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Characterization Output Protection Circuitry EL1528 Driver Lightning Surges
Technical Brief February 2004 TB426
Authors: Paul Traynham Mike Wong
EL1528 dual channel differential amplifier designed driving full rate ADSL signals very power dissipation. high drive capability 450mA makes this driver ideal both designs. contains pairs wideband, high-voltage, current mode feedback amplifiers optimized power consumption systems. unique feature EL1528 integrated protection circuitry designed protect driver outputs from transients such electrostatic discharge (ESD) lightning. order better understand capability internal protection circuitry, useful discuss typical architecture, types characteristics transients that circuit would encounter, Telecommunication Standards that apply circuits.
Power cross power faults occur when power lines come close proximity even contact with telecom lines. power cross event (such when power line falls telephone line utility pole), resulting transient easily exceed 600VAC. Even actual contact made, electromagnetic coupling between power line telecom line cause transients enter network.
Overview Telecom Standards
Telecommunications Standards have been developed provide greater reliability, prevent costly service interruptions allow users safely operate Telecommunication Equipment C.O. equipment, phones, machines, modems, etc. without threat personal injury electrical shock fire. Several standards lightning power cross telecommunication systems exist including Telcordia GR1089, UL60950, Part ITU-T K.20 K.21. Table summarizes various tests that must performed defined these standards. parameters defined lightning environmental testing wave shape. Figure defines lightning waveform Table defines rise time pulse duration. example, 8x20µs waveform, 20µs defined Figure Also defined Surge Voltage, Surge Current number repetitions. Each surge applied across Ring (Metallic) from Tip/Ring Earth Ground (Longitudinal). Several standards also exist, mostly widely accepted standard IEC-61000-4-2. requirements more severe than MIL-STD-883, Method 3015 preferred method worldwide.
Transients short-lived events which over voltage over current condition occurs. telecommunication equipment, transients that designers most concerned with include Electrostatic Discharge (ESD), Lightning, Power Faults Power Cross.
Electrostatic Discharge (ESD)
caused transfer electrical charge between objects caused imbalance electrons surface objects. most common transfer between human body metallic semiconducting surface. Such transfer very short duration (<1ns) exceed 25kV. While this generally harmless human, although smart little, devastating effects integrated circuit. Most have some level protection, special attention must placed those I.C.'s that come frequent contact with humans.
Lightning most common cause transients telecommunication systems. Around world, there approximately lightning strikes every second since telecommunication lines often exposed, there great concern over threat that lightning poses, only telecommunications network, humans that interface with them.
CAUTION: These devices sensitive electrostatic discharge; follow proper Handling Procedures. 1-888-INTERSIL 321-724-7143 Intersil (and design) registered trademark Intersil Americas Inc. Copyright Intersil Americas Inc. 2004. Rights Reserved. Elantec registered trademark Elantec Semiconductor, Inc. other trademarks mentioned property their respective owners.
FIGURE PEAK PULSE CURRENT TEST WAVEFORM
TABLE COMPARISON TELECOMMUNICATIONS TEST STANDARDS
Telcordia (previously known Bellcore) GR-1089, "Electromagnetic Compatibility Electrical Safety Generic Criteria Network Telecommunications Equipment," developed maintained Regional Bell Operating Companies Telecom industry. Telcordia GR-1089 more comprehensive than other specifications addressing both equipment performance safety issues covering requirements telecommunications equipment connected outside world through twisted pair copper wire. standard consists first level stresses which equipment must remain functional second level stresses that must create fire, fragmentation, electrical safety hazard.
TABLE 61000-4-2 SEVERITY LEVELS
UL1459 original standard covering Telecommunication equipment whose primary function protect users telecom equipment. UL1950 most recently UL60950 developed bi-national standard with based IEC950 including requirements UL1459. Most local governments require UL60950 compliance meet National Electric Code (NEC), giving UL60950 force law.
FIGURE IEC61000-4-2 WAVEFORM
rules Part intended ensure that equipment attached network will harm network. does specifically address safety issues, rather performance specification.
ITU-T K.20 K.21
These standards recognized Europe Asia designed address reliability equipment. ITU-T K.20 K.21 standards address telephone exchanges, switching centers, customer premise equipment that exposed environment. standard consists lightning simulation, inducted power power contact tests.
61000-4-2 defines several levels severity. levels separately defined plus minus polarity direct contact discharge (preferred) discharge shown Table Other voltage levels specified 61000-4-2 test equipment conditions. Figure shows defined waveform. Note extremely fast rise time.
Technical Brief Reference Designs System Compliance
that have better understanding standards which designer systems must comply, useful discuss typical reference design including components that necessary help this compliance. Figure shows typical simplified EL1507, EL1508 line driver reference design. pairs Schottky diodes used clamp outputs line driver diode voltage within ±12V supply line driver. Figure shows similar design, EL1507, EL1508 replaced dual driver EL1528 with internal protection circuitry. Note protection Schottky's removed intention this application note test capability internal protection circuitry.
FIGURE EL1507, EL1508 LINE INTERFACE CIRCUIT WITH SCHOTTKY PROTECTION DIODE
FIGURE EL1528 LINE INTERFACE CIRCUIT WITHOUT SCHOTTKY PROTECTION DIODE
FIGURE LIGHTNING SURGE TEST CIRCUIT
Figure shows complete lightning surge test setup. Teccor Sidactors (P2300SA) protection against metallic longitudinal transients. Teccor Telecom Fuses (F1250T). These fuses specifically designed withstand Environmental Testing without damage, clear when necessary during power cross event. transformer. D1-D4 Shotkky Diodes that help clamp transient energy that coupled through transformer. EL1528 test, D1-D4 diodes removed. series resistor varies depending reference design, typically smallest value used.
FIGURE Ring VOLTAGE, GROUND, Ring 2500V, 2/10µs
Figure worst case lightning test with 2500V applied across ring terminals line side.
FIGURE VOLTAGES LINE DRIVER SIDE TRANSFORMER, GROUND, Ring 2500V
Figure shows voltages line driver side transformer, lightning surge ground Ring 2500V, time duration 2/10µs. voltage coupled line driver side after Sidactor isolation transformer over 160V differential.
Figure shows over current going EL1528 when 2500V lightning surge voltage applied. output current measured with (back match resistor). With RBM, output current spike reduced
FIGURE LIGHTNING SURGE CURRENT INTO EL1528 WITH RBM, GROUND, Ring 2500V
EL1528 Lightning Surge Test Results
TABLE EL1528 LIGHTNING SURGE TEST RESULTS DEVICE DATECODE 0226A 0226A 0239A 0239A PB-MIL BEFORE/ AFTER Before After Before After 17.2 17.2 18.22 10.21 IS16.2 16.22 17.16 17.15 THD-A-2.5 THD-B-2.5 THD-A-2.85 THD-B-2.85 COMMENTS 68.5 output 69.2 71.7 69.2 71.7 49.3 48.4 50.5 49.5 Blown -12V Power Supply Fuse 68.9 49.8 49.7 Blown
0239A Datecode 0239A
Before Before/ After Before
67.8 THD-A-2.5 70.8
49.9 Comments changed
THD-B-2.5 THD-A-2.85 THD-B-2.85 70.7 43.1 41.4
0239A 0239A 0239A 0226A 0226A
After Before After Before After
18.33 18.55 18.51 17.48 17.55
17.2 17.46 17.46 16.57 16.57
68.8 69.7 69.7 68.8
69.7 69.7 68.8 67.9
47.1 49.5 49.1 51.4 53.4
46.9 50.5 51.1 47.8 48.9 2010 Resistor 2010 Resistor
qualify survial EL1528, addition product test, also test device supply current distortion. shown table EL1528 were tested with backmatch resistors. linearity performance device remains unchanged after lightning surge test.
Intersil Corporation reserves right make changes circuit design, software and/or specifications time without notice. Accordingly, reader cautioned verify that Application Note Technical Brief current before proceeding.
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