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The bq2018 is a low-cost charge/discharge counter peripheral packaged in an 8-pin TSSOP or SOIC. It works with an intelligent host controller, providing state-of-charge information for rechargeable batteries.

The bq2018 measures the voltage drop across a low-value series sense resistor between the negative terminal of the battery and the battery pack ground contact. By using the accumulated counts in the charge, discharge, and self-discharge registers, an intelligent host controller can determine battery state-of-charge information. To improve accuracy, an offset count register is available. The system host controller is responsible for the register maintenance by resetting the charge in/out and self-discharge registers as needed.

The bq2018 also features 128 bytes of NVRAM registers. The upper 13 bytes of NVRAM contain the capacity monitoring and status information. The RBI input operates from an external power storage source such as a capacitor or a series cell in the battery pack, providing register nonvolatility for periods when the battery is shorted to ground or when the battery charge state is not sufficient to operate the bq2018. During this mode, the register backup current is less than 100nA.

Packaged in an 8-pin TSSOP or SOIC, the bq2018 is small enough to fit in the crevice between two A-size cells or within the width of a prismatic cell.