どの程度の保護が必要か？

電子システムを設計するときは、見落とされたり過小評価されがちな保護対象を考慮する必要があります。場合によっては、設計者は静電気放電 (ESD) 耐性に関するIEC 61000-4-2などの特定の規格を満たすよう取り組んでいることもあります。遠隔メーター、ロボット、通信システムなど、過酷な動作環境に設置される機器には、より高いレベルの雷保護が必要になります。こうした要件は比較的明らかですが、その他にも、短絡、電圧スパイク、電力異常、ケーブル放電イベントといった考慮すべき課題があります。こうした一時的な脅威まで並べられると、設計者は圧倒され、信頼性の高いシステムを保証するにはどれだけの保護があれば十分なのかと尋ねたくなるかもしれません。

The Smart Home Analogy

In order to answer this question, let’s consider an analogy of a home security system. After all, components of a home security system provide protection for the contents inside the home. If any fail, the entire dwelling can be compromised. A home security system works on the basic principle of securing entry points such as doors and windows, as well as key interior spaces which contain valuables. A security system is comprised of a network of integrated devices which must work together to protect against home intruders. A comprehensive system would include door locks, window and door sensors, motion sensors, alarms, cameras, and a control panel. At the bare minimum, a “budget” system should include sensors that lead into the house as well as easily accessible windows. Like anything, a system is only as good as its weakest link. It wouldn’t make much sense to secure some windows or doors while leaving others vulnerable.

But what happens if an intruder manages to enter? The interior can be secured with motion sensors and alarms. Of course, the system can be professionally installed and monitored, or can be a DIY system without automatic monitoring. Either way, the system has to work in unison. Systems that are “pieced” together may work individually, but not function well as a whole. You would also take care to choose quality components. After all, if a component is not reliable, it’s as bad as not installing it at all. Studies have shown that homes without security systems are three times more likely to be burglarized as compared to homes with professionally monitored systems. It makes sense as an intruder would look to capitalize on the easiest target.

If we apply the home security concept to protecting an electronic system or equipment, we can think of the circuit board/equipment as the “dwelling”. Each connector is like a door or portal into the interior of the equipment. Devices such as displays, buttons and switches act as doors or windows into the system. Like the home security analogy, each of these is an entryway for an unwanted intruder, but in this case, the intruders are electrical overstress (EOS) events. These transient events are far more ever present and frequent than the typical neighborhood burglar. Protecting some of the connectors and lines while leaving others unprotected is like not adding a security sensor to one of your homes doors. Any lines which connect to the inside of the system should include Transient Voltage Suppressors (TVS) for ESD and EOS or surge protection.

Take No Shortcuts in Home Security, or in Circuit Protection

In the case of a home security system, some people might think they don’t need sensors on the second floor windows, for example. In this way, the homeowner may attempt to save a few dollars in the “hope” that all will be fine. In reality, these shortcuts can render the entire home vulnerable. The same principle applies when it comes to protecting buttons and displays. A designer might be tempted to think the chances of an EOS event at these interfaces is low. However, seams around these interfaces provide a path for EOS events to enter your system. The bottom line here is if there is an entryway into the dwelling, it should be protected. So if all “doors and windows” are protected, that should be enough right? Again refer back to the home system, motion detectors, cameras and alarms are used inside the dwelling to protect against internal threats. In the case of electronic equipment, devices such as load switches and e-fuses protect input power lines from events such as short circuits on the bus or to data lines, lightning surges and inductive switching. Like in the home, care should be used when choosing protection devices. A device with poor characteristics, such as high clamping voltage or slow response time, will not protect the circuit as expected and can provide a false sense of security.

Reliable Protection Comes Full Circle

As mentioned, choosing reliable home security equipment is important, and quality equipment designs apply these system protection concepts. Surveillance and wireless cameras for example use TVS for ESD and EOS protection on Ethernet, RS-485, memory card, audio, and video interfaces. Devices which also guard against electromagnetic interference (EMI) and radio frequency interference (RFI) can further enhance the memory card and audio ports. USB interfaces use TVS to protect high-speed data lines and an electronic fuse (e-fuse) for overcurrent and overvoltage protection on the power supply line. DC power inputs also require overcurrent protection as well as EOS protection. This is just one example of system protection. Other home security devices such as control panels, electronic locks, alarms, key fobs, proximity sensors, and video doorbells could all utilize similar protection solutions for increased system reliability.

Figure 1 – Surveillance Camera Protection Components © 2021 Semtech Corporation  

Secure Your Electronics Like You Would Secure Your Home

When trying to answer the question of how much protection is enough, a lot of factors need to be considered. Most electronic equipment will be required to meet certain immunity standards. This usually helps dictate what level or what type of protection is needed. In general, any potential path for an EOS event into the PCB should be protected. Sometimes these paths are not always obvious. There may be temptation to leave a line or connector unprotected for cost savings. But if you use the analogy of home security, ask yourself what you would be willing to compromise. What entry points would you leave unprotected? Then the question as to “how much protection is needed” will be answered. Semtech offers system protection solutions for a variety of applications. Our team of applications engineers and online resources can help you choose a protection scheme to work seamlessly in your system.

Semtech, the Semtech logo, RClamp, uClamp, HClamp, and EClamp are registered trademarks or service marks of Semtech Corporation or its affiliates.