LM3S316 Datasheet, PDF (356/421 Pages) List of Unclassifed Manufacturers – Microcontroller

Pulse Width Modulator (PWM)
16
16.1
Pulse Width Modulator (PWM)
Pulse width modulation (PWM) is a powerful technique for digitally encoding analog signal levels.
High-resolution counters are used to generate a square wave, and the duty cycle of the square
wave is modulated to encode an analog signal. Typical applications include switching power
supplies and motor control.
The LM3S316 PWM module consists of two PWM generator blocks and a control block. Each
PWM generator block contains one timer (16-bit down or up/down counter), two comparators, a
PWM signal generator, a dead-band generator, and an interrupt/ADC-trigger selector. The control
block determines the polarity of the PWM signals, and which signals are passed through to the
pins.
Each PWM generator block produces two PWM signals that can either be independent signals
(other than being based on the same timer and therefore having the same frequency) or a single
pair of complementary signals with dead-band delays inserted. The output of the PWM generation
blocks are managed by the output control block before being passed to the device pins.
The LM3S316 PWM module provides a great deal of flexibility. It can generate simple PWM
signals, such as those required by a simple charge pump. It can also generate paired PWM
signals with dead-band delays, such as those required by a half-H bridge driver.
Block Diagram
Figure 16-1 provides a block diagram of a Stellaris PWM module. The LM3S316 controller
contains two generator blocks (PWM0 and PWM1) and generates four independent PWM signals
or two paired PWM signals with dead-band delays inserted.
Figure 16-1. PWM Module Block Diagram
PWM Clock
PWMnLOAD
Timer
PWMnCOUNT
zero
load
dir
16
PWMnCMPA _cmpA
Comparator A
PWMnCMPB _cmpB
Comparator B
PWMnGENA
PWMnGENB
PWM Generator Block
Fault
PWM
Generator
pwma
pwmb
PWMnDBCTL
PWMnDBRISE
PWMnDBFALL
Dead-Band
Generator
PWMnINTEN
Interrupt and
Trigger Generate
PWMnRIS
PWMnISC
PWMENABLE
PWMINVERT
PWMFAULT
PWM Output
Control
Interrupt
ADC Trigger
16.2
16.2.1
Functional Description
PWM Timer
The timer in each PWM generator runs in one of two modes: Count-Down mode or Count-Up/
Down mode. In Count-Down mode, the timer counts from the load value to zero, goes back to the
load value, and continues counting down. In Count-Up/Down mode, the timer counts from zero up
to the load value, back down to zero, back up to the load value, and so on. Generally, Count-Down
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April 27, 2007
Preliminary