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DRV8880: Problem with setting holding torque

Part Number: DRV8880

I am driving a simple stepper motor in my application at 100% torque. To reduce heat and wear, I dial back TRQ to 25% between motor movements.

When I drive the motor normally, everything seems fine. However, if I attempt to issue a single pulse to the driver (in any step/microstep mode) the motor doesn't step! I did notice though, that if I issue 2 pulses, the motor successfully moves each time. (This is true in each step mode) Furthermore, when I completely remove the code that sets the 25% holding torque, single-pulse movements work as expected.

Finally, I probed my STEP pin and triggered a capture on the falling edge of TRQ0 (setting torque from 25% to 100%). I measured 10µs between the falling-edge of TRQ0 and the rising-edge of STEP. There are no timing requirements in the datasheet regarding the TRQ pins, however. But perhaps TRQ isn't meant to be used like this or there is actually a setup time required before stepping?

I actually have three motors in my system, all driven with 8880s, using almost identical code (so I know it's not a firmware issue). The other two motors are set to TRQ 25% for 100% of the time and the issue does not arise at all. They are able to move using single pulses.

Has anyone seen anything like this?

 

  • Hi Andrew,

    The TRQ pin is intended to be used as you are doing. Once the motor is stopped, lowering the current while holding is a common technique.

    If I understand, you are trying to move the motor when the torque has been reduced to 25%. Is that correct?
    What is the IFS setting?
    Have you checked the motor manufacturer if this current is acceptable?

    It could be you are on the edge of working/non-working.

    Are all three motors the same model?
    Are the motors mounted differently, or is the load different (vertical vs horizontal)?
    What microstep mode are you using?
    The motor may not be moving, but did the current in the motor change? Can you check the current with a current probe? This would be an indication the STEP input was accepted. If the STEP input was accepted, more torque may be required to make the one motor move than the others.

  • Hi Andrew,

    We have not heard from you in some time and are assuming your issue has been resolved.

    If it has not please reply to this thread, or if this thread has been locked select "+Ask a related question" at the top right of the page.