AN2456
Protection of single battery voltage SLICs for new networks in US market
Introduction
Despite the widespread proliferation of digital technologies, analog networks remain the most commonly used telecommunication means in the world. Thanks to its simple and cheap technology, POTS (plain old telephone set) are still utilized extensively.
Central Office / LT |
|
|
|
|
|
|
|
|
|
|
|
|
|
Long lines |
|
|
|
|
|
|
(Twisted pair) |
||
|
Opt |
|
|
|
|
|
|
n |
ical |
t |
|
|
|
|
|
o |
|
ra |
ns |
mi |
|
RCO |
|
i |
|
|
|
|
|
||
s |
|
|
|
|
ss |
io |
|
s |
|
|
|
|
|
n |
|
i |
|
|
|
|
|
|
|
m |
|
|
|
|
|
|
|
s |
|
|
|
|
|
|
|
n |
|
|
|
|
|
|
Short lines |
a |
|
|
|
|
|
|
|
r |
|
|
|
|
|
|
(Twisted pair) |
t |
|
|
|
|
|
|
|
l |
|
|
|
|
|
|
|
a |
|
|
|
|
|
|
|
c |
|
|
|
|
|
|
|
i |
|
|
|
|
|
|
|
t |
|
|
|
|
|
|
|
p |
|
|
|
|
|
|
|
O |
|
|
|
|
|
|
Optical |
|
|
|
|
|
|
on |
Network |
|
|
|
|
|
|
|
|
|
|
|
|
|
issi |
|
|
|
|
|
|
sm |
|
|
|
|
|
an |
|
|
Unit |
||
|
tical tr |
|
|
|
|||
|
Op |
|
|
|
|
|
|
|
|
|
|
|
|
|
Co |
|
|
|
|
|
|
|
a |
|
|
|
|
|
|
|
x |
|
|
|
|
|
|
|
i |
|
|
|
|
|
|
|
a |
|
|
|
|
|
|
|
l |
Central Office / LT |
|
|
|
|
|
|
|
Figure 1 shows a schematic of modern telecom networks that are expected to keep growing. These networks are essentially made up of two kinds of lines, classical long lines (several kilometers long) that directly connect the Central Office (CO) to the subscriber, and short lines (few tens of meters in length) that connect Remote Central Offices (RCO), Optical Network Units (ONU) or Radio Network Units (RNU) to subscriber terminals. In these networks SLICs can be present in either conventional Central Offices or any of the above mentioned remote locations or in Remote Terminals (RT) in the customer premises which connect to POTS through short lines. The link between these remote locations and the CO is established by a long high speed digital link e.g. coaxial cable, fiber optic cable, Wireless Local Loop (WLL). This disparity in line length has given rise to SLICs of two types. Protection of both kinds of SLICs is a very important aspect in the design of the system. The purpose of this application note is to propose a complete protection solution for short line SLICs located in RT in customer premises.
November 2006 |
Rev 1 |
1/15 |
www.st.com
Contents |
AN2456 |
|
|
Contents
Contents. |
. . . . . |
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 2 |
1 |
Telecom disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
3 |
|
2 |
LCP152xx concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
5 |
|
3 |
SLIC protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7 |
|
|
3.1 |
Lightning surge protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9 |
|
3.2 |
Power crossing protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
12 |
4 |
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
15 |
|
5 |
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
15 |
2/15
AN2456 |
Telecom disturbances |
|
|
Figure 2 shows the different disturbances that may appear on the telecom line. Among these, lightning and power crossing are the main considerations for wireline applications. These disturbances are well defined in the country standards.
Subscriber
Location
SLIC |
Central office |
Protection
Atmospheric effects (Lightning) 50/60Hz mains disturbances Electrostatic discharges
Protection
POTS
As the purpose of this application note is to illustrate the protection topology needed for short line SLICs located in RT in customer premises in the US, the standard to be considered for lightning and power crossing tests is the Telcordia GR1089 Intrabuilding (equipment port type 4).
The Telcordia GR1089 specifies two acceptance criteria:
●First level: the equipment shall continue to operate properly after the test.
●Second level: the equipment may be damaged, but should not become a fire or electrical hazard.
For intrabuilding equipment, however, only first level acceptance criterion need to be satisfied for lightning tests.
Table 1 and Table 2 give the list of lightning and power crossing tests in the Telcordia GR1089 intrabuilding standard for equipment port type 4.
Table 1. |
Telecordia GR1089 intrabuilding lightning tests |
|
||||
|
|
|
|
Voltage and |
|
|
Surge |
|
Peak voltage |
Peak current |
current |
Repetitions of |
Test |
|
(V) |
(A) |
waveforms |
each polarity |
configuration(1) |
|
|
|
|||||
|
|
|
|
(µs) |
|
|
|
|
|
|
|
|
|
1 |
|
±800 |
100 |
2/10 |
1 |
M (on tip and ring) |
|
|
|
|
|
|
|
2 |
|
±1500 |
100 |
2/10 |
1 |
L |
|
|
|
|
|
|
|
1. M: metallic; L: longitudinal |
|
|
|
|
3/15
Telecom disturbances |
|
|
|
|
|
|
|
|
|
|
|
|
AN2456 |
|||
|
|
|
|
|
|
|
|
|
|
|
|
|||||
|
Table 2. |
|
Telecordia GR1089 2nd level intrabuilding power crossing test |
|||||||||||||
|
|
|
|
(equipment port type 4) |
|
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
|
Test |
|
|
Test for |
|
Voltage |
Current |
|
Duration |
|
Test |
|||||
|
|
|
|
(V |
|
) |
(A ) |
|
|
configuration(1) |
||||||
|
|
|
|
|
|
|
|
rms |
|
rms |
|
|
|
|
|
|
|
1 |
|
Secondary contact |
|
120 |
|
25 |
|
15 minutes |
|
M (on tip and ring), L |
|||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
|
1. M: metallic; L: longitudinal |
|
|
|
|
|
|
|
|
|
|
|
||||
|
Table 3. |
|
IEC61000-4-2 ESD surge standard |
|
|
|
|
|||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
||||
|
|
|
|
Contact discharge |
|
|
|
|
|
|
Air discharge |
|||||
|
|
|
|
|
|
|
|
|
||||||||
|
Level |
|
Test voltage (kV) |
|
Level |
|
|
Test voltage (kV) |
||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
1 |
|
|
|
2 |
|
|
|
1 |
|
|
|
2 |
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
2 |
|
|
|
4 |
|
|
|
2 |
|
|
|
4 |
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
3 |
|
|
|
6 |
|
|
|
3 |
|
|
|
8 |
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
4 |
|
|
|
8 |
|
|
|
4 |
|
|
|
15 |
|||
|
|
|
|
|
|
|
|
|
|
|
|
|||||
|
X(1) |
|
|
Special |
|
|
X(1) |
|
|
|
Special |
1. “X” is a level to be defined.
Table 3 shows the most commonly used worldwide standard for ESD. Generally, Level 4 is required. Such tests appear in the Telcordia GR1089 standard and do apply to equipment port type 4.
The next section presents the protection concept of the LCP152xx used to protect short line SLICs with a single battery voltage.
4/15
AN2456 |
LCP152xx concept |
|
|
L 1 |
Fuse1 |
|
|
|
|
|
|
|
|
|
TIP |
V Tip |
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
IG |
T1 |
Th1 |
D1 |
ID1 |
GND |
-Vbat |
Gate |
|
|
|
GND |
|
|
|
|
|
|
|
|
C |
|
|
|
|
|
L 2 |
|
|
|
|
RING |
|
Fuse2 |
|
|
|
|
V Ring |
|
|
|
|
|
|
Figure 3 shows the protection circuit using the LCP152xx crowbar concept that can be used for protection of single battery high voltage SLICs. It’s noteworthy that the schematic does not show series resistors that would normally be used on wires L1 and L2. This configuration permits the negative firing threshold Vg of the LCP152xx to be programmed at the negative battery voltage of the SLIC (up to -150 V), while the positive clamping threshold is at the GND.
I
Vg
Vf |
V |
|
Ih |
||
|
It can be seen from the characteristics of the device (shown in Figure 4) that the device operates asymmetrically.
Under normal operating conditions i.e. when the voltage on the line is between 0 and –Vbat, the LCP152xx is transparent to the application.
For positive surges on either wire (e.g. L1), the diode D1 clamps the surge voltage to its forward voltage (Vf).
5/15