February 05, 2019
| By: Christine Young
Blogger, Maxim Integrated
Lithium-ion batteries are being asked to do a lot these days. With capacities limited by their small sizes, these batteries power the compact electronics that keep us entertained and informed, give us insights into our vital signs, control the lights and security systems in buildings, and much more. The challenge is, as the electronics become more sophisticated while shrinking in size, their advanced features will require more power. So, how can a designer provide the maximum run-time that consumers expect?
A variety of factors, including temperature, normal cycling, and even keeping batteries at full charge, can cause lithium-ion batteries to degrade. What’s more, fuel-gauging these battery types is more complicated than the process for, say, the sealed lead acid batteries that once commonly powered many portable devices.
Choosing a fuel-gauge IC with the right features can help you extend battery run-time of your small electronic devices. Fuel gauges indicate battery state-of-charge (SOC) and state-of-health, providing end users with an idea of how much time the battery can continue to power the device until it needs to be recharged. Traditionally, the way that fuel gauges have operated has been very dependent on battery type. As a result, time-consuming battery characterization in a lab is a mandatory step in the design process, allowing designers to tailor the gauges to their batteries. Newer fuel-gauge ICs, however, don’t require battery characterization, instead relying on algorithms that deliver highly accurate battery SOC information.
Coulomb-counting has traditionally been used to fuel-gauge lithium-ion batteries. This methodology measures the current going in and out of the battery at all times. While coulomb-counting is great from a short-term accuracy perspective, its effectiveness over time is diminished by offset accumulation drift. As a result, what might appear to be a small error can actually result in a larger over- or underestimation of battery capacity over an extended period of time. To take advantage of the long-term accuracy of coulomb-counters, some fuel-gauge ICs have incorporated various compensation techniques to remove the offset accumulation drift.
Other key characteristics to consider when evaluating fuel-gauge ICs include:
- Quiescent current—the lower the better to prevent battery drain
- The ability to deliver high accuracy while also monitoring voltage, temperature, and current, which supports safe fast-charging methods
- Current sensing capabilities to support coulomb-counting
For a deeper look at fuel-gauge IC characteristics and how they impact battery life, read this new white paper, “Optimizing Run-Time for Devices Powered by Lithium-Ion Batteries.”
A fuel-gauge IC with high accuracy, low quiescent current, and small size can extend run-time of battery-powered devices, like the smart watch pictured here.