TIDUF46 October   2023

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Multiplexer Network and Switch Strategy
      2. 2.2.2 Cell Balancing
      3. 2.2.3 Stacked AFE Communication
      4. 2.2.4 Isolated UART Interface to MCU
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ79616
      2. 2.3.2 TMUX1308
      3. 2.3.3 TMUX1574
      4. 2.3.4 TMUX1102
      5. 2.3.5 TPS22810
      6. 2.3.6 ISO7742
      7. 2.3.7 TSD05C
      8. 2.3.8 ESD441
      9. 2.3.9 ESD2CAN24-Q1
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Cell Voltage Accuracy
      2. 3.3.2 Temperature Sensing Accuracy
      3. 3.3.3 Cell Voltage and Temperature Sensing Timings
      4. 3.3.4 Cell Balancing and Thermal Performance
      5. 3.3.5 Current Consumption
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.3 Stacked AFE Communication

For very high cell count systems, BQ79616 devices can be stacked in series to monitor battery cells. This design uses two BQ79616 devices to monitor up to 32s battery cells. The bottom BQ79616 monitors the lower 16s battery cells, and the top BQ79616 monitors the upper 16s battery cells. The bottom BQ79616 device shares the same ground as BAT–, while the top BQ79616 references 16s top-of-stack voltage as ground. Isolation is required to communicate with the top BQ79616 device. This design uses a capacitor-isolated daisy chain between two BQ79616 devices and a transformer-isolated daisy chain to the offboard BMU or BCU. The BMU is designed to support both the forward and reverse communication directions. The communication direction from the bottom BQ79616 to the top BQ79616 is North (Forward). The communication direction from the top BQ79616 to the bottom BQ79616 is South (Reverse). Figure 3-14 shows the ring communication of the BMUs.

GUID-20230925-SS0I-JSQV-D7V1-2VPSDVZZL09P-low.svgFigure 2-4 BMU Ring Communication

The BCU issues pings to the BQ79600 using SPI. Pings are non-comm signals for simple actions, such as WAKE and SHUTDOWN. Commands are used to transmit data. The BQ79600 can send and receive tones to and from the stacked BQ79616 in the North and South in a duty cycle. Considering the GBT34131-2023 standards, the voltage cycle needs to be less than 100 ms, and the temperature cycle needs to be less than 1 second.