Motorola M68HC08 Reference Manual page 36

BLDC Motor Control
NOTE:
CAUTION:
3.2.5 Back-EMF Sensing Circuit
Designer Reference Manual
36
Freescale Semiconductor, Inc.
Figure 3-11. Balanced Capacity Coupling
The configuration of the phase windings end-turns has significant
impact; therefore, it needs to be properly managed to preserve the
balance in the mutual capacity. This is important, especially for prototype
motors that are usually hand-wound.
Failing to maintain balance in the mutual capacitance can easily
disqualify such a motor from using sensorless techniques based on the
back-EMF sensing. Usually, the BLDC motors with windings wound on
separate poles show minor presence of the mutual capacitance. Thus,
the disturbance is also insignificant.
An example of the possible implementation of the back-EMF sensing
circuit is shown in Figure
BLDC Motor Control
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3-12.
DRM028 — Rev 0
MOTOROLA