AN2053

Long line protection

Doc ID 10917 Rev 2

7/15

4

Long line protection

The long line concept is used in case of the classic wired telecom network. With this

topology, the core of the system is a huge central office from where many lines connect the

subscribers. In this case the line length can reach several kilometers. This type of subscriber

based on silicon integrated SLIC can be classified in two families:

●

With external ring signal management

●

With internal ring signal management

The classical one uses a mechanical relay to manage either ring generation or speech

mode.

Figure 9.

SLIC with external ring signal management

Figure 9 shows the protection circuit of a SLIC with mechanical ring relay. The protection

function is implemented in two stages. One is located between the line and the ring relay,

while the other is located between the ring relay and the SLIC.

The first stage, dedicated to the ring generator protection, supports a three-way protection

(THBTxxx11D for 30 A applications or TLPxxx for 100 A requirements). This stage acts

symmetrically at + or - V (For example +/-200 V) where V is chosen as slightly higher than

the maximum ring voltage trip.

The goal of the second stage is to manage a fine protection level in phase with the

requirements of the high integration technology modern SLIC. This stage must switch on for

a voltage higher than the voltage supply of the SLIC.

The resistors referenced by (**) allow the LCP15xx to manage both 100 A and 50 A

applications when no resistance is permitted at the PTC or fuse stage. In this case, when a

surge occurs the LCP15xx starts to act and before the current becomes too high in the

LCP15xx, the drop voltage across the resistor (**) allows the TLPxxx device to be fired.

Then all the surge current flows through the TLPxx device.

The resistors referenced (*) are not mandatory and are added when the SLIC to be

protected is very sensitive to the latch up phenomena.

SLIC

Ring generator

Tip

Ring

-V bat

Mechanical

relay

THBTxxx11D

or

TLPxxx

PTC or Fuse

PTC or Fuse

(**)

(**)

LCP1521S

(**) Used for 100A version

(*) Not mandatoy

(*)

(*)