Chapter 25 FlexPWM
MPC5602P Microcontroller Reference Manual, Rev. 4
696
Freescale Semiconductor
When deadtime is inserted in complementary PWM signals connected to an inverter driving an inductive
load, the PWM waveform on the inverter output will have a different duty cycle than what appears on the
output pins of the PWM module. This results in a distortion in the voltage applied to the load. A method
of correcting this, adding to or subtracting from the PWM value used, is discussed next.
Figure 25-45. Deadtime insertion
25.8.9
Top/bottom correction
In complementary mode, either the top or the bottom transistor controls the output voltage. However,
deadtime has to be inserted to avoid overlap of conducting interval between the top and bottom transistor.
Both transistors in complementary mode are off during deadtime, allowing the output voltage to be
determined by the current status of load and introduce distortion in the output voltage. See
.
On AC induction motors running open-loop, the distortion typically manifests itself as poor low-speed
performance, such as torque ripple and rough operation.
VAL1 (0x0100)
VAL3
VAL0 (0x0000)
VAL2
INIT (0xFF00)
PWMA
PWMB
no deadtime
PWMA
PWMB
with deadtime
DTCNT0
DTCNT1