mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 154

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Pulse-Width Modulator for Motor Control
9.6.3 Top/Bottom Correction with Motor Phase Current Polarity Sensing
Advance Information
154
UP/DOWN COUNTER
MOUDULUS = 3
NO DEAD TIME
NO DEAD TIME
DEAD TIME = 3
DEAD TIME = 3
PWM1 W/
PWM2 W/
PWM1 W/
PWM2 W/
PWM VALUE = 2
Figure 9-16. Dead Time and Small Pulse Widths
Ideally, when complementary pairs are used, the PWM pairs are
inversions of each other, as shown in
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.
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.
For a typical motor drive inverter as shown in
top/bottom transistor pair, only one of the transistors will be effective in
controlling the output voltage at any given time depending on the
direction of the motor current for that pair. To achieve distortion
correction, one of two different correction factors must be added to the
desired PWM value, depending on whether the top or bottom transistor
is controlling the output voltage. Therefore, the software is responsible
for calculating both compensated PWM values and placing them in an
odd/even PWM register pair. By supplying the PWM module with
information regarding which transistor (top or bottom) is controlling the
Pulse-Width Modulator for Motor Control (PWMMC)
3
PWM VALUE = 3
3
PWM VALUE = 2
3
Figure
PWM VALUE = 1
3
9-17. When PWM1 is
Figure
MC68HC908MR24
Freescale Semiconductor
3
9-12, for a given
—
3
Rev. 4.1