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Application Note:

Designing Protection Solutions for 10GbE/1GbE & PoE

Using SP4044-04ATG/SP4045-04ATG TVS Diode Arrays

Overview

Ethernet is a Local Area Network (LAN) technology that was

standardized as IEEE 802.3. Today, there are four dominant

• 10GbE (10 Gbps, Baseband signaling, twisted pair)

Voltage Surge and Overcurrent Threats

Ethernet is increasingly being used in applications located in

harsh environments that are subject to overvoltage events

such as electrostatic discharges (ESD), electrical fast transients

(EFT), cable discharge events (CDE) and lightning-induced

events. These overvoltage and overcurrent events are defined

in various industry standards such as:

• IEC 61000-4-2 ESD

• IEC 61000-4-4 EFT

NOTE: A comprehensive summary of these various standards

can be found in the Regulatory Requirements section of the

The 10GbE and 1GbE versions of Ethernet are very sensitive

to any additional line loading; therefore, any protection

components and circuits must be carefully considered to avoid

degrading Ethernet’s intrinsic high data rates and 100-meter

reach capability.

The Littelfuse SP4044 and SP4045 Series TVS (Transient

minimizes negative effects on the signal of interest, the low

dynamic resistance provides a superior clamping value over

other industry protection solutions, and the robust surge rating

provides a tertiary protection solution that is compliant with

most worldwide surge resistibility standards.

Both the SP4044-04ATG (for Ethernet PHY voltage references

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application to exceed an acceptable level of EMI radiation.

These PCB trace stubs can also cause signal reflections that

have a negative impact on the original signal, which can reduce

the data transmission rate and reach. These stubs can reduce

the effectiveness of the circuit protection component by adding

baseband signaling and does not cause the “eye” diagram

(Figure 3) to close. One way to characterize the protection

loading effects on the Ethernet signal integrity is to conduct

eye diagram testing. This test involves repetitively sampling

a digital signal and displaying the resulting eye pattern on an

oscilloscope. A mask is often used to define acceptable signal

qualities and compliance as seen in the eye diagram below.

This “eye” diagram is a method of measuring the integrity of

clamping components. Two of these flow-through components

are required because 10GbE and 1GbE versions of Ethernet

use all eight wires of the CAT5e bundle. The transformer

provides the first level of protection by limiting the coupling of

any surge energy as a result of its saturation characteristics and

its inter-winding capacitance parameters. Any surge energy

that manages to get through the transformer barrier is clamped

by the SP4045-04ATG, ensuring protection of the sensitive

Ethernet PHY IC. (If the Ethernet PHY voltage is ≤ 2.8V, the

SP4044-04ATG can be substituted for the SP4045-04ATG.)

and ensure highly effective protection for the Ethernet PHY.

These TVS Diode Arrays provide both differential protection

and common mode protection for the Ethernet PHY. The TVS

ground reference must be the same as the Ethernet PHY

ground reference.

For a comprehensive Ethernet solution, the designer will

often see a need for Power over Ethernet (PoE) protection

and overcurrent safety protection. The center tap connections

provide the means for delivering and receiving PoE. The

SMDJ58CA is a bi-directional TVS diode for these center-tap