W79E225A_08 Datasheet, PDF (114/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A Data Sheet
14.5 Dead-Time Insertion
The dead time generator inserts an “off” period called “dead time” between the turnings off of one pin
to the turning on of the complementary pin of the paired pins. This is to prevent damage to the power
switching devices that will be connected to the PWM output pins. Each complementary output pair for
the PWM module has 6-bits counter used to produce the dead time insertion. Each dead time unit has
a rising and falling edge detector connected to the duty cycle comparison output. The dead time is
loaded into the timer on the detected PWM edge event. Depending on whether the edge is rising or
falling, one of the transitions on the complementary outputs is delayed until the timer counts down to
zero. A timing diagram indicating the dead time insertion for one pair of PWM outputs is shown in
Figure 14-10 and Figure 14-11.
PWM0 without
Dead-Time
PWM1 without
Dead-Time
PWM0 with
Dead-Time
PWM1 with
Dead-Time
Dead-Time Interval
Note: PDTC0.4 selects insertion at rising edge
Figure 14-10: Effect of Dead-Time for complementary pairs (rising edge)
PWM0 without
Dead-Time
PWM1 without
Dead-Time
PWM0 with
Dead-Time
PWM1 with
Dead-Time
Dead-Time Interval
Note: PDTC0.4 selects insertion at falling edge
Figure 14-11: Effect of Dead-Time for complementary pairs (falling edge)
Note: User need to take care that power switches should not be use when PWM pair is
asserted (high) at the same time.
PDTCO and PDTC1 have time access protection in writing access. In Power inverter application,
a dead time insertion avoids the upper and lower switches of the half bridge from being active at the
same time. Hence the dead time control is crucial to proper operation of a system. Some amount of
time must be provided between turning off of one PWM output in a complementary pair and turning on
the other transistor as the power output devices cannot switch instantaneously.
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Publication Release Date: April 15, 2008
Revision A4.0