SELECTION GUIDE Telecom Circuit Protection Circuit Protection Solutions The Bourns Mission Our goal is to satisfy customers on a global basis while achieving sound growth with technological products of innovative design, superior quality and exceptional value. We commit ourselves to excellence, to the continuous improvement of our people, technologies, systems, products and services, to industry leadership and to the highest level of integrity. Index Introduction . .2 Applications - What Protection do you Need? What is a Surge? . .3 What is Protection? . .3 Lightning - Global and Different . .4 Where will the System be Used? . .5 Coordination is No Longer Optional . .6 Standards . .6 System Technology . .8 Location . .8 Application - Central Office (CO) and Access . .9 Application - Customer Premise Equipment (CPE) . .12 Digital Technology . .14 Useful Sources . .15 Network Diagram . .16 & 17 Technology - Which Protection Technology is Right for the Equipment? The Basics - Overvoltage and Overcurrent . .18 What Happens After a Surge or if the Device Fails? . .18 Speed and Accuracy are Major Factors in Determining Equipment Stress Levels . .19 Technology Selection - Overvoltage Protectors . .21 Gas Discharge Tubes (GDTs) . .22 Thyristor-Based Devices . .24 Metal Oxide Varistors (MOVs) . .24 Transient Voltage Suppressors (TVSs) . .25 Technology Selection - Overcurrent Protectors . .25 Positive Temperature Coefficient (PTC) Thermistors . .26 Fuses . .27 Heat Coils . .27 Line Feed Resistors . .27 Thermal Switches . .28 Modes of Overvoltage Protection . .28 Technology Selection - Integrated Solutions . .29 Multi-Stage Protectors . .29 Integrated Line Protection Modules . .30 Product Selection Guides Gas Discharge Tubes . .32 Multifuse® PPTC Resettable Fuses . .34 TISP® Thyristor Surge Protectors . .35 Surge Line Protection Modules . .41 Telefuse™ Telecom Fuses . .43 1 Introduction Bourns is pleased to present this comprehensive Technical and Design Support – Bourns’ team of guide to Telecom Circuit Protection, encompassing specialized Sales and Field Application Engineers are our broad range of technologies and products. This ready to bring additional in-depth expertise to your guide will provide the background information and next project. Through our interactive website and selection recommendations needed to ensure that customer service locations, Bourns is always available your next project achieves the level of cost-effective to answer circuit protection design questions and field reliability demanded by today’s customers. provide valuable assistance and support. Bourns commissioned a survey of Telecom Circuit Knowledge of Protection Technology – Bourns Protection users worldwide to determine their prior- boasts the industry’s widest range of Telecom over- ities and needs. We found that reliability, technical voltage and overcurrent protectors. Our active and design support, and exemplary knowledge of involvement in international protection standards protection technology were by far the three most organizations ensures world-class technology and cited items. Bourns is committed to meeting each of applications expertise. these three requirements: Bourns continues to develop an innovative range of Reliability – Reliability requires an understanding of integrated circuit protection products using our the capabilities and specifications of circuit protection knowledge and expertise to combine multiple technology. Bourns has a global reputation for quality technologies into optimized single devices designed products, and our circuit protection devices have to save both cost and board space. Whether you need consistently demonstrated reliability in field applica- a single product or a complete protection solution, tions. Bourns is committed to the complete support Bourns Telecom Circuit Protection team is there to of a circuit protection solution for the life of a help you. We look forward to working with you. program. 2 Applications - What Protection is Needed? Communication systems are vulnerable to electrical are significant for device survival and safety. Direct damage from lightning or other surges. As systems contact to the AC (power cross) causes high currents, become more complex, they also become more while lower currents result from power induction. vulnerable. Balancing the cost, standards compliance Obviously, a single device protection solution is and field reliability of protection is both a commercial seldom possible. and technical challenge, compounded by the addi- tional performance constraints of modern digital Amplitude Duration Bulk networks such as xDSL. Heating Lightning kA, kV µs Negligible This section is intended to outline those challenges, Power Cross 60 A <30 mins Significant illustrate the fundamentals of protection and identify Power 7 A <30 mins Crucial those international standards relevant to specific Induction applications. The next section will examine individual protection technologies and their selection. Table 1. Different surge sources result in very different effects Bourns engineers have helped designers with major projects in every region of the world, successfully Reliability Tip protecting hundreds of millions of telephone circuits. Effective protection usually requires overcurrent and Our uniquely broad range of protection solutions overvoltage devices. enables us to identify the most suitable technology for each application. Whether the goal is to achieve standards compliance or tackle a specific field prob- What is Protection? lem, Bourns’ experience and product offering are the Protection performs several key functions as outlined solution to a myriad of design requirements. in Figure 1: first it must prevent or minimize damage caused by a surge; then it must ensure that the system Reliability Tip returns to a working condition with minimal disrup- Complying with standards does not guarantee tion to service. It is vital that under normal conditions field reliability. the protection does not interfere with the signal, creating special challenges for xDSL and other digital technologies. The protection must also fail in a safe What is a Surge? manner during overstress. A “surge” is a short-term increase in voltage or current. Both lightning and the AC power distribution Field reliability system cause surges, but of very different magnitudes and durations (see Table 1). These events can either be via direct contact or by field or resistive coupling Quality from events close to the telephone system, resulting in a wide variety of threats. For example, the effects of service of a power line fault caused by lightning may even be Standards Signal more threatening to the telephone system than the compliance integrity original lightning. Figure 1. Protecting “Quality of Service” requires The dangers of large voltages and currents are obvious, more than standards compliance but time is also important. Lightning is too fast for bulk heating to be critical, whereas for the longer term currents of AC power faults, heating effects 3 Within each of the core protection types listed in boundary of the premises. It is designed to redirect Table 2, there are several individual technologies. the bulk of the surge energy away from personnel These will be reviewed in more detail in the and equipment by passing significant current to Technology section. Each technology has different ground. Secondary protection (Figure 3) is optimized strengths and weaknesses, and only by understanding to protect the most sensitive parts of the equipment their relative merits can protection be optimized for from any residual voltage surges let through by the a given installation. A quick review of Table 3 Primary protector. Some telecommunications ICs demonstrates that no single ideal solution exists for have very precisely defined time-dependent Safe all locations within the telephone network so cascaded Operating Areas, requiring precise and predictable protection is often employed. behavior as illustrated in Figure 4. There is typically some resistance added between the Primary and Secondary protection, either as part of the system Protection Action Connection Type requirements or the protection regime. Series (or parallel Overcurrent Limit peak current for primary) Primary Protection Overvoltage Limit peak voltage Parallel Overcurrent Overcurrent Coordinate voltage protector and and current Combination Overvoltage protection ected Table 2. Protection falls into three basic types side side Prot Unprotected Overvoltage Overvoltage Speed Accuracy Current protector Rating Figure 2. Typical format for Primary protection GDT Fair Poor Very high Thyristor Fair Good High MOV Fast Poor High Secondary Protection TVSVery fast Good Very low Overcurrent protector Overcurrent Speed Accuracy Current Rating ected side side Prot Polymer PTC Unprotected Slow Good Low Thermistor Overvoltage Ceramic PTC Slow Good Low protector Thermistor Medium/ Fuse Very slow Fair High Figure 3. Typical format for Secondary protection Heat Coil Very slow Poor Low Thermal Switch Very slow Poor High Lightning - Global and Different Weather does not understand national boundaries, Table 3. Summary of technology characteristics and varies with geography as shown in Figure 5. Partly for this reason, local standards have evolved to Primary protection (Figure 2) diverts most of the describe a lightning strike, usually containing major surge energy away from the more sensitive/important similarities, and critical differences. However, meeting areas of the system and is typically located at the each local standard is only the start of protection 4 design. It requires a PBL 3762A SLIC Ring and Tip Voltage Withstand vs Time deeper understanding of protection to achieve the 15 0.25 µs competitive advantage of 10 1 µs reliable operation under 5 10 ms field conditions. 0 Time VBAT Where will the System set to –50 V) –50 set to V – -50 BAT be.