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

2.10.2 RCOMP Selection

The RCOMP values is directly proportional to the mid-band gain of the control loop compensation, gMID and the crossover frequency. Increasing RCOMP increases the mid-band gain and thus the crossover frequency is increased. Knowing the desired crossover frequency, RCOMP is estimated using Equation 23.

Equation 23. RCOMP=2π∙ACS∙KFB∙RCS∙COUT∙VLOADmax∙fCROSSVSUPPLYmin∙gMea=2π∙10∙60∙1.5mΩ∙900µA∙35V∙2.45kHz8V∙1mAV=54.5 kΩ

where

  • gMea is the transconductance of the internal error amplifier and is 1 mA/V.
  • KFB is the attenuation factor of the internal feedback resistors dependent on the selected output voltage range.

RCOMP is selected to be 54.9 kΩ.