SLUSE96 November   2023 BQ76907

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information bq76907
    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, 100kHz Mode
    21. 6.21 Timing Requirements - I2C Interface, 400kHz Mode
    22. 6.22 Timing Diagram
    23. 6.23 Typical Characteristics
  8. 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. 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
  10. Power Supply Recommendations
  11. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  13. 12Revision History
  14. 13Introduction to Mechanical, Packaging, and Orderable Information

Package Options

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

Typical Application

BQ76907 7-Series Cell Typical Implementation (Simplified Schematic) shows a simplified application schematic for a 7-series battery pack, using the BQ76907 with an external secondary protector, a host microcontroller, and a communications transceiver. This configuration uses low-side CHG and DSG FETs in series. Several points to consider in an implementation are included below:

  • A series diode is recommended at the BAT pin, together with a capacitor from the pin to VSS. These components allow the device to continue operating for a short time when a pack short circuit occurs, which may cause the top-of-stack voltage to drop to approximately 0 V. In this case, the diode prevents the BAT pin from being pulled low with the stack, and the device will continue to operate, drawing current from the capacitor. Generally operation is only required for a short time, until the device detects the short circuit event and disables the DSG FET. A Schottky diode can be used if low voltage pack operation is needed, or a conventional diode can be used otherwise.
  • The FET CHG and DSG drivers use the REGSRC pin for their supply, so the user may also prefer to include a diode between the top of stack and the REGSRC pin, similar to that used for the BAT pin. If any resistance (> 1 Ω) is included in series between the top of stack and the REGSRC pin, it is recommended to include a 1 μF capacitor at the REGSRC pin to VSS. The REGSRC pin can be shorted to the BAT pin and a single diode used, but this may result in the BAT pin voltage dropping more rapidly during a short circuit event due to the increased loading of the REGOUT regulator drawing from the REGSRC pin.
  • The recommended minimum voltage on the VC0 to VC4 pins extends down to –0.2 V, while the recommended minimum voltage on the VC5 to VC7 pins is limited to 2.0 V, relative to VSS. This restriction exists to ensure the specified cell voltage measurement accuracy.
  • TI recommends using 100 Ω resistors in series with the SRP and SRN pins, and a 100 nF with optional 100 pF differential filter capacitance between the pins for filtering. The routing of these components, together with the sense resistor, to the pins should be minimized and fully symmetric, with all components recommended to stay on the same side of the PCB with the device. Capacitors connected from the pins to VSS can provide filtering of common mode transients from reaching the pins, but they may also have a slight impact on current measurement performance.
  • The filter network connected between the sense resistor and the SRP and SRN pins introduces an analog filter delay that can be important when fast current protections are required, such as in determining the short circuit in discharge (SCD) time until FETs are disabled. If the delay introduced by this network is too long, the resistance and capacitance values can be reduced. This will have a tradeoff of providing less analog filtering of high frequency components.
  • Due to thermistors often being attached to cells and possibly needing long wires to connect back to the device, it may be helpful to add a capacitor from the thermistor pin to the device VSS. However, it is important to not use too large of a value of capacitor, since this will affect the settling time when the thermistor is biased and measured periodically. A rule of thumb is to keep the time constant of the circuit < 5% of the measurement time. When Settings:Configuration:DA Config[IADCSPEED1:0] = 0x0, the measurement time is approximately 3 ms. When using this speed setting, the time constant should generally be less than (20 kΩ) × C, so a capacitor less than 7.5 nF is recommended. When using faster speed settings, the capacitor value should be reduced accordingly.
GUID-6804EFB1-CDCD-472C-A48C-DAD6D1CE4AE5-low.svg Figure 8-1 BQ76907 7-Series Cell Typical Implementation (Simplified Schematic)

A full schematic of a basic monitor circuit based on the BQ76907 for a 7-series battery pack evaluation module is shown below. Section 10.2 shows the board layout for this design.


GUID-AC23FFD1-706A-4B65-94E1-CD3BD0189435-low.svg

Figure 8-2 BQ76907 7-Series Cell Schematic Diagram—Monitor

GUID-14CD84F6-FA39-4B04-BE10-A2FBDB926B81-low.svg

Figure 8-3 BQ76907 7-Series Cell Schematic Diagram—Additional Circuitry