4.5 Reducing the Cell Count
The BQ76942 must have the top and bottom cells used for proper operation. Cell count can be reduced by
shorting the unused cell inputs from the next-to-top down. Cell count can be reduced for basic evaluation by
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 8 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 4-1. Reducing Cell Count
Unused Cell
(Numbered from Bottom
Cell 1)
Short cell input
terminals
Input resistor to
remove
Replace capacitor with
0 ohm
IC inputs shorted
Cell 9
CELL9 to CELL8
R5
C5
VC9 to VC8
Cell 8
CELL8 to CELL7
R6
C6
VC8 to VC7
DC Power Supply
+ -
Install cell
simulator shunts
Short
CELL9 to CELL8 and
CELL8 to CELL7
Figure 4-4. Example 8 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 will typically function on the EVM, when
implementing a design the configuration of the data sheet is recommended.
4.6 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 will 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 will be discharged by the constant drain of the cell
simulator resistors.
BQ76942 Circuit Module Use
SLUUC32A – NOVEMBER 2019 – REVISED OCTOBER 2020
BQ76942 Evaluation Module
19
Copyright © 2020 Texas Instruments Incorporated
