Managing device Li-ion battery power with MCU-controlled pulse width modulation

Tag: High Rate Discharge Battery

Portable CE devices are achieving improved performance and increasing functionality, thus requiring maximized runtimes out of each battery charge cycle. The addition of a growing number of features is also creating a demand for higher capacity batteries.

Li-ion batteries are ideal for a variety of portable-electronic applications because of their high cell voltage, high density, long shelf life and maintenance free nature. In addition to the popular 4.2V charge voltage regulation 1C maximum charge/ discharge rate, new technology in Li-ion batteries may require different charge voltages and deliver higher C-rates.

This article discusses some new trends in Li-ion batteries and shows how portable product designers can design a flexible Li-ion battery charge management system using an MCU-controlled pulse-width modulation (PWM) module or a stand-alone integrated battery charge-management controller-based solution.

Challenges in portable power design with Li-ion batteries include safety concerns, battery chemistries, available space and required features. For rechargeable Li-ion batteries, one must also consider the charge/discharge rate, life cycles, maintenance and charge algorithm. To maximize the capacity after each charge cycle, charge voltage-regulation accuracy is important.

Figure 1 above shows that an undercharged battery voltage of 0.6 percent can result in a 5 percent capacity loss for Li-ion batteries. However, overcharging a Li-ion battery is not recommended and can be dangerous.

Battery manufacturers recommend undercharging a 4.2V regulated Li-ion battery at 4.1V to extend its life for backup energy applications.

Production challenges are often associated with time-to-market, total system cost and reliability. Time-to-market is significant for consumer products that have a short product life cycle.

Fast response to market changes is important in today's fast-paced world. The short time permitted from concept to final product also minimizes the resources used and reduces cost by saving design time.

Additional components may result in extra failure factor points and, in some cases, increase in costs. Although it is not true in all applications, saving space by creating highly-integrated solutions may cost more than a system built from discrete components. Thus, reliability should always come first when designing a product, if performance is the trade-off.