To correct deadtime distortion, software can decrease or increase the value in the
appropriate VALx register.
• In edge-aligned operation, decreasing or increasing the PWM value by a correction
value equal to the deadtime typically compensates for deadtime distortion.
• 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.
37.5.2.8.2 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 CTRL[DT]. CTRL[DT] is a
timing marker especially indicating when to toggle between PWM value registers.
Software can then set MCTRL[IPOL] to switch between VAL2/VAL3 and VAL4/VAL5
register pairs according to CTRL[DT] values.
PWM_B
CLK
PWMX
PWMB
DT0
DT1
PWM_A
PWMA
Q
D
CLK
Q
D
POSITIVE
CURRENT
NEGATIVE
CURRENT
VOLTAGE
SENSOR
Figure 37-243. Current-status Sense Scheme for Deadtime Correction
Both D flip-flops latch low, CTRL[DT] = 00, during deadtime periods if current is large
and flowing out of the complementary circuit. See the preceding figure. Both D flip-flops
latch the high, CTRL[DT] = 11, 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 CTRL[DT] = b10. Thus, the
best time to change one PWM value register to another is just before the current
zero crossing.
Functional Description
KV4x Reference Manual, Rev. 2, 02/2015
846
Preliminary
Freescale Semiconductor, Inc.
Содержание freescale KV4 Series
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