SLUUBD4A April 2016 – November 2022 BQ27220
The BQ27220 device accumulates the measured quantities of charge and discharge and estimates self-discharge of the battery. The BQ27220 device compensates the charge current measurement for temperature and state-of-charge of the battery. The BQ27220 device also adjusts the self-discharge estimation based on temperature. The initial battery state-of-charge estimation on first insertion of the battery pack in the system may display a factor of the true value; the system must go through a full charge and then a full discharge cycle before the correct full-charge capacity (FCC) is estimated.
The main charge counter, RemainingCapacity() (RM), represents the available capacity or energy in the battery at any given time. The BQ27220 device adjusts RM for charge, self-discharge, and other compensation factors. The information in the RM register is accessible through the I2C interface. The FullChargeCapacity() (FCC) register represents the initial or last measured full discharge of the battery. It is used as the battery full-charge reference for relative capacity indication. The BQ27220 device updates FCC after the battery undergoes a qualified discharge from nearly full to a low battery level. FCC is accessible through the I2C interface.
The Discharge Count register (DCR) is an internal register that tracks discharge of the battery. The BQ27220 device uses the DCR to update the FCC register if the battery undergoes a qualified discharge from nearly full to a low battery level. In this way, the BQ27220 device learns the true discharge capacity of the battery under-system use conditions.