SLUSAT1B March 2013 – March 2020 BQ27510-G3
The fuel gauge measures the cell voltage, temperature, and current to determine battery SOC. The fuel gauge monitors charge and discharge activity by sensing the voltage across a small-value (5 mΩ to 20 mΩ typical) resistor between the SRP and SRN pins and in series with the cell. By integrating charge passing through the battery, the battery’s SOC is adjusted during battery charge or discharge.
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 present SOC with the measured voltage under load. Measurements of OCV and charge integration determine chemical state of charge and chemical capacity (Qmax). The initial Qmax values are taken from a cell manufacturers' data sheet multiplied by the number of parallel cells. It is also used for the value in Design Capacity. The fuel gauge acquires and updates the battery impedance profile during normal battery usage. It uses this profile, along with SOC and the Qmax value, 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 accessed by the Flags() function that warns when the battery’s SOC has fallen to critical levels. When StateOfCharge() falls below the first capacity threshold, specified in SOC1 Set Threshold, the [SOC1] (State of Charge Initial) flag is set. The flag is cleared once StateOfCharge() rises above SOC1 Clear Threshold. The fuel gauge’s GPOUT pin puts out 3 pulses 10ms wide and in 10ms intervals whenever the SOC1 flag is set. This flag is enabled when RMC_IND bit in Operation Configuration B is set. This behavior also applies to the [SOCF] (State of Charge Final) flag.
When Voltage() falls below the system shut down threshold voltage, SysDown Set Volt Threshold, the [SYSDOWN] flag is set, serving as a final warning to shut down the system. The GPOUT also signals. When Voltage() rises above SysDown Clear Voltage and the [SYSDOWN] flag has already been set, the [SYSDOWN] flag is cleared. The GPOUT also signals such change. All units are in mV. Additional details are found in the BQ27510-G3 Technical Reference Manual, BQ27510-G3 System-Side Impedance Track™ Fuel Gauge With Integrated LDO, SLUUA97.