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Original question:

DRV8889-Q1: Stall detection and TRQ_COUNT

DRV8889-Q1: How to increase TRQ_COUNT

Hans Lin
Prodigy 10 points
Part Number: DRV8889-Q1

Tool/software:

While I am turning the motor, I will read TRQ_COUNT periodically. And I will customize a threshold value as the standard for judging a stall. When I use Motor A, TRQ_COUNT can reach more than 50, but when I use Motor B, TRQ_COUNT is less than 20. How can I increase TRQ_COUNT?

  • 0
    TI__Mastermind 45445 points

    Hello Hans,

    What is the DC resistance DCR or Motor A and Motor B? Was the operating condition identical for the two motors? Higher DCR motors tend to result with low TRQ_COUNT. Likewise lower microstepping and lower STEP rate tend to produce low TRQ_COUNT. So to get higher torque count you can increase the microsteps for example to 1/16 or 1/32 and increase the STEP input frequency. There will also be some influence with IFS current setting. If these parameters cannot be changed the TRQ_COUNT cannot be improved. TRQ_COUNT for certain motors would be inherently low especially steppers with high DCR. 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    Prodigy 10 points
    Murugavel4637 said:
    put frequen

    Thanks for your reply!

    I only see the terminal resistance in the motor specs. Is this the DCR you are referring to?
    Motor A: 14 Ω
    Motor B: 20 Ω
    Both motors behave the same, but the gear ratio and therefore the PWM settings are different. The rest of the settings are the same.
    I believe the torque will be at its maximum during full-step operation; is my understanding correct?
    In the case of microstepping, will the torque at 1/256 step be greater than 1/2 step?

  • 0 in reply to Hans Lin
    TI__Mastermind 45445 points

    Hello Hans,

    Yes this was what I was requesting for. Thank you. Motor B is higher DCR compared A hence lower count.

    Generally in stepper motors the torque output will be highest with full-step operation. But they do perform smoothly without negative impact of mechanical resonance from 1/8 usteps and higher. For these small stepper motors we've observed usable torque counts with 1/32 or 1/16 uSteps mode. For reasonable torque counts a STEP rate of 8500 PPS with 1/32 uSteps may be used. 

    The DRV8889-Q1 torque counts for small steppers are usually very low at > 64 uSteps and it is better to avoid those settings. 1/64 may be marginal and usable with some motors. I hope this information will be helpful to you. Thank you.

    Regards, Murugavel