"Exposed" Ethernet Ports

Circuit Protection of Ethernet "Exposed" Ports

Design Notes:

Protection Application:
This note covers 10BaseT and 100BaseT Ethernet lines that have exposure to lighting and other significant surges. The data signals used in Ethernet communications are 2Vp-p with maximum data rates of up to 100Mbps, but PoE lines may see 20V during handshaking. At these data rates, the capacitance and linearity of the suppressor needs to be taken into account. The signal lines to be protected are the TX pair and the RX pair.
Solution Description:
Each pair is normally “floating" as shown in the top left figure. Some applications will use a ground referenced design and will require the circuit shown at the lower left for each pair. All of the diodes shown are MURS160T3 devices from ON Semiconductor and are needed to achieve the needed low capacitance and linearity. The P0300SAMC SIDACtor device is used as the protection element.
Companion Solutions:
P0080SAMC’s may be used where no PoE handshaking exists. Also, protection can be upgraded to “C" rated devices and 1.25A fuses to comply with inter-building requirements. Tiny QFN and thru-hole TO-92 packages are also available. Some short haul applications can use a simple P0642SA SIDACtor device without the extra diodes.
Regulatory Issues:
This solution is designed to comply with Telcordia’s GR-1089 intra-building requirements and can be upgraded to GR-1089 inter-building requirements.
Unique Features:
Littelfuse’s QFN package is the smallest in the industry.
Application Warnings:
Does not apply.



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