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DRV8833: DRV8833 output current distortion

Wayne Wang20
Expert 4390 points
Part Number: DRV8833
Other Parts Discussed in Thread: DRV8886, DRV8834

Hi team,

My customer is using our DRV8833 to drive a stepper motor in full step mode. VM is supplied by a 3.7V battery. When the Risense=1ohm, the chopping current should be 200mA and the current waveform is OK. But when they change the Risense to 0.5ohm to make the chopping current to be 400mA, the current waveform is distorted. Please see below picture for the 200mA and 400mA chopping current. Could you please help analyze the root cause? Thanks.

Best regards,

Wayne

  • 0
    TI__Guru** 114905 points
    Hi Wayne,

    Would you please ask the customer to half the step frequency and observe if the current settles?

    If the current settles, the customer may be experiencing the effects of the motor overshooting the target step and oscillating back to the target position.

    It is generally not a problem, although it can lead to missed steps if the oscillation is too much.

    This effect may be reduced by:
    Using non-circular half step (see a description in the DRV8886 datasheet) or
    considering the DRV8834 in half step mode.
  • 0 in reply to Rick Duncan
    TI__Expert 4390 points

    Hi Rick,

    Thanks for your reply. Customer also uses the DRV8833 in another project. In that case, the VM=7.8V, chopping current=400mA and the step frequency is much higher than this case. But the 400mA output current in that case is normal. So the current distortion may be not related to the overshooting.

    Is there any possibility that when VM=3.7V, the 400mA is beyond the maximum output current which leads to distortion? In the datasheet, we only have the maximum output current under 5V supply. Do you have the maximum output current data under 3.7V supply? Thanks.

    Best regards,

    Wayne

  • 0 in reply to Wayne Wang20
    TI__Guru** 114905 points
    Hi Wayne,

    Is the motor the same in the other project? Does the current settle at the top when running at a higher step rate?
    You may be correct that the current distortion is not related to overshooting, but it is one item that should be ruled out.

    The DRV8833 can provide 400mA at 3.7V assuming the local capacitors can provide the current and the stepper motor resistance does not limit the current.

    Please confirm the VM is stable at the DRV8833 pin.
  • 0 in reply to Rick Duncan
    TI__Expert 4390 points

    Hi Rick,

    The VM is supplied by a battery so it should be stable enough. We also tried to half the step frequency but the 400mA output current still distorted. Please see the waveform as below. Do you have any advice on how we should do next? Thanks.

    Best regards,

    Wayne