
CLP270M
4/24
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 :
I
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
by R
sense
.
I
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
ref
(+/- 270 V)
v
er oltage
erence
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