-burned), or it is a general problem, we would like to find out.
And if there is a known problem/limitation related to using current control (closing the current loop in stepper motor application) with these sense current signals as feedbacks on this particular chip, please advice.
Thank you!
Amin Kamalzadeh
Micronix USA
