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DRV8818: The current for the static torque is not as same as the design value

Cherry Zhou
Mastermind 22235 points
Part Number: DRV8818

Hi Team,

The customer intends to use a current clamp to measure coil current when the static torque of the stepper motor is driven by 8818, but the measured static torque current is not as expected.

The design has a static torque current Vref = 0.6V and the corresponding current calculated from the manual should be 0.75A. While in actual measurements, the voltage value of Vref is 0.6V without exception, but no current of 0.75A is measured.

More information:

  • Operating torque coil current is 1.8A and the measure is as expected.
  • Current clamp calibration is confirmed to be correct.
  • To verify if the measurement method is correct, the customer also measured 8818 die static torque current for other projects and the measurement was as expected by the design.

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Mastermind 23431 points

    Hey Cherry,

    I am a bit confused as to what the issue is - are you reading lower current than you expect?  if so, what current are you reading?   And does "static torque" mean current/torque under stall condition? 

    Does the same behavior exist if you try a lower VREF setting?  The stepper motor might not be capable of inducing this static torque. 

    What is the state of the USM1 and USM0 pins?  For measuring static torque I think these should be set to full-step (USM1=0 USM0=0).  The device should also be in Slow DECAY mode for this test.   

    Best,

    Jacob