LPC2921 datasheet(37/81 Pages) PHILIPS

37 / 81 page

LPC2921_2923_2925_0

Preliminary data sheet

Rev. 00.01 — 24 October 2008

37 of 81

NXP Semiconductors

LPC2921/2923/2925

ARM9 microcontroller with CAN and LIN

6.14.5.1

Functional description

The ability to provide flexible waveforms allows PWM blocks to be used in multiple

applications; e.g. dimmer/lamp control and fan control. Pulse-width modulation is the

preferred method for regulating power since no additional heat is generated, and it is

energy-efficient when compared with linear-regulating voltage control networks.

The PWM delivers the waveforms/pulses of the desired duty cycles and cycle periods. A

very basic application of these pulses can be in controlling the amount of power

transferred to a load. Since the duty cycle of the pulses can be controlled, the desired

amount of power can be transferred for a controlled duration. Two examples of such

applications are:

• Dimmer controller: The flexibility of providing waves of a desired duty cycle and cycle

period allows the PWM to control the amount of power to be transferred to the load.

The PWM functions as a dimmer controller in this application

• Motor controller: The PWM provides multi-phase outputs, and these outputs can be

controlled to have a certain pattern sequence. In this way the force/torque of the

motor can be adjusted as desired. This makes the PWM function as a motor drive.

The PWM block diagram in Figure 7 shows the basic architecture of each PWM. PWM

functionality is split into two major parts, a APB domain and a PWM domain, both of which

run on clocks derived from the BASE_MSCSS_CLK. This split into two domains affects

behavior from a system-level perspective. The actual PWM and prescale counters are

located in the PWM domain but system control takes place in the APB domain.

Fig 7.

PWM block diagram

002aad837

APB system bus

IRQ pwm

IRQ capt_match

PWM

CONTROL

REGISTERS

update

capture data

PWM counter value

config data

IRQ's

PWM,

COUNTER,

PRESCALE

COUNTER

SHADOW

REGISTERS

match outputs

capture inputs

trap input

carrier inputs

sync_in

sync_out

transfer_enable_in

transfer_enable_out

APB DOMAIN

PWM DOMAIN

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