SLVAES8 May   2020 DRV8424 , DRV8424E , DRV8426 , DRV8428 , DRV8428E , DRV8434 , DRV8434E , DRV8434S , DRV8436 , DRV8436E , DRV8889-Q1

 

  1.   How to Reduce Audible Noise in Stepper Motors
    1.     Trademarks
    2. 1 Introduction
    3. 2 Details of the Test Setup
    4. 3 Sources of Noise in a Stepper Motor
      1. 3.1 Magnetic Noise
      2. 3.2 Mechanical Noise
      3. 3.3 Electrical Noise
        1. 3.3.1 Effects of Current Ripple and Decay Mode
        2. 3.3.2 Effects of PWM Chopper Frequency
        3. 3.3.3 Effects of Current Zero-cross Error
        4. 3.3.4 Effects of Step Resolution and Step Frequency
        5. 3.3.5 Effects of Resonant Frequency
    5. 4 Summary
    6. 5 References

3.3.3 Effects of Current Zero-cross Error

Another potential cause to audible noise can be the smoothness around the zero current crossing. Most legacy stepper motor drivers distort the current waveform around the zero-current crossing when the current changes phase, as shown in Figure 16. The reason behind this distortion is high current-sense blanking time such as 2 µs or higher - which causes the average current for the step to be significantly higher than the intended value. Another reason for distortion around zero-cross is too high OFF time, which causes the average current to be significantly lower than the intended value, as shown in Figure 17. The impact of this distortion is to create unsmooth current waveform - which leads to wobbling, vibrations and audible noise.

Zero cross error_blanking.pngFigure 16. Current Distortion Due to High Blanking Time

Zero cross error_off time.pngFigure 17. Current Distortion Due to High OFF Time

The blanking time for the drivers listed in Table 1 is only 1 µs, therefore there is no distortion near the zero-crossing region of the coil current. This reduces current and torque ripple and a true sine wave form is approached, resulting in a much smoother motor operation. In Figure 18 and Figure 19, the current zero crossing is shown for DRV8424 at 1/16 and 1/64 microstepping, respectively, showing smoothness around zero-cross.

zero smooth_16.pngFigure 18. Smoothness of Zero-Cross at 1/16 Microstepping

zero smooth_64.pngFigure 19. Smoothness of Zero-Cross at 1/64 Microstepping