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

2.2.8 Backlight LED Driver

TIDA-010932 also features a backlight LED driver (Figure 2-12) which can be used to drive backlight LEDs on displays for thermostats, and so forth. If not needed, this device can be disabled by depopulating R39.

GUID-20230530-SS0I-XSLV-T3C0-G1NFSXHZFW8H-low.png Figure 2-12 TIDA-010932 String LED Driver Circuit

For the inductor selection, there are three important inductor specifications, inductor value, DC resistance, and saturation current. Considering inductor value alone is not enough. The inductor value determines the inductor ripple current. Choose an inductor that can handle the necessary peak current without saturating. Follow Equation 23 and Equation 24 to calculate the peak current of the inductor. To calculate the current in the worst case, use the minimum input voltage, maximum output voltage, and maximum load current of the application. In a boost regulator, the input DC current can be calculated as Equation 22:

Equation 22. I L ( D C ) = V O U T × I O U T V I N × η

where

  • VOUT = boost output voltage
  • IOUT = boost output current
  • VIN = boost input voltage
  • η = power conversion efficiency

The inductor current peak to peak ripple can be calculated as Equation 23.

Equation 23. ∆ I L ( P - P ) = 1 L × 1 V O U T - V I N + 1 V I N × F S

where

  • ΔIL(PP) = inductor peak-to-peak ripple
  • L = inductor value
  • FS = boost switching frequency
  • VOUT = boost output voltage
  • VIN = boost input voltage

Therefore, the peak current IL(P) seen by the inductor is calculated with Equation 24.

Equation 24. I L ( P ) = I L ( D C ) + ∆ I L ( P - P ) 2

For output capacitor selection, the voltage ripple is related to capacitor capacitance and the equivalent series resistance (ESR). The additional part of the ripple caused by ESR is calculated using: Vripple_ESR = IOUT × RESR. Due to the low ESR, Vripple_ESR can be neglected for ceramic capacitors, a 1-μF to 4.7-μF capacitor is recommended for typical applications, in this design a 1-μF output capacitor is chosen.