AVR430
11
8124C-AVR-10/08
4.4 Back-EMF For sensorless applications, the driving logic u ses back EMF from the motor’s phases
to ke ep track of the motor position. To observe the back EMF from a phase, the
phase is left floating, i.e. with the high or low side MOS not powered, and the voltage
on the phase is read. For motors with center tap, Vn (V neutral) provides feedback to
device board.
4.4.1 Back-EMF feedback filters
Each phase (U/V/W/X) and the center tap (Vn) are fed via a filter/damping block to
the device board interface. The block for phase U is shown in Figure 4-5. The board
is shipped with a zero o hm resistor, so it has no damping/filter function. The signals
are named U’, V’, W’, X’ and Vn’ after going through the filter blocks.
Vmotor (Vm) is a lso fed thru a filter/damping block, and is available on the device
board interface as Vm’.
Figure 4-5. Filter/damping block for back-EMF feedback.