Chapter 25 FlexPWM
MPC5602P Microcontroller Reference Manual, Rev. 4
698
Freescale Semiconductor
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In center-aligned operation, decreasing or increasing the PWM value by a correction value equal
to one-half the deadtime typically compensates for deadtime distortion.
25.8.10 Manual correction
To detect the current status, the voltage on each PWMx pin is sampled twice in a PWM period, at the end
of each deadtime. The value is stored in the DTx bits in the CTRL1 register. The DTx bits are a timing
marker especially indicating when to toggle between PWM value registers. Software can then set the IPOL
bit to switch between VAL2/VAL3 and VAL4/VAL5 register pairs according to DTx values.
Figure 25-47. Current-status sense scheme for deadtime correction
Both D flip-flops latch low, DT0 = 0, DT1 = 0, during deadtime periods if current is large and flowing out
of the complementary circuit. See
.
Both D flip-flops latch the high, DT0 = 1, DT1 = 1,
during deadtime periods if current is also large and flowing into the complementary circuit.
However, under low-current, the output voltage of the complementary circuit during deadtime is
somewhere between the high and low levels. The current cannot free-wheel through the opposition
anti-body diode, regardless of polarity, giving additional distortion when the current crosses zero. Sampled
results will be DT0 = 0 and DT1 = 1. Thus, the best time to change one PWM value register to another is
just before the current zero crossing.
PWMA
PWMB
D
Q
CLK
D
Q
CLK
Voltage
sensor
PWMX
PWMA
PWMB
DT0
DT1
Positive
current
Negative
current