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DRV8889-Q1: Stall Detection when not running in regulation

ReedKacz
Expert 3462 points
Part Number: DRV8889-Q1

Hi Motor Driver experts,

If I am running a stepper motor outside of current regulation. Is the stall detection circuit still able to function properly? Or do we need to be hitting the current trip point to ensure there is enough back EMF?

Thank you,

Reed

  • 0
    TI__Guru 56650 points

    Reed,

    The stall detection is based on the Torque_count measurement value. Torque_count value is proportional to the motor back EMF. The Torque_count measurement error is related to the I*R drop in the motor winding. To reduce the Torque_count error, you may need to reduce the stepper motor full scale current.

    What is the full scale current regulation point? What is the winding resistance?

  • 0 in reply to Wang5577
    TI__Expert 3462 points

    Hi Wang,

    Thanks for the response! This was a customer question, no for a specific motor, but more for a trying to understand if this will be a fit for their system needs. 

    They operate the majority of the time outside of current regulation. So with that being known, they want to understand if the DRV8889 stall detect would be applicable.

    Thanks,
    Reed

  • 0 in reply to ReedKacz
    TI__Guru 56650 points

    Reed,

    How does the motor run "outside of current regulation"? I cannot say the stall detection circuit works or not if I don't understand how the motor runs "outside of current regulation.

    For Current Regulation, The current through the motor windings is regulated by a PWM current-regulation circuit.

    For the Stall Detection,  the algorithm compares the back-EMF between the rising and falling current quadrants by monitoring PWM off time and

    generates a value represented by the 8-bit register TRQ_COUNT.

    If the "outside of current regulation" operation doesn't change the back-EMF comparing result between the rising and falling current quadrants, the stall detection works.