Under the sleek frames of smart glasses and augmented-reality (AR) devices lies a lot of advanced technology. However, these devices tend to deliver only several hours of active operation. That’s because cameras and sensors must continuously capture the surroundings while processors render digital objects on the high-resolution displays and overlay them on the physical world in real-time. The hefty power demands of real-time spatial computing run up against their lightweight form factors and limited battery capacity.
Since the devices are worn on the face, the battery pack must be tiny, typically tucked into the thin temples of the frames or embedded in the arms, severely limiting their capacity. With the devices resting directly on the skin, the amount of heat they can safely produce is restricted. Consequently, that puts a cap on processor performance and battery discharge rate.
But as smart glasses rapidly move into the mainstream, engineers are getting more creative when it comes to stretching out the limited runtime of these devices.
One trend is to distribute several small batteries throughout the device and connect them in parallel, so that they function as a single higher-capacity pack. This architecture allows designers to use otherwise unused spaces within the frame or enclosure, effectively increasing total battery capacity without enlarging the device.
However, parallel batteries can present some difficulties to designers, specifically when it comes to balancing the voltages between cells, matching their impedances, and preventing unintended cross-charging.
Managing these issues requires accurate, real-time monitoring of voltage, current, and temperatures within the cells. It also demands precise control to speed up charging and increase runtimes without compromising safety and reliability.
At CES, Analog Devices demoed a battery-management IC called the MAX17335 that integrates charging, monitoring, and protection functions in a single chip to simplify battery management for parallel cells
What’s the Difference Between Connecting Batteries in Parallel and Series?
As battery life becomes a more critical factor for consumer devices, companies are increasingly adopting multi-cell designs that physically separate cells to help extend the battery’s effective capacity and lifespan.
In a “series” configuration, separate battery cells are connected end-to-end to increase the voltage without increasing the overall capacity, typically to boost efficiency. In contrast, placing the cells side-by-side in a “parallel” configuration provides more total ampere-hour (Ah) capacity while maintaining the voltage.
Cells placed in series require the same voltage and capacity ratings to maximize performance and safety. Though the cells in a parallel configuration should share the same nominal voltage, their capacities can differ.
Parallel configurations also make it possible to place batteries in unique locations, such as opposite sides of smart glasses or different sides of a foldable phone, giving engineers more flexibility in form factor. For instance, instead of integrating a single 200-mAh battery in one arm of the smart glasses, a smaller 150-mAh cell can take its place before being connected in parallel with a 100-mAh battery located in the tip that loops around the ear, adding up to 250 mAh (Fig. 1). The additional 50 mAh increases the total capacity by 25%.
