LM3S2110 Datasheet, PDF (401/485 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S2110 Microcontroller
16
16.1
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 one PWM generator block and a control block. The 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 selector. The control block determines
the polarity of the PWM signals, and which signals are passed through to the pins.
The 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 block
is 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.
Block Diagram
Figure 16-1 on page 401 provides a block diagram of a Stellaris^® PWM module. The LM3S2110
controller contains one generator block (PWM0) and generates two independent PWM signals or
one paired PWM signal with dead-band delays inserted.
Figure 16-1. PWM Module Block Diagram
PWM Clock
PWMnLOAD
Timer
PWMnCOUNT
zero
load
dir
16
PWMnCMPA _cmpA
Comparator A
PWMnCMPB _cmpB
Comparator B
PWMnGENA
PWMnGENB
PWM Generator Block
Fault
PWM
Generator
pwma
pwmb
PWMnDBCTL
PWMnDBRISE
PWMnDBFALL
Dead-Band
Generator
PWMENABLE
PWMINVERT
PWMFAULT
PWM Output
Control
PWMnINTEN
Interrupt and
Trigger Generate
PWMnRIS
PWMnISC
Interrupt
16.2
16.2.1
Functional Description
PWM Timer
The timer runs in one of two modes: Count-Down mode or Count-Up/Down mode. In Count-Down
mode, the timer counts from the load value to zero, goes back to the load value, and continues
counting down. In Count-Up/Down mode, the timer counts from zero up to the load value, back
down to zero, back up to the load value, and so on. Generally, Count-Down mode is used for
November 29, 2007
401
Preliminary