Preventing the nasty surprise of an unexpected system shutdown

December 13, 2015 //By Steve Sheard
Preventing the nasty surprise of an unexpected system shutdown
Steve Sheard of ON Semiconductor considers what can be done to prevent an unexpected system shutdown.

The irritation and inconvenience brought about by unexpected system shutdowns could soon be a distant memory as new technology for battery fuel gauging offers the potential for a far more accurate picture of how much charge is truly left.

Mobile devices in their many forms underpin much of modern life. Whether it is using a laptop in a public place, a smartphone while out of the office, or even watching a film on a tablet while travelling, productivity, connectivity and entertainment all depend upon the remaining battery life of the device.

However, when the remaining charge begins to drop low, the percentage shown on the device can offer little more than guesswork and could let the user down at a vital moment. This can be particularly notable for laptop users who might lose vital, unsaved work under the assumption that their device has not yet reached a critical point.

Given the importance to the user of knowing accurately how much energy is remaining in the battery at any time, accurate battery 'fuel-gauging' is highly important. However, existing methods are not only inaccurate, leading to a greater chance of an unexpected shutdown, but can also be subject to errors caused by temperature and will consume additional battery energy at a point when it is most desperately needed.

The traditional approach
Coulomb-counting has for a long time been the most common method used in mobile devices to inform the user of just how much charge remains within a device. This method uses a precision current-sensing resistor to continuously monitor the battery output current. The current is integrated over time, and the result is compared with the known maximum battery charge to calculate the remaining charge available.

The biggest issue with Coulomb counting is its inherent inaccuracy. An inability to detect battery self-discharge events is owed to the self-discharge current not passing through the coulomb counter’s sense resistor. Further disadvantages of coulomb counting

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