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DRV8701: DRV8701 & OCP

Prodigy 210 points

Replies: 3

Views: 52

Part Number: DRV8701

I am considering using the DRV8701 for driving a linear motor.  I would appreciate any comments or recommendations for setting the current regulation components/parameters (Data sheet 7.3.3, Current Regulation) as I am experiencing high inrush currents with the motor during bench testing.  The normal operating current with no load on the motor is less than 1A.  However I am recording inrush current spikes as high as 39A which last for 20µsec or so.  The high current spikes occur when the motor is at the end of it's travel (either extended or retracted) and power is re-applied to try to drive the motor in the already bottomed out direction.   It sounds like if a fault were to occur that it would reset automatically based on the information of 7.3.13.3, OCP but I would appreciate confirmation of this.  Thank you in advance for your assistance.

  • Larry,

    1. Where do you measure the 39A?
    The inductor winding current cannot be suddenly changed.
    If you measure it on the current sense resistor, we have to ignore the switching noise period.
    2. Can you measure the motor winding current and SO pin voltage?
    3. PWM blanking time is about 2us. Overcurrent deglitch time is 4.5us. "inrush current spikes as high as 39A which last for 20µsec".
    a. 20us 39A high current spike should trigger the current limit.
    b. SO pin should shows this current spike. Please check SO pin voltage to confirm the 20us current spike.

    What is the input voltage and linear motor resistance? When the motor is at the end of it's travel, if the motor speed is reduced, it is like stall condition, the input voltage could drive the current up.

    Regards,
    Wang Li

    Best Regards,

    Wang Li

    Motor Drive Solutions

  • In reply to Wang5577:

    My apologies as I seem to have created a lot of confusion. I am not currently using the DRV8701 (DRV8701E) but would like to for my application if the information in my first post can be determined.

    I am powering my linear motor with a bench power supply. I am measuring the 39A using a current probe connected to my scope. At this point this is strictly bench testing of the motor.

    The motor voltage is 24VDC and the linear motor resistance measures 4.5 ohms with a DVM.
  • In reply to Larry Brick:

    Larry,

    Ok. As the analysis before, DRV8701 has the current regulation and overcurrent protection. Both response times are much smaller than 20us. So, it can prevent the motor current going crazy.
    24VDC input and 4.5ohm motor resistance, the stall current seems less than 24V/4.5ohm= 5.3A. If you see 39A, it could be other issue.

    Best Regards,

    Wang Li

    Motor Drive Solutions