SLVU957A September   2019  – November 2021 BQ76922

 

  1.   Trademarks
  2. 1Features
    1. 1.1 Kit Contents
    2. 1.2 Ordering Information
    3. 1.3 BQ76922EVM Circuit Module Performance Specification Summary
    4. 1.4 Required Equipment
  3. 2BQ76922EVM Quick Start Guide
    1. 2.1 Before You Begin
    2. 2.2 Quick Start
  4. 3Interface Adapter
  5. 4Battery Management Studio Software
    1. 4.1 System Requirements
    2. 4.2 Installing BQStudio
    3. 4.3 BQ76922 bqz File Installation
    4. 4.4 BQStudio Operation and Registers View
    5. 4.5 Commands
    6. 4.6 Data Memory
      1. 4.6.1 Entering, Saving, and Loading Configuration
      2. 4.6.2 OTP Programming
    7. 4.7 Calibration
    8. 4.8 Command Sequences
  6. 5BQ76922EVM Circuit Module Use
    1. 5.1 Cell Simulator
    2. 5.2 Evaluating with Load Current
    3. 5.3 Evaluating Charge and Discharge Currents
    4. 5.4 Evaluating with Simulated Current
    5. 5.5 Reducing the Cell Count
    6. 5.6 Connecting Cells
    7. 5.7 Connecting to a Host
    8. 5.8 Hardware Configuration
      1. 5.8.1 Configuration Jumpers
      2. 5.8.2 Unused Components
    9. 5.9 Configuration Register Programming
  7. 6BQ76922EVM Circuit Module Physical Construction
    1. 6.1 Board Layout
    2. 6.2 Bill of Materials
    3. 6.3 REACH Compliance
    4. 6.4 Schematic
  8. 7Related Documents from Texas Instruments
  9. 8Revision History

5.5 Reducing the Cell Count

The BQ76922 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 Figure 5-4 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. Table 5-1 shows configuration recommendations for reduced cell count.

Table 5-1 Reducing Cell Count
Unused Cell
(Numbered from Bottom Cell 1)		Short Cell Input TerminalsInput Resistor To RemoveReplace Capacitor With 0 ΩIC Inputs Shorted
Cell 4CELL4 to CELL3R4C5VC4 to VC3
Cell 3CELL3 to CELL2R5C7VC3 to VC2
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.