SNVA941A June   2020  – November 2022 LM5156 , LM5156-Q1 , LM51561 , LM51561-Q1 , LM51561H , LM51561H-Q1 , LM5156H , LM5156H-Q1

 

  1.   How to Design a Boost Converter Using the LM5156
  2. 1LM5156 Design Example
  3. 2Example Application
  4. 3Calculations and Component Selection
    1. 3.1  Switching Frequency
    2. 3.2  Inductor Calculation
    3. 3.3  Current Sense Resistor Calculation
      1. 3.3.1 Current Sense Resistor and Slope Compensation Resistor Selection
      2. 3.3.2 Current Sense Resistor Filter Calculation
    4. 3.4  Inductor Selection
    5. 3.5  Diode Selection
    6. 3.6  MOSFET Selection
    7. 3.7  Output Capacitor Selection
    8. 3.8  Input Capacitor Selection
    9. 3.9  UVLO Resistor Selection
    10. 3.10 Soft-Start Capacitor Selection.
    11. 3.11 Feedback Resistor Selection
    12. 3.12 Control Loop Compensation
      1. 3.12.1 Select the Loop Crossover Frequency (fCROSS)
      2. 3.12.2 Determine Required RCOMP
      3. 3.12.3 Determine Required CCOMP
      4. 3.12.4 Determine Required CHF
    13. 3.13 Efficiency Estimation
  5. 4Component Selection Summary
    1.     25
  6. 5Small-Signal Frequency Analysis
    1. 5.1 Boost Regulator Modulator Modeling
    2. 5.2 Compensation Modeling
    3. 5.3 Open-Loop Modeling
  7. 6Revision History

3.4 Inductor Selection

RS, the inductor must be selected according to three parameters; calculated inductance value (LM), RMS inductor current at the minimum supply voltage and the peak inductor current limit (ILPEAK_LIMIT) set by the current sense resistor (RS).

  • The inductance value is selected to be 2.2 µH. This is a standard value that is produced by most magnetic vendors.
  • The RMS current of the inductor can be estimated by calculating the average inductor current (ILAVG) and is approximately equal to the average supply current. The average inductor current is estimated to be 16 A when VSUPPLY = 2.5 V. The inductor RMS current rating should be higher than calculated average inductor current and keep the inductor temperature rise to a reasonable level based on the application.
  • The saturation current rating of the inductor should be larger than the calculated ILPEAK_LIMIT value, 25 A. If the inductor becomes saturated, proper operation of the regulator is not ensured.

For this design example, the inductor is selected to have an inductance value of 2.2 µH, 40°C component temperature rise at an RMS of 20 A, and a saturation current limit of 32 A.