LTC4040 adds brick and tile to your backup power supply design

Background Information

Regardless of the external working conditions, the electronic system must continue to operate. To put it another way, any interference in the system's power supply must be considered during system design, whether the interference is instantaneous or lasts for a few seconds or even minutes. The most common way to deal with this type of environment is to use an uninterruptible power supply (UPS) to prevent transient downtime caused by such interference, thus ensuring that the system operates continuously with high reliability. Similarly, many people today use and emergency backup systems provide backup power to the building systems to ensure that regardless of the time to what causes power outages, security systems and key equipment are able to maintain uninterrupted operation.

 

Another obvious example can be easily found in hand-held electronic devices that are used in our daily lives and are ubiquitous. Because reliability is paramount, handheld devices are carefully designed to use light power supplies for reliable use under normal conditions. However, no matter how carefully designed, it is impossible to prevent such devices from being accidental when people use them. For example, if a worker in the factory loses a bar code scanner, what happens ? Will the battery fall out ? Such an event is unpredictable from the electronic design. If there is no form of security, it is stored in the volatile. The important data in the memory is lost. The so-called security guarantee is a short-term power retention system that stores sufficient energy to provide backup power before replacing the battery or storing data in the permanent storage. These examples clearly show the need to provide a replaceable power supply to prevent the main power interruption from affecting the system's continued operation.

 

Automotive electronics systems, there are many applications that require continuous power supply, even after the car stopped car is no exception, such as remote keyless entry, security of personal information and even entertainment systems, which typically include navigation, GPS positioning and eCall function. It may be difficult to understand why such systems must remain switched on, even when the car is not in the running state, too, but for emergency and security purposes, GPS functionality in such systems must be "always-on." This requirement is necessary to allow basic control functions to be used by external operations when needed.

 

The following is an explanation of the eCall system as an example. eCall   The system is a safety feature that is becoming more and more popular in newer cars, and many manufacturers have already introduced this feature in each series. This is a fairly simple technique: the eCall system automatically contacts the emergency services when the car's airbag deploys after a collision . The system uses the GPS function to send information to the relevant authorities about the time, the location of the vehicle, the type of vehicle, what fuel the vehicle uses, and when the system is activated, the driver can use the microphone in the vehicle to directly talk to the call handler.

 

The eCall system also provides information on the direction of travel of the vehicle at the time of the accident, so that in the event of a collision, the authorities can know which side of the highway to travel from the incident. All of this allows ambulances, police and firefighters to get as much information as possible and to get in as soon as possible after the accident. Individuals can also activate the eCall system with a single button , so if the driver is ill ( or injured in a vehicle collision and the airbag is not deployed ) , it is still very convenient to ask for help.

Storage medium

Recognizing that any given system requires backup power, the problem is: what kind of storage medium can be used to provide this backup power supply ? The traditional choice is capacitors and batteries.

 

I think it is fair to say that capacitor technology has been playing an important role in power transmission applications for decades. For example, conventional thin film and oil immersed capacitor designs provide various functions such as power factor correction and voltage balancing. However, in the past 10 years, a lot of research and development has been carried out, and great progress has been made in capacitor design and function. These new capacitors are called supercapacitors and are ideal for use in battery energy storage and backup power systems. Supercapacitors may be limited in terms of total energy stored, but such capacitors are "energy intensive". In addition, supercapacitors are capable of quickly releasing large amounts of energy and recharging quickly.

 

Supercapacitors are also compact, rugged, and reliable, meeting the requirements of backup systems for the short-lived power loss events already mentioned. Supercapacitors can be conveniently connected in parallel, or stacked in series or even in series and parallel to meet the voltage and current requirements necessary for the final application. However, a supercapacitor is not only a capacitor with a large capacitance. Supercapacitors provide greater energy density and capacitance in a similar form factor and weight compared to standard ceramic, tantalum or electrolytic capacitors. Moreover, while supercapacitors need to be "careful and fed" to some extent, they enhance or even replace batteries in data storage applications that require high current / short duration backup power.

 

In addition, supercapacitors are used in a variety of high peak power and portable applications that require large current bursts such as UPS or instantaneous battery backup. Compared to batteries, supercapacitors are smaller in size, provide bursts with higher peak power, and provide longer charge cycle life over a wider operating temperature range. The life of the supercapacitor can be maximized by reducing the capacitor's Top-off voltage and avoiding high temperatures (>50 °C) .

 

On the other hand, the battery can store a large amount of energy, but the power density and power supply capability are limited. Due to the chemical reaction inside the battery, the battery cycle life is limited. Therefore, the battery is most effective when providing the right amount of power over a long period of time because the current drawn from the battery is very fast and severely limits its useful working life. Table 1 summarizes the advantages and disadvantages of comparison between supercapacitors, capacitors and batteries.

  

  Table 1 : Comparison of supercapacitors with capacitors and batteries

New backup power solution

Now that we have established the notion that supercapacitors, batteries and / or a combination of the two can be used as backup power in almost any electronic system, what are the available IC solutions ? The answer is that Linear Technology has A wide range of ICs designed to meet the needs of these applications .

 

The LTC4040 is a complete lithium-ion battery backup power management system for 3.5V to 5V power rails that must remain active in the event of a mains failure . Batteries provide much more energy than supercapacitors, making them ideal for applications that require a backup power supply to extend working hours. The LTC4040 uses a built-in bidirectional synchronous converter to provide high efficiency battery charging and high current, high efficiency backup power. When external power is available, the device operates as a step-down battery charger for single-cell Li-Ion or   The LiFePO4 battery is also powered preferentially for the system load. When the input supply drops below the adjustable power supply fault input (PFI) threshold, the LTC4040 operates as a boost regulator that can deliver up to 2.5A from the backup battery to the system output . In the event of a power failure, the device's PowerPathTM control provides reverse isolation and seamless switching between input and backup power. Typical applications for the LTC4040 include fleet and asset tracking, automotive GPS data loggers, automotive telematics systems, toll collection systems, security systems, communications systems, industrial backup power supplies, and USB powered devices. Please see the typical application schematic shown in Figure 1 .

 

Figure 1 : 4.5V backup power supply with 4.22V PFI threshold

The LTC4040 also features an optional overvoltage protection (OVP) feature that protects the IC from an input voltage above 60V through an external FET . Its adjustable input current limit allows operation with a current-limited power supply while providing system load current in preference to battery charging current. An external disconnect switch isolates the main input power and system while the backup power supply is operating. The LTC4040 's 2.5A battery charger provides 8 lithium ions and   Optional charging voltage optimized for LiFePO4 batteries. The device also provides input current monitoring, an input power loss indicator, and a system power loss indicator.

 

in conclusion

Some designs require the system to be always available whenever the main power supply fails, so it is always a good idea to use a backup power supply. Fortunately, we have a lot of IC options, just like the LTC4040, whether the storage medium is a supercapacitor, an electrolytic capacitor or a battery, it can be easily used to implement a backup power supply. Obviously, in the case of the eCall system in a car environment, if an accident occurs and the main power is disconnected, then enabling backup power can save lives. Therefore, be sure to provide a good backup power plan for your eCall users.