TIDUFD0 August   2025

 

  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 Wireless Hardware Configurations
      2. 2.2.2 Auxiliary Power Strategy
      3. 2.2.3 Thermistor Multiplexer
      4. 2.2.4 Cell Balancing
    3. 2.3 Highlighted Products
      1. 2.3.1 CC2662R-Q1
      2. 2.3.2 BQ78706
      3. 2.3.3 TMUX1308
      4. 2.3.4 LM5168
      5. 2.3.5 TMP61
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
    3. 3.3 Test Setup
    4. 3.4 Test Results
      1. 3.4.1 Network Performance
        1. 3.4.1.1 Network Initiation
        2. 3.4.1.2 Network Latency
        3. 3.4.1.3 PDR, PS
        4. 3.4.1.4 Low-Power Mode
      2. 3.4.2 Cell Voltage Accuracy
      3. 3.4.3 Temperature Sensing Using TMP61
      4. 3.4.4 Thermistor Multiplexer Timing
      5. 3.4.5 Current Consumption
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 Layout Prints
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.1 Block Diagram

Figure 2-1 shows the system block diagram.

TIDA-010976 wBMU Block Diagram Figure 2-1 wBMU Block Diagram

The design uses wBMS MCU CC2662R-Q1 to enable the wireless communication between BMU. This wBMS MCU is Systems-on-Chip (SoC) that integrate a radio frequency (RF) physical layer and user-programmable MCU core that can implement communication protocol stacks and application software (SW). The protocol is self-developed, proprietary wireless BMS protocol based on Bluetooth® Low Energy technology operating in the 2.4GHz frequency band.

The design uses four BQ78706 devices to monitor each cell voltage, monitor the temperature of a 52-cell battery pack, and to protect the pack against all unusual situations, including cell overvoltage, cell undervoltage, and overtemperature. In Figure 2-1, the top BQ78706 device is the BQ78706#S3 and the bottom BQ78706 device is the BQ78706#B0. The forward daisy-chain communication direction is from the BQ78706#B0 device to the BQ78706#S1 device.

Each BQ78706 has 11 GPIO pins for temperature sensing and 14 VC pins for voltage sensing. To monitor the temperatures for all the VC channels with fewer GPIO pins, two TMUX1308 multiplexers are used. The multiplexers expand temperature-sensing capabilities of one BQ78706 from 11 channels to 18 channels, which includes14 MUX-related thermistors, 2 constant resistors, and 4 independent thermistors.

To run diagnostics for the TMUX1308 to prevent the MUX from failure mode, one channel of each TMUX1308 is connected to a constant resistor. This constant resistor is out of the range of thermistors which enable a plausibility check. This diagnostic method can show if the MUX is stuck on a specific channel or reporting voltages corresponding to incorrect channels.

The AVDD pin on the BQ78706 is used to supply power to the TMUX1308. Since AVDD can be configured as off state by shorting RX to AVDD, AVDD can enable a low shutdown current with no leakage current to external MUX devices. When BQ78706 is waked, then AVDD supplies all the external loads with 20mA capacity which is enough for MUX or other devices. #B0 is different. The AVDD need be configured as on to enable UART when #B0 is shutdown so the TMUX1308 of #B0 is powered by the output of LM5168.

To avoid the supply current difference of different BQ78706 devices, this design build an onboard power rail to power the wBMS MCU rather than use #B0 AVDD. A 120V input, 0.3A, ultra-low IQ synchronous buck DC/DC converter LM5168 with a low IQ is used as a pre-regulator. A discrete step-down circuit is added before LM5168 because the 52s battery pack voltage can exceed 120V.

The internal passive cell balancing resistors can support up to 100mA of balancing current per channel. An odd and even cell balancing can be used to achieve an average 50mA balancing current.

A ±1%, 10kΩ linear thermistor with positive temperature coefficient TMP61 is utilized to monitor the cell temperature and is measured by the BQ78706 device.