23 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 TM4C1294NCPDT microcontroller contains one PWM module, with four PWM generator blocks
and a control block, for a total of 8 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 MnPWM0
and MnPWM1 or MnPWM2 and MnPWM3, and so on.
The TM4C1294NCPDT 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. Three generator blocks can
also generate the full six channels of gate controls required by a 3-phase inverter bridge.
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
1669June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller
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