SLUSE97 November   2023 BQ76905

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Supply Current
    6. 6.6  Digital I/O
    7. 6.7  REGOUT LDO
    8. 6.8  Voltage References
    9. 6.9  Coulomb Counter
    10. 6.10 Coulomb Counter Digital Filter
    11. 6.11 Current Wake Detector
    12. 6.12 Analog-to-Digital Converter
    13. 6.13 Cell Balancing
    14. 6.14 Internal Temperature Sensor
    15. 6.15 Thermistor Measurement
    16. 6.16 Hardware Overtemperature Detector
    17. 6.17 Internal Oscillator
    18. 6.18 Charge and Discharge FET Drivers
    19. 6.19 Comparator-Based Protection Subsystem
    20. 6.20 Timing Requirements—I2C Interface, 100-kHz Mode
    21. 6.21 Timing Requirements—I2C Interface, 400-kHz Mode
    22. 6.22 Timing Diagram
    23. 6.23 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Device Configuration
      1. 7.3.1 Commands and Subcommands
      2. 7.3.2 Configuration Using OTP or Registers
      3. 7.3.3 Device Security
    4. 7.4 Device Hardware Features
      1. 7.4.1  Voltage ADC
      2. 7.4.2  Coulomb Counter and Digital Filters
      3. 7.4.3  Protection FET Drivers
      4. 7.4.4  Voltage References
      5. 7.4.5  Multiplexer
      6. 7.4.6  LDOs
      7. 7.4.7  Standalone Versus Host Interface
      8. 7.4.8  ALERT Pin Operation
      9. 7.4.9  Low Frequency Oscillator
      10. 7.4.10 I2C Serial Communications Interface
    5. 7.5 Measurement Subsystem
      1. 7.5.1 Voltage Measurement
        1. 7.5.1.1 Voltage ADC Scheduling
        2. 7.5.1.2 Unused VC Pins
        3. 7.5.1.3 General Purpose ADCIN Functionality
      2. 7.5.2 Current Measurement and Charge Integration
      3. 7.5.3 Internal Temperature Measurement
      4. 7.5.4 Thermistor Temperature Measurement
      5. 7.5.5 Factory Trim and Calibration
    6. 7.6 Protection Subsystem
      1. 7.6.1 Protections Overview
      2. 7.6.2 Primary Protections
      3. 7.6.3 CHG Detector
      4. 7.6.4 Cell Open-Wire Protection
      5. 7.6.5 Diagnostic Checks
    7. 7.7 Cell Balancing
    8. 7.8 Device Operational Modes
      1. 7.8.1 Overview of Operational Modes
      2. 7.8.2 NORMAL Mode
      3. 7.8.3 SLEEP Mode
      4. 7.8.4 DEEPSLEEP Mode
      5. 7.8.5 SHUTDOWN Mode
      6. 7.8.6 CONFIG_UPDATE Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Performance Plot
      4. 8.2.4 Random Cell Connection Support
      5. 8.2.5 Startup Timing
      6. 8.2.6 FET Driver Turn-Off
      7. 8.2.7 Usage of Unused Pins
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2 Detailed Design Procedure

  • Determine the number of series cells.
    • This value depends on the cell chemistry and the load requirements of the system. For example, to support a minimum battery voltage of 12 V using Li-CO2 type cells with a cell minimum voltage of 3 V, at least 4-series cells are required.
    • For the correct cell connections, see Section 7.5.1.2.
  • Protection FET selection and configuration
    • The BQ76905 device is designed for use with low-side NFET protection
    • The configuration should be selected for series versus parallel FETs, which may lead to different FET selection for charge versus discharge direction.
    • These FETs should be rated for the maximum:
      • Voltage, which should be approximately 5 V (DC) to 10 V (peak) per series cell.
      • Current, which should be calculated based on both the maximum DC current and the maximum transient current with some margin.
      • Power Dissipation, which can be a factor of the RDS(ON) rating of the FET, the FET package, and the PCB design.
  • Sense resistor selection
    • The resistance value should be selected to maximize the input range of the coulomb counter but not exceed the absolute maximum ratings, and avoid excessive heat generation within the resistor.
      • Using the normal maximum charge or discharge current, the sense resistor = 200 mV / 40.0 A = 5 mΩ maximum.
      • Considering a short circuit discharge current of 80 A, the recommended maximum SRP, SRN voltage of ≈0.75 V, and the maximum SCD threshold of 500 mV, the sense resistor should be below 500 mV / 80 A= 6.25 mΩ maximum.
    • Further tolerance analysis (value tolerance, temperature variation, and so on) and PCB design margin should also be considered, so a sense resistor of 1 mΩ is suitable with a 50-ppm temperature coefficient and power rating of 1 W.
  • The REGOUT is selected to provide the supply for an external host processor and the pullup supply for the I2C bus and ALERT pin, with output voltage selected for 3.3 V.
    • A 1 μF or larger capacitor should be placed at the REGOUT pin.
    • The REGOUT draws its input current from the REGSRC pin. This pin is connected to PACK+ through a series diode and 10 Ω resistor, with a 1 μF capacitor to VSS placed at the REGSRC pin.