LM3S6950 Datasheet, PDF (420/524 Pages) List of Unclassifed Manufacturers – Microcontroller

Pulse Width Modulator (PWM)
17
17.1
Pulse Width Modulator (PWM)
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. Each
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.
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. It can also generate the full six
channels of gate controls required by a 3-Phase inverter bridge.
Block Diagram
Figure 17-1 on page 420 provides a block diagram of a Stellaris^® PWM module. The LM3S6950
controller contains three generator blocks (PWM0, PWM1, and PWM2) and generates six independent
PWM signals or three paired PWM signals with dead-band delays inserted.
Figure 17-1. 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
PWMnINTEN
Interrupt and
Trigger Generate
PWMnRIS
PWMnISC
PWMENABLE
PWMINVERT
PWMFAULT
PWM Output
Control
Interrupt
17.2
17.2.1
Functional Description
PWM Timer
The timer in each PWM generator 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
420
June 14, 2007
Luminary Micro Confidential-Advance Product Information