LM3S3768 Luminary Micro, Inc, LM3S3768 Datasheet - Page 605

• Manufacturer Part Number: LM3S3768
• Description: Lm3s3768 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

19
19.1
June 02, 2008
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
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
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 605 provides the Stellaris
606 provides a more detailed diagram of a Stellaris
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
Interrupts
Triggers
®
®
PWM module consists of four PWM generator blocks and a control block. Each PWM
PWM module provides a great deal of flexibility. It can generate simple PWM signals,
PWMFAULTVAL
Control and
PWMSTATUS
PWMENABLE
PWMINVERT
PWMFAULT
PWMINTEN
PWMSYNC
Interrupt
PWMCTL
PWMRIS
PWMISC
Output
Status
Preliminary
®
PWM module unit diagram and Figure 19-2 on page
Generator 0
Generator 1
Generator 2
Generator 3
®
PWM generator. The LM3S3768 controller
PWM
PWM
PWM
PWM
PWM0_A
PWM0_B
PWM0_Fault
PWM1_A
PWM1_B
PWM1_Fault
PWM2_A
PWM2_Fault
PWM3_A
PWM3_B
PWM3_Fault
PWM2_B
LM3S3768 Microcontroller
Control
Output
PWM
Logic
PWM 0
PWM 1
PWM 2
PWM 3
PWM 4
PWM 5
PWM 6
PWM 7
605