PXS20RM Datasheet, PDF (661/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Flexible Motor Control Pulse Width Modulator Module (FlexPWM)
Timer compare events (represented by the long vertical lines in the diagram) are scheduled based on the
zero crossings of the back-EMF waveforms. The PWM module is configured via software ahead of time
with the next state of the PWM pins in anticipation of the compare event. When it happens, the output
compare of the timer drives the FORCE_OUT signal which immediately changes the state of the PWM
pins to the next commutation state with no software latency.
Rotor Electrical Position (degrees)
0
60
120
180
240
300
360
Phase R
Phase S
Phase T
PWMA0
zero
crossings
PWMA1
PWMA2
PWMB0
PWMB1
PWMB2
Figure 25-12. Sensorless BLDC Commutation Using the Force Out Function
25.3.3 Functional details
This section describes the implementation of various sections of the PWM in greater detail.
25.3.3.1 PWM clocking
Figure 25-13 shows the logic used to generate the main counter clock. Each submodule can select between
three clock signals: the IPBus clock, EXT_CLK, and AUX_CLK. The EXT_CLK is generated by an
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
25-15