3 BQ77207 Circuit Module Use
The BQ77207 circuit module contains the BQ77207 IC and related circuitry to demonstrate the features of
the IC. The board does not control current, the COUT and DOUT signals pass directly to the J2 connector.
J2 has no current limit or ESD protection on the signals, provide any necessary protection during evaluation
external to the EVM. J3 provides a method to separate the supply feed from the input terminal block to measure
current or to apply a voltage for customer test mode. A thermistor provides temperature sensing on the board.
Other components provide support for the IC and connections to the board. Basic operation is described in the
BQ77207 EVM Getting Started Guide
section. For details of the circuit, refer to the
section.
3.1 Cell Simulator
The EVM includes a resistive cell simulator made up of 499-Ω series resistors. The taps of the resistor network
are connected to the cell inputs using shunts on the J4 header. BAT- is always connected to the resistor divider
network. Install a shunt on the top cell location to connect BAT+ to the resistor divider to provide simulated
voltages for the other cell inputs. With the top shunt installed the resistor divider is connected and shunts on the
lower cell positions connect the inputs to the simulated voltages. With the top shunt removed all lower inputs
with installed shunts are pulled to VSS. There is no indication of the cell simulator connection, the user must be
aware of the shunt installation. The 499-Ω resistors provide a load of 2 mA per volt on each cell.
3.2 Reducing the Cell Count
The BQ77207 cell count is reduced by shorting unused cells, normally from the top down but cells between the
top and bottom may be shorted. The inputs are usually shorted at the IC as shown in the data sheet. The bottom
cell must be used for proper operation. Power for the IC comes from the BAT+ terminal so it must be connected
when using the EVM. While not recommended the inputs of the EVM can typically be shorted at the terminal
block for quick evaluation. For the best transient environment and to match the data sheet example, 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 also suggested since it should be apparent if the board is reused for a
different cell count. While different connections are possible,
shows configuration recommendations for
five cells.
Table 3-1. 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 7
BAT+ to CELL6
R2
C2
VC7 to VC6
Cell 6
CELL6 to CELL5
R3
C3
VC6 to VC5
3.3 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. The board is not configured to control current into or out of the cells.
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. The shunts
must be removed or the cells will be 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. The
recommended connection sequence for the EVM when connecting cells is bottom up:
1. Connect BAT–
2. Connect cells bottom up; CELL1, CELL2, CELL3 ...
3. Ensure the cell simulator shunts are removed
BQ77207 Circuit Module Use
6
BQ77207 Evaluation Module
SLUUCI0 – OCTOBER 2021
Copyright © 2021 Texas Instruments Incorporated
