SLUSAM9E July   2011  – April 2020 BQ76925

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics: Supply Current
    6. 7.6  Internal Power Control (Startup and Shutdown)
    7. 7.7  3.3-V Voltage Regulator
    8. 7.8  Voltage Reference
    9. 7.9  Cell Voltage Amplifier
    10. 7.10 Current Sense Amplifier
    11. 7.11 Overcurrent Comparator
    12. 7.12 Internal Temperature Measurement
    13. 7.13 Cell Balancing and Open Cell Detection
    14. 7.14 I2C Compatible Interface
    15. 7.15 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Internal LDO Voltage Regulator
      2. 8.3.2 ADC Interface
        1. 8.3.2.1 Reference Voltage
          1. 8.3.2.1.1 Host ADC Calibration
        2. 8.3.2.2 Cell Voltage Monitoring
          1. 8.3.2.2.1 Cell Amplifier Headroom Under Extreme Cell Imbalance
          2. 8.3.2.2.2 Cell Amplifier Headroom Under BAT Voltage Drop
        3. 8.3.2.3 Current Monitoring
        4. 8.3.2.4 Overcurrent Monitoring
        5. 8.3.2.5 Temperature Monitoring
          1. 8.3.2.5.1 Internal Temperature Monitoring
      3. 8.3.3 Cell Balancing and Open Cell Detection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power Modes
        1. 8.4.1.1 POWER ON RESET (POR)
        2. 8.4.1.2 STANDBY
        3. 8.4.1.3 SLEEP
    5. 8.5 Programming
      1. 8.5.1 Host Interface
        1. 8.5.1.1 I2C Addressing
        2. 8.5.1.2 Bus Write Command to BQ76925
        3. 8.5.1.3 Bus Read Command from BQ76925 Device
    6. 8.6 Register Maps
      1. 8.6.1 Register Descriptions
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Recommended System Implementation
        1. 9.1.1.1 Voltage, Current, and Temperature Outputs
        2. 9.1.1.2 Power Management
        3. 9.1.1.3 Low Dropout (LDO) Regulator
        4. 9.1.1.4 Input Filters
        5. 9.1.1.5 Output Filters
      2. 9.1.2 Cell Balancing
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.3.2.2.2 Cell Amplifier Headroom Under BAT Voltage Drop

Voltage differences between BAT and the top cell potential come from two sources as shown in Figure 11: V3P3 regulator current that flows through the RBAT filter resistor, and the voltage drop in the series diode DBAT of the hold-up circuit. These effects cause BAT to be less than the top-cell voltage measured by the cell amplifier.

BQ76925 source_vdrop_lusam9.gifFigure 11. Sources of Voltage Drop Affecting the BAT Pin

The top-cell amplifier (VC6 – VC5) is designed to measure an input voltage down to 1.4 V with a difference between the BAT and VC6 pin up to 1.2 V (that is, BAT can be 1.2 V lower than VC6). However, in applications with fewer than 6 cells, the upper-cell inputs are typically shorted to the top-cell input. For example, in a 5-cell application VC6 and VC5 would be shorted together and the (VC5 – VC4) amplifier would measure the top-cell voltage. The case is similar for 4-cell and 3-cell applications.

For these cases when using the (VC5 – VC4), (VC4 –VC3), or (VC3 – VC2) amplifier to measure the top cell, the difference between BAT and the top-cell amplifier must be less than 240 mV in order to measure cell voltages down to 1.4 V. Note that at higher-cell input voltages the top amplifier tolerates a greater difference. For example, in a 5-cell configuration (VC6 and VC5 tied together) the (VC5 – VC4) amplifier is able to measure down to a 1.7 V input with a 600-mV difference between VC5 and BAT.

Accordingly, in systems with fewer than 6 cells, it is important in system design to minimize RBAT and to use a Schottky type diode for DBAT with a low forward voltage. If it is not possible to reduce the drop at BAT to an acceptable level, then for 4-cell and 5-cell configurations, the (VC6 – VC5) amplifier may be used as the top cell amplifier as shown in Table 1, which allows up to a 1.2 V difference between BAT and the top cell.

Table 1. Alternate Connections for 4 and 5 Cells

Configuration Cell 5 Cell 4 Cell 3 Cell 2 Cell 1 Unused Cell Inputs
5-cell VC6 – VC5 VC4 – VC3 VC3 – VC2 VC2 – VC1 VC1 – VC0 Short VC5 to VC4
4-cell VC6 – VC5 VC3 – VC2 VC2 – VC1 VC1 – VC0 Short VC5 to VC4 to VC3