PWM23
PWM23
DTCNT0
zero
PWM45
DTCNT1
zero
INDEP
DBLEN
PWM45
1
1
1
1
1
DBLPWM
IPOL
start
start
0
0
0
0
0
from Force
Out logic
rising
edge
detect
down
counter
down
counter
to Output
logic
falling
edge
detect
Figure 37-240. Deadtime Insertion Logic
While in the complementary mode, a PWM pair can be used to drive top/bottom
transistors, as shown in the figure. When the top PWM channel is active, the bottom
PWM channel is inactive, and vice versa.
Note
To avoid short circuiting the DC bus and endangering the
transistor, there must be no overlap of conducting intervals
between top and bottom transistor. But the transistor's
characteristics may make its switching-off time longer than
switching-on time. To avoid the conducting overlap of top and
bottom transistors, deadtime needs to be inserted in the
switching period, as illustrated in the following figure.
The deadtime generators automatically insert software-selectable activation delays into
the pair of PWM outputs. The deadtime registers (DTCNT0 and DTCNT1) specify the
number of IPBus clock cycles to use for deadtime delay. Every time the deadtime
generator inputs change state, deadtime is inserted. Deadtime forces both PWM outputs
in the pair to the inactive state.
Chapter 37 Pulse Width Modulator A (PWMA/eFlexPWM)
KV4x Reference Manual, Rev. 2, 02/2015
Freescale Semiconductor, Inc.
Preliminary
843
Содержание freescale KV4 Series
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