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

3.3.2 Current Sense Resistor Filter Calculation

For all designs is it recommended to add the low pass filter to the current sense signal. RF and CF implement a low pass filter as shown in Figure 3-1. The filter is added to help mitigate the impact of the leading edge spike on the current sense signal. RF is selected to be between 10 Ω and 200 Ω. For this design RF is selected to be 100 Ω. CF must be less than the value specified in Equation 11 to ensure proper operation.

Equation 11. GUID-2177874C-C09C-48AD-99DC-26C3FB5EB969-low.gif

CF is selected to be 100 pF. Due to the delay of the low pass filter, the current limit is not valid when VSUPPLY is greater than a given voltage calculated in. For this design the current limit is valid for the entire supply voltage range. Equation 12 is used to calculate this value.

Equation 12. GUID-1F32CBF0-21BA-48AE-A9EC-DAD8AC2FE8D1-low.gif