VREG
t
S
Cell
Balance
Interval
Cell
Balance
Min.
Cell
Balance
Window
Higher Cell Voltage
Middle Cell Voltage
Lower Cell Voltage
Bypass is Active
Cell
Balance
Threshold
54
SLUUBD3D – September 2015 – Revised September 2018
Copyright © 2015–2018, Texas Instruments Incorporated
Cell Balancing
Chapter 7
SLUUBD3D – September 2015 – Revised September 2018
Cell Balancing
7.1
Introduction
Cell balancing in bq78350-R1 is accomplished by connecting an external parallel bypass load to each cell
of the associated AFE, and enabling the bypass load depending on each cell's charge state. The bypass
load is typically formed by a P-CH MOSFET and a resistor connected in series across each battery cell.
The filter resistors that connect the cell tabs to VC1~VC15 pins of the associated AFE are required to be
1 k
Ω
.
Using this circuit, the bq78350-R1 balances the cells during charge by enabling the bypass around those
cells above the threshold set in
Cell Balance Threshold
if the maximum difference in cell voltages
exceeds the value programmed in
Cell Balance Min
. During cell balancing, the bq78350-R1 measures
the cell voltages at an interval set in
Cell Balance Interval
.
The cell(s) to be balanced are prioritized by highest cell voltage but the bq78350-R1 will not try to balance
adjacent cells. If adjacent cells need to be balanced, the bq78350-R1 will alternate between the highest
and next-highest adjacent cells until they are balanced.
On the basis of the cell voltages, the bq78350-R1 either selects the appropriate cell to discharge or
adjusts the cell balance threshold up by the value programmed in
Cell Balance Window
when all cells
exceed the cell balance threshold or the highest cell exceeds the cell balance threshold by the cell
balance window.
More in-depth details and data on this cell balancing algorithm can be found in:
Figure 7-1. Cell Balancing
Cell balancing only occurs when charging current is detected, and on non-adjacent cells at the same time.
The cell balance threshold is reset to the value in Cell Balance Threshold at the start of every charge
cycle. The threshold is only adjusted once during any balance interval.
The configuration data flash is stored in
Charge Algorithm: Cell Balancing Config.
