Feature: Batteries
mode battery chargers. They are classic switch-mode power supply (SMPS) devices with special features enabling battery charging. They can charge with constant voltage or constant current, sometimes even both and they provide special features to make charging safe. This can be a timer to detect if an attached battery is defective or it may include a temperature sensor to limit battery temperature during charging to avoid thermal runaway in different circumstances. A feature that is becoming more and more popular is the safety check between a battery pack and a battery charger, which monitors whether an authorised battery is attached to the system. Figure 4 shows a standalone SMPS battery charger solution.
It is the MAX77985 and it implements the step-down SMPS battery charger as well as a power path switch. The power path switch is essential to most applications. It can disconnect the input voltage rail from the battery, once the battery is fully charged, to prevent the battery power from dissipating through any circuitry that might be attached to the input power line. Also, the solution has a digital I2C interface to change certain settings to the charger IC as well as for telemetry purposes. To make a battery charger as flexible as possible, digital interfaces enable settings for different battery types and battery sizes. Among many different features, one item is especially
noteworthy. The integrated power switches in the MAX77985 can not only be used in step-down mode for charging the battery but the switches can also be used to boost the battery voltage to a higher system voltage. In a way, this specific battery charger combines the system power converter with a pure battery charger. Battery-powered equipment requires many different
electrical functions. Some products offer only basic functionality, while other products are highly integrated with most functions available in an integrated circuit. Such products are called system power management integrated circuits (PMICs) and are especially popular in battery- powered applications. This has multiple reasons. One is that many battery-operated systems are rather small and as such require a compact system solution. The second reason is that each separate IC has some quiescent current; some power that is always consumed when the IC is turned on or off. This will eventually drain the battery. Combining many different integrated circuits into one PMIC device reduces the system’s quiescent current in most cases. The availability of high-capacity lithium-ion batteries has
especially transformed the landscape for battery-powered systems within the past 20 years. Many integrated circuits are available for charging and discharging those batteries efficiently. Today a lot of research is being performed for future battery construction to increase the capacitance per weight and volume and to increase the possible charging speed while maintaining the safety of operation. There is no end in sight to innovations in battery charging and discharging integrated circuits to keep up with these battery developments. Analog Devices:
www.analog.com
Figure 2. The power conversion efficiency of an ADP2370 buck regulator with low load power saving mode activated and with fixed 600kHz switching frequency at all loads
Figure 3. An example of a four-switch buck-boost power converter such as an LT3154 buck-boost DC-to-DC converter
Figure 4. A MAX77985 standalone battery charger simplified circuit diagram
www.electronicsworld.co.uk April 2025 35
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