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

2.11.2 RCOMP Selection

The RCOMP value directly affects the crossover frequency of the control loop. The higher the crossover frequency, the faster the control loop reacts to transient conditions. Knowing the desired loop crossover frequency, 16.6kHz, RCOMP is calculated using Equation 22.

Equation 22. RCOMP= 2π∙COUT∙ACS∙VLOAD2 ∙fCROSSgm∙VSUPPLY_min = 2π∙22µF∙0.095∙12V2∙16.6kHz2mA/V∙6V=2.62kΩ

where

  • gm is the transconductance of the error amplifier, 2mA/V
  • ACS is the equivalent current sensing gain, 0.095

RCOMP is selected to be 2.63kΩ.