CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
367
Digital Blocks
17.3.3
Dead Band Timing
Figure 17-16. Basic Dead Band Timing
Enable/Disable Operation.
Initially both outputs are low.
There are no critical timing requirements for enabling the
block because dead band processing does not start until the
first incoming positive or negative reference edge. In typical
operation, it is recommended that the dead band block be
enabled first, then the Pulse Width Modulator (PWM) gener-
ator block.
When the block is disabled, the clock is immediately gated
low. All outputs are gated low, including the interrupt output.
All internal states are reset to their configuration specific
reset states, except for DR0, DR1, and DR2 which are unaf-
fected.
shows typical dead band
timing. The incoming reference edge can occur up to one 24
MHz system clock before the edge of the block clock. On
the edge of the block clock, the currently asserted output is
negated and the dead band counter is enabled. After Period
+ 1 clocks, the phase associated with the current state of the
PWM reference is asserted (Reference High = Phase 1,
Reference Low = Phase 2). The minimum dead time occurs
with a period value of 00h and that dead time is one clock
cycle.
17.3.3.1
Changing the PWM Duty Cycle
Under normal circumstances, the dead band period is less
than the minimum PWM high or low time. As an example,
consider
where the low of the PWM is four
clocks, the dead band period is two clocks, and the high
time of the PHI2 is two clocks.
Figure 17-17. DB High Time is PWM Width Minus DB
Period
illustrates the reduction of the width of the
PWM low time by one clock (to three clocks). The dead
band period remains the same, but the high time for PHI2 is
reduced by one clock (to one clock). Of course the opposite
phase, PHI1, decreases in length by one clock.
Figure 17-18. DB High Time is Reduced as PWM Width is
Reduced
If the width of the PWM low time is reduced to a point where
it is equal to the dead band period, the corresponding
phase, PHI2, disappears altogether. Note that after the ris-
ing edge of the PWM, the opposite phase still has the pro-
grammed dead band.
shows an example
where the dead band period is two and the PWM width is
two. In this case, the high time of PHI2 is zero clocks. Note
that the Phase 1 dead band time is still two clocks.
CLOCK
PWM REFERENCE
PHI2 (Auxiliary Output)
Dead Time
PHI1 (Primary Output)
Dead time in clocks is
the Period + 1.
A PWM reference edge
running on the same
clock occurs here.
A Bit Bang clock can occur
anywhere up to one 24
MHz clock, before the next
block clock edge.
A high on the reference
asserts PH1, a low PHI2.
COUNT
P-1
P-2
1
0
P
P
CLK
PWM
PHI1
PHI2
2
2
2
4
CLK
PWM
PHI1
PHI2
2
2
1
3
Содержание CY8C28 series
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