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DRV8834 Phase/Enable Mode

Rahul Shah1
Prodigy 145 points
Other Parts Discussed in Thread: DRV8834, DRV8837

I am using DRV8834 in one of my project. Where in I am not getting enough torque. If I increase current, keeping Vref constant, both Avref and Bvref connected directly to VREFO, and changing (decreasing) value of sense resistors, heating of coil will become an issue.

I am using in indexer mode.

Can a better torque be achieved by configuring the IC in phase/enable mode?

Also Phase/Enable mode is not clearly explained in the datasheet, can you please explain it in more detailed manner, how to use it, in a simpler language?

  • 0
    TI__Mastermind 21320 points

    Hi Rahul,

    What is the max rated current of the stepper motor? This should be a given value that you can set the chopping current to for max torque. If you are trying to exceed this, you are exceeding the ratings of the motor. Stepper motors will heat up in max operating conditions by there nature. Details on setting the chopping current level are provided in the datasheet.

    Phase/Enable mode is generally for driving DC motors but can be used with steppers. It gives you direct control of the H-bridge, instead of the indexer driving the proper waveforms for the microsteps. You will have to generate the microstepping waveforms yourself in Phase/Enable mode and you would not likely see an improvement in performance.

  • 0
    TI__Mastermind 20985 points

    Rahul, another thing to consider is that different motors have different current vs torque characteristics.  If your motor is getting too hot when you apply the amount of current you need for your torque target, you might look into using a different motor.

    Best regards,
    RE

  • 0 in reply to RE
    Prodigy 145 points

    Thank You Nick and RE,

    Well in my project, its not a stepper motor. Instead its a combination of four coils, which we have made ourselves. Please find the attached block diagram.

    Hope it makes a sense. The product is called Magnetic Stirrer. There will be a magnetic bar rotating in the glass flask, placed at the top of the coil.Check this video fo0r reference. http://www.youtube.com/watch?v=r2EnpiKacw4

    Now I want more attraction for the coil, which can certainly be achieved by increasing current. But when I increase current, heating is an issue.

    Now I want to know if there is any issue with Electronics or if there is something wrong with Magnetics. Please find the attached schematic for review.6014.SCHEMATIC1 _ PAGE1-Magnetic Stirrer.pdf

    Thanks and Regards

    Rahul Shah

  • 0 in reply to Rahul Shah1
    TI__Mastermind 20985 points

    Rahul, I reviewed the schematic and have 2 comments:

    1. The recommended value for C10 on VINT is a minimum of 2.2uF.
    2. It seems that R18 doesn't do anything, populated or not.  You might be better off making a voltage divider to VREFO, using a zero ohm for the top resistor and not-installed bottom resistor.

    For the heat problem, maybe the product's exterior could have some vents, and possibly also a low-profile fan like ones used in laptops.  A simple device for controlling brushed DC motors is the DRV8837.

    Best regards,
    RE