AND8022/D TSPD (Thyristor Surge Protection Devices) Telecom Circuit Protection Using ON Semiconductor Protection Devices http://onsemi.com APPLICATION NOTE Overview The ON Semiconductor NP series of circuit protectors are used in the secondary overvoltage protection block. Circuits are first protected by primary protection which is usually located at or near the building entrance, known as the Main Distribution Frame (MDF). Primary protectors are generally Gas Discharge Tube (GDT) or Carbon Blocks. The primary protectors limit the very high energy transients, and the secondary protectors limit the voltage and current to acceptable levels and are incorporated on the telecom linecard itself. While there are other types of overvoltage protectors, such as Metal Oxide Varistor (MOV) and Gas Discharge Tube, the TSPD offers unique advantages, making them the preferred choice for Telecom Circuit protection applications. Today’s increasingly complex telecommunication systems, many using high density ASIC’s are allowing telecommunications equipment manufacturers to continually improve services and support more lines in tighter spaces with smaller packages. However, these systems are more susceptible than ever to overvoltage and overcurrent transients. Solid state Subscriber Line Interface Circuit (SLIC) devices, and high speed Digital Subscriber Line (DSL) IC’s are located on the telecom “linecard” and require secondary protection to provide reliable operation, prevent costly service interruptions, allow safe operation, and achieve regulatory compliance. THREATS LINECARD MDF Primary Protection Central Office Wiring Secondary Protection Lightning GDT Resistor, PTC, Fuse Thyristor SLIC Overvoltage Ring Overcurrent Crossing Wires Overvoltage Tip Copper Pair NP Series TSPD Figure 1. Typical Protection Design © Semiconductor Components Industries, LLC, 2007 November, 2007 − Rev. 1 1 Publication Order Number: AND8022/D AND8022/D THREATS Transients are short−lived events in which an overvoltage or overcurrent condition occurs. In telecommunication equipment, these transients include lightning and AC Power Fault or induction. Power Fault, Power Induction Power Fault or Power Cross occurs when AC power lines come in close proximity of, or even contact the telecom lines. Power cross events occur when a power line falls on a telephone line on a utility pole, or with maintenance errors or cabling faults. The resulting transient can result in moderate currents of less than 25 A flowing for a long period of time, up to 15 minutes as an example. They are usually at mains power supply voltage levels of 100−240 Vrms. Power induction is caused by faults which couple into the system. These are typically short duration, high voltage AC transients. These are a few cycles of AC to several seconds in duration and at voltages up to 600 Vrms. Lightning Ipp − PEAK PULSE CURRENT − % Ipp Lightning is the most common cause of transients in telecommunications systems. Equivalent circuits have been developed to simulate a lightning strike event. There are two types of tests performed to evaluate a telecommunication system’s ability to withstand lightning strikes. These are Transverse (between Tip or Ring to ground individually) and Longitudinal (Tip and Ring to ground simultaneously). These Surge tests are defined by an peak open circuit voltage and peak short circuit current, along with maximum rise and minimum decay times. 100 Peak Value STANDARDS Telecommunication standards and recommendations have been developed to help engineers design circuits and protection schemes to provide greater reliability, safe operation, and cost effective systems. These tests are used to verify a system’s ability to safely withstand and protect a circuit from the transients caused by lightning and power cross threats. The most common test standards are highlighted below. t r = rise time to peak value t f = decay time to half value Half Value 50 0 0t r tf Primary Region Standard Application GR−1089−CORE Central Office/Access USA K.20 Central Office International K.21 Customer Premises International K.45 Trunk Networks International TIA−968/UL60950 Customer Premises USA Figure 2. Exponential Decay Pulse Waveform The following tables (tables 1−4) are grouped by lightning surge and powercross. They are also separated by first and second level test definitions. Under first level conditions the device must be undamaged and continue to operate after the stress is removed. Under second level conditions the device can fail, but must fail in a safe manner. http://onsemi.com 2 AND8022/D Lightning Surge Tests Table 1. First Level − Parts Must Continue to Function Test Surge Voltage (V) Surge Current (A) Waveform Repetitions Each Polarity Telecordia GR−1089−CORE Test 1 600 100 10x1000 ms 25 Test 2 1000 100 10x360 ms 25 Test 3 1000 100 10x1000 ms 25 Test 4 2500 500 2x10 ms 10 1500 37.5A 10x700 ms 5 4000 100A 10x700 ms 5 1500 37.5 10x700 ms 5 6000 150 10x700 ms 5 Test 1 1500 37.5 9x720 ms 2 Test 2 1000 25 9x720 ms 2 Surge Current (A) Waveform Repetitions Each Polarity 5000 500 2x10 ms 1 Test 1 1500 200 10x160 ms 2 Test 2* 4000 100 10x700 ms 5 ITU−T K.2/K.21/K.45 Basic Level Test 1 Test 2* Enhanced Level Test 1 Test 2* TIA−968−A *Primary Protector Included in Test Circuit Table 2. Second Level − Parts Can Fail Safe Test Surge Voltage (V) Telecordia GR−1089−CORE Test 1 TIA−968−A *Primary Protector Included in Test Circuit http://onsemi.com 3 AND8022/D Power Cross Tests Table 3. First Level − Parts Must Continue to Function Test Open Circuit Voltage (V) Short Circuit Current (A) Duration(s) Test 1 50 0.33 900 Test 2 100 0.17 900 Test 3 600 1 1 Test 4 1000* 1 1 Test 6 600 0.5 30 Test 7 440 2.2 2 Test 8 600 3 1.1 Test 9 1000* 5 0.4 Basic Level Test 1 600 1 0.2 Test 2 600* 1 1 Enhanced Level Test 1 600 1 0.2 Test 2 1500* 2.24 − 7.5 0.18 − 2 Test 3 230 1.44, 0.77, 0.38 900 Open Circuit Voltage (V) Short Circuit Current (A) Duration(s) Test 1 277 25 900 Test 2 600 60 5 Test 3 600 7 5 Test 4 600 2.2 900 Basic Level Test 1 230 0.23 − 23 900 Enhanced Level Test 1 230 2.9 − 23 900 Telecordia GR−1089−CORE ITU−T K.2/K.21/K.45 *Primary Protector Included in Test Circuit Table 4. Second Level − Parts Can Fail Safe Test Telecordia GR−1089−CORE ITU−T K.2/K.21/K.45 http://onsemi.com 4 AND8022/D +I IT I(BO) IH −VOLTAGE +VOLTAGE VT V DRM V(BO) −I Figure 3. TSPD Operation Table 5. Voltage Current Characteristics and Definitions Symbol Title Description V(BO) Max Breakover Voltage The maximum voltage across the device in or at breakdown measured under a specified voltage and current rate of rise. I(BO) Breakover Current The instantaneous current flowing at the breakover voltage (VBO). IH Holding Current The minimum current required to maintain the device in the on−state. IT On−State Current The current through the device in the on−state condition. VT On−State Voltage The voltage across the device in the on−state condition at a specified current (IT). VDRM Rated Repetitive Peak Off−State Voltage Rated maximum (peak) continuous voltage that may be applied in the off−state condition. IDRM Repetitive Peak Off−State Current The maximum (peak) value of the current that results from the application of (VDRM). FUNCTIONALLY DEVICE SELECTION The TSPD has two modes of operation: When selecting a TSPD use the following key selection parameters. Open Circuit − Transparent: Off−State Voltage VDRM It must remain transparent during normal circuit operation. This is achieved by the very small leakage current (<5 mA) when the device is in its’ off state. The device looks like an open across the two wire line. Choose a TSPD that has an Off−State Voltage greater than the normal system operating voltage. The protector should not operate under these conditions: Example: Short Circuit − Protection: Vbat = 48 Vmax When a transient exceeds the device VDRM , the device switches on, and shorts the transient current to ground, safely protecting the circuit. Once the fault is removed the device must switch back to it’s original open circuit condition allowing normal operation to resume. Vring = 150 Vrms = 150*1.414 = 212 V peak VDRM should be greater than the peak value of these two components: VDRM > 212 + 48 = 260 VDRM http://onsemi.com 5 AND8022/D Breakover Voltage V(BO) resistance is used. When a series current limiter is used in the circuit a lower current level of “A” or “B” may be used. To determine the peak current divide the maximum surge current by the series resistance. Verify that the TSPD Breakover Voltage is a value less than the peak voltage rating of the circuit it is protecting. Example: Relay breakdown voltage, SLIC maximum voltage, or coupling capacitor maximum rated voltage. Hold Current (IH) Peak Pulse Current Ipps The Hold Current must be greater than the maximum system generated current. If it is not then the TSPD will remain in a shorted condition, even after a transient event has passed. Choose a Peak Pulse current value which will exceed the anticipated surge currents in testing. In some cases the 100 A “C” series device may be needed when little or no series TSPD Compared to Other Overvoltage Protection Devices GDT’s and MOV’s Gas Discharge Tube (GDT) Metal Oxide Varistor (MOV) The GDT has a sealed construction with two terminals and inside two electrodes with a small gap between. In this small volume, is trapped a gas with a specific ionization level, therefore, when a voltage transient occurs the ionized gas serves as a current path. The following plot shows the typical operation behavior of a GDT (V−I characteristics): These solid state devices are in essence two Zener Diodes with the cathodes tied together and the voltage limitation is dependent of the Zener voltage of each Zener diode. In these devices the power dissipation is very high. The following plot shows the typical operation behavior of a MOV (V−I characteristics): GAS SURGE ARRESTER I Second Breakdown Occurs MOV I V V Vclamp Figure 4. Figure 5. In this plot, it is possible to observe that the GDT’s response is relatively slow, and sometimes this factor could be very critical for telecom applications in which fast response is needed. In addition, as a result of this slow response, some gas tubes’ electrodes burn out after a few hundred hits. When an MOV reaches its Zener voltage, it starts to dissipate power, so this is why, if a high transient voltage occurs, the MOV may be damaged because of the high power dissipation that this transient may cause. At the same time, it is very common that the MOV becomes degraded each time it is activated. http://onsemi.com 6 AND8022/D Thyristor TSPD Applications Tip LCAS or Ring Relay NP3100SC NP3100SC Ring Figure 6. Central Office POTS Card NP1800SC NP0640SC NP0640SC NP1800SC TX POWER RX NP1800SC NP0640SC NP0640SC NP1800SC Figure 7. T1/E1 http://onsemi.com 7 AND8022/D Tip NP3100SC Voice NP3100SC Ring DSL Figure 8. ADSL NP3100SA Figure 9. 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