ANALOG DEVICES
A guide to battery fast charging
While higher battery capacity increases a device’s operating life, keeping charging time down presents additional challenges for designers, says Franco Contadini, staff engineer, field applications; and Alessandro Leonardi, account manager, field sales, both with Analog Devices
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hile higher battery capacity increases a device’s operating life, keeping charging time down presents additional challenges for designers. Fast charging applies to a wide range of devices, including consumer, medical, and industrial applications. This article provides an overview of the challenges associated with implementing battery fast charging capabilities and discusses partitioning of the charger and fuel gauge between the host and battery pack to increase system flexibility, minimise power dissipation, and improve the overall user experience. It also covers monitoring functions that ensure safe charging and discharging.
Introduction
In this era of mobile devices, battery life is one of the primary factors that affects the user experience. While implementing power saving technology inside devices is important, it is only one part of the solution. Given the increasing capabilities - and greater power requirements - of mobile devices, original equipment manufacturers (OEMs) also improve battery life by substantially increasing battery capacity. For example, architectures like 1S2P (1 cell in series with 2 cells in parallel) that use two cells in parallel to increase overall capacity have become more popular. The downside of higher battery capacity is a corresponding increase in charging time. To minimise charging time, improvements in battery technology increase charge current from 2C up to 3C or 6C (that is, xC is x times the current that would pass through the rated ampere-hours of a battery in an hour). For example, a 2000mAh cell could
16 JUNE 2023 | ELECTRONICS TODAY
Figure 1: The battery fuel gauge can be implemented on the host side or in the battery pack
utilise up to 12A of charging current without negatively affecting battery reliability. High current requires special care to ensure safe charging and discharging. When using cells in parallel, developers also need to take care of impedance and initial capacity mismatches. Here in this article we will provide an overview of the challenges associated with implementing battery fast charging capabilities for devices of all types, including those for consumer, medical, and industrial applications.
We’ll also explore how to charge batteries in a 1S2P arrangement with high
performance, as well as how to partition the charger and fuel gauge between the host and battery pack to increase system flexibility, minimise power dissipation, and improve the overall user experience.
Charger basics and why fuel gauge partitioning matters
The key components of a battery charging system are the charger itself and the fuel gauge that reports metrics such as the battery state of charge (SOC), time to empty, and time to full. The fuel gauge can be implemented either on the host side or in the
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