TIDUFB6 December   2024

 

  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 MCU and CAN Interface
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ78706
      2. 2.3.2 TMUX1308
      3. 2.3.3 TCAN1044-Q1
      4. 2.3.4 MSPM0G3519
      5. 2.3.5 LMR51406
      6. 2.3.6 ISO7731
      7. 2.3.7 UCC33420
      8. 2.3.8 UCC33421
      9. 2.3.9 TMP61
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Daisy Chain
      2. 3.3.2 Cell Voltage Accuracy
      3. 3.3.3 Temperature Sensing Using TMP61
      4. 3.3.4 Temperature Sensing Timings
      5. 3.3.5 Cell Balancing and Thermal Performance
      6. 3.3.6 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

2.2.4 MCU and CAN Interface

MCU and CAN interface is an optional choice to replace daisy chain. CAN interface is a widely-used standard interface. MCU MSPM0G3519 transfers the data from AFE1, AFE2, AFE3, and AFE4 to CAN interface. AFE1 works as a bridge device. The ISO7731 is used to connect the UART interface of the AFE1 and the MCU. A reinforced insulation is required since MCU is in low-voltage ground and AFE1 is in high-voltage ground. Two isolated stages are built with UCC33421 and ISO7731. Each stage has a 1500V working voltage and two stages are connected in series to meet 15mm creepage.

Since the TX pin of the BQ78706 supplies a constant voltage in both SHUTDOWN and ACTIVE modes, the ISO7731 is powered from the input (TX) when the BQ78706 SHUTDOWN mode of the ISO7731 is directly connected to BQ78706. A switch is added between BQ78706 and ISO7731 to prevent a leakage current. The switch can be a FET.

Figure 2-5 shows the MCU and CAN interface.

TIDA-010279 MCU and CAN interface Figure 2-5 MCU and CAN interface

UCC33420 and ISO6721 provide a functional isolation for CAN interface. This CAN interface is usually connected to the CAN bus of BCU. The working current of the CAN transceiver, such as TCAN1044, is quite small. A functional isolation is set for the CAN transceiver not the MCU for a higher efficiency.