Upon completing the motor position initialization with either align, double align, IPD or slow first cycle, the MCT8315A begins to accelerate the motor in open loop. During open loop, fixed duty cycle is applied and the cycle by cycle current limit functionality is used to regulate the current.

In MCT8315A, open loop current limit threshold is selected through OL_ILIMIT_CONFIG and is set either by CBC_ILIMIT or OL_ILIMIT based on the configuration of OL_ILIMIT_CONFIG. Open loop duty cycle is configured through OL_DUTY. While the motor is in open loop, speed (and commutation instants) is determined by Equation 4. In MCT8315A, open loop acceleration coefficients, A1 and A2 are configured through OL_ACC_A1 and OL_ACC_A2 respectively. The function of the open-loop operation is to drive the motor to a speed at which the motor generates sufficient BEMF to allow the BEMF zero-crossing based commutation control to accurately drive the motor.