LM3S3748 Datasheet, PDF (603/753 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S3748 Microcontroller
19
19.1
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 four 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. Three generator blocks can
also generate the full six channels of gate controls required by a 3-phase inverter bridge.
Block Diagram
Figure 19-1 on page 603 provides the Stellaris^® PWM module unit diagram and Figure 19-2 on page
604 provides a more detailed diagram of a Stellaris^® PWM generator. The LM3S3748 controller
contains four generator blocks (PWM0, PWM1, PWM2, and PWM3) and generates eight independent
PWM signals or four paired PWM signals with dead-band delays inserted.
Figure 19-1. PWM Unit Diagram
PWM Clock
Faults
System Clock
Control and
Status
PWMCTL
PWMSYNC
PWMSTATUS
Interrupts
Triggers
Interrupt
PWMINTEN
PWMRIS
PWMISC
Output
PWMENABLE
PWMINVERT
PWMFAULT
PWMFAULTVAL
PWM0_A
PWM
PWM0_B
Generator 0
PWM0_Fault
PWM1_A
PWM
PWM1_B
Generator 1
PWM1_Fault
PWM2_A
PWM
PWM2_B
Generator 2
PWM2_Fault
PWM3_A
PWM
PWM3_B
Generator 3
PWM3_Fault
PWM 0
PWM 1
PWM
Output
Control
Logic
PWM 2
PWM 3
PWM 4
PWM 5
PWM 6
PWM 7
April 08, 2008
603
Preliminary