SLUUBD4A April 2016 – November 2022 BQ27220
RM represents the remaining capacity in the battery. The BQ27220 device computes RM in units of mAh.
RM counts up during charge to a maximum value of FCC and down during discharge and self-discharge to a minimum of 0. In addition to charge and self-discharge compensation, the BQ27220 device calibrates RM at three low-battery-voltage thresholds, EDV2, EDV1, and EDV0. This provides a voltage-based calibration to the RM counter.
DC is the user-specified battery full capacity. It is calculated from Design Capacity mAh and is represented in units of mAh. It also represents the full-battery reference for the absolute display mode.
FCC is the last measured discharge capacity of the battery. It is represented in units of mAh. On initialization, the BQ27220 device sets FullChargeCapacity() to the data flash value stored in Learned Full Charge Capacity (FCC). During subsequent discharges, the BQ27220 device updates FullChargeCapacity() with the last measured discharge capacity of the battery. The last measured discharge of the battery is based on the value in the DCR after a qualified discharge occurs. Once updated, the BQ27220 device writes the new FullChargeCapacity() value to data flash in mAh to Learned Full Charge Capacity. FullChargeCapacity() represents the full battery reference for the relative display mode and relative state-of-charge calculations.
The DCR counts up during discharge, independent of RM. The DCR counts discharge activity, battery load estimation, and self-discharge increment. The BQ27220 device initializes the DCR at the beginning of a discharge to FCC – RM when RM is within the programmed value in Near Full. The DCR initial value of FCC – RM is reduced by FCC/128 if [SC] = 1 in CEDV Gauging Configuration and is not reduced if [SC] = 0. The DCR stops counting when the battery voltage reaches the EDV2 threshold on discharge.