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CLP270M
OVERVOLTAGE AND OVERCURRENT PROTECTION FOR TELECOM LINE
CLP270MOVERVOLTAGE AND OVERCURRENT
PROTECTION FOR TELECOM LINE
Application Specific Discretes
A.S.D.
PRELIMINARY DATASHEET
SCHEMATIC DIAGRAM
MAIN APPLICATIONSAny telecom equipment submitted to transient
overvoltages and lightning strikes such as :
Analog and ISDN line cards
PABX
Main Distribution Frames
Primary protection modules
DESCRIPTIONThe CLP270M is designed to protect
telecommunication equipment. It provides both a
transient overvoltage protection and an
overcurrent protection.
It is housed in a PowerSO-10TM package.
FEATURESDUAL BIDIRECTIONAL PROTECTION DEVICE.
HIGH PEAK PULSE CURRENT :
Ipp = 100A (10/1000 μs SURGE)
Ipp = 500A (2/10 μs SURGE)
MAX. VOLTAGE AT SWITCHING-ON : 380V
MIN. CURRENT AT SWITCHING-OFF : 150mA
FAILURE STATUS OUTPUT PIN
BENEFITSBoth primary and secondary protection levels in
one device.
Voltage and current controlled suppression.
Surface Mounting with PowerSO-10TM package.
Line card cost reduction thanks to the very low
power rating of external components required :
balanced resistors, ring relay, low voltage SLIC
protection.
Falls into short circuit if destroyed, still ensuring
protection.
January 1998 - Ed: 5B 1/24
BLOCK DIAGRAM
CLP270M2/24
Figure 1 is a simplified block diagram of a subscriber line protection that is commonly used.
This shows two different topologies :
A "primary protection" located on the Main Distribution 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 protection level (first stage) and a
residual protection (second stage) which eliminates finely the remaining transients that have not been totally
suppressed by the first stage.
2.1. Evolution of the SLIC protectionOver the years, the silicon protection performances have considerably changed.
The first generation of products like SMTHBTxx and SMTHDTxx offered fixed overvoltage protection
against surges on either TIP or RING line in four packages.
The following generation like THBTxx and
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
LCP1511D which brought the advantage of full
programmable voltage.
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 hold the SLIC inside its
correct voltage and current values.
Fig. 2: Line card protection3/24
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 :
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 Rsense.
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.
Fig. 3 : CLP270M in line card
CLP270M4/24
2.3. Ringing modeIn 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.
If an overvoltage occuring between TIP (or RING) and GND reaches the internal 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 negative surges). Once the surge current falls below
the switch off current ISWOFF, the device returns to its initial state (region 1).
For surges occuring between TIP and RING, the CLP270M acts in the same way. This means that the
CLP270M ensures a tripolar protection.
When used alone, the CLP270M acts at the internal overvoltage reference level (+/- 270 V). Furthermore,
it is possible to adjust this threshold level to a lower voltage by using:
up to 4 fixed external voltage reference (VZ1 to VZ4) (see fig. 5a, here-below).
external reference supplies, Vb1 and Vb2 (see fig. 5b, on next page).
Fig. 4: Switching by voltage during ringing mode.
Fig. 5a: Method to adjust the reference voltage.
CLP270M5/24
2.4. Speech modeIn speech mode (Ring relay in position 1), the protection is provided by the combination of both CLP270M
and the external voltage reference device.
In normal conditions, the working point of this circuit is located in region 4 of A2 curve : the CLP270M is idle.
When a surge occurs on the line, the external voltage reference device clamps at GND or -Vbat respectively
for positive and negative surges.
This generates a current which is detected by Rsense 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 ISWOFF, the CLP270M returns to its initial state
(region 4).
Fig. 5b: Method to adjust the reference voltage.
Fig. 6: Switching by current during speech mode.
CLP270M6/24
The choice of the switching-on currents is function of the Rsense resistors.
In normal operating condition the current (typically below -100 mA) should not activate the protection
device CLP270M. Therefore the level of activation is to be chosen just above this limit (-200 mA). This level
is adjusted through Rsense.
Figures 7a and 7b enable the designers to choose the right Rsense value.
EXAMPLE :The choice of Rsense = 4 Ω ensures a negative triggering of -190 mA min and -320 mA max. In this case, the
positive triggering will be 150mA min and 280 mA max.
2.5. Failure StatusThe 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 provide 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 CLP270M 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 CLP270M.
The upper curve shows the limit above which the CLP270M is completely destructed . In this case, the
Fail Diagnostic pin is on.
Fig. 7a and 7b: Switching-on current versus Rsense.
Fig. 8: Failure Status circuit and diagnostic.
Fig. 9 : Operation limits and destruction zone of theCLP270M.
CLP270M7/24
3.1. BELLCORE GR-1089-CORE requirements:
Table 2: Second level lightning surge.Tables 1 and 2 summarize the lighting surges required by the bellcore 1089.
Table 1: First level lightning surge.
CLP270M8/24
Table 4: Second level AC power fault (table 4-8 of GR-1089-CORE issue 2, december 1997).
Table 3: First level AC power fault (table 4-7 of GR-1089-CORE issue 2, december 1997).
CLP270M9/24
Table 5: Test connection (table 4-1 of GR-1089-CORE).Voltage
Source
Table 6: Application of lightning and AC power fault test voltages (table 4-2 of GR-1089-CORE).Tables 1 to 6 summarize the surge needs defined by Bellcore regarding both lightning and 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.
CLP270M10/24
Fig. 10: Lightning simulation test.
Fig. 11: CLP270M response to a positive surge. Fig. 12 : CLP270M response to a negative surge.
3.2. First level lightning surge:3.2.1. 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.
3.2.2. Speech mode
Fig. 13: Lightning test in speech mode.
CLP270M11/24
Fig. 14: CLP270M response to a positive surge. Fig. 15: CLP270M reponse to a negative surge.Figures 14 and 15 give the voltage and current behavior during positive and negative 2.5kV, 2/10μs, 500A
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 remaining voltage does not exceed +8.5V for positive surges and
-65V for negative surges.
CLP270M12/24
