Often I hear an analogy made about transient voltage suppressor (TVS) protection components that goes something along the lines of this: “TVS components are a great insurance policy,” or, “think of using electrostatic discharge (ESD) protection diodes as an insurance against ESD damage,” or, “you may not need it, but if you want a little additional insurance, consider adding a TVS array on this circuit.” The idea is that when design engineers invest in using TVS components for circuit protection it is like a “hedge” or added “insurance” against some unforeseen ESD or transient damage that might occur in the future.
While this analogy is well intentioned it is deficient in describing the state of electromagnetic compatibility (EMC) compliance and protecting electronic devices from ESD in today’s world.
When you or I purchase insurance – be it automobile insurance, renter’s, home owner’s, or life insurance – we pay a premium over a time frequency to hedge against losses that could occur for unexpected and unforeseen events. On the underwriting side of the business, the premiums are set by actuaries who have meticulously calculated the risks. Insurance companies can monetize “favorable” risk scenarios in which the premiums more than cover the risk exposure. In practical terms, you and I pay our automobile insurance premiums with the likelihood that we will never total our vehicles in an accident. For most insurance scenarios, the risk event is on the fringes of the risk model. It has a low probability of occurring. When this risk profile is applied over a wide audience, the insurance companies can optimize profits. If the risk rises, the insurance company will raise its premiums to factor in the increased risk. Similarly, in the case where the risk becomes too great, the insurance companies may back off altogether. With this background, let’s look at some ways in which designing in system level ESD circuit protection is different from purchasing insurance.
#1: Conventional Insurance Does Nothing to Address the Threat Event
The first reason that ESD protection is unlike insurance pertains to the nature of the risk itself. This is probably stating the obvious, but insurance companies do nothing to address the underlying risks being protected against. Insurance as a product only becomes useful or effective after a loss. Fire insurance does nothing to prevent the damage from a fire. Likewise, car insurance by itself has zero effect on preventing the damage from an automobile accident. The common insurance policies you and I hold are completely ineffectual at actually dealing with the threat event itself.
ESD components, by contrast, are providing an active safeguard. For a passive component, they are extremely active and exist to prevent the loss in the first place! The main purpose of these devices is to safeguard transceiver ICs. ESD manufacturers like Semtech are providing tangible value by actually preventing damage from the risk event. The insurance company can only provide value that aims to soften the ill effects after a loss, while the TVS component exists to prevent the loss from ever occurring.
#2: In ESD Protection, the Threat is Ubiquitous and Frequent
As mentioned above, when people talk about insurance, they are referring to hedging against downside events that might occur in the future. We also said that insurance companies achieve profit on the underwriting side when the threat events are relatively rare. However, with respect to circuit protection, the ESD event is ubiquitous and frequent. Electronic products will be subjected to ESD transients – with great frequency. That is a well-known fact in the electronics industry; it is fundamental to the physical properties of the world we live in.
Unlike buying insurance, implementing ESD protection is not a hedge against something that could possibly occur. ESD components safeguard against a known and present threat that will occur frequently. In electronic systems, nearly 100 percent of exposed ports are affected. If insurance companies knew that the fire or earthquake or flood were to occur every day and affect 100 percent of the insured population, there would be an absence of underwriting on those threats.
#3: Today’s Integrated Circuits Are Far Too Sensitive
Despite point #2, the analogy that using TVS is similar to insurance might still be tenable if the chips and transceivers being protected were sufficiently robust against system level ESD such that the probability of their failure was small. In this case, design engineers could approach this risk like an added insurance boost to safeguard a circuit against failure in the presence of a rouge ESD storm. To be fair, I think this is primarily where the whole notion of ESD protection as insurance arises in the first place, and it does have some basis in the history of semiconductor IC manufacturing. The integrated circuits and chips of yesteryear may have exhibited a stronger resilience to system level ESD events. These ICs, built on a larger lithography nodes, afforded a greater percentage of the chip’s active area for ESD protection (though this was only protection to the device level standard). In some cases, circuit designers might have met the EMC system compliance requirements by using system design techniques alone.
However, that was then, and life moves and changes extremely rapidly in the IC manufacturing world. As the industry has progressed and as IC geometries have scaled to below 45 nanometer technology, the risk that ESD presents to today’s microelectronics is predictably malicious and catastrophic. In today’s environment, system level ESD protection has moved from the realm of the optional to the realm of the necessary. Practically, if circuit designers choose a “do nothing” approach regarding system level ESD protection on today’s high performance chipsets, their designs will likely fail in the presence of these transients.
System Level ESD Robustness by Process Node © Semtech Corporation
So the next time you hear that system level ESD protection is like a little added insurance hedge, question if that analogy really makes sense. The broad community of design engineers we work with increasingly tell us that the chips they are using need external ESD protection more than ever before. While in the past using TVS devices might have helped an engineer “sleep a little bit better at night,” in today’s world of highly sensitive sub-45 nanometer ICs, designs require TVS solutions in order to prove robust against a lifetime of ESD transient threats. Not using the best protection may actually keep engineers “awake all night,” and in that sense, using system level ESD protection may be the best defense against a self-inflicted case of insomnia.
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