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

4.2 Compensation Modeling

Table 4-2 includes equations model a type II compensation network implemented using a transconductance error amplifier.

Figure 4-2 Compensation network transfer function
Table 4-2 Compensation Modeling Equations
Simplified FormulaComprehensive Formula
Feedback Equations
Feedback Transfer Function v ^ C O M P v ^ L O A D = - A F B 1 + s ω Z e a s ∙ 1 + s ω P e a
Feedback DC Gain A F B = g M e a K F B ∙ C C O M P (1)(2) A F B = g M e a K F B ∙ C C O M P + C H F (1)(2)
Low Frequency Zero ω Z e a =   1 R C O M P ∙ C C O M P
High Frequency Pole ω P e a =   1 R C O M P ∙ C H F ω P e a =   C C O M P + C H F R C O M P ∙ C C O M P ∙ C H F
Mid-band Gain g m i d =   R C O M P ∙ g M e a K F B (1)(2) g m i d =   R C O M P ∙ g M e a ∙ C C O M P K F B ∙ C C O M P + C H F (1)(2)
  1. gm is the transconductance of the error amplifier, 1 mA/V
  2. KFB is the attenuation factor of the internal feedback resistors. This is either 20 for the low load voltage range or 60 for the high voltage load range