ZHCSH31B August 2017 – February 2018 DRV10987
Start-up timing is determined by the align and accelerate time. The align time can be set by AlignTime[2:0]. The accelerate time is defined by the open-loop to closed-loop threshold Op2ClsThr[4:0] along with the first-order acceleration coefficient StAccel[2:0](A1) and second-order acceleration coefficient StAccel2[2:0](A2) acceleration coefficients. Figure 24 shows the motor start-up process.
Select the first-order and second-order acceleration coefficients to allow the motor to reliably accelerate from zero velocity up to the closed-loop threshold in the shortest time possible. Using slow acceleration coefficients for open loop stage can help improve reliability in applications where it is difficult to initialize the motor accurately 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 BEMF constant of the motor based on the relationship described in Equation 2.