LXT360/361 Line Protection Circuitry This application note provid

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LXT360/361 Line Protection Circuitry
This application note provides guidelines line protection circuitry required typical LXT360/361 applications such Network Channel Termination Equipment (NCTE), Channel Service Units (CSUs) Wide Area Network (WAN) interfaces. NCTE installed customer premises lines. these lines between customer facilities central office, they subject overvoltage/overcurrent stresses from lightning strikes, power crosses other noise impairments. Protection circuitry required protect line from injected impairments protect terminal equipment (CSU, NTU, mux, PBX, etc.) from overload stresses. Protection requirements equipment specified Part (lightning hazards), 1459 hazards), Bell Core TR-TSY-000007 AT&T 62411. These documents differentiate between longitudinal stress (differential tip/ring ground) metallic stress (differential between ring). Longitudinal stresses more common include impulsive noise events such lightning induced surges. Metallic stresses less likely usually caused power crosses during maintenance activity. Similar protection circuitry suggested applications LXT360/361. network described this application note targets compliance with 046-3 K17-K20. ensure compliance with applicable requirements, final design should undergo appropriate testing approved lab.
Protective Circuitry Discussion
power ground planes should located circuit board area near T1/E1 Line connector back transformers. Select resistors match line impedance. Their values impact amplitude transmitted signal transmit return loss. Positive Temperature Coefficient Resistors (PTCs) permit healing after overvoltage event. Their pretrip resistance specified between PTCs will slightly reduce amplitude transmitted signal. When using transformer, carefully selecting series resistors (see Table negate this effect. breakdown voltage line transformers must least designs require breakdown voltage kV.) Some harmful signal voltage from interface lines will cross T1/E1 transformer side; recommended varistor (V1) with sufficient stand voltage will provide additional protection LIU. Sidactors provide primary protection against bidirectional transient voltages transmit receive sides. final board design determines values chokes L2). Join line side center taps Transmit receive line transformers only applications requiring path sealing currents (i.e., some applications). RJ48C configuration shown recommended applications.
LXT360/LXT361 Line Protection Circuitry
TTIP TRING RJ48C2 RRING
LXT360/ LXT361
Note
NOTES
Interconnection transformers optional support current E1/T1 loop. Connections RJ48C jack applications only. applications, refer standards. Assign space Capacitor installed improve return loss needed.
RTIP
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LXT360/361 Line Protection Circuitry Table Component Selection Guide-LXT360/LXT361 (E1/T1, Long-Haul/Short-Haul
Applications) Rtx1 1.0% EC4-13 1.0% 120/75 Transmit Transformer2 1.53 Receive Transformer
Application Long-Haul twisted-pair lines (with line protection) Short-Haul twisted-pair lines (without line protecti Short-Haul coax lines (without line protection) Short-Haul twisted-pair lines (without line protecti Long-Haul twisted-pair/ coax line protection) Long-Haul twisted-pair lines (with line protection) Long-Haul coax lines (with line protecti
protecti circuit reduces amplitude transmitted signal. lower value restore ampl itude nomi value. lower value compensates resistance protecti resistors line side (PTC used example). transmit receive transformers must have center (1:2 support simplex current E1/T1 loop requi red. EC4-1 columns indicates "don't care". Refer LXT360/361 Data Sheet full description transmit equalizer codes.
Table Common Components LXT360/LXT361 Applications
SD1, Description Sidactor-Instantaneous clamping voltage TO-92 packaging Positive Temperature Coefficient Resistors Line Feed Resistor-Thermal, fused, Varistor-Stand-off voltage Off-state capacitance 470pF Ceramic capacitor-0-470 radial leaded, Choke-Vari based board design typically Typical Part (Manufacturer) PO720EA70 (TECCOR ectronics) TR600-160-RA-B-0.5-.130 (Raychem) LFR-2-5.6-1 (IRC) MSV701A (Microsemi) B529-2 (EDAL Industries)
manufacturer (e.g., KEMET, AVX) 500-1164 Electronics)
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LXT360/361 Line Protection Circuitry Figure Enhanced Line Protection Circuitry
TVcc
TVcc
TTIP
TVcc
TRING
TVS14
LXT360/ LXT361 1%,1/4
Note
RJ48C2 SD26
TGND
RTIP RRING 1%,1/4
NOTES:
Interconnecting transformers optional support current looping E1/T1 loop. Connections RJ48C jack applications only. applications, refer standards. Schottky diode 11DQ04 (International Rectifier) typical component D1-4. TVS1 bidirectional TVS. Semtech SMCJ5.0AC (surface mount part) typical. Value Capacitor vary between improve transmit return loss. Test determine optimum value each design Sidactors replaced with capacitance array. Semtech Corporation manufactures suitable 1500 watt surface mount, capacitance array (part number LC01-6).
Figure shows enhanced version protection circuit LXT360/361 shown first page this data sheet. Please notice that circuit requires additional components, including Schottky diodes D1-4 bidirectional (TVS1). enhanced circuit provides better protection from metallic stresses from surges coupled VCC. However, these advantages come price increased component count, space, higher unit cost.
PTCs have advantage recovering from stress condition once condition disappears. Many similar designs Line Feed Resistor (LFR) like LFR-2-5.6.1 from IRC, Inc. combination precision resistor (5.6 thermal fuse. primary benefit stable resistance over temperature variances. However, opens permanently must replaced. affected line must switched redundant circuit until primary circuit restored.
Table Manufacturers Mentioned this Note
Company Electronics Contact Information 12219 Wood Lake Drive Burnsville, 55337 (612) 894-9590 Fax: (612) 894-9380 Short Beach Road East Haven, 06512 (203) 467-2591 Fax: (203) 469-5928 P.O. 1860 Boone, 28607 (704) 264-8861 Fax: (704) 262-1972 8700 Thomas Road Scottsdale 85251 (602) 941-6300 Fax: (602) 947-1503 Company Raychem Corp SEMTECH Corp TECCOR Electronics Contact Information Constitution Drive Menlo Park, 94025-1164 (800) 227-2040 Fax: (800) 227-4866 Mitchell Road Newburg Park, 91320 (805) 498-2111 Fax: (805) 498-3804 1801 Hurd Drive Irving, 75038 (214) 580-1515 Fax: (214) 550-1309
EDAL Industries IRC,
Microsemi Corp
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LXT360/361 Line Protection Circuitry This application note provid

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