In today's constantly operating world, it is common for many electronic systems to run continuously, regardless of external environment or operating conditions. In other words, any power failure in a system, whether momentary, measured in seconds, or minutes, must be considered during the design phase. The most common way to handle such situations is to use an uninterruptible power supply (UPS) to compensate for these brief downtimes, thereby ensuring the system operates continuously with high reliability. Similarly, many emergency and backup systems are now available to provide backup power for building systems, ensuring that security systems and critical equipment remain operational during power outages, regardless of the underlying cause.
Obvious examples can be easily found in the ubiquitous handheld electronic devices we use in our daily lives. Because reliability is paramount, handheld devices are carefully designed with lightweight power supplies to operate reliably under normal conditions. However, even the most meticulous design cannot prevent human error. For example, a handheld portable scanner might fall from a factory worker's hand, causing its battery to spill out. These events are electronically unpredictable, and without some form of safety net—a short-term power reserve system that stores enough energy to provide backup power until the battery is replaced or the data is stored in permanent memory—critical data stored in volatile memory will be lost.
This example clearly illustrates that electronic systems require alternative forms of power so that electricity is available when the main power supply is interrupted.
In automotive electronic systems, many applications require a continuous power supply, even when the vehicle is parked (engine off), such as remote keyless entry, security, and even personal infotainment systems. These systems typically include navigation, GPS positioning, and eCall functionality. It's easy to understand why these systems must remain on even when the car is not moving, as their GPS must always be online for emergency and safety purposes. This is a necessary requirement so that basic controls can be activated by an external operator if necessary.
Consider eCall systems (such as General Motors' OnStar® system), which are becoming increasingly common in new cars worldwide, with many manufacturers equipping their models with this system. In fact, Europe mandates that all new cars and light trucks sold after March 31, 2018, must be equipped with such a system. It's a fairly simple technology: when a collision occurs and the car's airbags deploy, the eCall system automatically contacts emergency services. It transmits the time, location, vehicle type, and fuel type to the relevant agencies via GPS. Simultaneously, once activated, you can use your car's microphone to speak directly with the call handler. The eCall system can inform you which direction you were traveling when the accident occurred, so that the relevant agencies know which side of the road to approach the accident scene from. All of this allows ambulances, police, and firefighters to arrive at the scene as quickly as possible after an incident, with as much information as possible. Individuals can also activate eCall by pressing a button, so if someone is sick (or injured in a collision but the airbags haven't deployed), they can still easily call for help.
storage media
After recognizing that many systems require backup power, the question arises: what are the options for storage media for such backup power? Traditionally, the options are capacitors and batteries.
Capacitor technology has played a vital role in power transmission and distribution applications for decades. For example, traditional thin-film and oil-based capacitors are designed to perform a variety of functions, including power factor correction and voltage balancing. However, significant research and development over the past decade has led to substantial advancements in capacitor design and capacity. These advanced capacitors, known as supercapacitors, are ideally suited for battery energy storage and backup power systems. Supercapacitors have a limited total energy storage capacity but extremely high energy density. Furthermore, they possess the ability to rapidly release high energy and recharge quickly.
Supercapacitors are not only compact but also robust and reliable, meeting the requirements of backup power systems and handling the aforementioned short-term power loss events. Furthermore, supercapacitors can be easily connected in parallel or series, or even in a series-parallel combination, to provide the necessary voltage and current for the end application. However, supercapacitors are not merely capacitors with very large capacitance values. Compared to standard ceramic, tantalum, or electrolytic capacitors, supercapacitors of the same size and weight offer higher energy density and greater capacitance. While supercapacitors require special maintenance, they surpass and can even replace batteries in data storage applications requiring high-current/short-term backup power.
In addition, supercapacitors can be used in a variety of peak power and portable applications requiring high burst current or short-term backup batteries, such as UPS systems. Compared to batteries, supercapacitors offer higher burst peak power in a smaller size, more charge cycles, and a wider operating temperature range. The lifespan of supercapacitors can be maximized by lowering their upper cutoff voltage and avoiding high temperatures (>50°C).
Batteries, on the other hand, can store a lot of energy, but are limited in terms of power density and delivery.
On the other hand, batteries can store a large amount of energy, but they have limitations in power density and delivery. Chemical reactions occur inside batteries, thus limiting their number of charge cycles. Therefore, batteries are most efficient for delivering a suitable amount of power over a longer period, while rapidly outputting large currents will severely shorten their effective lifespan. Table 1 summarizes the advantages and disadvantages of supercapacitors, ordinary capacitors, and batteries.
Table 1. Comparison of characteristics between supercapacitors, ordinary capacitors, and batteries
New Backup Manager Power Solution
Now that we understand that supercapacitors, batteries, and/or combinations of both can be used as backup power for almost all electronic systems, what solutions are available?
First, any IC solution will require a complete lithium-ion battery backup power management system that can maintain power on the 3.5V to 5V power rails in the event of a mains power failure. Batteries provide significantly more energy than supercapacitors, making them more suitable for applications requiring long-term backup power. Accordingly, any IC solution will need an on-chip bidirectional synchronous converter for efficient charging of the backup battery; it can also provide high-current backup power to downstream loads if the mains power rail is interrupted. Therefore, when an external power supply is available, the device will act as a buck charger for a single-cell lithium-ion or LiFePO4 battery, prioritizing the system load. However, if the input power suddenly drops below the adjustable power failure input (PFI) threshold, the IC will need to act as a boost regulator to provide several amps of current from the backup battery to the system output. Therefore, in the event of a power failure, the IC will need to perform power path control to provide reverse blocking and seamless switching between the input and backup power supplies. Typical applications for this IC include fleet and asset tracking, automotive GPS data loggers, automotive telematics systems, toll collection systems, security systems, communication systems, industrial backup power supplies, and USB-powered devices. Figure 1 shows a schematic diagram of a typical application using Analog Devices' Power by Linear™ LTC4040 lithium-ion battery backup manager.
The LTC4040 also features optional overvoltage protection (OVP), protecting the IC from input voltages exceeding 60 V via an external FET. Its adjustable input current limiting function supports current-limited power supply operation, prioritizing system load current over battery charging current. An external disconnect switch isolates the main input power supply from the system during backup power operation. The LTC4040's 2.5 A battery charger offers eight selectable charging voltages optimized for both lithium-ion and LiFePO4 batteries. The device also features input current monitoring, an input power loss indicator, and a system power loss indicator.
Similar to batteries are supercapacitors. However, supercapacitors are not suitable for prolonged mains power outages, but they are an excellent choice for systems requiring high-power, short-duration backup power. Therefore, any IC supporting such applications typically needs to be able to support 2.9 V to 5.5 V power rails during mains power interruptions. Supercapacitors are known to have a higher power density than batteries, making them ideal for systems requiring short-duration peak power backup. For example, Analog Devices' Power by Linear product line includes the LTC4041, which uses an on-chip bidirectional synchronous converter to provide efficient buck supercapacitor charging and high-current, high-efficiency boost backup power. When an external power source is available, the device acts as a buck battery charger for one or two supercapacitor cells while prioritizing the system load. When the input power drops below the adjustable PFI threshold, the LTC4041 switches to boost mode, providing up to 2.5 A of current from the supercapacitor to the system load. During power failures, the device's PowerPath™ control provides reverse blocking and seamless switching from the input power source to the backup power source. Typical applications for the LTC4041 include power supplies that traverse dying gasp conditions, high-current 3V to 5V UPS systems, power meters, industrial alarms, servers, and solid-state drives. Figure 2 shows a schematic diagram of a typical LTC4041 application.
The LTC4041 features an optional OVP (Over-Power Verification) function, using an external FET to protect the IC from input voltages exceeding 60 V. An internal supercapacitor balancing circuit ensures equal voltage across each supercapacitor and limits the maximum voltage of each supercapacitor to a predetermined value. Its adjustable input current limiting function supports current-limited power supply operation, prioritizing system load current over battery charging current. An external disconnect switch isolates the main input power supply from the system during standby power supply operation. The device also features input current monitoring, an input power failure indicator, and a system power failure indicator.
in conclusion
If a system must be continuously available, and cannot be shut down even in the event of a mains power failure or brief interruption, then providing a backup power supply is always a wise choice. Fortunately, there are many IC options available for designers to consider to meet specific needs, including the LTC4040/LTC4041 backup manager. These ICs easily enable backup power when the mains power is interrupted or lost, regardless of whether the storage medium is a supercapacitor, electrolytic capacitor, or battery. The LTC4040 and/or LTC4041 have the capability to provide backup power to the end system, whether for a brief burst of power or a long-term power supply. Therefore, ensure that your system has a suitable backup power supply available when needed. Got it?
