TIDUEY5 January   2021

 

  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
    3. 2.3 Highlighted Products
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
  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 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author

1 System Description

The e-bike market is growing rapidly. Because of the weight limited and longer endurance needs, the battery cell chemistry of the battery pack is shifting from Lead-acid to Li-ion, Li-polymer, or Li-iron phosphate types. This chemistry is good in both volumetric and gravimetric energy density. While this chemistry provides high energy density and thereby lower volume and weight as an advantage, they are associated with safety concerns and need 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 may lead to thermal runaway and explosion. Therefore the pack current, cell temperature, and each cell voltage should be monitored timely in case of some 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 focuses on e-bike or e-scooter battery pack applications and is also suitable for other high-cell applications, such as a mowing robot battery pack, 48-V family energy storage system battery packs, and so forth. It contains both primary and secondary protections to ensure safe use of the battery pack. The primary protection protects the battery pack against all unusual situations, including: cell overvoltage, cell undervoltage, overtemperature, overcurrent in charge and discharge, and short-circuit discharge. The secondary protection which supports independent cell overvoltage protection, cell undervoltage protection, and overtemperature protection is an add-on board and is easily removed and added based on actual demands. It achieves within ±5-mV cell voltage measurement accuracy at 25°C and ±10 mV at 0°C to 60°C without any further calibrations. This solution carefully designs the auxiliary power architecture, which achieves quite low ship mode (10 μA) and standby mode (100 μA) current consumption with a limited number of components and simple control strategy.