8.4.3.6 Start-Up Timing

Start-up timing is determined by the align and accelerate time. The align time can be set by AlignTime[2:0], as described in Register Definition. The accelerate time is defined by the open-to-closed loop threshold Op2ClsThr[4:0] along with the first order StAccel[2:0](A1) and second order StAccel2[2:0](A2) acceleration coefficient. Figure 19 shows the motor start-up process.

Figure 19. Motor Start-Up Process

Select the first order and second order acceleration coefficient to allow the motor to reliably accelerate from zero velocity up to the closed loop threshold in the shortest time possible. Using a slow acceleration coefficient during the first order accelerate stage can help improve reliability in applications where it is difficult to accurately initialize the motor with either align or IPD.

Select the open-to-closed loop threshold to allow the motor to accelerate to a speed that generates sufficient BEMF for closed loop control. This is determined by the velocity constant of the motor based on the relationship described in Equation 2.