TIDUF20 December   2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  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 Support Resources
    5. 4.5 Trademarks
  10. 5About the Author

2.2.2 High-Side N-Channel MOSFET

This design supports high-side N-channel MOSFET architecture and uses top the BQ76942 charge pump to drive the MOSFETs. Since the top BQ76942 references the top of the bottom stack for cell voltage measurement, when the top BQ76942 turns DSG MOSFET off, the voltage on the DSG pin of the top BQ76942 is the bottom stack voltage, which is too high to completely turn the DSG MOSFET off. This reference design adds some discrete components to make sure the DSG MOSFET turns off completely and quickly.

When DSG MOSFETs need to be off, the MCU or the bottom BQ76942 device turns on Q47. P-channel MOSFET Q48 is turned on to discharge Vgs of DSG MOSFET. The top BQ76942 drives TOP_DSG towards TOP_LD to turn off Q41, allowing Dri_Test to ground and turn off DSG MOSFET completely. When DSG MOSFET is off, Q47 is able to turn off to save power. When the system needs to turn on DSG MOSFET, the system first makes sure Q47 is off and then drives TOP_DSG with the charge pump voltage, Q40 is on and charges Vgs of DSG MOSFET.