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DRV8825: a question about the current waveform

david sun36
Prodigy 90 points
Part Number: DRV8825
Other Parts Discussed in Thread: DRV8846, DRV8846EVM

Dear Support, 

I am using a DRV8825 to drive a step motor. it is 1.8degree, 12V,  rated current is .25A. phase resistance is 48 ohm. phase inductance is 17mH. holding torque is 380g.cm. 

yellow trace is step, roughly 6Khz. green trace is isense pin. reference voltage is 1V, Rsense is 1.5ohm. 

looks like the current waveform is not very pretty. any idea to optimize the design. 

thanks,

David Sun

it works but sometimes makes noise. 

  • 0
    TI__Guru** 114905 points
    Hi David,

    May I suggest the DRV8846 as an alternate device based on your stated voltage and current. The device has a maximum operating voltage of 18V and has many additional decay modes available that may clean up the current. The DRV8846 has a mode that automatically adjust the percentage of fast/slow decay to maintain current regulation.

    A DRV8846EVM is available for evaluation.

    If you need to continue with the DRV8825, please provide/confirm the following settings
    microstep settings (is it 1/8)
    decay mode (is it mixed)

    If you are using mixed decay, please try fast decay.
  • 0 in reply to Rick Duncan
    Prodigy 90 points

    Hi， Rick

    Thank you very much for your prompt response, we'd like to try DRV8846, but this DRV8825 is on a released product, the vendor recently updated the motor, that introduced the problem. 

    the microstep setting is 1/16. fast decay. 

    Sincerely,

    David Sun

  • 0 in reply to david sun36
    TI__Guru** 114905 points
    Hi David,

    Thanks for the information.

    As an experiment, can you try raising VREF to 2.6V and increasing the sense resistor to 4 Ohms? This will provide a little more headroom to the current sense comparators between steps.
  • 0 in reply to Rick Duncan
    Prodigy 90 points
    Thank you for the suggestion, I will give it a try.