Block Diagram; Layout Notes - Intel PXA27 Series Design Manual

Pulse-Width Modulator Interface
23.3

Block Diagram

Refer to Chapter 24, "General Purpose Input/Output Interfaces"
regarding the proper hardware implementation of the pulse-width modulator (PWM) signals.
The connection of the PWM to the peripheral device using the PWM is typically direct. However,
if the PWM is used as a software controlled voltage source, a low pass filter must be placed in line.
An example of this is the contrast control on an LCD panel. If the PWM output is used for
generating audio, an appropriate filter is also required. In this case, the filter is a band pass filter.
The specification and design of the filter depends on the exact purpose of the application. See the
block diagram for a design requiring a filter in
Figure 23-1. PWM Block Diagram For Applications Requiring a Filter
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23.4

Layout Notes

Refer to Chapter 24, "General Purpose Input/Output Interfaces"
regarding the proper layout practices for the PWM signals.
The maximum switching frequency of the PWM signals is approximately 1.6 MHz. Therefore,
layout and routing considerations are not as stringent as for other GPIOs and are somewhat relaxed.
However, for best results, adhere to all GPIO layout recommendations.
A typical use for pulse-width modulated outputs is the contrast control for LCD panels. In this
situation, the panel backlight inverter is a serious source of noise. To ensure the noise is not
induced into the contrast control or the processor, follow all recommendations for shielding the
inverter and separating the inverter as far as possible from the contrast control line (PWM output.)
II:23-2
PXA27x
Processor
GPIOx
of this document for information
Figure 23-1.
Low Pass
or
Band Pass
Filter
of this document for information
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Intel PXA27x Processor Family Design Guide
Peripheral
Using
PWM