TIDUF44 January   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 BQ76907
      2. 2.2.2 BQ76905
      3. 2.2.3 BQ77207
      4. 2.2.4 MSPM0L1106
      5. 2.2.5 TCAN1042
      6. 2.2.6 TPSM365R6V5
      7. 2.2.7 TLV704
      8. 2.2.8 TMP61
  9. 3System Design Theory
    1. 3.1 Primary Protection Design
    2. 3.2 Secondary Protection
    3. 3.3 Other Circuit Design
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 Cell Voltage Accuracy
      2. 4.4.2 Pack Current Accuracy
      3. 4.4.3 Protection
      4. 4.4.4 Cell Balancing
      5. 4.4.5 Working Modes Transition
      6. 4.4.6 Thermal Performance
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

1 System Description

The battery packs of power and garden tools are increasingly using Li-ion, Li-polymer, or Li-iron phosphate cell 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, the chemistries 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 can lead to thermal runaway and explosion. Therefore the pack current, cell temperature, and each cell voltage need to be monitored in a timely manner 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 battery pack applications for power tools or garden tools and is also an excellent choice for other 5–7-cell applications, such as vacuum cleaner battery pack. The design contains both primary and secondary protections to provide 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 supports independent cell overvoltage protection, open wire protection, and overtemperature protection. This design can achieve within ±5- mV cell voltage measurement accuracy at 25°C and ±10 mV at 0°C to 60°C without any further calibrations.