“In telecommunications, industrial, and automotive applications where embedded systems rely on continuous power supplies, data loss is a cause for concern. Sudden interruption of power supply can cause data damage while reading and writing the hard disk drive and flash memory. Generally, embedded systems only need 10ms to 50ms to back up volatile data to prevent loss. Nevertheless, unreliable power supplies make it difficult to achieve. Long power cords, drained batteries, unregulated AC adapters, load dumping, and switching operations of high-power motors can all lead to unreliable power supplies.
In telecommunications, industrial, and automotive applications where embedded systems rely on continuous power supplies, data loss is a cause for concern. Sudden interruption of power supply can cause data damage while reading and writing the hard disk drive and flash memory. Generally, embedded systems only need 10ms to 50ms to back up volatile data to prevent loss. Nevertheless, unreliable power supplies make it difficult to achieve. Long power cords, drained batteries, unregulated AC adapters, load dumping, and switching operations of high-power motors can all lead to unreliable power supplies.
If there is no safety net of some kind (that is, a short-term power retention system that can store sufficient power to provide backup power until the battery can be replaced or data can be stored in permanent memory), the power supply is unreliable It will cause the important data stored in the volatile memory to be lost. The most common way to deal with such situations is to use an uninterruptible power supply to cover these short downtimes to ensure the continuous operation of a highly reliable system, or to provide some alternative form of power to prevent the main power supply from being connected (main Backup plan for occasions where power supply is interrupted.
The basic medium of power storage-Capacitor & battery characteristic analysis
Since the embedded system needs a backup power supply, what should be used as the energy storage medium for this power supply? Traditionally, people have always chosen capacitors and batteries.
Capacitor technology has played a role in power transmission and distribution applications for decades. With nearly ten years of research and development, the design and capacity of capacitors have improved significantly. These new types of capacitors are called supercapacitors and are very suitable for battery energy storage and backup power systems. Its energy density is very high, and it has the ability to quickly release high energy and quickly charge. Compared with batteries, supercapacitors provide higher burst peak power with a smaller size, more charging cycles, and a wider operating temperature range. The battery provides much more energy than the super capacitor, so for applications that require backup power to extend the working time, the battery has more advantages.
Table 1 summarizes the advantages and disadvantages of supercapacitors, ordinary capacitors, and batteries.
Therefore, based on different usage scenarios, supercapacitors, batteries or a combination of the two can be used as backup power sources for almost all Electronic systems. The storage medium is selected, how should it be used in the specific system? What are the differences in circuit design? ADI has introduced many ICs specially designed to meet the needs of the application for the standby power system. This article gives the company’s standby power management circuit for batteries, supercapacitors and electrolytic capacitors. The comparative analysis can find the right for related applications. The best backup power solution.
Battery-based power retention solution
LTC4040 is a complete lithium battery backup power management system for 3.5V to 5V power rails. It uses a built-in two-way synchronous converter to provide high-efficiency battery charging and high-current, high-efficiency backup power. When an external power source is available, the device works as a step-down battery charger for single-cell Li-ion or LiFePO4 batteries, while giving priority to the system load. When the input power drops below the adjustable power failure input (PFI) threshold, the LTC4040 works as a step-up regulator that can provide up to 2.5A of current from the backup battery to the system output.
In the event of a power failure, the device’s power path (PowerPath™) control provides reverse isolation and seamless switching between the input power supply and the backup power supply. Typical applications of the LTC4040 include automotive GPS data loggers, in-vehicle multimedia systems, toll systems, security systems, communication systems, industrial backup and USB-powered devices.
4.5V backup power supply with 4.22V PFI threshold
Power retention solution based on super capacitor
LTC3110 is a two-way, programmable input current buck-boost super capacitor charger, the device has active charge balance function, suitable for single or two series super capacitors. Its proprietary low-noise buck-boost topology makes the device equivalent to two separate switching regulators, thereby reducing size and cost, and reducing complexity. LTC3110 can work in both backup and charging modes.
In the backup mode, the device is powered by the energy stored in the super capacitor and maintains a system voltage (VSYS) of 1.71V to 5.25V. In the charging mode, when the main power system is active, the LTC3110 can change the power flow to the opposite direction autonomously or through user commands, and use a stable system voltage to charge the supercapacitor and balance it. In addition, the device also has a charging mode average input current limit, which can be set up to 2A with an accuracy of ±2% to prevent system power overload and minimize capacitor recharging time.
LTC3110 backup solution based on super capacitor (VIN up to 5.25V)
Power retention solution based on electrolytic capacitor
The solution in the figure below is centered on the LTC®3643 bidirectional backup power supply. When the input voltage is present, the LTC3643 charges the storage capacitor CSTORAGE in boost mode (up to 40V). When the input voltage is interrupted, the LTC3643 releases the power of the storage capacitor to the load in the step-down mode, thereby keeping the nominal voltage (VSYS) on the load within the range of 3V to 17V.
The relatively high voltage of the backup storage power rail increases the energy storage of the solution (E = CV2/2) and allows the electrolytic capacitor to be used as a backup energy storage component. Electrolytic capacitors are cheap and widely used, which significantly reduces the cost of backup solutions. Another advantage of LTC3643 is its ability to support 12V systems. In many automotive and industrial applications, 12V is the default standard voltage rail.
LTC3643 high voltage backup solution; VIN up to 17V
As shown in the figure, the LTM®4607 μModule® buck-boost converter acts as a front-end regulator, generating a 12V (up to 5A current) output from a 5V to 36V input (for example, a car battery). As long as the input voltage is maintained within the specified range, the buck-boost regulator can maintain a stable 12V output, so that VSYS can safely survive undervoltages and overvoltages such as cold car engine and load dump. condition. When the input voltage is interrupted or out of the range, the backup power solution based on LTC3643 will maintain the VSYS system voltage to provide short-term data backup.
“Pack lightly” power retention solution
For those projects that require relatively short retention time and are cost-sensitive, the solution in the figure below can shorten the retention time in exchange for the lowest component cost. The program is centered on LTC3649, which is generally used as a step-down converter. But here, the LTC3649 turns to perform a boost conversion operation when the input voltage is disconnected. The LTC3649 maintains the programming voltage on the critical load terminals by discharging its own output capacitor.
LTC3649 “cheaper” backup solution, VIN up to 60V
LTC3649 is a monolithic step-down regulator with integrated power MOSFET. It has high efficiency and low quiescent current, which is very important in many battery-powered systems. It also has high versatility, programmable frequency, a wide VIN range up to 60 V, and an output voltage range as low as ground. It simplifies the design of automotive and industrial products, especially when considering its potential as a holding circuit.
Whenever the system requires that it is always available even if the main power fails, it is always a good idea to have a backup power supply. Regardless of whether the storage medium is a super capacitor, an electrolytic capacitor, or a battery, ADI can provide available IC options for simple backup power. With the further development of capacitor and battery technology, the continued optimization of power IC performance will also add more market and application potential for the backup power supply.