SLUUCD5 January 2023 BQ27427
The BQ27427 battery fuel gauge measures the cell voltage, temperature, and current to determine battery SOC. The fuel gauge monitors the charging and discharging of the battery by sensing the voltage across an integrated sense resistor (7 mΩ, typical) between the BAT and SRX pins. By integrating the charge passing through the battery, the battery SOC is adjusted during the charging or discharging of the battery.
The total battery capacity is found by comparing states of charge before and after applying the load with the amount of charge passed. When an application load is applied, the impedance of the cell is measured by comparing the OCV obtained from a predefined function for the present SOC with the measured voltage under load. Measurements of OCV and charge integration determine chemical SOC and chemical capacity (Qmax). The initial value for Qmax is defined by Design Capacity and should match the cell manufacturers' data sheet. The fuel gauge acquires and updates the battery-impedance profile during normal battery usage. The impedance profile along with SOC and the Qmax value are used to determine FullChargeCapacity() and StateOfCharge(), specifically for the present load and temperature. FullChargeCapacity() is reported as capacity available from a fully-charged battery under the present load and temperature until Voltage() reaches the Terminate Voltage. NominalAvailableCapacity() and FullAvailableCapacity() are the uncompensated (no or light load) versions of RemainingCapacity() and FullChargeCapacity(), respectively.
The fuel gauge has two flags, [SOC1] and [SOCF], accessed by the Flags() command that warn when the battery SOC has fallen to critical levels. When StateOfCharge() falls below the first capacity threshold, as specified in SOC1 Set Threshold, the [SOC1] (state-of-charge initial) flag is set. The flag is cleared once StateOfCharge() rises above SOC1 Set Threshold. All units are in %.
When StateOfCharge() falls below the second capacity threshold, SOCF Set Threshold, the [SOCF] (state-of-charge final) flag is set, serving as a final discharge warning. If SOCF Set Threshold = –1, the flag is inoperative during discharge. Similarly, when StateOfCharge() rises above SOCF Clear Threshold and the [SOCF] flag has already been set, the [SOCF] flag is cleared. All units are in %.