LM3S2739 Datasheet, PDF (449/532 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S2739 Microcontroller
18
18.1
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 Stellaris^® PWM module consists of three PWM generator blocks and a control block. Each
PWM generator block contains one timer (16-bit down or up/down counter), two PWM 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 Stellaris^® 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. It can also generate the full six
channels of gate controls required by a 3-Phase inverter bridge.
Block Diagram
Figure 18-1 on page 449 provides a block diagram of a Stellaris^® PWM module. The LM3S2739
controller contains three generator blocks (PWM0, PWM1, and PWM2) and generates six independent
PWM signals or three paired PWM signals with dead-band delays inserted.
Figure 18-1. 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
PWMENABLE
PWMINVERT
PWMFAULT
PWM Output
Control
PWMnINTEN
Interrupt and
Trigger Generate
PWMnRIS
PWMnISC
Interrupt
18.2
18.2.1
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
June 04, 2007
449
Preliminary