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DRV Limits and Recommendation

R11
Expert 1485 points
Other Parts Discussed in Thread: DRV8834, DRV8846, DRV8834EVM, DRV8846EVM

From the website it looks like DRV8834 and DRV8846 have eval boards.  I would like some help in deciphering some of the information.  For example, the DRV8834 eval board user’s guide discusses motion control and setting the start speed and target speed in PPS (pulses per second or full steps per second).  It identifies a minimum allowed of 200 PPS.  Based on the motor that we would be driving, I believe the minimum would be a problem.  Is this software-limited on the eval board or hardware limited in the DRV8834?  From what I can tell, the motor with speed of 200 degrees per second, would be equivalent to 11.1 steps per second (200 deg/sec divided by 18 deg/step).  Based on the definition of PPS, this is less than the minimum allowed 200 PPS.

Am I reading all this correctly?  Based on the motor we are trying to drive, what does TI recommend as the best fit?  Here is a link to the motor: http://bit.ly/1lD0c6m

  • 0
    TI__Guru** 114905 points

    Hi R11,

    This is a software limit of the DRV8834EVM and DRV8846EVM. This can potentially be worked around by issuing single steps for evaluation.

    Other possible workarounds is to use 1/32 microstep mode which works out to 6.25 full steps/second, or drive the step command using a signal generator after the connection to the mcu is removed.

    All workarounds could be a little painful, but for initial evaluation of the device it may work.

    These EVMs are typically used with hybrid steppers with 1.8 degrees/step and run much faster.

    The DRV8834 appears to be a better fit between the two.

  • 0 in reply to Rick Duncan
    Expert 1485 points

    Using a signal generator, could this simply be done by removing R12 and wiring the generator signal into J3 Pin 9 on the DRV8834EVM?

  • 0 in reply to R11
    TI__Guru** 114905 points

    Yes, removing R12 and connecting the signal generator to J3 Pin 9 or TP11 will work.