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

2.2.8 Battery LM74800 HGATE

Adjustments were made to the HGATE design of U7 to reduce the turn on time of Q5. This reduction is made by increasing the gate current delivered to Q5 from 55 μA to 600 μA. To increase the HGATE current that can be delivered by U7, a circuit including D10, Q21, and R84 was added. This circuit amplifies the source current of the HGATE pin by driving an NPN transistor (Q21) that is connected between the charge pump output (CAP, U7 pin 11) and the gate of Q5. A series resistance (R84) is also added to this path to limit the current injection. Diode (D10) is also added between the gate of Q5 and HGATE (U7 pin 8) to allow the HGATE pin to sink current when turning the FET off. Equation 4 provides an example calculation for the HGATE current injection limit. The charge pump of the LM74800 provides an output of VS + 13.2 V. In this case VS is connected to the output of the batteries and is assumed to be 16.8 V. The charge pump can supply a maximum current of 2.4 mA. The current design has the injection current set to be 600 μA, but this current can be increased by reducing R84.

Example 1.

R84=VVS+VCHGPUMPIgate

Example 2.

R84=16.8 V+13.2 V600 μA=50.0 kΩ
Equation 4. R84=16.8 V+13.2 V2.0 mA=15.0 kΩ