SLUSE14B December   2020  ā€“ December 2021 BQ76942

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and 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 BQ76942
    5. 7.5  Supply Current
    6. 7.6  Digital I/O
    7. 7.7  LD Pin
    8. 7.8  Precharge (PCHG) and Predischarge (PDSG) FET Drive
    9. 7.9  FUSE Pin Functionality
    10. 7.10 REG18 LDO
    11. 7.11 REG0 Pre-regulator
    12. 7.12 REG1 LDO
    13. 7.13 REG2 LDO
    14. 7.14 Voltage References
    15. 7.15 Coulomb Counter
    16. 7.16 Coulomb Counter Digital Filter (CC1)
    17. 7.17 Current Measurement Digital Filter (CC2)
    18. 7.18 Current Wake Detector
    19. 7.19 Analog-to-Digital Converter
    20. 7.20 Cell Balancing
    21. 7.21 Cell Open Wire Detector
    22. 7.22 Internal Temperature Sensor
    23. 7.23 Thermistor Measurement
    24. 7.24 Internal Oscillators
    25. 7.25 High-Side NFET Drivers
    26. 7.26 Comparator-Based Protection Subsystem
    27. 7.27 Timing Requirements ā€“ I2C Interface, 100kHz Mode
    28. 7.28 Timing Requirements ā€“ I2C Interface, 400kHz Mode
    29. 7.29 Timing Requirements ā€“ HDQ Interface
    30. 7.30 Timing Requirements ā€“ SPI Interface
    31. 7.31 Interface Timing Diagrams
    32. 7.32 Typical Characteristics
  8. 8 Device Description
    1. 8.1 Overview
    2. 8.2 BQ76942 Device Versions
    3. 8.3 Functional Block Diagram
    4. 8.4 Diagnostics
  9. 9 Device Configuration
    1. 9.1 Commands and Subcommands
    2. 9.2 Configuration Using OTP or Registers
    3. 9.3 Device Security
    4. 9.4 Scratchpad Memory
  10. 10Measurement Subsystem
    1. 10.1  Voltage Measurement
      1. 10.1.1 Voltage Measurement Schedule
      2. 10.1.2 Usage of VC Pins for Cells Versus Interconnect
      3. 10.1.3 Cell 1 Voltage Validation During SLEEP Mode
    2. 10.2  General Purpose ADCIN Functionality
    3. 10.3  Coulomb Counter and Digital Filters
    4. 10.4  Synchronized Voltage and Current Measurement
    5. 10.5  Internal Temperature Measurement
    6. 10.6  Thermistor Temperature Measurement
    7. 10.7  Factory Trim of Voltage ADC
    8. 10.8  Voltage Calibration (ADC Measurements)
    9. 10.9  Voltage Calibration (COV and CUV Protections)
    10. 10.10 Current Calibration
    11. 10.11 Temperature Calibration
  11. 11Primary and Secondary Protection Subsystems
    1. 11.1 Protections Overview
    2. 11.2 Primary Protections
    3. 11.3 Secondary Protections
    4. 11.4 High-Side NFET Drivers
    5. 11.5 Protection FETs Configuration and Control
      1. 11.5.1 FET Configuration
      2. 11.5.2 PRECHARGE and PREDISCHARGE Modes
    6. 11.6 Load Detect Functionality
  12. 12Device Hardware Features
    1. 12.1  Voltage References
    2. 12.2  ADC Multiplexer
    3. 12.3  LDOs
      1. 12.3.1 Preregulator Control
      2. 12.3.2 REG1 and REG2 LDO Controls
    4. 12.4  Standalone Versus Host Interface
    5. 12.5  Multifunction Pin Controls
    6. 12.6  RST_SHUT Pin Operation
    7. 12.7  CFETOFF, DFETOFF, BOTHOFF Pin Functionality
    8. 12.8  ALERT Pin Operation
    9. 12.9  DDSG and DCHG Pin Operation
    10. 12.10 Fuse Drive
    11. 12.11 Cell Open Wire
    12. 12.12 Low Frequency Oscillator
    13. 12.13 High Frequency Oscillator
  13. 13Device Functional Modes
    1. 13.1 Overview
    2. 13.2 NORMAL Mode
    3. 13.3 SLEEP Mode
    4. 13.4 DEEPSLEEP Mode
    5. 13.5 SHUTDOWN Mode
    6. 13.6 CONFIG_UPDATE Mode
  14. 14Serial Communications Interface
    1. 14.1 Serial Communications Overview
    2. 14.2 I2C Communications Subsystem
    3. 14.3 SPI Communications Interface
      1. 14.3.1 SPI Protocol
    4. 14.4 HDQ Communications Interface
  15. 15Cell Balancing
    1. 15.1 Cell Balancing Overview
  16. 16Application and Implementation
    1. 16.1 Application Information
    2. 16.2 Typical Applications
      1. 16.2.1 Design Requirements (Example)
      2. 16.2.2 Detailed Design Procedure
      3. 16.2.3 Application Performance Plot
      4. 16.2.4 Calibration Process
      5. 16.2.5 Design Example
    3. 16.3 Random Cell Connection Support
    4. 16.4 Startup Timing
    5. 16.5 FET Driver Turn-Off
    6. 16.6 Unused Pins
  17. 17Power Supply Requirements
  18. 18Layout
    1. 18.1 Layout Guidelines
    2. 18.2 Layout Example
  19. 19Device and Documentation Support
    1. 19.1 Third-Party Products Disclaimer
    2. 19.2 Documentation Support
      1. 19.2.1 Receiving Notification of Documentation Updates
    3. 19.3 Support Resources
    4. 19.4 Trademarks
    5. 19.5 Electrostatic Discharge Caution
    6. 19.6 Glossary
  20. 20Mechanical, Packaging, Orderable Information

Package Options

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

16.2.2 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 25 V using Li-CO2 type cells with a cell minimum voltage of 2.5 V, 10-series cells should be used.
    • For the correct cell connections, see Usage of VC Pins for Cells Versus Interconnect.
  • Protection FET selection and configuration
    • The BQ76942 device is designed for use with high-side NFET protection (low-side protection NFETs can be used by leveraging the DCHG / DDSG signals).
    • 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.
    • The overdrive level of the BQ76942 device charge pump should be selected based on RDS(ON) requirements for the protection FETs and their voltage handling requirements. If the FETs are selected with a maximum gate-to-source voltage of 15 V, then the 11-V overdrive mode within the BQ76942 device can be used. If the FETs are not specified to withstand this level, or there is a concern over gate leakage current on the FETs, the lower overdrive level of 5.5 V can be selected.
  • 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 / 20.0 A = 10 mĪ© maximum.
      • However, considering a short circuit discharge current of 80 A, the recommended maximum SRP, SRN voltage of ā‰ˆ0.75 V, and the maximum SCD threshold of 500 mV, the sense resistor should be below 500 mV / 80 A = 6.25-mĪ© 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 mĪ© is suitable with a 50-ppm temperature coefficient and power rating of 1 W.
  • The REG1 is selected to provide the supply for an external host processor, with output voltage selected for 3.3 V.
    • The NPN BJT used for the REG0 preregulator should be selected to support the maximum collector-to-emitter voltage of the maximum charging voltage of 42.5 V. The gain of the BJT should be chosen so it can provide the required maximum output current with a base current level that can be provided from the BQ76942 device.
    • The BJT should support the maximum current expected from the REG1 (maximum of 45 mA, with short circuit current limit of up to ā‰ˆ80 mA).
    • A diode can optionally be included in the collector circuit of the BJT, in order to avoid reverse current flow from BREG through the base-collector junction of the BJT to PACK+ during a pack short circuit event. This diode can be seen in Figure 16-1 at D2.
    • A large resistor (such as 10 MĪ©) is recommended from BREG to VSS to avoid any unintended leakage current that may occur during SHUTDOWN mode.