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DRV10987: Motor current calculation

Franz Schellhase
Expert 3605 points
Part Number: DRV10987


Hi team,

Can you have a look at my customers question regarding motor current calculation?

I am currently testing the DRV10987 for suitability for our application. I have the chip in operation with the MCU to the point where a motor is rotating.

Now I want to optimize the parameters and want to read out the registers. Unfortunately, I do not yet understand how the motor current should be calculated. According to the measurement with current clamp 660 mA pk-pk flow in each phase, the value of the register for the motor current is 0x0413 (). How can I calculate the motor current from this? The description in the data sheet (Rev. C) is not quite conclusive:


Thank you,

Franz

  • 0
    TI__Mastermind 18900 points

    Hello Franz,

    Let's use the values provided as an example. Assuming the MotorCurrent register was read a produced a value of 0x0413, we are given an equation below:

    • If MotorCurrent[10:0] >= 1023
      • Peak Current (A) = 3*(MotorCurrent[10:0] - 1023) / 512
    • Else
      • Peak Current (A) = 3*(MotorCurrent[10:0]) / 512

    So we need to convert MotorCurrent from a hex value to a decimal value to see where it lines up. 0x413 = 1043 which is >= 1023. This means, we use the top equation.

    • Peak Current (A) = 3*(MotorCurrent[10:0] - 1023) / 512
    • = 3*((1043) - 1023) / 512
    • = 0.117 A
    • = 117 mA (peak)

    Assuming 660mA is peak to peak and the current looks very sinusoidal (with little distortion), 330mA peak measured vs. 117mA peak calculated feels a bit too much error. We should expect some error but not this amount.

    Can they provide a picture of the waveform and their motor phase to phase resistance number? And have the tuned lead time (advanced control, lead angle, etc) for their target speed?

    Best,

    -Cole

  • 0 in reply to Cole Macias
    TI__Mastermind 18900 points

    Moved to email, so closing here.

    Best,

    -Cole