CLP270M

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The figure 2 summarizes the firing modes of the CLP270M which basically hold the SLIC inside its correct

voltage and current values.

2.2 Application circuit: CLP270M in line card.

Figure 3 above shows the topology of a protected analog subscriber line at the exchange side. The

CLP270M is connected to the ring relay via two balanced Rp resistors, and to the Subscriber Line Interface

Circuit. A second device is located near the SLIC : it can be either a LCP1511D, a THDT series or a

LCDP1511D.

These two devices are complementary and their functions are explained below :

s

The first stage based on CLP270M manages the high power issued from the external surges. When

used in ringing mode, the CLP270M operates in voltage mode and provides a symmetrical and

bidirectional overvoltage protection at +/- 270 V on both TIP and RING lines. When used in speech

mode, the CLP270M operates in current mode and the activation current of the CLP270M is adjusted

s

The second stage is the external voltage reference device which defines the firing threshold voltage

during the speech mode and also assumes a residual power overvoltage suppression. This protection

stage can be either a fixed or programmable breakover device. The THDTxx family acts as a fixed

breakover device while the LCP1511D or the LCDP1511D operates as a programmable protection.

Thanks to this topology,

the surge current in the line is reduced after the CLP270M. Because the

remaining surge energy is low, the power ratings of Rp, the ring relay contacts and the external voltage

reference circuit can be downsized. This results in a significant cost reduction.

RINGS

-Vbat

-Vbat

Rp

Rsense

TIP

1

1

2

2

SLIC

(*)

(*) LCP1511D or THDT series or LCDP1511D

Ov v

ref

er oltage

erence

(+/- 270 V)

Overvoltage

detector

Overcurrent

detector

OR

Overvoltage

reference

(+/- 270 V)

Overvoltage

detector

Overcurrent

detector

OR

TIPL

TIPS

RINGL

FS

GND

SW3 SW1

SW4 SW2

Rsense

Rp

Ring

Generator

Fuse

Fuse

TIP

RING

External

voltage

reference

RING

I

Fig. 3 : CLP270M in line card