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DRV8881: how to calculate power consumption of step motor and driver IC?

Genius 3870 points
Part Number: DRV8881
Other Parts Discussed in Thread: OPA564, , DRV8889-Q1

Hi there,

we are designing a simple 2-phase step motor driver. Motor spec is below. 

We are considering design TWO demo boards using different Driving solution: PWM voltage drive(DRV8881) and linear current drive(howland current source with OPA564) , both open-loop control. 

the current freq. in motor coil would be f_max=500HZ sine wave, and current amplitude <500mA as required by motor coil spec. Power supply of driver will be +/-10V.

A simulation may help, but I hope to learn the math in this :

(1) How should we  calculate  the power consumption of step motor   

(2) How should we calculate  the power consumption of PWM driver IC DRV8881 and linear driver OPA564? Linear SCH is below for reference while PWM SCH is in develeping. 

Thanks very much.

  • Yi,

    1. There is no simple answer for the power consumption of stepper motors. From the motor design point of view, the power consumption includes iron loss and copper loss (https://www.geckodrive.com/support/step-motor-basics.html ). If we don't go that complicate route, the motor power consumption is equal to the motor driver output power minus the motor output mechanical power. The motor driver output is an AC output. The power P is equal to |S|*cosȹ (https://en.wikipedia.org/wiki/AC_power ).

    2. The motor driver power dissipation calculation example can be found in DRV8889-Q1 datasheet https://www.ti.com/lit/ds/symlink/drv8889-q1.pdf

  • Hi Wang  Li

    thanks for help.

    I would like to ask another question. I think in order to form a sin/cos CURRENT curve in motor coils, the output volatge wave on DRV8889's H-Bridge( pin A/B_OUT1/2) should be like a sine-modulated wave , one example is as below. Is this understanding correct?  Thanks!

  • Yi,

    If the motor doesn't move (without back EMF), the output voltage wave on DRV8889's H-Bridge( pin A/B_OUT1/2) should be like a sine-modulated wave as your example.

    If the motor spins, the back EMF could cause the phase shift between the average voltage and current. Please check DRV8889 datasheet " 7.3.11.5 Stall Detection" section.