How Much Protection Is Enough?

When designing an electronic system, the often overlooked and underestimated subject of protection must be considered. In some cases, the designer may be working to meet a certain standard such as IEC 61000-4-2 for electrostatic discharge (ESD) immunity. Equipment which is installed in harsh operating environments, such as remote meters, robotics and telecommunications systems, will require higher levels of lightning protection. These are somewhat obvious requirements. Other protection concerns include short circuits, voltage spikes, dirty power, cable discharge events, and so on. With all these transient threats, a designer may become overwhelmed and ask: how much protection is enough to ensure a reliable system?

TVS Peak Pulse Power: Higher Is Better, Right?

One of the most misunderstood ratings for transient voltage suppressor (TVS) diodes is peak pulse power (P_PP). Many engineers will select surge protection components based primarily on rated peak pulse power and assume that their system will be well protected. After all, it seems logical to assume that a higher power rating means the device can absorb higher transient currents and therefore should be superior. While peak pulse power ratings may be considered in the selection process, the device should not be chosen solely on this parameter. To illustrate why, let us review the definition of TVS peak pulse power.

TVS? It’s Just a Diode, Right? Part Two

Reducing Clamping Voltage

In part one, we learned transient voltage suppressor (TVS) clamping voltage is a key protection parameter. TVS manufacturers are constantly working to lower clamping voltage to keep up with ever shrinking IC geometries and increased sensitivity to overvoltage events. One method to achieve lower clamping is to engineer the device to “snapback” to a lower voltage once triggered. The snapback can be shallow, or deep depending on the intended application. One method of achieving a deep snapback is to design a self-triggering thyristor TVS structure (Figure 4).

TVS? It’s Just a Diode, Right? Part One

I cannot tell you how many times I have heard this in reference to silicon-based Transient Voltage Suppressors (TVS). In all fairness, TVS manufacturers have probably perpetuated this notion. After all, we usually refer to these devices as TVS diodes or electrostatic discharge (ESD) protection diodes. Technically, a diode is a two terminal device that conducts current primarily in one direction. A TVS, or TVS diode, is a two terminal device that is designed to conduct current in the reverse breakdown region. However, calling it “just a diode” implies any TVS diode, or any diode type for that matter, can be effortlessly chosen and relied upon to protect your circuit. Following this assumption will most likely lead to disappointing results.

Ethernet Protection Methodology

Ethernet ports are exposed to external transient events in the form of electrostatic discharge (ESD), electrical fast transient (EFT), lightning, and cable discharge events (CDE). External transient voltage suppressor (TVS) diodes are commonly used to protect the Ethernet PHY chips from these threats. However, we find that a lot of confusion exists on how to best connect the TVS diode for maximum effectiveness. Common wisdom would suggest connecting the diode near the RJ-45 connector, from each signal line to ground. In actuality, the TVS should be connected across the signal pair and located on the PHY side of the connector. In this blog, we will examine why.

Transient Protection of RS-485 Buses in Industrial Applications

Modern industrial networks rely on robust RS-485 communication links for long distance data transmission. These networks operate in harsh electromagnetic environments and must be capable of withstanding electrical overstress (EOS) events without damage. Semtech’s Protection Products Group application engineering team recently had the opportunity to work with Renesas Corporation engineers on a reference design for protecting Renesas’ fault-protected RS-485 transceivers, used in industrial applications.