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

2.2.6 3.3-V Power Rail

The 3.3-V rail serves as the main power output that directly supplies power to the various system components in the end product. The input of the TLV62568 is connected to the output of the bq24072.

The 3.3-V rail ultimately receives power from either the 24-VAC line, USB, or the battery, depending on which source is available. Devices powered from this rail are battery backup protected and benefit from the power assistance features of the bq24072.

The TLV62568 is a very lost cost, low BOM count, high-efficient step-down converter. The device has a 100% duty cycle capability, which is particularly useful in battery-powered applications such as the TIDA-010932 to achieve the longest operation time by taking full advantage of the whole battery voltage range. The TLV62568 has an output current maximum of 1 A. In case more than a 1-A output is required, the TLV62569 offers pin-to-pin compatibility (though the input and output capacitors as well as inductor may need to be changed appropriately) with the TLV62568 but features a 2-A output current. Figure 2-10 shows the specific system implementation in the TIDA-010932 and highlights the simplicity of the part and the low external BOM count.

GUID-20230530-SS0I-SZSF-BG02-GZQ4QM6W5HFM-low.png Figure 2-10 TIDA-010932 3.3V Rail Circuit

To set the output voltage of the TLV62568 to 3.3 V, Equation 16 is used to calculate the values of R19 and R20. When sizing R20, to achieve low current consumption and acceptable noise sensitivity, use a maximum of 200 kΩ. Larger currents through R20 improve noise sensitivity and output voltage accuracy but increase current consumption. A feed forward capacitor (C14) is added to the circuit, which improves the loop bandwidth to make a fast transient response.

Equation 16. V O U T = V F B × 1 + R 19 R 20 = 0.6 × 1 + R 19 R 20

The main parameters for inductor selection is inductor value and then saturation current of the inductor. To calculate the maximum inductor current under static load conditions, Equation 17 and Equation 18 are given:

Equation 17. I L M A X = I O U T M A X + ∆ I L 2
Equation 18. ∆ I L = V O U T × 1 - V O U T V I N L × f S W

where:

  • IOUT,MAX is the maximum output current
  • ΔIL is the inductor current ripple
  • fSW is the switching frequency
  • L is the inductor value

For this design, a 2.2-μH inductor is chosen.