The series resitors Rs1 and Rs2 designed in figure 1 represent the fuse resistors or the PTC which are man-

datory to withstand the power contact or the power inductance tests imposed by the different country stand-

ards. Taking into account this fact the actual lightning surge current flowing through the LCP is equal to:

I surge = V surge / (Rg + Rs)

With

V surge = peak surge voltage imposed by the standard.

Rg = series resistor of the surge generator

Rs = series resistor of the line card (e.g. PTC)

e.g. For a line card with 30

Ω of series resistors which has to be qualified under Bellcore 1000V 10/1000µs

surge, the actual current through the LCP1521 is equal to:

I surge = 1000 / (10 + 30) = 25A

The LCP1521 is particularly optimized for the new telecom applications such as the fiber in the loop, the

WLL, the decentralized central office for example. These short line applications need smaller operating

voltages than the long line applications and then allow the use of high voltage SLIC’s operating without ring

relay. The schematics of figure A3 gives the most frequent topology used for these emergent applications.

Fig. A3: Protection of high voltage SLIC.

Rs (*) = PTC or Resitor fuse

Gate

GND

GND

TIP

RING

-Vbat

LCP1521

220nF

SLIC

Rs (*)

Rs (*)

Line

Line card

TIP

RING

GND

LCP1521

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