SNVA991 October   2022 LM5123-Q1

 

  1.   How to Design a Boost Converter Using LM5123
  2.   Trademarks
  3. 1Design Example
  4. 2Calculations and Component Selection
    1. 2.1  Switching Frequency
    2. 2.2  Initial Inductor Calculation
    3. 2.3  Current Sense Resistor Selection
    4. 2.4  Inductor Selection
    5. 2.5  Output Capacitor Selection
    6. 2.6  Input Capacitor Selection
    7. 2.7  Feedback Resistor Selection
    8. 2.8  UVLO Resistor Selection
    9. 2.9  Soft-Start Capacitor Selection
    10. 2.10 Control Loop Compensation
      1. 2.10.1 Crossover Frequency (fcross) Selection
      2. 2.10.2 RCOMP Selection
      3. 2.10.3 CCOMP Selection
      4. 2.10.4 CHF Selection
    11. 2.11 MOSFET selection
  5. 3Implementation Results
  6. 4Small Signal Frequency Modeling
    1. 4.1 Boost Regulator Modulator Modeling
    2. 4.2 Compensation Modeling
    3. 4.3 Open Loop Modeling
  7. 5Resources

2.4 Inductor Selection

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

  • The inductance is selected to be 2.6 µH. This value is a standard inductance value supplied by many magnetic vendors.
  • The inductor RMS current is approximated by the average supply current at the minimum supply voltage, maximum load target voltage and maximum output power, 25 A. The inductor RMS current rating should be higher than the estimated RMS current and keep the inductor temperature to suitable level based on the application.
  • The saturation current of the inductor should be larger than the maximum peak inductor current limit, 40A. The magnetic material and constructions of the inductor dictate the saturation profile. A hard saturation profile has a dramatic decrease in inductance when the inductor becomes saturated, while a softer saturation profile has a slower roll off. Check the inductor data sheet to ensure the saturation is above the peak inductor current limit.

For this design example, the inductor is selected to have an inductance value of 2.6 µH, a saturation current limit of 50 A, and a 30°C temperature rise at 25 A RMS.