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Battery fuel measurement using delta-sigma ADC devices

Posted: 18 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:battery fuel? ADC? battery management?

The battery fuel status indicator is a common feature of the battery-supported handheld devices. The battery fuel measurement is achieved by measuring the discharging and charging currents in real time. The discharging current is the current coming out from the battery and the charging current is the current flowing into the battery. The fuel used (mAH) and the fuel remaining (mAH) are calculated by tracking the discharging and charging currents over time. The fuel used is the total discharged current over time and the remaining fuel is simply the subtraction of the fuel used from the fully charged fuel.

The behavior of the battery fuel is greatly affected by temperature and the battery aging. A true battery management needs to consider these effects by measuring current, voltage, and temperatures with a function of time.

The battery voltage and current measurement is achieved using an ADC. The accuracy of the fuel management relies on the accuracy of the ADC performance. Measuring the battery voltage is straightforward. However, the current measurement is achieved indirectly using a current sensor. The current sensor has a resistive component. When the current flows through the current sensor, there is a voltage drop across the sensor element. The current is calculated by measuring the voltage drop on the known resistive value of the sensor. The system designers must be aware that the voltage drop across the current sensor is waste that brings down the battery voltage budget for the system. Therefore, it is best to use a current sensor that has the smallest resistance value, as possible.

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