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DRV8889-Q1: About TRQ_Count

yuki.ando
Prodigy 50 points
Part Number: DRV8889-Q1

Hello team.

Please tell me how to determine the torque count value specifically.

I understand from the data sheet that the torque count value is determined from the difference between the back electromotive force under load and under no load, but I would like to know how to derive the specific value.

Best regards.

  • 0
    TI__Mastermind 26055 points

    Hi Ando-san,

    The torque count is internally derived using TI proprietary algorithm. This is dynamically calculated based on the back EMF (BEMF) load angle and other parameters related to the drive output and the motor. The theory of operation is described in this application note, https://www.ti.com/lit/an/slvaei3/slvaei3.pdf. 

    It is not possible to externally derive the torque count as there is no simplified formula for it. The torque count is derived from the load angle (the phase difference between the coil current and the BEMF. The range for the count is between 0 and 255. The torque count value approaches 0 for load angle = 0, motor in stall or one the verge of stall.

    When the motor is not stalling and is lightly loaded the torque count will be maximum. The maximum count depends on the motor speed, motor time constant L/R etc. Sometimes 30 to 40 counts may be the maximum value for the torque count. I hope this helps. Thanks.

    Regards, Murugavel