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

2.11.3 CCOMP Selection

The RCOMP resistor and CCOMP capacitor set the low frequency zero of the compensation network. For a desired settling time constant, the low frequency zero are placed as a phase boost. A good strategy used here is placing the zero directly at the geometric mean of the crossover frequency (fCROSS) and the low frequency pole of the plant (ωP_LF). Equation 23 produces the value of CCOMP.

Equation 23. CCOMP= COUT∙RLOAD4π∙RCOMP2∙ fCROSS  = 22µF∙7.5Ω4π∙2.63kΩ2∙16.6kHz=10.7nF

CCOMP is chosen to be 10nF.