Do you start getting twitchy at the 30% mark? 15%? Or do you squeeze as much use as you can from your smartphone, waiting until it has just 5% battery life before scrambling for a place to plug in? Like the range anxiety experienced by electric vehicle drivers, low-battery anxiety is a legit feeling among mobile device users. There’s actually a name for this affliction: nomophobia, the fear of being separated from your smartphone, perhaps because of a signal issue or a lack of battery power.
And so it goes that much of the care and feeding of our electronic devices centers around battery management. Each time you’ve charged your device, you want to get as much use from it as possible before plugging in again. And, depending on your device, you might even adjust your charging activity to make sure said charge doesn’t exceed or fall below the battery’s limits, so you don’t overcharge the gadget (and cause it to overheat or, worse, catch on fire!) or take it under its discharge threshold (which can permanently reduce capacity).
For engineers designing portable electronic products, battery management encompasses a deeper level of challenges. Devices are getting smaller, which impacts battery capacity. Yet consumers still demand long battery life. The lithium batteries typically inside call for sophisticated battery management technologies that haven’t been entirely accessible until recently. Let’s take a closer look at lithium batteries and the key challenges involved in managing their performance.
Many Flavors of Lithium Batteries
The first commercially available lithium batteries hit the market in the early 1970s. These were non-rechargeable, and their rechargeable counterparts emerged a couple of decades later, with Sony’s 1991 introduction of the first commercial lithium-ion (Li-ion) battery.1 Li-ion batteries provide advantages including high energy densities, low rates of self-discharge, and negligible memory effects. There are also various chemistry types, each ideal for particular applications. Here’s an overview:
- Lithium cobalt oxide (LCO) offers high energy density that’s suitable for mobile devices such as phones, laptops, and digital cameras.
- Lithium manganese oxide (LMO), with its low internal cell resistance, supports fast charging and high-current discharging, and is often used in power tools, medical instruments, and hybrid and electric vehicles.
- Lithium nickel manganese cobalt oxide (NMC) provides high capacity and power, ideal for power tools, e-bikes, and other electric powertrains.
- Lithium iron phosphate (LiFePO4) provides high current rating, a long lifecycle, and good thermal stability and is often used to replace a lead acid starter battery or for energy storage.
- Lithium nickel cobalt aluminum oxide (LiNiCoAIO2) offers high specific energy, good specific power, and a long lifespan and is used in electric vehicle powertrains.
- Lithium titanate (Li4Ti5O12) provides fast charging and a high discharge current and is considered quite safe. It’s typically used in electric powertrains, uninterruptible power supply (UPS), and solar-powered street lighting.2
Extending Battery Life for Portable Devices
For portable devices, having a robust battery management system is an important element in addressing key design challenges, which I’ll discuss here.
Extending Battery Life
While long-lasting battery life is the Holy Grail for portable device makers, it is also one of the most challenging. Despite the capacity limitations, the devices still support more functions—with greater sophistication—with each generation. Take the smartwatch. Early iterations provided features such as television reception (Seiko T001), a calculator, and applications for scheduling and memos (Seiko RC-20 Wrist Computer). The TV watch could run for several hours on AA batteries. Today’s smartwatches are sleeker than ever and serve as health and fitness monitors, messengers, music players, and more. The best on the market have batteries that last for several days per charge. To squeeze the most use out of Li-ion batteries, considerations such as quiescent current of the battery management ICs play an integral role. For example, fuel-gauge ICs that consume just microamperes of quiescent current do their part to extend battery life.
Maintaining Device Reliability and Safety
Better device reliability and safety calls for careful management of power dissipation, the ability to provide users with accurate battery SOC data, and reliable protection of the battery cells. The thermal issues give rise to an interesting conundrum. Notes a U.K. battery consultancy on its battery and energy technologies website, “It is ironic that as battery engineers strive to cram more and more energy into ever smaller volumes, the applications engineer has increasing difficulty to get it out again.”3 Battery charge controller technology can help by providing battery qualification to detect various conditions (such as short-circuit, open, or under cutoff), by sensing the battery temperature and by providing timeouts for all states of the charger. For battery SOC data, fuel-gauge ICs can predict how much longer a battery can power a device until it needs to be recharged. And protecting battery cells calls for ICs such as reliable battery monitors and protectors that deliver high-accuracy measurements for precise voltage determination and that monitor individual cell voltages while also preventing over/undervoltage conditions, respectively.
Shrinking Solution Sizes and Cost
Portable devices are getting increasingly compact, which means that the batteries inside must power an array of rich functions without taking up too much space. That’s why the coin-cell form factor is so prevalent inside these gadgets. As a result, the more functions integrated into battery management ICs, the better this is for meeting space constraint demands as well as bill of materials (BOM) costs.
Protecting Against Battery Cloning and Counterfeiting
Battery pack cloning is detrimental to revenue streams as well as brand reputation. In a worst-case scenario, counterfeit batteries can cause personal harm or property damage. The fake versions often lack the safety components or protective devices designed into the authentic versions. Authentication ensures that a product is genuine and provides protection against counterfeiting. Today’s fuel-gauge ICs implement a method that is secured by a cryptographic SHA-256 hash algorithm, providing a cost-effective and relatively easy way to safeguard the battery.
Designing Charging Circuits for USB-C
More mobile devices are being designed with USB-C, the small and versatile connector for bi-directional data transmission and power delivery. Developing the charging circuits for USB-C, however, is a unique skillset, especially compared to the effort involved in designing for legacy USB variants. USB-C buck charger technology can simplify the process, eliminating the need for a separate port controller IC, reducing host software development, and reducing BOM costs.
Battery Management ICs to Reduce Cost, Save Space, Extend Battery Life
Battery management technology has traditionally not been particularly accessible to many engineers. Core capabilities in a battery management system include charging and fuel gauging, also critical for any mobile or internet of things (IoT) application. However, driving a high level of performance from the battery requires a high-quality battery model to drive the fuel-gauging algorithm. Extracting the right model for a particular battery involves complex, expensive work that, typically, only a few large manufacturers can manage. Fortunately, modern fuel-gauge ICs designed with sophisticated algorithms have opened up access to accurate battery models. Maxim, for example, provides fuel gauges with the ModelGauge m5 EZ algorithm, which provides highly accurate battery SOC data without requiring battery characterization. Designers can use a simple configuration wizard in the evaluation kit software to generate battery models themselves. These fuel-gauge ICs are part of Maxim’s larger battery management portfolio, which includes battery chargers, monitors, protectors, selectors, and identification and authentication solutions. Check out the development boards, application notes, videos, and more on our battery management page for a head start on your next battery-powered portable design.