SLVAFO8A April   2024  – May 2024 DRV8214 , DRV8234

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Need for Sensorless Designs
  5. 2Ripple Counting − Concept
    1. 2.1 Ripple Counting Algorithm Details
  6. 3Case Study: Robotic Wheel Drive
    1. 3.1 Robotic Wheel Motor Operating Conditions
    2. 3.2 Tuning Parameters for Ripple Counting
      1. 3.2.1 Resistance Parameters
      2. 3.2.2 KMC and KMC_SCALE
        1. 3.2.2.1 Tuning KMC_SCALE
        2. 3.2.2.2 Tuning KMC
    3. 3.3 Robotic Wheel Motor with Ripple Counting
      1. 3.3.1 Inrush and Steady State Performance
        1. 3.3.1.1 Motor Speed Calculation
      2. 3.3.2 Soft Start
      3. 3.3.3 Loaded Conditions
  7. 4Challenges and Workarounds
    1. 4.1 Low Average Currents
    2. 4.2 Motor Inertia During Stop
    3. 4.3 Inrush
    4. 4.4 High Load Conditions
  8. 5Summary
  9. 6References
  10. 7Revision History

3.3.2 Soft Start

To protect against high inrush current transients as observed in Section 3.3.1, DRV8214 and DRV8234 have a soft-start feature that allows current to ramp-up to a preset value during the speed and voltage regulation modes. Figure 3-7 demonstrates the performance during soft start.

Performance During Soft Start Figure 3-7 Performance During Soft Start
Soft Start - Zoomed Figure 3-8 Soft Start - Zoomed

From Figure 3-7, we can see that all ripples are accurately tracked during soft start. This is validated by the accuracy calculation shown in Table 3-8. Counting is stopped when the motor completes 8 revolutions since the motor current value reaches steady state.

Table 3-8 Accuracy During Soft-Start
Parameter Soft-Start
Encoder Counts 32
RC_OUT Counts 48
Accuracy 100%