SLVSLM6 May   2026 BQ76972-Q1

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 BQ76972-Q1
    5. 6.5  Supply Current
    6. 6.6  Digital I/O
    7. 6.7  LD Pin
    8. 6.8  Precharge (PCHG) and Predischarge (PDSG) FET Drive
    9. 6.9  FUSE Pin Functionality
    10. 6.10 REG18 LDO
    11. 6.11 REG0 Pre-regulator
    12. 6.12 REG1 LDO
    13. 6.13 REG2 LDO
    14. 6.14 Voltage References
    15. 6.15 Coulomb Counter
    16. 6.16 Coulomb Counter Digital Filter (CC1)
    17. 6.17 Current Measurement Digital Filter (CC2)
    18. 6.18 Current Wake Detector
    19. 6.19 Analog-to-Digital Converter
    20. 6.20 Cell Voltage Measurement Accuracy
    21. 6.21 Multifunction Pin ADC Measurement
    22. 6.22 Cell Balancing
    23. 6.23 Cell Open Wire Detector
    24. 6.24 Internal Temperature Sensor
    25. 6.25 Thermistor Measurement
    26. 6.26 Internal Oscillators
    27. 6.27 High-side NFET Drivers
    28. 6.28 Comparator-Based Protection Subsystem
    29. 6.29 Timing Requirements - I2C Interface, 100kHz Mode
    30. 6.30 Timing Requirements - I2C Interface, 400kHz Mode
    31. 6.31 Timing Requirements - HDQ Interface
    32. 6.32 Timing Requirements - SPI Interface
    33. 6.33 Interface Timing Diagrams
    34. 6.34 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1  Overview
    2. 7.2  Functional Block Diagram
    3. 7.3  Diagnostics
    4. 7.4  Device Configuration
      1. 7.4.1 Commands and Subcommands
      2. 7.4.2 Configuration Using OTP or Registers
      3. 7.4.3 Device Security
      4. 7.4.4 Scratchpad Memory
    5. 7.5  Measurement Subsystem
      1. 7.5.1  Voltage Measurement
        1. 7.5.1.1 Voltage Measurement Schedule
        2. 7.5.1.2 Usage of VC Pins for Cells Versus Interconnect
        3. 7.5.1.3 Cell 1 Voltage Validation During SLEEP Mode
      2. 7.5.2  General Purpose ADCIN Functionality
      3. 7.5.3  Coulomb Counter and Digital Filters
      4. 7.5.4  Synchronized Voltage and Current Measurement
      5. 7.5.5  Internal Temperature Measurement
      6. 7.5.6  Thermistor Temperature Measurement
      7. 7.5.7  Factory Trim of Voltage ADC
      8. 7.5.8  Cell Voltage Measurement Accuracy
        1. 7.5.8.1 Cell Offset Calibration
      9. 7.5.9  Voltage Calibration (ADC Measurements)
      10. 7.5.10 Voltage Calibration (COV and CUV Protections)
      11. 7.5.11 Current Calibration
      12. 7.5.12 Temperature Calibration
    6. 7.6  Primary and Secondary Protection Subsystems
      1. 7.6.1 Protections Overview
      2. 7.6.2 Primary Protections
      3. 7.6.3 Secondary Protections
      4. 7.6.4 High-Side NFET Drivers
      5. 7.6.5 Protection FETs Configuration and Control
        1. 7.6.5.1 FET Configuration
        2. 7.6.5.2 PRECHARGE and PREDISCHARGE Modes
      6. 7.6.6 Load Detect Functionality
    7. 7.7  Device Hardware Features
      1. 7.7.1  Voltage References
      2. 7.7.2  ADC Multiplexer
      3. 7.7.3  LDOs
        1. 7.7.3.1 Preregulator Control
        2. 7.7.3.2 REG1 and REG2 LDO Controls
      4. 7.7.4  Standalone Versus Host Interface
      5. 7.7.5  Multifunction Pin Controls
      6. 7.7.6  RST_SHUT Pin Operation
      7. 7.7.7  CFETOFF, DFETOFF, and BOTHOFF Pin Functionality
      8. 7.7.8  ALERT Pin Operation
      9. 7.7.9  DDSG and DCHG Pin Operation
      10. 7.7.10 Fuse Drive
      11. 7.7.11 Cell Open Wire
      12. 7.7.12 Low Frequency Oscillator
      13. 7.7.13 High Frequency Oscillator
    8. 7.8  Device Functional Modes
      1. 7.8.1 Overview
      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. 7.9  Serial Communications Interface
      1. 7.9.1 Serial Communications Overview
      2. 7.9.2 I2C Communications
      3. 7.9.3 SPI Communications
        1. 7.9.3.1 SPI Protocol
      4. 7.9.4 HDQ Communications
    10. 7.10 Cell Balancing
      1. 7.10.1 Cell Balancing Overview
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design Requirements (Example)
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Performance Plot
      4. 8.2.4 Calibration Process
    3. 8.3 Random Cell Connection Support
    4. 8.4 Startup Timing
    5. 8.5 FET Driver Turn-Off
    6. 8.6 Unused Pins
    7. 8.7 Power Supply Requirements
    8. 8.8 Layout
      1. 8.8.1 Layout Guidelines
      2. 8.8.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, Orderable Information

8.5 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 might not fall to a voltage near VSS quickly, the DSG FET gate must not be driven significantly below PACK+, otherwise the DSG FET can 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 stops the discharge when the DSG pin voltage drops below the LD pin voltage. When the discharge has stopped, the DSG pin voltage can 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 100μs to 200μs, after which the driver remains in a high impedance state if within approximately 500mV 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 100Ω) provides a fast turn-off during a short circuit event, but this can result in an overly large inductive spike at the top of stack when the FET is disabled. A larger resistor value (such as 1kΩ or 4.7kΩ) 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 9250pF. Figure 8-6 shows the signals when using a 1kΩ 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 170μs.


BQ76972-Q1 Moderate Speed DSG FET Turn-Off, Using a 1kΩ Series Gate Resistor, and a Light Load on PACK+

Figure 8-6 Moderate Speed DSG FET Turn-Off, Using a 1kΩ 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 8-7, this time with PACK+ shorted to the top of stack.


BQ76972-Q1 Zoomed-In View of the Pulsing on the DSG Pin During FET Turn-Off

Figure 8-7 Zoomed-In View of the Pulsing on the DSG Pin During FET Turn-Off

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


BQ76972-Q1 A Slower Turn-Off Case Using a 4.7kΩ Series Gate Resistor, and the PACK+ Connector Shorted to the Top of the Stack

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

A fast turn-off case is shown in Figure 8-9, in which a 100Ω series gate resistor is used between the DSG pin and the FET gate.


BQ76972-Q1 A Fast Turn-Off Case with a 100Ω Series Gate Resistor

Figure 8-9 A Fast Turn-Off Case with a 100Ω Series Gate Resistor