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

1 System Description

Because of the weight limit and longer endurance needs, the battery cell chemistry of the e-motorcycle, light electric vehicles, and garden tools battery packs is shifting from Lead-acid to Li-ion, Li-polymer, or Li-ion phosphate (LiFePO4) types and the pack voltage is shifting from 36 V or 48 V to 60 V or 72 V, or even higher. These battery chemistries are good in both volumetric and gravimetric energy density. While these battery chemistries provide high energy density and thereby lower volume and weight as an advantage, these battery products are associated with safety concerns and have a need for more accurate and complicated monitoring and protections. Those concerns are cell undervoltage (CUV) and cell overvoltage (COV), overtemperature (OT), both overcurrent in charge (OCC) and discharge (OCD), and short-circuit discharge (SCD), all of which contribute to the accelerating cell degradation and can lead to thermal runaway and explosion. Therefore, the pack current, cell temperature, and each cell voltage must be monitored in a timely manner in case of unusual situations. The battery pack must be protected against all these situations. Good measurement accuracy is always required, especially the cell voltage, pack current, and cell temperature. Precision is necessary for accurate protections and battery pack state of charge (SoC) calculations. This is especially true for LiFePO4 battery pack applications because of the flat voltage. Another important feature for battery-powered applications is the current consumption, especially when in ship mode or standby mode. Lower current consumption saves more energy and gives longer storage time without over-discharging the battery.

This design with two stacked BQ769x2 battery monitors to cover up to 32s battery cells, focuses on 60 V and higher e-motorcycle battery pack applications and is also designed for other high-cell applications, such as a mowing robot and garden tool battery pack, energy storage system battery packs, UPS battery packs, and so forth. The design contains full set protection to protect the battery pack against all unusual situations including: cell overvoltage, cell undervoltage, overtemperature, overcurrent in charge and discharge, and short-circuit discharge. With high-side MOSFET control, normal communication outside is allowed even during faults and MOSFETs in the off status. This design has carefully formed the auxiliary power architecture, which achieves an ultra-low ship mode (10 μA) and standby mode (300 μA) current consumption with a limited number of components and simple control strategy. Furthermore, the design gives optimization ideas to match the current within stacked groups.