SNVA940 November   2021 LM5157 , LM5157-Q1 , LM51571-Q1 , LM5158 , LM5158-Q1 , LM51581 , LM51581-Q1

 

  1.   Trademarks
  2. 1LM5157 Boost Design Example
  3. 2Calculations and Component Selection
    1. 2.1  Switching Frequency
    2. 2.2  Inductor Calculation
    3. 2.3  Slope Compensation Check
    4. 2.4  Inductor Selection
    5. 2.5  Diode Selection
    6. 2.6  Output Capacitor Selection
    7. 2.7  Input Capacitor Selection
    8. 2.8  UVLO Resistor Selection
    9. 2.9  Soft-Start Capacitor Selection
    10. 2.10 Feedback Resistor Selection
    11. 2.11 Control Loop Compensation
      1. 2.11.1 Crossover Frequency (fcross) Selection
      2. 2.11.2 RCOMP Selection
      3. 2.11.3 CCOMP Selection
      4. 2.11.4 CHF Selection
    12. 2.12 Power Loss and Efficiency Estimation
  4. 3Implementation Results
  5. 4Small Signal Frequency Analysis
    1. 4.1 Boost Regulator Modulator Modeling
    2. 4.2 Compensation Modeling
    3. 4.3 Open Loop Modeling

2.4 Inductor Selection

The inductor are selected according to three parameters: calculated inductance value (LM), RMS inductor current and the maximum peak inductor current.

  • The inductance is selected to be the standard 1.5µH, which is a common value that is commercially available.
  • The saturation current of the inductor should be larger than the maximum current limit of the converter device selected. If the inductor becomes saturated, the components can be damaged and the converter cannot operate correctly .
  • With the ripple ignored, the inductor RMS current can be approximated by the average inductor current, which is estimated to be 3.6 A. The inductor RMS current rating should be higher than the estimated RMS current and keep the inductor temperature within a reasonable level based on the application.

For this design example, the inductor is selected to have an inductance value of 1.5µH, a saturation current limit of 15 A, and a 20°C temperature rise at 10A RMS.