LM3S610 Data Sheet
October 8, 2006 333
Preliminary
15 Pulse W i dth Modul ato r (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
supplie s a nd moto r contr ol .
The LM3S610 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 comparators, a
PWM signal generator, a dead-band generator, and an interrupt/ADC-trigger 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 LM3S610 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.
15.1 Block Diagram
Figure 15-1 provides a block diagram of a Stellaris PWM module. The LM3S610 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 15-1. PWM Module Block Diagram
15.2 Functional Description
15.2.1 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 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
Interrupt and
Trigger Generate
PWMnINTEN
PWMnRIS
PWMnISC
PWM Clock
Interrupt
Dead-Band
Generator
PWMnDBCTL
PWMnDBRISE
PWMnDBFALL
PWM Output
Control
PWMENABLE
PWMINVERT
PWMFAULT
PWM
Generator
PWMnGENA
PWMnGENB
pwma
pwmb
Timer
PWMnLOAD
PWMnCOUNT
Comparator A
PWMnCMPA
Comparator B
PWMnCMPB
zero
load
dir
16
cmpA
cmpB
Fault
PWM Generator Block
ADC Trigger
