SLUSE14B December   2020  – 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 – I2C Interface, 100kHz Mode
    28. 7.28 Timing Requirements – I2C Interface, 400kHz Mode
    29. 7.29 Timing Requirements – HDQ Interface
    30. 7.30 Timing Requirements – 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

16.5 FET Driver Turn-Off

The high-side CHG and DSG FET drivers operate differently when they are triggered to turn off their respective FET. The CHG driver includes an internal switch which discharges the CHG pin toward the BAT pin level. The DSG FET driver will discharge the DSG pin toward the LD pin level, but it includes a more complex structure than just a switch, to support a faster turn off.

When the DSG driver is triggered to turn off, the device will initially begin discharging the DSG pin toward VSS. However, since the PACK+ terminal may not fall to a voltage near VSS quickly, the DSG FET gate should not be driven significantly below PACK+, otherwise the DSG FET may be damaged due to excessive negative gate-source voltage. Thus, the device monitors the voltage on the LD pin (which is connected to PACK+ through an external series resistor) and will stop the discharge when the DSG pin voltage drops below the LD pin voltage. When the discharge has stopped, the DSG pin voltage may relax back above the LD pin voltage, at which point the device will again discharge the DSG pin toward VSS, until the DSG gate voltage again falls below the LD pin voltage. This repeats in a series of pulses which over time discharge the DSG gate to the voltage of the LD pin. This pulsing continues for approximately 100 to 200 μs, after which the driver remains in a high impedance state if within approximately 500 mV of the voltage of the LD pin. The external resistor between the DSG gate and source then discharges the remaining FET VGS voltage so the FET remains off.

The external series gate resistor between the DSG pin and the DSG FET gate is used to adjust the speed of the turn-off transient. A low resistance (such as 100 Ω) will provide a fast turn-off during a short circuit event, but this may result in an overly large inductive spike at the top of stack when the FET is disabled. A larger resistor value (such as 1 kΩ or 4.7 kΩ) will reduce this speed and the corresponding inductive spike level.

Oscilloscope captures of DSG driver turn-off are shown below, with the DSG pin driving the gate of a CSD19536KCS NFET, which has a typical Ciss of 9250 pF. Figure 16-6 shows the signals when using a 1-kΩ series gate resistor between the DSG pin and the FET gate, and a light load on PACK+, such that the voltage on PACK+ drops slowly as the FET is disabled. The pulsing on the DSG pin can be seen lasting for approximately 170 μs.


GUID-864E1DD9-38C6-4084-8F09-656D1461089B-low.png

Figure 16-6 Moderate Speed DSG FET Turn-Off, Using a 1-kΩ Series Gate Resistor, and a Light Load on PACK+

A zoomed-in version of the pulsing generated by the DSG pin is shown in Figure 16-7, this time with PACK+ shorted to the top of stack.


GUID-58833C31-BF8B-4AD8-8CBC-BE262891EC5F-low.png

Figure 16-7 Zoomed-In View of the Pulsing on the DSG Pin During FET Turn-Off

A slower turn-off case is shown in Figure 16-8, using a 4.7-kΩ series gate resistor, and the PACK+ connector shorted to the top of stack.


GUID-6178E9D3-CE3F-4094-BB4B-63BF4140772E-low.png

Figure 16-8 A Slower Turn-Off Case Using a 4.7-kΩ Series Gate Resistor, and the PACK+ Connector Shorted to the Top of the Stack

A fast turn-off case is shown in Figure 16-9, in which a 100-Ω series gate resistor is used between the DSG pin and the FET gate.


GUID-DE9EBE2C-3CC6-4F06-99F5-49ACA7734AE0-low.png

Figure 16-9 A Fast Turn-Off Case with a 100-Ω Series Gate Resistor