Power Electronics

Chip Makers Hear the Li-ion's Roar

Demand for power in portable electronics continues to grow as portable devices become more sophisticated. However, rechargeable batteries — the traditional energy source for most handheld portable equipment — generally aren't experiencing dramatic increases in their capacity. This presents a dilemma for portable equipment designers, who want to maintain or extend their battery runtimes, while enhancing the performance or functionality of their products. Micro fuel cells represent a potential long-term solution but are not yet ready for most applications.

For now, the desire for longer runtimes is driving two trends. One is the adoption of Lithium-ion (Li-ion) batteries or the related Lithium-polymer (Li-poly) types. Because Li-ion batteries offer the highest energy density of the mass-produced rechargeable cells, many new equipment designs are migrating to Li-ion cells and away from the older NiCd and NiMH chemistries. This trend is partly fueled by the steady reduction in Li-ion pricing that has resulted from years of mass production and greater competition among suppliers.

Li-ion cells currently represent the fastest growing rechargeable chemistry in terms of sales. According to data gathered by TIAX, 1.5 billion Li-ion cells were sold in 2003. Though many of the Li-ion cells are used in multi-cell applications, such as laptops, about 70% of the cells being sold today appear in applications with just one or two cells.

Cellular phones have long been the major application for 1-cell Li-ion batteries. But in recent years, a variety of popular applications have begun to take power from a single Li-ion cell. Some of the well-known examples include digital still cameras, PDAs, MP3 players, GPS receivers and Bluetooth headsets. Meanwhile, several 2-cell Li-ion applications are emerging. Although portable DVD players are the most prominent example, the list also includes digital video cameras, 3-D gaming devices, medical instruments and LED flashlights.

But while many applications are benefiting from the use of Li-ion, the performance of these batteries may be reaching a plateau as cell makers are only able to achieve incremental increases in cell performance from year to year. This situation is helping to spur a second trend, a surge in the development of sophisticated, Li-ion battery charging ICs aimed particularly at the 1- and 2-cell designs.

In developing these battery charging or battery management ICs, semiconductor vendors aim to extend battery runtime by:

  • Developing more versatile battery chargers that can accept power from multiple sources

  • Improving charger IC performance for faster, more accurate charging

  • Extending fuel gauging for an increase in the effective capacity of the battery.

In the first case, the flexibility of the charger IC in selecting a power source gives the equipment user more opportunities to recharge the battery. For instance, some charge controllers can take power off the USB port or an ac adapter.

In terms of higher performance, battery charger chips can use techniques such as thermal regulation to ensure battery charging is carried out as quickly as operating conditions allow. In addition, more accurate charging circuits will reduce the loss of battery capacity associated with undercharging batteries. Finally, migrating fuel-gauging technology from multicell to 1- and 2-cell applications will increase battery runtimes by reducing the guard bands used by system designers in their power management schemes.

These aren't the only developments occurring in 1- and 2-cell battery management chips. There are also ongoing efforts to reduce system costs and board space requirements by creating more integrated charging circuits in smaller packages; extending input voltage ranges to allow use of unregulated adapters; improving charger efficiency; and honing charger safety features for better system reliability. While charger developments won't effectively produce an order of magnitude improvement in battery runtimes, they will help Li-ion batteries to proliferate. That success should encourage cell makers to develop new chemistries that push battery performance to higher levels.

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