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DRV8711 Current Limiting Resistor Watt?

Erhan Ergun
Intellectual 270 points
Other Parts Discussed in Thread: DRV8711

Hello,

I am going to use drv8711 to drive a stepper motor with 48V and 4.2A max.

As i calculated  i need 0.130 Ohm resistor but can not figure out what should limiting resistor watt is?

P=I^2xR = (4.2)^2x0.130=2.3 Watt according to DC.

But i think current is feeded to motor from driver as sine wave and it acts like AC.

Is there any mistake in my calculations?

Thank You

  • 0
    TI__Mastermind 21320 points

    Hi Erhan,

    While you will see a sine wave when stepping this is not the case for when you are holding the motor in a fixed position.

    When holding it is possible for the motor coil to see 4.2A DC (100%). So it will depend on how you intend to drive the motor.

    One option is to raise the GAIN of the DRV8711 in order to lower the value of the SENSE resistor. This comes at the cost of decreased resolution.

  • 0 in reply to Nicholas Oborny
    Intellectual 270 points

    A small question. I am new about drv8711.

    What is the difference between decreasing value of tourque and gain.

    The affect of %50 decrasing is the same? Or the purposes of that values are different? I thought that tourque is used to make small changes in power of stepper motor and gain is for huge changes but i read tourque value is for holding tourque but gain value is for acceleration and decelerate power.

    Can you enlighten me. Thank You

  • 0 in reply to Erhan Ergun
    TI__Mastermind 21320 points

    In the end, they do the same thing (adjust the chopping current level). They are just different ways to adjust this level. The TORQUE settings also gives you more precise control (more bits/levels).

    In a typical application you would scale the GAIN and SENSE resistor to your max current level with 100% TORQUE. During operation you would then use the TORQUE register to adjust the current level based on your torque needs.

    Feel free to ask any other questions you have.