View AN1220_1320570.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1/13 AN1220 application note ? linecard protection by overvoltage and overcurrent with a clp270m a.s.d p.merceron / a.bremond january 2000 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. introduction clp270m clp270m slic slic thdtxx or lcp1511d or lcdp1511d aprimary protectiono asecondaryprotectiono asecondary protectiono telecommunication line telecommunication line mdf exchange exchange line card line card mdf fig. 1: subscriber line protection topology this shows two different topologies : n a aprimary protectiono located on the main distribution frame (mdf) eliminates coarsely the high energy environmental disturbances (lightning transients and ac power mains disturbances) n a asecondary protectiono 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.
application note 2/13 1. evolution of the slic protection over 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 lcp devices 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 holds the slic inside its correct voltage and current values. stmicroelectronics clp270m concept line card operating conditions v i -i +i swon swon programmab le thanks to an external resistor programmab le thanks to any external voltage reference fig. 2: line card protection rings -vbat -vbat rp rsense tip 1 1 2 2 slic (*) (*) lcp1511d orthdt series or lcdp1511d ov v ref er oltage erence (+/- 270v) 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
application note 3/13 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 : n 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 . n 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. rsense rp 1 2 overvoltage reference (+/- 270v) overvoltage detector overcurrent detector or tipl tips fs sw3 sw1 fuse tip gnd i lg v lg 1/2 clp270m i lg v 1 2 3 -270 +270 a1 fig. 4: switching by voltage during ringing mode. 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. 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 i swoff , 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: n up to 4 fixed external voltage reference (v z1 to v z4 ) (see fig. 5a, here-below). n external reference supplies, v b1 and v b2 (see fig. 5b, on next page).
application note 4/13 rings rsense rsense 1 2 overvoltage reference (+/- 270 v) overvoltage detector overcurrent detector or overvoltage reference (+/- 270 v) overvoltage detector overcurrent detector or tipl tips ringl fs gnd sw3 sw1 sw4 sw2 1 2 fuse fuse tip ring vz1 vz2 vz3 vz4 rp rp fig. 5a: method to adjust the reference voltage . rings rsense 1 2 overvoltage reference (+/- 270 v) overvoltage detector overcurrent detector or overvoltage reference (+/- 270 v) overvoltage detector overcurrent detector or tipl tips ringl fs gnd sw3 sw1 sw4 sw2 rsense 1 2 fuse fuse tip ring vb1 vb2 rp rp fig. 5b: method to adjust the reference voltage .
application note 5/13 rsense rp 1 2 overvoltage reference (+/- 270 v) overvoltage detector overcurrent detector or tipl tips fs sw3 sw1 fuse tip gnd -vbat external voltage reference i lg v lg i lg v a2 lg 4 5 6 v ref1 -v ref2 fig. 6: switching by current during speech mode. 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 -v bat respectively for positive and negative surges. this generates a current which is detected by r 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 clp270m returns to its initial state (region 4). the choice of the switching-on currents is function of the r sense resistors. 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 sense . figures 7a and 7b enable the designers to choose the right r sense value. example: the choice of r sense =4 w 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. fig. 7a and 7b: switching-on current versus r sense . 3 5 7 9 11 13 0.2 0.3 0.5 1 2 rsense ( ) w iswon (t, rsense) / iswon (25 c, 4 ) w @-20 c @25 c @75 c 357911 50 100 200 300 500 rsense ( ) w iswon @ 25 c (ma) iswon min negative iswon max negative iswonmin positive iswon max positive 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)
application note 6/13 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 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. clp270m rsense rsense 1 failure +12v 1k status fig. 8: failure status circuit and diagnostic. 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 10 20 50 100 200 500 1 000 2 000 5 000 t (ms) fig. 9 : operation limits and destruction zone of the clp270m. 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 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. clp270m test results according to bellcore 1089 requirements 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.
application note 7/13 surge minimum peak voltage (volts) minimum peak current per conductor (amps) maximum rise / minimum decay time for voltage and current ( m s) repetitions, each polarity test connections per table 4.1 1 +/- 5000 500 2/10 1 b table 2: second level lightning surge. test voltage (v rms ) short circuit current per conductor (amps) duration primary protection test connections per table 4.1 1 50 0.33 15 minutes removed a 2 100 0.17 15 minutes removed a 3 200, 400 and 600 1 (at 600v) 60 1 s application of each voltage removed a 4 1000 1 60 1s applications operative protector in place b 5 see figure 4-3 see figure 4-3 60 5s applications removed see figure 4-3 6 600 0.5 30s removed a 7 600 2.2 2s removed a 8 600 3 1s removed a 9 1000 5 0.5s operative protector in place b table 3: first level ac power fault (table 4-7 of gr-1089-core issue 2, december 1997). surge minimum peak voltage (volts) minimum peak current per conductor (amps) maximum rise / minimum decay time for voltage and current ( m s) repetitions, each polarity test connections per table 4.1 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 1: first level lightning surge.
application note 8/13 test test for voltage (v rms ) short circuit current per conductor (amps) duration test connections per table 4.1 1 secondary contact 120, 277 25 15 minutes a 2 primary contact 600 60 5 seconds a 3 short-term fault induction 600 7 5 seconds a 4 long-term fault induction 100-600 2.2 (at 600 v) 15 minutes a 5 high impedance induction 15 minutes table 4: second level ac power fault (table 4-8 of gr-1089-core issue 2, december 1997). test two-wire interface four-wire interface a 1. tip to generator, ring to ground 2. ring to generator, tip to ground 3. tip to generator, ring to generator simultaneously 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 3. t1 and r1 to generator simultaneously, tip and ring to ground b tip to generator, ring to generator simultaneously t, r, t1, r1 to generator simultaneously table 5: test connection (table 4-1 of gr-1089-core). test voltage source limiting resistance (if specified) s1 s3 s2 s4 switch unit under test t e r m t e r m
application note 9/13 test s1 s2 s3 s4 t to generator, r to ground (condition a1 of table 4-1) closed open open closed r to generator, t to ground (condition a2 of table 4-1) open closed closed open t to generator, r to generator simultaneously (condition a3 of table 4-1) closed open closed open table 6: application of lightning and ac power fault test voltages (table 4-2 of gr-1089-core). 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 2/10 m s generator. 2/10 m s generator +/- 2.5 kv (500 a) 4 tipl tips gnd 1/2 clp270m i1 v1 rsense rp fig. 10: lightning simulation test. fig. 11: clp270m response to a positive surge. fig. 12 : clp270m response to a negative surge.
application note 10/13 2.2. speech mode figures 14 and 15 give the voltage and current behavior during positive and negative 2.5kv, 2/10 m s, 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. 2/10 m s generator +/- 5 kv (500 a) 4 tipl tips gnd 1/2 clp270m i v1 50 i2 slic lcp1511d -48v v2 1 rsense rp fig. 13: lightning test in speech mode. fig. 14: clp270m response to a positive surge. fig. 15: clp270m reponse to a negative surge.
application note 11/13 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, 2/10 m s,500a surge with the clp270m acting in ringing mode. 2/10 m s generator +/- 5 kv (500 a) 4 tipl tips gnd 1/2 clp270m i v1 1 rsense rp fig. 16: lightning test in ringing mode. fig. 17: clp270m response to a positive surge. fig. 18: clp270m response to a negative surge. 3.2. speech mode the figures 20 and 22 give the voltage and current behavior during positive and negative 5kv, 2/10 m s,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.
application note 12/13 2/10 m s generator +/- 5 kv (500 a) 4 tipl tips gnd 1/2 clp270m i v1 50 i2 slic lcp1511d -48v v2 1 rsense rp fig. 19: lightning test in speech mode. fig. 20: clp270m response to a positive surge. fig. 21: clp270m response to a negative surge. 4. first and second level ac power fault. 4.1. ringing mode the figures 23 and 25 give the voltage and current at the clp270m terminals in ringing mode and speech mode. 4 i1 v1 v(rms) 50hz rsense rp tipl tips gnd 1/2 clp270m rs fig. 22: ac power fault test in ringing mode. fig. 23: example of behavior when facing test 3 (400v, 600 w) .
application note 13/24 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. conclusion 4 w w tipl tips gnd 1/2 clp270m 50 slic lcp1511d -48v v2 rsense rp v(rms) 50 hz i1 rs fig. 24: ac power fault test in speech mode. fig. 25: example of behavior when facing test 3 (400v, 600 w ). information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted 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 ap- proval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2000 stmicroelectronics - printed in italy - all rights reserved. stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia malta - morocco - singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com

▲Up To Search▲

Price & Availability of AN1220

	To Download AN1220 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .