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

1 LM5157 Boost Design Example

This design example walks through the typical design procedures and calculations to implement a non-synchronous Boost converter with LM5157. The design with LM51571, LM5158, and LM51581 is very similar. The configuration is designed to provide a regulated 12 V of up to 1.6 A load current from an unregulated 6 V rail (3 V-9 V) (load derated by half at input below 6 V). A switching frequency of 2.1MHz is selected to avoid interference in the AM band (530kHz to 1.8MHz). The parameters are presented in Table 1-1 and the component selection is discussed in Section 2.

Table 1-1 Design Parameters
PARAMETER SPECIFICATIONS
VSUPPLY 3 V to 9 V
VLOAD 12 V
ILOAD 1.6 A (VSUPPLY= 6 V to 9 V)
0.8 A (VSUPPLY= 3 V to 6 V)
fSW 2.1MHz
η (estimated efficiency) 90%