7.1 Introduction
The BQ28Z610-R2 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
. 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.
7.2 Cell Balancing Setup
The BQ28Z610-R2 is required to be in RELAX mode before it can check if the cells are unbalanced and how
much balancing is required. The BQ28Z610-R2 enters RELAX mode when:
Current()
<
Quit Current
for at least
Dsg Relax Time
when coming from DISCHARGE mode for
Chg Relax
Time
when coming for CHARGE mode.
Chapter 7
Cell Balancing
Cell Balancing
SLUUCO0 – APRIL 2022
BQ28Z610-R2
43
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