In brushed DC motors, there is a large inrush current during start-up due to the absence of any back emf. Figure 3-2 shows the performance of ripple counting algorithm during inrush using the tuned parameters mentioned in Table 3-5. To improve accuracy, the T_MECH_FLT register was set to 000b, displayed in Figure 3-3. Please refer to Section 4.3 for the description of the T_MECH_FLT register. Section 4.3 explains more workarounds for transient conditions, including inrush. Operating conditions are unchanged from the tuning process. PWM is at 100% duty cycle. For examples on how to workaround low average currents due to PWM at low duty cycles, please refer to Section 4.1.

Using Equation 5, accuracy calculations for Figure 3-2 and Figure 3-3 are described in Table 3-6. In the figures, counting is stopped when the motor completes 7 full revolutions since the motor current reaches steady state value.

Figure 3-4 shows the performance of the ripple counting algorithm during steady state. Clearly, all ripples are tracked accurately through the RC_OUT pin. Table 3-7 compares ripple counting accuracy against an encoder.