OVERVOLTAGE AND OVERCURRENT PROTECTION FOR TELECOM LINE

CLP200M

OVERVOLTAGE AND OVERCURRENT

PROTECTION FOR TELECOM LINE

Application Specific Discretes

A.S.D.

™

PowerSO-10

SCHEMATIC DIAGRAM

MAIN APPLICATIONS

Any telecom equipment submitted to transient

overvoltages and lightning strikes such as :

Analog and ISDN line cards

PABX

Main Distribution Frames

Primary protection modules

DESCRIPTION

The CLP200M is designed to protect telecommuni-

cation equipment.It provides both a transient over-

voltage protection and an overcurrent protection.

It is housed in a PowerSO-10

package.

FEATURES

DUAL BIDIRECTIONAL PROTECTION DEVICE.

HIGH PEAK PULSE CURRENT :

Ipp = 100A (10/1000

s SURGE)

MAX. VOLTAGE AT SWITCHING-ON : 290V

MIN. CURRENT AT SWITCHING-OFF : 150mA

FAILURE STATUS OUTPUT PIN

BENEFITS

Both primary and secondary protection levels in

one device.

Voltage and current controlled suppression.

Surface Mounting with PowerSO-10

package.

Line card cost reduction thanks to the very low

power rating of external components required :

balanced resistors, ring relay, low voltage SLIC

protection.

COMPLIESWITH THE FOLLOWINGSTANDARDS :

CCITT K20 :

10 / 700

4kV

5 / 310

100 A

BELLCORE TR-NWT-000974

10 / 1000

1kV

10 / 1000

100A

TIP

RING

TIP

RING

TAB is connected to GND

February 1998 Ed : 3

1/21

Fig. 1 : Subscriber line protection topology

”PRIMARY PROTECTION”

”SECONDARY PROTECTION”

MDF

LINE CARD

telecommunication

EXCHANGE

line

”SECONDARY PROTECTION”

MDF

LINE CARD

telecommunication

EXCHANGE

line

CLP200M

SLIC

THDTxx or

LPC1511D

or LB200B

SLIC

CLP200M

Fig. 2 : Line card protection

- I

SWON

Programmable thanks to

an external resistor

Programmable thanks to

any external voltage reference

Line card operating conditions

+ I

SWON

APPLICATION NOTE

1. INTRODUCTION

The aim of this section is to show the behavior of

our new telecom line protection device. This device

includes a primary protection level and is suitable

for main distribution frames and line cards. This

protection concept is explained and, in addition,

the CLP200M performances are analysed when

facing different surges as described in the CCITT

recommendations.

Figure 1 is a simplified block diagram of a sub-

scriber line protection that is mainly used so far.

This shows two different things :

A ”primary protection” located on the Main Distri-

bution Frame (MDF) eliminates coarsely the high

energy environmental disturbances (lightning

transients and AC power mains disturbances)

A ”secondary protection” located on the line card

includes a primary protectionlevel (first stage)and

a residual protection (second stage) which elimi-

nates finely the remaining transients that have not

beentotally suppressed by the first stage.

The CLP200M can be used both in MDFs and in

line cards. In that case, any line card may be

swapped from one MDF to another one without re-

ducing the efficiency of the whole system protec-

tion.

The CCITT requirements are different for these

two protection locations (MDFs and line cards).

Concerning the ”primary protection”, the CCITT re-

quires a 4kV, 10/700

s surge test whereas the

”secondary protection” has to withstand a 1kV,

10/700

s surge test.

The explanations which follow are ba sically

covering the line card application.

2. SGS-THOMSON CLP200M CONCEPT

2.1 Evolution of the SLIC protection

Over the years, the silicon protection per-

formances have consider ably changed.

The first generation of products like SMTHBTxx

and SMTHDTxx offered fixed overvoltage protec-

tion against surges on either TIP or RING line in

four packages.

The following gene ration like THBTxx and

THDTxx still offered fixed overvoltage protection

against surges on both TIP and RING lines in two

package s.

The next step was the introduction of the

LCP1511D which brought the advantage of full

programmable voltage.

Today, the CLP200M combines the features of all

the previous generations. In addition to that, it of-

fers an overcurrent detection when operating in

speech mode and also a Failure Status output sig-

nal.

The figure 2 summarizes the performance of the

CLP200M which basically holds the SLIC inside its

correct voltage and current values.

CLP200M

3/21

APPLICATION CIRCUIT : CLP200M in line card

Fig. 3 : CLP200M in line card

RINGS

-Vbat

R sense

TIP

SLIC

(*)

(*) LCP1511D or THDT series

Overvoltage

reference

(+/- 215 V)

Over voltage

detector

Overcurrent

detector

Overvoltage

reference

(+/- 215 V)

Over voltage

detector

Overcurrent

detector

TIPL

TIPS

RINGL

GND

SW3 SW1

SW4 SW2

R sense

Ring

Generator

Fuse

TIP

RING

External

voltage

reference

RING

Figure 3 above shows the topology of a protected

analog subscriber line at the exchange side. The

CLP200M 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 or a THDT

series.

These two devices are complementary and their

functions are explained below :

The first stage based on CLP200 M manages

the high power issued from the external

surges. When used in ringing mode, the

CLP200M operates in voltage mode and pro-

vides

symmetrical

and

bidirectional

overvoltage protection at +/-215 V on both TIP

and RING lines. When used in speech mode,

the CLP200M operates in current mode and

the activation current of the CLP200M is ad-

justed by R

SENSE

The second stage is the external voltage refer-

ence device which defines the firing threshold

voltage during the speech mode and also as-

sumes

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 operates as a programma-

ble protection.

Thanks to this topology, the surge current in the

line is reduced after the CLP200M. Because the

remaining surge energy is low, the power ratings of

Rp, the ring relay contacts and the external voltage

reference circuit may be downsized. This results in

a significant cost reduction.

CLP200M

4/21

2.3 Ringing mode

Fig. 4 : Switching by voltage during ringing mode.

R sens e

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

SW3 SW1

Fuse

TIP

GND

1/2 CLP200M

-215

+215

Fig. 5a : Method to adjust the reference voltage.

RINGS

R sense

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

RINGL

GND

SW3 SW1

SW4 SW2

R sense

Fuse

TIP

RING

VZ1

VZ2

VZ3

VZ4

In ringing mode (Ring relay in position 2), the only

protectiondevice involved is the CLP200M.

In normal conditions, the CLP200M operates in re-

gion 1 of A1 curve, and is idle.

If an overvoltage occuring between TIP (or RING)

and GND reaches the internal overvoltage refe-

rence (+/- 215V), the CLP200M acts and the line is

short-circuited to GND. At this time the operating

point moves to region 2 for positive surges (region

3 for negative surges). Once the surge current dis-

appears, the device returns to its initial state (re-

gion 1).

For surges occuring between TIP and RING, the

CLP200M acts in the same way. This means that

the CLP200M ensures a tripolar protection.

When used alone, the CLP200M acts at the inter-

nal overvoltage reference level (+/- 215V). Further-

more, it is possible to adjust this threshold level to

a lower voltage by using :

up to 4 fixed external voltage reference (V

) (see fig.5a).

CLP200M

5/21

external reference supplies, V

and V

(see fig.5b)..

Fig. 5b : Method to adjust the reference voltage.

RINGS

R sense

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

RINGL

GND

SW3 SW1

SW4 SW2

R sense

Fuse

TIP

RING

VB1

VB2

2.4 Speech mode

Fig. 6 : Switching by current during speech mode.

R sense

Overvoltage

reference

(+/- 215 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

SW3 SW1

Fuse

TIP

GND

-Vbat

External

voltage

reference

REF1

-V

REF2

In speech mode (Ring relay in position 1), the pro-

tection is provided by the combination of both

CLP200M and the external voltage reference de-

vice.

In normal conditions, the working point of this cir-

cuit is located in region 4 of A2 curve : the

CLP200M is idle.

When a surge occurs on the line, the external volt-

age reference device clamps at GND or -V

bat

re-

spectively for positive and negative surges.

This generates a current which is detected by

SENSE

and causes the protection to act : the line is

short-circuited to GND.

The operating point moves to region 5 for positive

surges or region 6 for negative surges.

Once the surge current falls below the switching-

off current I

SWOFF

, the CLP200M returns to its in-

itial state (region 4).

Furthermore, the CLP200M switches when an

overvoltage, either positive or negative, occurs

either :

simultaneously on both TIP and RING lines ver-

sus GND.

between TIP and RING.

on TIP (or RING) versus GND.

CLP200M

6/21

Fig. 7a and 7b

: Switching-on current versus

SENSE

Fig. 9 : Operation limits and destructionzone of the

CLP200M.

Fig. 8 : Failure Status circuit and diagnostic.

100

200

300

500

Rsense ( )

Ω

ISWON (mA)

-20

100

200

300

500

Rsense ( )

Ω

Iswon @ 25

C (mA)

Iswon min

Iswon max

Iswon min

negative

positive

CLP200M

Rsense

FAILURE

+12V

STATUS

0.01

0.1

100

1000

t (ms)

Ipp (A)

The choice of the switching-on current is function

of the R

SENSE

resistors.

In normal operating condition, only the negative

current of the signal is of interest.This current (typi-

cally below -150 mA) should not activate the pro-

tection device CLP200M. Therefore the level of

activation is to be chosen just above this limit (typi-

cally -200 mA). This level is adjusted through

SENSE

Figures 7a and 7b enable the designers to choose

the right R

SENSE

value.

EXAMPLE :

The choice of R

SENSE

= 4

Ω

ensures a negative

triggering of -220 mA min and -320 mA max. In this

case, the positive triggering will be 180mA min and

280 mA max.

2.5 . Failure Status

The CLP200M has an internal feature that allows

the user to get a Failure Status (FS) indication.

When the CLP200M is short-circuiting the line to

GND, a signal can be managed through pin 1. This

signal can be used to turn a LED on in order to pro-

vide a surge indication. It may also be used with a

logic circuitry to count the number of disturbances

appearing on the lines.

If a surge exceeding the maximum ratings of the

CLP200M occurs on the line, the device will fail in

a short-circuit state.

The figure 9 shows two different curves :

The lower one indicates the maximum guaranted

working limits of the CLP200M.

The upper curve shows the limit above which the

CLP200M is completely destructed . In this case,

the Fail Diagnostic pin is on.

CLP200M

7/21

Fig. 10 : Transversal and longitudinal test

topologies.

Fig. 12 : Power contact test circuit.

Fig. 11 : Power induction test circuit.

A or B

B or A

0.2

4kv

ITEM

UNDER

TEST

0.2

ITEM

UNDER

TEST

4kv

TRANSVERSAL TEST

LONGITUDINAL TEST

ITEM

UNDER

TEST

100

<10

ITEM

UNDER

TEST

<10

600

3. CLP200M TESTS RESULTS ACCORDING TO

CCITT K20 RECOMMENDATIONS

3.1 CCITT K20 Recommendations

In respect with the CCITT recommendations, the

CLP200M has to withstand three kinds of distur-

bances.

3.1.1. Lightning simulation

(Test 2, table 2/K20)

This test shall be done in transversaland longitudi-

nal modes as shown in figure 10.

The test generator is the 10/700

s with 4kV of

peak voltage.

3.1.2. Power induction

(Test 3a and 3b, table 2/K20)

Two kinds of tests using the same circuit topology

(see fig.11) are defined in the CCITT K20.

Test 3a :

Vac(max) = 300V

RMS

, R1 = R2 = 600

Ω

S2 operating and test duration = 200 ms.

Test 3b :

Vac(max) = 300V

RMS

(*), R1 = R2 = 200

Ω

S2 operating and test duration not defined.

(*) Recommended value.

3.1.3. Power contact (Test 3, table 1/K20)

This test shall be done with the test circuit of figure

12.

Vac(max) = 220V

RMS

, with switch S in each posi-

tion and duration 15 min.

3.1.4. Acceptance criteria and number of tests

For the tests described in chapter3.1.1., 3.1.2. and

3.1.3. two criteria are defined :

A: Equipment shall withstand the test without dam-

age and shall operate properly within the specified

limits.

B: A fire hazard should not occur in the equipment

as a result of the tests.

The criteria are affected to the different tests as

mentioned in the table 1.

CLP200M

8/21

TEST ACCEPTANCE

CRITERIA

NUMBER TO TESTS

10 for longitudinal A

10 for longitudinal B

and 10 for transversal

1 for each position of s

Table 1 : Acceptance criteria and number of tests.

Fig. 13 : Lightning simulation test.

10/700

GENERATOR

+/- 4kV

Ω

Rsense

TIPL

TIPS

GND

1/2 CLP200M

Fig. 14 : CLP200M response to a positive surge.

Fig. 15 : CLP200M response to a negative surge.

Fig. 16 : Power inductance test.

TEST

(RMS)

Ω

)

Duration

300

600

0.2s

300

200

3.2. Ringing mode

3.2.1. Lightning simulation test

Lightning phenomena are the most common surge

causes. The purpose of this test is to check the ro-

bustness of the CLP200M against these lightning

strikes.

Figures 14 and 15 show that the remaining over-

voltage does not exceed +/- 260 V. The CLP200M

switches on within 0.7

s and withstands the 100 A

given by the CCITT K20 generator.

Consequently,the CLP200M totally fulfills this test.

3.2.2 Power induction

(Test 3a and 3b table 2/K20)

Surges of long duration with medium voltage value

are mainly produced by the proximity of a sub-

scriber line with an AC mains line or equipment.

The purpose of this test is to check the robustness

of the CLP200M against these capacitive coupling

disturbances.

CLP200M

9/21

Fig. 17 : CLP200M response to the induction test

(Test 3a).

Fig. 18 : CLP200M reponse to the induction test

(Test 3b).

Fig. 19 : Power contact test.

Fig. 20 : Power contact test 3 (With 10

Ω

series).

V(RMS)

50Hz

600

< 10

Ω

15min

PTC

Rsense

TIPL

TIPS

GND

1/2 CLP200M

Fig. 21: Lightning test in speech mode.

10/700

GENERATOR

+/- 4kV

TIPL

TIPS

GND

1/2 CLP200M

SLIC

LCP1511D

-48V

Rsense

Figures 17 and 18 show that the remaining voltage

does not exceed 270 V.

Consequently,the CLP200M totally fulfills this test.

The test duration is not specified in test 3b. If the

duration exceeds 5s we do suggest to follow the

soldering and mounting recommendations given

on page 17 of this document.

3.2.3 Power contact (Test 3 table 1/K20)

This long duration surge is produced when con-

necting a subscriber line to an AC mains line or

equipment. The purpose of this test is to check the

robustness of the CLP200M against these distur-

bances.

The test 3 of CCITT K20 requires a serial PTC (or

fuse) which is inserted in the test circuit to limit the

current rate. This PTC acts like an open-circuit in a

non-instantaneous way when a surge occurs on

the line. Meanwhile, the CLP200M has to with-

stand the surge.

Figure 20 shows that the remaining overvoltage

does not exceed 250 V and shows that the PTC

acts like an open-circuit after 60 ms.

Consequently,the CLP200M totally fulfills this test.

3.3. Speech mode

3.3.1. Lightning simulation test

(Test 2, table 2/K20)

CLP200M

10/21

Fig. 22 : CLP200M response to a positive surge.

Fig. 23 : CLP200 M response to a negative surge.

Fig. 24 : Power induction test.

Ω

TIPL

TIPS

GND

1/2 CLP200M

SLIC

LCP1511D

-48V

Rsense

V(RMS)

50 Hz

TEST

(RMS)

Ω

)

Duration

300

600

0.2s

300

200

Fig. 25 : Induction test behavior (Test 3a).

Figures 22 and 23 give the voltage and current be-

havior during positive and negative 4kV, 10/700

surge tests using a LCP1511D as second stage

protection device. The firing threshold values are

now adjusted to GND and to -Vbat (-48V) by the

action of the second stage protection which acts as

an external voltage reference.

As shown on these figures, the maximum remain-

ing voltage does not exceed +2.5V for positive

surges and -60V for negative surges.

Consequently,the CLP200M totally fulfills this test.

3.3.2 Power induction test

(Test 3a and 3b, table 2/K20)

Figures 25 and 26 show that the maximum remain-

ing voltage does not exceed +2V for positive

surges and -55V for negative surges.

Consequently,the CLP200M totally fulfills this test.

The test duration is not specified in test 3b. If the

duration exceeds 5s we do suggest to follow the

soldering and mounting recommendations given

on page 17 of this document.

CLP200M

11/21

Fig. 26 : Induction test behavior (Test 3b).

Fig. 28 : Power contact test 3 (with R

≤

Ω

series).

Fig. 27 : Power contact test.

4Ω

TIPL

TIPS

GND

1/2 CLP200M

V(RMS)

50Hz

600 or < 10

15min

PTC

Rsense

SLIC

LCP1511D

-48V

3.3.3 - Power contact test (Test 3 table 1/K20)

The test 3 of CCITT K20 requires a serial PTC (or

fuse) which is inserted in the test circuit to limit the

current rate. This PTC acts like an open-circuit af-

ter 60 ms when a surge occurs on the line. Mean-

while, the CLP200M has to withstand the surge.

The protection device CLP200M totally fulfills this

test.

CLP200M

12/21

Symbol

Parameter

Test Conditions

Value

Unit

Line to GND peak surge

current

10/1000

s (open circuit voltage

wave shape 10/1000

100

5/310

s (open circuit voltage

wave shape 10/700

130

TSM

Mains power induction

current

RMS

= 300V, R = 600

Ω

t = 200ms

0.5

Mains power contact current

RMS

= 220V, R = 10

Ω

(failure status threshold)

t = 200 ms

RMS

= 220V, R = 600

Ω

t = 15 mn

0.30

stg

Storage temperature range

Maximum junction temperature

- 40 to + 150

150

Maximum lead temperature for soldering during 10 s

260

ABSOLUTE MAXIMUM RATINGS (R

SENSE

= 4

Ω

, and T

amb

= 25

Symbol