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DRV8833: DRV8833 current ripple is larger in low speed

Wayne Wang20
Expert 4390 points
Part Number: DRV8833

Hi team,

My customer is using DRV8833 to drive s stepper motor in full step mode. The VM=7.7V and the full scale current is set to 500mA. When the motor is in operation, we found that the current ripple in low speed period is larger than the ripple in high speed period. Please see below picture for the waveform.

In the left picture, when the step frequency is low, the current ripple is large. When the step frequency becomes higher, the current ripple becomes smaller.

Do you have any advice on what causes the larger ripple in low speed period?

What's more, when we amplify the waveform, we found that there's a distortion when the current increases as the right picture shows. Do you have any advice on this issue?

What's more, We tried to increase the VM to 8.4V and reduce full scale current to 400mA. But the issue still exists. please see below waveform. So this issue may be not related to the VM or the full scale current value. Hope this is helpful to you. Thanks.

Best regards,

Wayne

  • 0
    TI__Guru 56650 points
    Wayne,

    The motor winding is an inductor. In general, an inductor ripple is decided by the voltage across the winding and how long keeping that voltage. But for motor, when the motor is rotated, the back EMF can generate a voltage in opposition to the current change. Higher speed would generate a higher winding voltage to against the winding current change. That is why you can see a higher winding ripple at lower speed.

    From the last picture you post, we can see:
    phenomenon a. the first winding pulse current doesn't have the glitch
    phenomenon b. when the stepper motor speeds up, the winding current also doesn't have a big glitch

    If we assume the motor is not in motion yet at the first pulse, there is no back EMF voltage to affect the winding current. So, we don't see the current glitch at the first pulse (phenomenon a.).
    When the motor is in motion, the back EMF can generate a voltage in opposition to the current change. The back EMF voltage slows down the current goes up which is shown on your waveform. The back EMF voltage is related to the motor speed. At low speed, the step motor speed from one position to next position could have a big variation which could cause the winding current glitch.
    When the motor is speeded up, the motor speed is more smooth due to itself weight or load force. So, the back EMF voltage is more stable. So, we don't see the winding current glitch.