LM3S1165_16 Datasheet, PDF (560/679 Pages) Texas Instruments – Stellaris LM3S1165 Microcontroller

Pulse Width Modulator (PWM)
Figure 16-5. PWM Generation Example In Count-Up/Down Mode
Load
CompA
CompB
16.3.4
Zero
PWMA
PWMB
In this example, the first generator is set to drive High on match A up, drive Low on match A down,
and ignore the other four events. The second generator is set to drive High on match B up, drive
Low on match B down, and ignore the other four events. Changing the value of comparator A
changes the duty cycle of the PWMA signal, and changing the value of comparator B changes the
duty cycle of the PWMB signal.
Dead-Band Generator
The two PWM signals produced by the PWM generator are passed to the dead-band generator. If
disabled, the PWM signals simply pass through unmodified. If enabled, the second PWM signal is
lost and two PWM signals are generated based on the first PWM signal. The first output PWM signal
is the input signal with the rising edge delayed by a programmable amount. The second output
PWM signal is the inversion of the input signal with a programmable delay added between the falling
edge of the input signal and the rising edge of this new signal.
This is therefore 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 16-6 on page 560 shows the effect of the dead-band generator on an input
PWM signal.
Figure 16-6. PWM Dead-Band Generator
Input
PWMA
PWMB
16.3.5
Rising Edge
Delay
Falling Edge
Delay
Interrupt/ADC-Trigger Selector
The 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 PWM 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.
560
July 15, 2014
Texas Instruments-Production Data