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
®
microcontroller contains one PWM module, with three PWM generator blocks and a
control block, for a total of 6 PWM outputs. 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 share the same timer and frequency
and can either be programmed with independent actions or as a single pair of complementary signals
with dead-band delays inserted. The output signals, pwmA' and pwmB', of the PWM generation
blocks are managed by the output control block before being passed to the device pins as PWM0
and PWM1 or PWM2 and PWM3, and so on.
The Stellaris PWM module provides a great deal of flexibility and can generate simple PWM signals,
such as those required by a simple charge pump as well as paired PWM signals with dead-band
delays, such as those required by a half-H bridge driver.
Each PWM generator block has the following features:
■ Four fault-condition handling inputs to quickly provide low-latency shutdown and prevent damage
to the motor being controlled
■ 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 signal 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
July 24, 2012828
Texas Instruments-Production Data
Pulse Width Modulator (PWM)
OBSOLETE: TI has discontinued production of this device.
