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AN2064
APPLICATION NOTE
Compliance of series/parallel protections for Telecom CO
REV. 1AN2064/0705
ST and Cooper Bussmann, experts of wireline networks protection, have jointly prepared this application
note to present a full protection solution based on companion devices from both companies.
Even with all the wireless telecommunication options (GSM, DCS, PCS, UMTS, Wi-Fi, etc…), the wireline
network remains the most cost effective wide range solution to exchange data over the world. The use of
this copper carrier requires system designers to provide adequate protection against overvoltage and
overcurrent events occurring on the line. The goal of this document is to provide telecom system card
designers the necessary information to make proper protection choices.
An example of a wireline telecom network is shown in figure 1. Two different kinds of equipment are con-
nected together by means of a copper line. One line termination is connected to the Central Office (CO)
while the other is connected to the terminal. In the CO, the line goes through the Main Distribution Frame
(MDF), which connects network to the signal cabinet, and is then connected to a subscriber line card.
The following pages show how to implement the protection stage utilizing series overcurrent protection
devices and Transient Voltage Suppressor (TRISIL™) devices (figure 2). Both elements work together
during surges, TRISIL acts to suppress overvoltages while the series overcurrent devices protect the cir-
cuit from lethal overcurrents.
Figure 1: Classical topology of wireline network subscriber line card
Subscriber line card
Central office
MDF
Terminal
Copper line
TM: TRISIL is a trademark of STMicroelectronics.
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