ESD Protection
Ethernet Data Lines
Ethernet Product (Card or Box)
Circuit Board
PHY Chip
Figure 1. Simple Ethernet circuit diagram (ESD suppressors protect the data lines which have exposure to the outside world.
Ethernet and Fast Ethernet use 4 data lines, while Gigabit Ethernet uses 8 data lines).
Ethernet products (PCI adapter
cards, hubs/routers, etc.) can be
susceptible to ESD events when
the cable is disconnected from the
Ethernet port. The ESD pulse can
be introduced directly into the
open port, or into the disconnected
end of the cable. Either way, the
integrated circuitry that controls
the Ethernet functionality can be
The Problem
After the ESD pulse is introduced
into the Ethernet port, it will travel
through the connector to the PC
board. Once on the PC board, it
will propagate down the data lines
toward the integrated circuitry.
Specifically, the IC of concern is the
PHY chip and/or Ethernet
Controller. Without sufficient
protection, the PHY/Controller chip
can be rendered inoperable.
The Solution
In order to provide the IC with
protection against ESD transients,
the use of suppression products is
recommended. The suppressors
are installed between the data line
and the chassis ground (parallel
connection) and shunt the ESD
transient from the data line to the
For high-speed protocols like Fast
Ethernet and Gigabit Ethernet,
suppressors with very low capacitance levels should be used.
Suppressors with high capacitance
can affect the data stream by
distorting the data waveforms
Littelfuse offers MHS multilayer
varistors, SP series rail clamp arrays,
and PulseGuard® ESD suppressors
as a solution for Fast and Gigabit
Ethernet ESD protection. These
products are surface mount devices
with 3.0 pF (or less) of capacitance.
So they will provide ESD protection
and maintain the integrity of the
Ethernet signals.
Examples of Ethernet products
which can benefit from ESD
protection include:
• PCI adapter cards
• Hubs and routers
(Layer 2-3 switches)
• Intelligent content managers
(Layer 4-7 switches)
• PLC units, Process controller units
• Residential gateways and other
broadband internet access products
Capacitance and Signal
As new I/O data protocols
continue to be introduced, it is
important to realize that the nonsuppression characteristics of an
ESD suppressor must be taken into
account during the design process.
For example, at the 10BaseT
Ethernet data bit rate (10 Mbps), a
higher level of capacitance can be
tolerated than at the
100/1,000BaseT Ethernet data bit
rate (125 Mbps). The following eye
diagrams can be used to demonstrate this phenomenon.
In the first set of diagrams, data is
shown for the USB 1.1 (12 Mbps)
data rate and is used to replicate
the 10BaseT system. The first
diagram shows the eye diagram for
a control board which only contains
traces for the data lines. The
second diagram shows the
response of a data line which has a
V18MLE0603 (75.0 pF) multilayer
varistor installed. The third diagram
is included for reference, and shows
the response when a 3 pF capacitor
is installed on a data line and is
used to replicate Littelfuse 3 pF
multilayer varistors and diode
arrays. The multilayer varistor and
capacitor were referenced to
The second set of diagrams replicates the same tested devices, but
raises the data rate to 100 Mbps.
So, for the 10BaseT system, the
higher capacitance multilayer varistor can be used for ESD protection
and EMI filtering without affecting
signal integrity. However, in the
100/1,000BaseT system, it is necessary to use lower capacitance
devices (3 pF and lower) such as
the MHS series multilayer varistor,
the SP series rail clamp array, or the
PulseGuard® polymer suppressor. In
all cases, the overall system capacitance should be considered when
choosing an ESD suppressor.
The signals replicate the USB 1.1
(12 Mbps, section 7.1) and IEEE
1394-1995 (100 Mbps, section 4.2)
protocols; created on Agilent 81250
ParBERT equipment and measured
with an Agilent Digital
Communications Analyzer.
Figure 2. Test board traces for an Ethernet 10BaseT data
Figure 5. Test board traces for an Ethernet 100BaseT /
1000BaseT data line
Figure 3. MLE traces for an Ethernet 10BaseT data line
Figure 6. MLE traces for an Ethernet 100BaseT /
1000BaseT data line
Figure 4. Surface mount capacitor (3pF) traces for an
Ethernet 10BaseT data line
Figure 7. Surface mount capacitor (3pF) traces for an
Ethernet 100BaseT / 1000BaseT data line
Specifications, descriptions and illustrative material in this literature are as accurate as known at time of publication, but are
subject to change without notice. Littelfuse is a registered trademark of Littelfuse Incorporated.
100BaseT / 1000Base T
Copyright © 2001 Littelfuse, Inc., All Rights Reserved. Printed in U.S.A. JANUARY 2002
Littelfuse, Inc.
800 E. Northwest Highway
Des Plaines, IL 60016
(847) 824-1188
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