FEATURE COVER STORY GOT BACKUP? MAINTAIN POWER CONTINUITY
Tony Armstrong and Steve Knoth from Analog Devices, Inc. present the latest lithium ion battery backup manager, offering an additional, reliable power supply for always-on devices
I
n today’s world of constant connectivity, it is commonplace for
many electronic systems to be always operational - regardless of their external environment or operating conditions. Said another way, any glitch in a system’s power supply, whether momentary, seconds, or even minutes, must be taken into account during its design process. The most common way of dealing with such circumstances is to use uninterruptible power supplies (UPSs) to cover these brief downtimes, thus ensuring high reliability, continuous operation of the system. Similarly, many of today’s emergency and standby systems are used to provide backup power for building systems to provide assurance that safety systems and critical equipment can maintain their operation during a power outage - whatever the root cause. Obvious examples can be readily found
in the ubiquitous handheld electronic devices used in our everyday lives. Because dependability is paramount, handhelds are carefully engineered with lightweight power sources for reliable use under normal conditions. But no amount of careful engineering can prevent the mistreatment they will undergo at the hands of people. For example, what happens when a factory worker drops a handheld portable scanning device, causing its battery to detach? Such events are electronically unpredictable and important data stored in volatile memory would be lost without some form of safety net - namely some sort of short-term power holdup system that stores sufficient energy to supply standby power until the battery can be replaced or the data can be stored in permanent memory. This example clearly demonstrates the
need for an alternative form of power source to be available in electronic systems, just in case there is an interruption in their primary power source. In automotive electronic systems there are many applications that require continuous power even when a car is
12 OCTOBER 2018 | ELECTRONICS
parked (engine not running), such as remote keyless entry, security, and even personal infotainment systems. These systems usually incorporate navigation, GPS location, and eCall functionality. It is easy to understand why these systems have to remain on even when the car is not moving, since the GPS aspect of these systems must be always-on for emergency and security purposes. This is a necessary requirement so that rudimentary control can be activated by an external operator when necessitated. Consider an eCall system (take General
Motor’s OnStar system in the USA as a prime example), which is becoming more pervasive in newer automobiles across the globe, with many manufacturers having already rolled them out across their ranges. In fact, these systems became mandatory in Europe in all new cars and light trucks sold after March 31st, 2018. It’s a pretty simple bit of technology: in the event of a collision in which a car’s airbags are deployed, the eCall system automatically contacts emergency services. It uses GPS to relay the time, your location, what type of car you’re in, and what kind of fuel it uses to the authorities, while a microphone in
Figure 1:
Analog Devices’ Power by Linear LTC4040 lithium ion battery backup manager
the car allows you to speak directly to call handlers when the system is activated. These eCall systems can share what direction you were travelling in when the incident occurred, allowing authorities to know which side of the motorway they need to head to in the event of a collision. Having acknowledged the need for backup power in a wide array of systems, the question then arises: what are the options for storage mediums for this type of backup power? Traditionally, the choices have been capacitors and batteries.
It is fair to say that capacitor
technology has played a major role in power transmission and delivery applications for multiple decades. For example, traditional thin film and oil- based capacitor designs performed a variety of functions, such as power factor correction and voltage balancing. However, in the past decade there was substantial research and development that has led to significant advances in capacitor design and capabilities. These advanced capacitors have been called supercapacitors (also known as ultracapacitors) and they are ideal for use in battery energy storage and backup power systems. Supercapacitors may be limited in terms of their total energy storage; nevertheless, they are energy dense. Furthermore, they possess the ability to discharge high levels of energy quickly and recharge rapidly. Supercapacitors are not only compact, but they are robust and reliable, and they can support the requirements of a backup system for short-term power- loss events such as the ones already outlined herein. Furthermore, they can easily be paralleled or stacked in series or even a combination of both to deliver the necessary voltage and current demand by the end application. Nevertheless, a supercapacitor is more than just a capacitor with a very high level of capacitance. Compared to standard ceramic, tantalum, or electrolytic capacitors, supercapacitors offer higher energy density and higher capacitance in
/ ELECTRONICS
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