CLP270M

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APPLICATION NOTE

1. INTRODUCTION

This device includes a primary protection level and is suitable for main distribution frames and line cards.

This protection concept is explained and, in addition, the CLP270M performances are analysed when

facing different surges as described in the BELLCORE GR 1089 recommendations.

Figure 1 is a simplified block diagram of a subscriber line protection that is commonly used.

This shows two different topologies :

s

A “primary protection” located on the Main Distribution Frame (MDF) eliminates coarsely the high energy

environmental disturbances (lightning transients and AC power mains disturbances)

s

A “secondary protection” located on the line card includes a primary protection level (first stage) and a

residual protection (second stage) which eliminates finely the remaining transients that have not been totally

suppressed by the first stage.

2. STMicroelectronics CLP270M CONCEPT

2.1. Evolution of the SLIC protection

Over the years, the silicon protection performances have considerably changed.

The first generation of products like SMTHBTxx and SMTHDTxx offered fixed overvoltage protection

against surges on either TIP or RING line in four

packages.

The following generation like THBTxx and

THDTxx still offered fixed overvoltage protection

against surges on both TIP and RING lines in two

packages.

The next step was the introduction of the

LCP1511D which brought the advantage of full

programmable voltage.

Today, the CLP270M combines the features of all

the previous generations. In addition to that, it

offers an overcurrent detection when operating in

speech mode and also a Failure Status output

signal.

CLP270M

CLP270M

SLIC

SLIC

THDTxx

or

LCP1511D

or

LCDP1511D

“PRIMARY PROTECTION”

“SECONDARY PROTECTION”

“SECONDARY PROTECTION”

Telecommunication

line

Telecommunication

line

MDF

EXCHANGE

EXCHANGE

LINE CARD

LINE CARD

MDF

Fig. 1: Subscriber line protection topology

Line card

operating

conditions

V

I

-I

+I

SWON

SWON

Programmable

thanks to an

external resistor

Programmable

thanks to any

external voltage

reference

Fig. 2: Line card protection