DRV8424: The AOUT pin output have a drop

Tool/software:

we set the step pin frequency is 5KHZ and the motor can rotate normally, but from the waveform of AOUT pin we found a "drop" and a abnormal pulse, colud ti team can help to confirm if it is correct?  

If it is abnormal, can you help to give us some advice for this. 

Thanks.