TIDUEB2A July   2022  – July 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  Power Multiplexing Circuit Design Parameters
      2. 2.2.2  Input Connections and Filter
      3. 2.2.3  Reverse Polarity Protection
      4. 2.2.4  Battery Charger Input
      5. 2.2.5  Battery Ideal Diode-OR
      6. 2.2.6  Input and Battery Switchover Mechanics
      7. 2.2.7  LM74800 (U1) HGATE
      8. 2.2.8  Battery LM74800 HGATE
      9. 2.2.9  BQ25731 Design Considerations
      10. 2.2.10 BQ25731 Component Selection
      11. 2.2.11 ILIM Circuit
      12. 2.2.12 MCU and I2C Bus Design Considerations
      13. 2.2.13 MSP430FR2475
      14. 2.2.14 I2C Bus Overview
      15. 2.2.15 MSP430 Connectors
      16. 2.2.16 MSP430 Power Supply
      17. 2.2.17 Sensing Circuits
      18. 2.2.18 Current Sensing
      19. 2.2.19 Voltage Sensing
      20. 2.2.20 Input Comparators
      21. 2.2.21 Software Flow Chart
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ25731
      2. 2.3.2 LM7480-Q1
      3. 2.3.3 LM74700-Q1
      4. 2.3.4 MSP430FR2475
      5. 2.3.5 PCA9546A
  8. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Adaptive Charge Current Limiting
      2. 3.3.2 Battery ORing System
      3. 3.3.3 Circuit Switchover From Adapter to Battery
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5Revision History

2.2.6 Input and Battery Switchover Mechanics

This design provides an input and battery MUX that prioritizes the input adapter in all cases where the adapter voltage exceeds the UVLO setting of U1. When the UVLO threshold is triggered, the input adapter is disconnected from the system and the batteries are connected to power the system load. This prevents the batteries from discharging while an input adapter is present.

This threshold is set by the resistor divider consisting of R87 and R88. For U1 (input adapter connection) the UVLO thresholds are 1.13 V falling for turn off, and 1.23 V rising for turn on. For U7 (battery connection) the OV pin is connected to the same divider and the thresholds operate inversely. These thresholds are 1.13 V falling for turn on, and 1.23 V rising for turn off. In the schematic this voltage is connected to the net labeled UV/OV_SET. In the current schematic the switchover from input adapter to battery is triggered when VIN reaches 10.56 V and the switchover from battery to input adapter is triggered when VIN reaches 11.5 V.

Equation 3 shows an example of the resistor divider calculation:

Battery to Input Adapter Transition=1.23 VR88R87+R88
Input Adapter to Battery Transition=1.13 VR88R87+R88
R87=5.97 kΩ, R88=715 Ω
Battery to Input Adapter Transition=1.23 V715 Ω5.97 kΩ+715 Ω=11.5 V
Equation 3. Input Adapter to Battery Transition=1.13 V715 Ω5.97 kΩ+715 Ω=10.56 V