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Full step mode using DRV8811

claud blevins
Prodigy 30 points
Other Parts Discussed in Thread: DRV8811

We are using this motor driver on a small 2 phase stepper motor with ~5mH inductance per phase.  We are having a hard time getting multiple motors to do full and 1/2 steps without decreasing step to ~ 2KHZ.  RCA/B have 47K and 1000pf; VM = 12v.  Anyone have ideas for solution?

Claud

  • 0
    TI__Mastermind 20985 points

    Hi Claud, it sounds like you might be reaching the max RPM that you can commutate this stepper at.  Does 2kHz translate to 10 revolutions per second in this case?

    You might be able to reach faster speeds by increasing VM, or by using a different regulated current level.

    Best regards,
    RE

  • 0 in reply to RE
    Prodigy 30 points

    Thanks for the quick response and I'll look into your 10 rps question.  The motor is spec'd at ~4500 steps/sec.  We have no problem running at 1/4 and 1/8 step at 4400khz.  Current sense is .1 ohm.  Vref is ~ 2v.

  • 0
    Prodigy 30 points

    Looks like we need to keep Fs, frequency start, < max F and then step our way up.  Started at 500Hz and stepped my way up to 4Khz..

    Claud

  • 0 in reply to claud blevins
    TI__Mastermind 20985 points

    Yes, ramping up the speed can help due to internal resonance.

    If VREF = 2V and RISENSE = 0.1Z, the DRV8811 will regulate current to 2.5A.  Does that match what you want?  Some of the smaller steppers use much less than that.  An option you have is to see if you get better results with a larger RISENSE.

    Best regards,
    RE