Datasheet

18 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. 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.
Each Stellaris PWM module has the following features:
■ Three PWM generator blocks, each with one 16-bit counter, two PWM comparators, a PWM
signal generator, a dead-band generator, and an interrupt/ADC-trigger selector
■ One fault input in hardware to promote low-latency shutdown
■ One 16-bit counter
– Runs in Down or Up/Down mode
– Output frequency controlled by a 16-bit load value
– Load value updates can be synchronized
– Produces output signals at zero and load value
■ Two PWM comparators
– Comparator value updates can be synchronized
– Produces output signals on match
■ PWM generator
– Output PWM signal is constructed based on actions taken as a result of the counter and
PWM comparator output signals
– Produces two independent PWM signals
■ Dead-band generator
– Produces two PWM signals with programmable dead-band delays suitable for driving a half-H
bridge
– Can be bypassed, leaving input PWM signals unmodified
659June 18, 2012
Texas Instruments-Production Data
Stellaris
®
LM3S8962 Microcontroller
NRND: Not recommended for new designs.