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

3.12.3 Determine Required CCOMP

The RCOMP resistor and CCOMP capacitor set the low frequency zero of the compensation network resulting in a phase boost. Placement of this zero frequency largely impacts the transient response of the control loop. A good strategy is placing the zero at the geometric mean of the crossover frequency (fCROSS) and the low frequency pole of the plant. Equation 26 places the low frequency zero of error amplifier a the geometric mean of fCROSS and low frequency pole of the plant (ωP_LF). For this design the desired zero location is 999 Hz.

Equation 26. GUID-20BD6559-BAEF-4D38-969F-B5E17C757DD8-low.gif

With the zero frequency selected, Equation 27 produces the value of CCOMP.

Equation 27. GUID-6F368ECB-71B5-43E9-BF43-00B813E56D7A-low.gif

CCOMP is chosen to be 68 nF.