JAJU880 December   2022

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Auxiliary Power Strategy
      2. 2.2.2 High-Side N-Channel MOSFET
      3. 2.2.3 Stacked AFE Communication
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ76942
      2. 2.3.2 LM5168
      3. 2.3.3 ISO1640
      4. 2.3.4 TCAN1042HV
      5. 2.3.5 THVD2410
      6. 2.3.6 TPS7A25
      7. 2.3.7 MSP430FR2155
      8. 2.3.8 TMP61
      9. 2.3.9 TPD2E007
  8. 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 Pack Current Accuracy
      3. 3.3.3 Auxiliary Power and System Current Consumption
      4. 3.3.4 Protection
      5. 3.3.5 Working Modes Transition
      6. 3.3.6 ESD Performance
  9. 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 サポート・リソース
    5. 4.5 Trademarks
  10. 5About the Author

2.2.1 Auxiliary Power Strategy

With the requests of low current consumption in standby mode and ship mode and good thermal performance in normal mode, this design uses the auxiliary power strategy shown in Figure 2-2.

Figure 2-2 Auxiliary Power Strategy

The design has a 120-V input, 0.3-A, ultra-low IQ synchronous buck DC/DC converter LM5168P with a low IQ 0.3-A LDO TPS7A25 as the main power source when the system is working in normal mode which requires hundreds of mA with normal CAN or RS-485 communications with the system side, giving the system better efficiency and thermal performance than LDOs only. The bottom BQ76942 regulator REG2 is configured to 5-V output which is the power source when the system is working in standby mode. The series diode on the BQ76942 regulator output makes sure all power is from the DC/DC converter in normal mode preventing the BQ76942 regulator circuits from overheating, so design the DC/DC output a little higher than 5 V, BQ76942 regulator output. Detailed component design guidance is available from the LM5169 Quick Start Calculator. When the system experiences a serious cell undervoltage and must enter ship mode, the MCU configures both of the BQ76942 devices to enter shutdown mode through an I2C command or RST_SHUT PIN and turns off the LM5168P output through the EN pin, which configures the system to very low current consumption mode. This design supports both charger attach and system attached wake up functions. Both methods wake up the bottom BQ76942 device and enable normal 3.3-V regulator REG1, then the MCU is powered on and enables the LM5168P through the EN pin. The whole system then returns to normal mode.

To cover 20s battery systems, two stacked BQ76942 devices are used to monitor cell voltage and temperature. Avoiding imbalance between the two stacked groups is important for longer lifetime. Although cell balancing is useful to balance all battery cells voltage equally, the best way is to avoid too much load gap between two groups. In this design, ISO1640, an isolated I2C interface, is used for communications between the MCU and top BQ76942 device. Small supply current gap between VCC1 and VCC2 of ISO1640 benefits the system. Another option is to use TI reinforced digital isolator with integrated power ISOW77xx to replace ISO1640 and powered from DC/DC.