DocID025336 Rev 1

19/23

AN4370

CSA and OC comparator

22

10

CSA and OC comparator

Besides Overcurrent (OC) monitoring, the combination of CSA and OC comparator can be

used for the sensorless initial Rotor Position Detection. The sensorless initial RPD is

performed by energizing the motor coils in a specific way and sequence in order to measure

the phase-to-phase inductance variation, which depends on the relative position between

rotor and stator. Based on the known relationship V = Ldi/dt, this can be achieved by

measuring the time needed to reach a given overcurrent level in the energized phases that

is low enough to keep the rotor still. The microcontroller can program the desired

overcurrent level and measure the required time. Before starting the sensor-less initial RPD

process, the OCFT_DIS bit has to be set to 1 to disable the OC filtering time. This also

prevents the CSAOC flag from being set in case an OC event is detected. Moreover, the

DMUX bit has to be set to 1 to have the output of the OC comparator connected to the

DOUT pin.