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Choose the right battery fuel-gauge for smartphones, tablets

23 Jul 2012  | Ming Yu, David Maxwell

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An advanced fuel-gauge independently provides the gauging function to reduce the system overhead and power consumption, and actively tracks the battery impedance change to accurately report the battery status. With smartphones and tablets running ever more applications and serving more functions, accurate gauging has become more critical than ever.

Sidebar: Pros and cons of embedded batteries
A debate continues over removable versus embedded battery packs. Let's look at some considerations, both good and bad, that are driving the trend toward embedded batteries.

The benefits are considerable and include:

 • Product designers can design a more aesthetic form without concerns about battery position, compartment, and cover. Smaller form factors can be achieved by avoiding the standard connectors and thick battery case required for removable batteries.
 • It's less likely the user will toss out an expired embedded battery as it could be replaced at a service center, or the entire device could be recycled. Additionally, during the life of the product, fewer batteries will be produced overall, using fewer resources.
 • The embedded fuel-gauge is always in-sync with an embedded battery. Swapping batteries can be a challenge for some gauging solutions when profiles or ages are different. It can require cycling for some system-side gauges to "learn" the newly inserted battery and for state-of-charge (SOC) and state-of-health (SOH) predictions to become fully accurate. This is avoided by either embedding the gauge in a removable battery and/or embedding the battery in the system with the gauge.
 • Embedding the battery increases overall safety since cheap aftermarket batteries are less likely to be inserted. These cheap aftermarket batteries often skimp on quality and protection features, making them more likely to catch fire and "vent with flame." Many device makers are now turning to higher voltage (4.3V or 4.35V max) batteries. At least one case of fire was reported when a user introduced a low-voltage (4.2V max) aftermarket battery into a system designed to charge to 4.35V. Unfortunately, the equipment maker usually takes the blame and gets the tarnished image. Embedding authentication into a removable battery pack is another solution to this problem.
There are also several drawbacks for embedded batteries:

 • First, it requires a robust system design with fail-safes to prevent or recover from system lockups. Users are practiced at rebooting frozen phones by re-inserting the battery, but this is not possible with an embedded battery.
 • Users want to go all day without the need to recharge. Carrying a spare battery is no longer an option with embedded batteries. Shrinking the internal battery to meet marketable size specs means accurate gauging is a must in order to utilize the entire available capacity.
 • Users who want extra run-time must use an external battery pack, making the phone bulky.
 • If the battery wears out, replacing an embedded battery usually costs more and is difficult to replace, versus simply buying and swapping out an accessible batteries.
Despite the drawbacks of embedding batteries, the general trend that started with tablets is moving to smartphones, and users are becoming accustomed to the idea of non-removable batteries in their consumer electronics.

References
Fundaro, Peter. "Impedance Track Based Fuel Gauging," White Paper, Texas Instruments, September 2007

About the authors
Ming Yu is Asia Business Development Manager for Texas Instruments. Ming received his MS Physics and MSEE from Iowa State University, Ames, Iowa, and his BSEE from the University of Elec. Science and Tech of China.

David A. Maxwell is an application engineer for TI's Battery Management group. David received his BSEE from Texas A&M University, College Station and his MSEE from the University of Texas at Arlington, both in Texas.

To download the PDF version of this article, click here.


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