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DRV8886AT: About change magnitude of current waveform as increasing speed

Michiaki Tanii
Expert 4340 points
Part Number: DRV8886AT

Hi

Our customer is evaluating DRV8886AT and see the below phenomenon.
Could you kindly advise why the phenomenon was seen and how DRV8886AT control at high speed range.


Operating conditions
- Motor : 2,000 pps -> 18,000pps (increasing speed gradually)
- Driver : ILIM 1.4A, 1/4 step, Autotune

Let me share the current wave internally.
Customer see the magnitude of current waveform changes large -> small -> middle as speed increases

Motor manufacturer mentioned that when magnitude is decreasing from large to small is caused by back electromotive current but when magnitude changes small to middle is DRV886AT would control something.
Could you kindly advise how DRV8886AT controll at high-speed range ?

Thank you and best regards,
Michiaki

  • 0
    TI__Guru 56650 points

    Michiaki,

    When the motor is spinning, a higher speed would have a higher back EMF which could against the motor winding current change.

    That is why "Customer see the magnitude of current waveform changes large -> small" and "Motor manufacturer mentioned that when magnitude is decreasing from large to small is caused by back electromotive current".

    When the motor speed is too high, the motor could stuck or miss some steps. If the motor is stuck, the back EMF is zero. The current could be changed from "small" to high again.

    Please share the current waveform and output voltage on H-bridge.

  • 0 in reply to Wang5577
    TI__Guru 56650 points

    Michiaki,

    Since this post is converted to a private discussion. Let me close this post.

    Basically, a higher speed provides a higher back EMF which against the winding current reaching the set point. If the speed is kept going higher, the motor could be stopped which doesn't have back EMF. But, the speed is too high, the winding inductance can also limit the current change rate.