shorting unused cells at the input terminal block. Follow the recommendations in the datasheet for which cells
to short. This works for both operation with the cell simulator and cells, but can have some side effects in
transient tests because it parallels the shorted resistors to the cell IC where the capacitor provides a signal path
to the used input. See
for an example of simple reduced cell configuration for 3 cells. For the best
evaluation with reduced cells in a transient environment, short the VCx pins at the capacitor and remove the
unused input resistor. When using the cell simulator, shorting the unused cell at the terminal block is still required
to eliminate the simulated cell voltage. Shorting the cell inputs at the terminal block screw terminals is suggested
since it should be apparent if the board is re-used for a different cell count.
shows configuration
recommendations for reduced cell count.
Table 5-1. Reducing Cell Count
Unused Cell
(Numbered from Bottom
Cell 1)
Short Cell Input
Terminals
Input Resistor To
Remove
Replace Capacitor
With 0 Ω
IC Inputs Shorted
Cell 4
CELL4 to CELL3
R4
C5
VC4 to VC3
Cell 3
CELL3 to CELL2
R5
C7
VC3 to VC2
DC Power Supply
+ -
Install cell
simulator shunts
Short
CELL4 to CELL3
and
CELL3 to CELL2
Figure 5-4. Example 3-Cell Simple Evaluation Configuration
When reducing the cell count with the top cell used, the resulting configuration of the BQ7718 secondary
protector does not match its data sheet configuration. While the circuit typicaly function on the EVM, when
implementing a design the configuration of the data sheet is recommended.
After changing the physical connection the Vcell Mode must be changed in Data Memory Settings for proper
operation. The default setting of 0x0000 selects all cells and will be the same as 0x001F. For 3 cells as shown
above set the Vcell Mode to 0x0013.
5.6 Connecting Cells
The EVM is constructed with a single connection to the top and bottom of the cell stack. Cell voltage for these
cells is sensed on the board.
While the EVM has a place to mount an activated fuse, the pattern is shorted to allow easy evaluation without
the concern of activating the fuse. When connecting cells use a fuse in the current path and any other signal
path appropriate for your application.
The cell simulator provides resistors between the cell inputs. When the cell simulator shunts are installed, these
resistors load the cells, and divide the voltage to any unconnected inputs as cells are connected. If desired,
the cell simulator shunts can be installed during cell connection and removed after cell connection. The shunts
must be removed after connection of cells, or the cells are discharged by the constant drain of the cell simulator
resistors.
BAT- is the reference voltage for the IC and should be connected first. After BAT- cells may be connected in any
order. Cell connection from the bottom up minimizes the voltage step size applied to the board. Recommended
connection sequence for the EVM when connecting cells is bottom up:
1. Connect BAT–
2. Connect cells bottom up; CELL1, CELL2, CELL3 ...
BQ76922EVM Circuit Module Use
16
BQ76922EVM Evaluation Module
SLVU957A – SEPTEMBER 2019 – REVISED NOVEMBER 2021
Copyright © 2021 Texas Instruments Incorporated