SLUUCO9A April 2023 – November 2023 BQ28Z620
The BQ28Z620 can determine the chemical state-of-charge of each cell using the Impedance Track algorithm. The cell balancing algorithm used in the device decreases the differences in imbalanced cells in a fully charged state gradually, which prevents fully charged cells from becoming overcharged, causing excessive degradation. This increases overall pack energy by preventing premature charge termination.
The algorithm determines the amount of charge needed to fully charge each cell. There is a bypass FET in parallel with each cell connected to the gas gauge. The FET is enabled for each cell with a charge greater than the lowest charged cell to reduce charge current through those cells. Each FET is enabled for a precalculated time as calculated by the cell balancing algorithm. When any bypass FET is turned on, then the OperationStatus()[CB] flag is set; otherwise, the [CB] flag is cleared.
The gas gauge balances the cells by balancing the SOC difference. Thus, a field updated QMax (Update Status = 0E) is required prior to any attempt of Cell Balance Time calculation. This ensures the accurate SOC delta is calculated for the cell balancing operation. If QMax update has only occurred once (Update Status = 06), then the gauge will only attempt to calculate the Cell Balance Time if a fully charged state is reached, GaugingStatus()[FC] = 1.
Cell balancing is enabled if Settings:Balancing Configuration [CB] = 1. Cell balancing at rest can be enabled separately by setting Balancing Configuration [CBR] = 1. If Settings:Balancing Configuration [CB] = 0, both cell balancing at charging and at rest are disabled.
Cell balancing at rest can be configured by determining the data flash Min Start Balance Delta, Relax Balance Interval, and Min RSOC for Balancing. For the data flash setting descriptions, see Cell Balancing Config. The gas gauge balances cells by bypassing the energy. It is recommended to perform cell balancing at rest when there is capacity in the battery pack.