MC908MR16CFUE Datasheet, PDF (130/282 Pages) Freescale Semiconductor, Inc – On-chip programming firmware for use with host personal computer, Clock generator module (CGM)

Pulse-Width Modulator for Motor Control (PWMMC)
UP/DOWN COUNTER
MOUDULUS = 3
PWM VALUE = 2
PWM1 W/
NO DEAD-TIME
PWM2 W/
NO DEAD-TIME
PWM VALUE = 3
PWM VALUE = 2
PWM VALUE = 1
PWM1 W/
3
DEAD-TIME = 3
3
3
PWM2 W/
DEAD-TIME = 3
3
3
3
Figure 12-17. Dead-Time and Small Pulse Widths
12.5.3 Top/Bottom Correction with Motor Phase Current Polarity Sensing
Ideally, when complementary pairs are used, the PWM pairs are inversions of each other, as shown in
Figure 12-18. When PWM1 is active, PWM2 is inactive, and vice versa. In this case, the motor terminal
voltage is never allowed to float and is strictly controlled by the PWM waveforms.
UP/DOWN COUNTER
MODULUS = 4
PWM1
PWM VALUE = 1
PWM2
PWM3
PWM VALUE = 2
PWM4
PWM5
PWM VALUE = 3
PWM6
Figure 12-18. Ideal Complementary Operation (Dead-Time = 0)
However, when dead-time is inserted, the motor voltage is allowed to float momentarily during the
dead-time interval, creating a distortion in the motor current waveform. This distortion is aggravated by
dissimilar turn-on and turn-off delays of each of the transistors.
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
130
Freescale Semiconductor