LM3S5956-IQR80-C1 Datasheet, PDF (953/1144 Pages) Texas Instruments – Stellaris® LM3S5956 Microcontroller

NRND: Not recommended for new designs.
Stellaris^® LM3S5956 Microcontroller
19.3.4
19.3.5
19.3.6
Dead-Band Generator
The pwmA and pwmB signals produced by each PWM generator are passed to the dead-band
generator. If the dead-band generator is disabled, the PWM signals simply pass through to the
pwmA' and pwmB' signals unmodified. If the dead-band generator is enabled, the pwmB signal is
lost and two PWM signals are generated based on the pwmA signal. The first output PWM signal,
pwmA' is the pwmA signal with the rising edge delayed by a programmable amount. The second
output PWM signal, pwmB', is the inversion of the pwmA signal with a programmable delay added
between the falling edge of the pwmA signal and the rising edge of the pwmB' signal.
The resulting signals are a pair of active High signals where one is always High, except for a
programmable amount of time at transitions where both are Low. These signals are therefore suitable
for driving a half-H bridge, with the dead-band delays preventing shoot-through current from damaging
the power electronics. Figure 19-6 on page 953 shows the effect of the dead-band generator on the
pwmA signal and the resulting pwmA' and pwmB' signals that are transmitted to the output control
block.
Figure 19-6. PWM Dead-Band Generator
pwmA
pwmA’
pwmB’
Rising Edge
Delay
Falling Edge
Delay
Interrupt/ADC-Trigger Selector
Each PWM generator also takes the same four (or six) counter events and uses them to generate
an interrupt or an ADC trigger. Any of these events or a set of these events can be selected as a
source for an interrupt; when any of the selected events occur, an interrupt is generated. Additionally,
the same event, a different event, the same set of events, or a different set of events can be selected
as a source for an ADC trigger; when any of these selected events occur, an ADC trigger pulse is
generated. The selection of events allows the interrupt or ADC trigger to occur at a specific position
within the pwmA or pwmB signal. Note that interrupts and ADC triggers are based on the raw events;
delays in the PWM signal edges caused by the dead-band generator are not taken into account.
Synchronization Methods
The PWM module provides three PWM generators, each providing two PWM outputs that may be
used in a wide variety of applications. Generally speaking, the PWM is used in one of two categories
of operation:
■ Unsynchronized. The PWM generator and its two output signals are used alone, independent
of other PWM generators.
■ Synchronized. The PWM generator and its two outputs signals are used in conjunction with
other PWM generators using a common, unified time base. If multiple PWM generators are
configured with the same counter load value, synchronization can be used to guarantee that
they also have the same count value (the PWM generators must be configured before they are
synchronized). With this feature, more than two PWMn signals can be produced with a known
relationship between the edges of those signals because the counters always have the same
values. Other states in the module provide mechanisms to maintain the common time base and
mutual synchronization.
October 06, 2012
953
Texas Instruments-Production Data