SLUSE14A December   2020  – February 2021 BQ76942

PRODMIX  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  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. Device Description
    1. 8.1 Overview
    2. 8.2 BQ76942 Device Versions
    3. 8.3 Functional Block Diagram
    4. 8.4 Diagnostics
  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
    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

SPI Protocol

The first byte of a SPI transaction consists of an R/W bit (R = 0, W = 1), followed by a 7-bit address, MSB-first. If the controller (host) is writing, then the second byte will be the data to be written. If the controller is reading, then the second byte sent on SPI_MOSI is ignored (except for CRC calculation).

If CRC is enabled, then the controller must send as the third byte the 8-bit CRC code, which is calculated over the first two bytes. If the CRC is correct, then the values clocked in will be put into the incoming buffer. If the CRC is not correct, then the outgoing buffer will be set to 0xFFFF, and the outgoing CRC will be set to 0xAA (these are clocked out on the next transaction).

During this transaction, the logic will clock out the contents of the outgoing buffer. If the outgoing buffer has not been updated since the last transaction, then the logic will clock out 0xFFFF, and if the CRC is clocked, it will clock out 0x00 for the CRC (if enabled). Thus the 0xFFFF00 will indicate to the controller that the outgoing buffer was not updated by the internal logic before the transaction occurred. This can occur when the device did not have sufficient time to update the buffer between consecutive transactions.

When the internal logic takes the write-data from the interface logic and processes it, it also causes the R/W bit, address, and data to be copied into the outgoing buffer. On the next transaction, this data is clocked back to the controller.

When the controller is initiating a read, the internal logic will put the R/W bit and address into the outgoing buffer, along with the data requested. The interface will compute the CRC on the two bytes in the outgoing buffer and clock that back to the controller if CRC is enabled (with the exceptions associated with 0xFFFF as noted above). A diagram of three transaction sequences with and without CRC are shown below, assuming CPOL=0.

GUID-D9963365-16BA-4ECE-BBB4-27B1A5709900-low.svg Figure 14-5 SPI Transaction #1 Using CRC
GUID-23E12F39-35F5-4601-8687-C367250FBD64-low.svg Figure 14-6 SPI Transaction #2 Using CRC
GUID-0388DCB7-6F9A-45B1-A034-BBB4DE86A551-low.svg Figure 14-7 SPI Transaction #3 Using CRC
GUID-FA870CCD-365C-4071-872C-1084A1D7D9CB-low.svg Figure 14-8 SPI Transaction #1 Without CRC
GUID-9EB4E06A-CEB0-410D-A4CF-3644BD0A3DA9-low.svg Figure 14-9 SPI Transaction #2 Without CRC
GUID-9B3A1980-0ED4-490E-AA6A-FFA6ACB403B3-low.svg Figure 14-10 SPI Transaction #3 Without CRC

The time required for the device to process commands and subcommands will differ based on the specifics of each. The direct commands generally will complete within 50 μs, while subcommands can take longer, with different subcommands requiring different duration to complete. For example, when a particular subcommand is sent, the device requires approximately 200 μs to load the 32-byte data into the internal subcommand buffer. If the host provides sufficient time for this load to complete before beginning to read the buffer (readback from addresses 0x40 to 0x5F), the device will respond with valid data, rather than 0xFFFF00. When data has already been loaded into the subcommand buffer, this data can be read back with approximately 50 μs interval between SPI transactions. The BQ76942 Technical Reference Manual provides more details on the approximate time duration required for specific commands and subcommands.

The host software should incorporate a scheme to retry transactions that may not be successful. For example, if the device returns 0xFFFFFF on SPI_MISO, then the internal clock is not powered, and the transaction needs to be retried. Similarly, if the device returns 0xFFFFAA on a transaction, this indicates the previous transaction encountered a CRC error, and so the previous transaction must be retried. As described above, if the device returns 0xFFFF00, then the previous transaction had not completed when the present transaction was sent, which may mean the previous transaction should be retried, or needs more time to complete.