TIDUF26 june   2023 BQ24072 , LMR36520 , TLV62568 , TPS2116

 

  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 Design Considerations
      1. 2.2.1 24 VAC to DC Rectification
      2. 2.2.2 eFuse Protection
      3. 2.2.3 5-V Rails
        1. 2.2.3.1 LMR36520 Voltage Rail
        2. 2.2.3.2 USB Power Input
      4. 2.2.4 Power Source ORing
      5. 2.2.5 Battery Management
      6. 2.2.6 3.3-V Power Rail
      7. 2.2.7 Power Rail Current Sensing
      8. 2.2.8 Backlight LED Driver
      9. 2.2.9 BoosterPack Overview
    3. 2.3 Highlighted Products
      1. 2.3.1 LMR36520
      2. 2.3.2 TPS2116
      3. 2.3.3 TLV62568
      4. 2.3.4 INA2180
      5. 2.3.5 TPS92360
      6. 2.3.6 TPS2640
      7. 2.3.7 BQ24072
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1  24-VAC Start-Up and Shutdown
      2. 3.3.2  USB Start-Up and Shutdown
      3. 3.3.3  ORing
      4. 3.3.4  LMR36520
      5. 3.3.5  TLV62568 Transient Response
      6. 3.3.6  BM24072 Transient Response
      7. 3.3.7  TLV62568 (3V3 Power Rail)
      8. 3.3.8  LMR36520 (LMOut Power Rail)
      9. 3.3.9  BM24072 (BMOut Power Rail)
      10. 3.3.10 Reference
        1. 3.3.10.1 TLV62568
        2. 3.3.10.2 LMR36520
  10. 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 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.7 Power Rail Current Sensing

TIDA-010932 also integrates an INA2180 (Figure 2-11) for current sensing of the two power rails (5 V from LMR36520 and 5 V from USB). The output of this device is also tied to the BoosterPack™ header for easier data collection as well as the ability to monitor system power if an MCU LaunchPad™ is connected.

GUID-20230530-SS0I-CZTM-VCLV-NZVGKRV3PDHJ-low.png Figure 2-11 INA2180 Power Rail Current Sensing Circuit

The accuracy of the INAx180 is maximized by choosing the current-sense resistor to be as large as possible. A large sense resistor maximizes the differential input signal for a given amount of current flow and reduces the error contribution of the offset voltage. However, there are practical limits as to how large the current-sense resistor can be in a given application. Equation 19 gives the maximum value for the current sense resistor for a given power dissipation budget:

Equation 22. R S E N S E < P D M A X I M A X 2

where

  • PDMAX is the maximum allowable power dissipation in RSENSE
  • IMAX is the maximum current that flows through RSENSE

To make sure that the current-sense signal is properly passed to the output, both positive and negative output swing limitations must be examined. Equation 20 provides the maximum values of RSENSE and GAIN to keep the device from hitting the positive swing limitation.

Equation 20. I M A X × R S E N S E × G a i n < V S P

where

  • IMAX is the maximum current that flows through RSENSE
  • GAIN is the gain of the current sense amplifier
  • VSP is the positive output swing as specified in the data sheet

The negative swing limitation places a limit on how small of a sense resistor can be used in a given application. Equation 21 provides the limit on the minimum size of the sense resistor.

Equation 21. I M I N × R S E N S E × G a i n > V S N

where

  • IMIN is the minimum current that flows through RSENSE
  • GAIN is the gain of the current sense amplifier
  • VSN is the negative output swing of the device