Lock4 is used to detect locked-motor conditions while the motor start sequence is in open loop.

For a successful startup, motor speed should be equal to the open-to-closed-loop handoff threshold when the motor is transitioning into closed loop. However, if the motor is locked, the motor speed is not able to match the open-loop drive rate.

If the motor BEMF is not detected for one electrical cycle after the open-loop drive rate exceeds the threshold, then the open loop was unsuccessful as a result of a locked-rotor condition.