SLUUCP8 June 2024 BQ41Z50
The BQ41Z50 can balance cells either based on state-of-charge or voltage.
The BQ41Z50 can determine the chemical state-of-charge of each cell using the Dynamic Z 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] operation status 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 the 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.
The cell balancing is enabled if Settings:Balancing Configuration [CB] = 1. State-of-charge based cell balancing is enabled if Balancing Configuration [CBV] = 0 and voltage based cell balancing is enabled if Balancing Configuration [CBV] = 1. The State-of-charge based cell balancing at rest can be enabled separately by setting Balancing Configuration [CBR] = 1 when Balancing Configuration [CBV] = 0. Likewise, the voltage based cell balancing at rest can be enabled separately by setting Balancing Configuration [CBV_REST] = 1 when Balancing Configuration [CBV] = 1. If Settings:Balancing Configuration [CB] = 0, all cell balancing operations are disabled.
The 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 description, see Section 17.4.22. 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.