ST AN1220 APPLICATION NOTE

AN1220

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®

APPLICATION NOTE

LINECARD PROTECTION BY OVERVOLTAGE

A.S.D

INTRODUCTION

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 CLP270M performances are analysed when
facing different surges as described in the BELLCORE GR 1089 recommendations.

Figure 1 is a simplified block diagram of a subscriber line protection that is commonly used.

Fig. 1: Subscriber line protection topology

ä

Telecommunication

line

AND OVERCURRENT WITH A CLP270M

P.Merceron / A.Bremond

“PRIMARY PRO TECTION”

CLP270M

MDF

EXCHANGE

“SECONDARY PROTECTION”

SLIC

LINE CARD

“SECONDARY PROTECTION”

Telecommunication

line

CLP270M

MDF

EXCHANGE

THDTxx

or

LCP1511D

or

LCDP1511D

LINE CARD

SLIC

This shows two different topologies :

n

A“primaryprotection”locatedontheMainDistributionFrame(MDF) eliminates coarsely the high energy
environmental disturbances (lightning transients and AC power mains disturbances)

n

A “secondary protection” located on the line card includes a primary protection level (first stage) and a
residual protection (second stage) which eliminates finely the remaining transientsthat have not been totally
suppressed by the first stage.

January 2000

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APPLICATION NOTE

STMICROELECTRONICS CLP270M CONCEPT

1. Evolution of the SLIC protection

Fig. 2: Line card protection

Over the years, the silicon protection
performances have considerably changed.

The first generation of products like SMTHBTxx
and SMTHDTxx offered fixed overvoltage
protectionagainst surges oneither TIP orRING line
in four packages.

The following generation like THBTxx and

Programmable

thanks to any

external v o ltage

reference

+I

I

SWON

Programmable

thanks to an

external resistor

V

THDTxx still offered fixed overvoltage protection
against surges on both TIP and RING lines in two
packages.

The next step was the introduction of the LCP
devices which brought the advantage of full
programmable voltage.

-I

SWON

Line card
operating
conditions

Today, the CLP270M combines the features of all
the previous generations. In addition to that, it offers an overcurrent detection when operating in speech
mode and also a Failure Status output signal.

The figure 2 summarizes the firing modes of the CLP270M which basically holds the SLIC inside its correct
voltage and current values.

Fig. 3 : CLP270M in line card

er oltage

erence

I

-Vbat

TIP

-Vbat

(*)

SLIC

RING

Rp

Rp

1

2

1

2

External

voltage

reference

Ring

Generator

(*) LCP1511D orTHDT series or LCDP1511D

TIP

RING

Fuse

Rsense

TIPL TIPS

Overcurrent

detector

detector

detector

RINGS

Ov v

ref

(+/- 270V)

Overvoltage

reference

(+/- 270 V)

OR

SW3 SW1

FS GND

Fuse

SW4 SW2

OR

Overcurrent

RINGL

Rsense

Overvoltage

Overvoltage

detector

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APPLICATION NOTE

2. Application circuit: CLP270M in line card

Figure 3 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 :

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

n

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 incurrent mode and the activation current of the CLP270Mis adjusted

sense

.

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

n

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.

Fig. 4: Switching by voltage during ringing mode.

Fuse

TIP

ILG

Rsense

TIPL TIPS

1/2 CLP270M

Overcurrent

detector

V

Overvoltage

Overvoltage

detector

OR

SW3 SW1

FS

reference

(+/- 270V)

LG

GND

1

Rp

2

-270

I

LG

A1

2

1

+270

3

3. Ringing mode

In ringing mode (Ring relay in position 2), the only protection device involved is the CLP270M.
In normal conditions, the CLP270M operates in region 1 of A1 curve, and is idle.
Ifan overvoltage occuring between TIP (or RING)and GND reaches theinternal overvoltage reference

(+/- 270 V), the CLP270M 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 negativesurges). Once the surge current falls below
the switch off current I

, the device returns to its initial state (region 1).

SWOFF

For surges occuring between TIP and RING, the CLP270M acts in the same way. This means that the
CLP270M ensures a tripolar protection.

V

Whenused alone, theCLP270M acts atthe internal overvoltagereference level (+/-270 V). Furthermore,it
is possible to adjust this threshold level to a lower voltage by using:

n

up to 4 fixed external voltage reference (VZ1to VZ4) (see fig. 5a, here-below).

n

external reference supplies, Vb1and Vb2(see fig. 5b, on next page).

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APPLICATION NOTE

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

Fuse

TIP

Rsense

1

Rp

TIPL TIPS

Overcurrent

detector

Overvoltage

detector

Overvoltage

detector

RING

OR

SW3 SW1

FS GND

SW4 SW2

RINGL

OR

Overcurrent

detector

Rsense

Fuse

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

Fuse

TIP

Rsense

TIPL TIPS

RINGS

Overvoltage

reference

(+/- 270 V)

Overvoltage

reference

(+/- 270 V)

2

VZ1

VZ2

VZ3

VZ4

1

Rp

2

1

Rp

2

Overcurrent

detector

VB1

VB2

1

2

RING

Overvoltage

OR

SW3 SW1

FS GND

SW4 SW2

RINGL

OR

Overcurrent

detector

detector

Overvoltage

detector

RINGS

Overvoltage

reference

(+/- 270 V)

Overvoltage

reference

(+/- 270 V)

Rsense

Fuse

Rp

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APPLICATION NOTE

4. Speech mode

In speech mode (Ring relay in position 1), the protection is provided by the combination of both CLP270M
and the external voltage reference device (see figure 6)

Fig. 6: Switching by current during speech mode.

I

Fuse

TIP

Innormal conditions, theworking pointof this circuitis located inregion 4 ofA2 curve :the CLP270M isidle.
Whena surge occurs on the line, theexternal voltage reference deviceclamps at GNDor -V
for positive and negative surges.
This generates a current which is detected by R
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 belowthe switching-off current I
(region 4).

The choice of the switching-on currents is function of the R
In normal operating condition the current (typically below -100 mA) should not activate the protection

device CLP270M. Therefore the level of activation has to be chosen just above this limit (-200 mA). This
level is adjusted through R

Figures 7a and 7b enable the designers to choose the right R

Example:

Thechoice of R
positive triggering will be 150mA min and 280 mA max.

LG

Rsense

TIPL TIPS

Overcurrent

detector

Overvoltage

Overvoltage

detector

OR

SW3 SW1

FS

sense

=4Ωensuresa negative triggering of-190 mA min and -320mA max. In this case, the

sense

reference
(+/- 270 V)

.

GND

V

LG

1

Rp

2

sense

-Vbat

External

voltage

reference

-V

and causes the protection to act : the line is

, the CLP270M returns to itsinitial state

SWOFF

resistors.

sense

value.

sense

REF2

ILG

A2

5

4

V

REF1

6

respectively

bat

V

LG

Fig. 7a and 7b: Switching-on current versus R

sense

.

ISWON (T, Rsense) / ISWON (25°C, 4 )Ω

2

@-20°C @25°C @75°C

1

Iswon @ 25°C (mA)

500
300

Iswon min

negative

Iswon max

negative

Iswon min

positive

Iswon max

positive

200

0.5

0.3

0.2
3 5 7 9 11 13

100

50

357911

Rsense ( )Ω

Rsense ( )Ω

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APPLICATION NOTE

5. Failure Status

The CLP270M has an internal feature that allows
the user to get a Failure Status (FS) indication.
When the CLP270M 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
providea surge indication.It may alsobe used with
a logic circuitry to count the number of
disturbances appearing on the lines.

If a surge exceeding the maximum ratings of the
CLP270Moccurs on theline, thedevice will failin a
short-circuit state.

The figure 9 shows two different curves :

n

The lower one indicates the maximum
guaranted working limits of the CLP270M.

The upper curve shows the limit above which the
CLP270M is completely destructed . In this case,
the Fail Diagnostic pin is on.

Fig. 8: Failure Status circuit and diagnostic.

Rsense

1

FAILURE

STATUS

1k

+12V

CLP270M

Rsense

Fig. 9 : Operation limits and destruction zone of

the CLP270M.

5 000
2 000

1 000

500
200

100

50
20

10

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10

t (ms)

CLP270M TEST RESULTS ACCORDING TO BELLCORE 1089 REQUIREMENTS

1. BELLCORE GR-1089-CORE requirements:

Tables 1 and 2 summarize the lighting surges required by the bellcore 1089.
Tables 1 to 6 summarize the surge needs defined by Bellcore regarding both lightningand AC power fault.
In case of first level test, the equipment under test shall be operating after the surge. For the second level
tests, the equipment under test may be damaged, but no fire or electrical safety hazard may occur.

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Table 1: First level lightning surge.

APPLICATION NOTE

Surge Minimum

peak voltage

(volts)

1 +/- 600 100 10/1000 25 A
2 +/- 1000 100 10/360 25 A
3 +/- 1000 100 10/1000 25 A
4 +/- 2500 500 2/10 10 B
5 +/- 1000 25 10/360 5 B

Table 2: Second level lightning surge.

Surge Minimum

peak voltage

(volts)

1 +/- 5000 500 2/10 1 B

per conductor

per conductor

Minimum

peak current

(Amps)

Minimum

peak current

(Amps)

Maximum rise

/ Minimum

decay time for

voltage and

current

(µs)

Maximum rise

/ Minimum

decay time for

voltage and

current

(µs)

Repetitions,

each polarity

Repetitions,

each polarity

Test

connections

per

table 4.1

Test

connections

per

table 4.1

Table 3: First level AC power fault (table 4-7 of GR-1089-CORE issue 2, december 1997).

Test Voltage

)

(V

RMS

1 50 0.33 15 minutes Removed A
2 100 0.17 15 minutes Removed A
3 200, 400

and 600

4 1000 1 60 1s

5 see figure 4-3 see figure 4-3 605s

6 600 0.5 30s Removed A
7 600 2.2 2s Removed A

Short circuit

current per

conductor

(Amps)

1 (at 600V) 60 1 s

Duration Primary

application of

each voltage

applications

applications

protection

Removed A

Operative

protector in place

Removed see figure 4-3

connections

table 4.1

Test

per

B

8 600 3 1s Removed A
9 1000 5 0.5s Operative

protector in place

B

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APPLICATION NOTE

Table 4: Second level AC power fault (table 4-8 of GR-1089-CORE issue 2, december 1997).

Test Test for Voltage

(V

RMS

1 Secondary

contact

2 Primary

contact

3 Short-term

fault induction

4 Long-term

fault induction

5 High impedance induction 15 minutes

Table 5: Test connection (table 4-1 of GR-1089-CORE).

Test Two-wire interface Four-wire interface

A

1. Tip to generator, Ring to ground

2. Ring to generator, Tip to ground

120, 277 25 15minutes A

600 60 5seconds A

600 7 5 seconds A

100-600 2.2

Short circuit

)

current per

conductor

(Amps)

(at 600 V)

1. Each lead (T, R, T1, R1) to generator with
other three leads grounded

2. Tip and Ring to generator simultaneously, T1
and R1 to ground

Duration

15 minutes A

Test

connections

per

table 4.1

3. Tip to generator, Ring to generator
simultaneously

B

Tip to generator, Ring to generator
simultaneously

S1

Limiting
resistance
(IF specified)

V oltage
Source

Test

S3

3. T1 and R1 to generator simultaneously,
Tip and Ring to ground

T, R, T1, R1 to generator simultaneously

Switch

S2

S4

unit

under

test

T
E
R
M

T
E
R
M

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APPLICATION NOTE

Table 6: Application of lightning and AC power fault test voltages (table 4-2 of GR-1089-CORE).

Test S1 S2 S3 S4

T to generator, R to ground
(condition A1 of table 4-1)

R to generator, T to ground
(condition A2 of table 4-1)

T to generator, R to generator
simultaneously
(condition A3 of table 4-1)

2. First level lightning surge:

2.1. Ringing mode

Lightning phenomena are the most common surge causes. The purpose of this test is to check the
behavior of the CLP270M against these lightning strikes.

Figures 11 and 12 show that the remaining overvoltage does not exceed +/- 500 V. The CLP270M
switches on within 250ns and withstands the 500A given by the BELLCORE 2/10µs generator.

Fig. 10: Lightning simulation test.

Closed Open Open Closed

Open Closed Closed Open

Closed Open Closed Open

I1

2/10 µs

GENERATOR

+/- 2.5 kV

(500 A)

Fig. 11: CLP270M response to a positive surge. Fig. 12 : CLP270M response to a negative surge.

TIPL

1/2 CLP270M

4

Rsense

GND

Rp

TIPS

V1

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APPLICATION NOTE

Fig. 13: Lightning test in speech mode.

I

1

2/10 µs

GENERATOR

+/- 5 kV

(500 A)

2.2. Speech mode

Figures 14 and 15 give the voltage and current behaviorduring positive andnegative 2.5kV, 2/10µs,500A
surge tests using a LCP1511D as second stage protection device. The firing threshold values are now
adjustedto GND and to -Vbat (-48V) by theaction of the second stage protection whichacts as an external
voltage reference.

Asshown on thesefigures, the maximumremaining voltage doesnot exceed +8.5Vfor positive surgesand

-65V for negative surges.

Fig. 14: CLP270M response to a positive surge. Fig. 15: CLP270M reponse to a negative surge.

TIPL

1/2 CLP270M

4

Rsense

TIPS

GND

50

Rp

V1

I2

-48V

LCP1511D

SLIC

V2

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APPLICATION NOTE

3. Second level lightning surge

3.1. Lightning test in ringing mode

The figures 17 and 18 give the voltage and current behavior during positive and negative 5kV,
2/10µs,500A surge with the CLP270M acting in Ringing mode.

Fig. 16: Lightning test in Ringing mode.

I

1

2/10 µs

GENERATOR

+/- 5 kV

(500 A)

Fig. 17: CLP270M response to a positive surge.

TIPL

1/2 CLP270M

4

Rsense

TIPS

GND

Fig. 18: CLP270M response to a negative surge.

Rp

V1

3.2. Speech mode

Thefigures 20 and22 give thevoltage and currentbehavior during positiveand negative 5kV,2/10µs,500A
surge with the CLP270M acting in speech mode.

The CLP270M withstands the second level lightning surge test without trouble in both ringing and speech
mode.

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APPLICATION NOTE

Fig. 19: Lightning test in Speech mode.

I

1

2/10 µs

GENERATOR

+/- 5 kV
(500 A)

TIPL

1/2 CLP270M

Fig. 20: CLP270M response to a positive surge.

4

Rsense

GND

50

Rp

I2

SLIC

TIPS

-48V

V1

V2

LCP1511D

Fig. 21: CLP270M response to a negative surge.

4. First and second level AC Power fault.

4.1. Ringing mode

Thefigures 23 and 25 give thevoltage and current at the CLP270M terminals in Ringing mode and Speech
mode.

Fig. 22: AC power fault test in Ringing mode. Fig. 23: Example of behavior when facing test 3

(400V, 600Ω).

I1

Rs

V(RMS)
50Hz

4

Rsense

TIPL TIPS

1/2 CLP270M

GND

Rp

V1

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APPLICATION NOTE

Fig. 24: AC power fault test in Speech mode.

Fig. 25: Example of behavior when facing test 3

(400V, 600Ω).

V(RMS)
50 Hz

I1

Rs

TIPL

1/2 CLP270M

4Ω

Rsense

GND

TIPS

Ω

50

Rp

-48V

LCP1511D

SLIC

V2

CONCLUSION

The CLP270M is able to withstand all the first level AC power fault tests as required in the table 4-7 of
GR-1089-CORE standard, and then is suitable to protect the linecard.

As usual, for the second level AC power fault tests serial protection as PTC or fuse are needed.
All these curves, lightning and AC power fault represent the behavior of the CLP270M in worst case tests,

anyhow the CLP270M withstands all the others surges of the Bellcore GR1098 standard. For the second
level AC power fault test, the use of series protection elements (PTC or fuses) are needed.

The FS pin allows the system to monitor and record the number of surges occuring on the telecom line.

Informationfurnishedisbelieved to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of
useof such information nor for any infringement of patents or otherrightsof third parties which may result from its use. No licenseisgranted by
implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to
change without notice. This publication supersedes and replaces all information previously supplied.
STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written ap­proval of STMicroelectronics.

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