COVER STORY
How to Choose the Right Protection for Your Circuit
Diarmúid Carey, applications engineer at Analog Devices (ADI) explores what active circuit protection solutions can replace TVS diodes and fuses and go with a surge stopper
anufacturers in all industries constantly push cutting-edge performance, while trying to balance such innovation against tried-and-true robust solutions. Designers are faced with the difficult task of balancing design complexity, reliability, and cost. One subsystem in particular, electronics protection, rebuffs moves to innovate due to its nature. These systems protect sensitive and expensive downstream electronic devices (FPGAs, ASICs, and microprocessors), requiring a zero failure rate.
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Many traditional and historically proven protection methodologies - such as diodes, fuses, and TVS devices - retain their go-to status, but these are often inefficient, bulky, and require maintenance. To address these deficiencies, active, intelligent protection ICs have proven they can match the protection requirements of traditional methods but in many ways are more robust. Because of the wide range of devices available, the most difficult problem for the designer is simply choosing appropriate solutions.
To help designers narrow their choices, this article compares traditional protection methods to the ADI protection portfolio, presenting the features of these products and suggested applications.
The increase in the amount of electronics used in all industries, and the expansion of functions handled by expensive FPGAs and processors, has elevated the need to protect these devices from the harsh environments in which they operate. Layer on top of this a need for small form factors, high reliability, and fast response to overvoltage and overcurrent surge events. This article discusses the challenges faced in many applications and why protection is needed. Traditional protection methodologies are discussed and compared to newer, alternative solutions, which offer better accuracy, reliability, and design flexibility.
14 MAY 2021 | ELECTRONICS TODAY Figure 1:
Overview of some of the tougher ISO 16750-2 tests
Why consider voltage and current protection devices?
Automotive, industrial, communications, and aviation electronic systems must operate through a range of power supply surges, such as those shown in Figure 1. In each of these markets, transient events are defined in a number of industry specifications. For example, automotive transients are covered by the ISO 7637-2 and ISO 16750-2 specifications, which outline both the details of expected transients and test procedures to ensure these are consistently validated. The types of surge events and their energy content can vary depending on the area in which the electronic device is used; circuitry can be exposed to overvoltage, overcurrent, reverse voltage, and reverse current conditions. Ultimately, many electronic circuits would not survive, let alone operate, if directly facing the transient conditions shown in Figure 1, so the designer must consider all of the input events and implement protection mechanisms that protect the circuit from these voltage and current surges.
Design challenges
There are many different causes of transient voltage and current surges in electronic systems, but some electronic environments are more prone to transient events than others. Applications in automotive, industrial, and communications-based environments notoriously experience potentially harmful events, wreaking havoc on downstream electronic devices, but surge events are not limited to these environments. Other possible candidates for surge protection circuitry include any application that requires high voltage or high current supplies, or those that feature supply connections that are hot plugged, or systems that have motors or that may be exposed to potential lightning induced transients. High voltage events can occur over a wide range of time bases, from microseconds to hundreds of milliseconds, so a flexible and reliable protection mechanism is imperative to ensure the longevity of costly downstream electronic devices.
For instance, automotive load dump can occur when the alternator (charging the battery) is momentarily disconnected from
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