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AN-1161
APPLICATION NOTE
One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
EMC-Compliant RS-485 Communication Networks
by James Scanlon
Rev. 0 | Page 1 of 16
INTRODUCTION
In real industrial and instrumentation (I&I) applications, RS-485
communication links must work in harsh electromagnetic
environments. Large transient voltages caused by lightning strikes,
electrostatic discharge, and other electromagnetic phenomenon
can cause damage to communication ports. These data ports must
meet certain electromagnetic compatibility (EMC) regulations to
ensure that they can survive in their final installation environments.
Within these requirements, there are three transient immunity
standards: electrostatic discharge, electrical fast transients, and
surge. Leaving EMC considerations to the end of the design
cycle leads to penalties, such as engineering budget and
schedule overruns. Many EMC problems are not simple or
obvious and must be considered at the start of product design.
This application note describes each of these transients,
presents the design solution methodology, and demonstrates
three different EMC-compliant solutions for three different
cost/protection levels for RS-485 communication ports. These
different solutions are illustrated in Figure 1.
Analog Devices, Inc., and Bourns, Inc., have partnered to
extend their offering of system oriented solutions by co-
developing the industry’s first EMC-compliant RS-485 interface
customer design tool.
This tool provides, up to and including, Level 4 protection levels
for IEC 61000-4-2 ESD, IEC 61000-4-4 EFT, and IEC 61000-4-5
surge. It gives designers the design options depending upon the
level of protection required and available budgets. These design
tools allow designers to reduce risk of project slippage due to
EMC problems by considering them at the start of the design cycle.
Figure 1. Three EMC Compliant Solutions
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