LM3S317-IQN20-A0T Luminary Micro, Inc., LM3S317-IQN20-A0T Datasheet - Page 321

• Manufacturer Part Number: LM3S317-IQN20-A0T
• Description: Microcontroller
• Manufacturer: Luminary Micro, Inc.

15.2.4
15.2.5
15.2.6
May 4, 2007
Figure 15-4. PWM Generation Example In Count-Up/Down Mode
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 15-5 shows the effect of the dead-band generator on
an input PWM signal.
Figure 15-5. PWM Dead-Band Generator
Interrupt Selector
The PWM generator also takes the same four (or six) counter events and uses them to generate
an interrupt. 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. The selection of events
allows the interrupt to occur at a specific position within the PWM signal. Note that interrupts 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
There is a global reset capability that can synchronously reset any or all of the counters in the
PWM generator.
CompA
CompB
PWMA
PWMB
Load
Zero
PWMA
PWMB
Input
Rising Edge
Preliminary
Delay
Falling Edge
Delay
LM3S317 Data Sheet
321