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

2.2.18 Current Sensing

Two INA213B devices are used for current sensing in this design. The INA213 is a current-shunt monitor design for both high- and low-side current measurements. Both of these devices are supplied by 3.3 V, referenced to ground, and provide a gain of 50 V/V. U2 measures the current across the 2-mΩ sense resistor R1, which provides an input current measurement for both the system rail and battery charge currents. U4 measures the current across the 2-mΩ sense resistor R2, which provides a measurement of the current on the system output rail.

GUID-20220516-SS0I-M8VR-9LXZ-S01H4186PBZK-low.gif Figure 2-7 Current Sensing Schematic

There are also two current-sense buffers that are used to filter the system current rail. The buffer including U6 includes a low-pass filter with a corner frequency of 159 Hz. This provides the MCU with an accurate measurement of the system current while mitigating high-frequency noise. The buffer including U8 includes a low-pass filter with a corner frequency of 0.159 Hz. This provides the MCU with an average current signal over about 6 seconds.

The MCU only has one ADC pin available for current sensing so a 0-Ω resistor was added in series with each of these outputs to provide the ability to manually select between which current sense output is delivered to the MCU.