Compare Units
Dead
Dead
-
-
Band Functionality
Band Functionality
(EVA)
(EVA)
PHx
DT
dead time
Clock
DTPH
x
Asymmetric PWM Example
DTPH
x_
4-bit period
Prescaler
4-bit
Counter
ENA
reset
HSPCLK
comparator
DTPH
x
DTPH
x_
PH
x
DT
edge
detect
DBTCONA . 4 - 2
DBTCONA . 11 - 8
Two basic approaches exist for controlling shoot-through: modify the transistors, or modify the
PWM gate signals controlling the transistors. In the first case, the opening time of the transistor
gate must be increased so that it (slightly) exceeds the closing time. One way to accomplish this
is by adding a cluster of passive components such as resistors and diodes in series with the
transistor gate, as shown in the next figure.
PWM
signal
R
by-pass diode
Shoot-through control via power circuit modification
The resistor acts to limit the current rise rate towards the gate during transistor opening, thus
increasing the opening time. When closing the transistor however, current flows unimpeded from
the gate via the by-pass diode and closing time is therefore not affected. While this passive
approach offers an inexpensive solution that is independent of the control microprocessor, it is
imprecise, the component parameters must be individually tailored to the power converter, and it
cannot adapt to changing system conditions.
The second approach to shoot-through control separates transitions on complimentary PWM
signals with a fixed period of time. This is called dead-band. While it is possible to perform
software implementation of dead-band, the C28x offers on-chip hardware for this purpose that
requires no additional CPU overhead. Compared to the passive approach, dead-band offers more
C28x - Event Manager 7 - 23
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