SNVAA43 March   2023 LM5157 , LM5157-Q1 , LM51571-Q1 , LM5158 , LM5158-Q1 , LM51581 , LM51581-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Application Parameters
  5. 3Calculations and Component Selection
    1. 3.1 Switching Frequency
    2. 3.2 Coupled Inductor Selection
      1. 3.2.1 Coupling Capacitor (AC Cap)
    3. 3.3 Diode Selection
    4. 3.4 MOSFET Selection
    5. 3.5 Output Capacitor Selection
    6. 3.6 Input Capacitor Selection
    7. 3.7 Output Voltage Setting
  6. 4Simplified SEPIC Schematic
  7. 5References

3.7 Output Voltage Setting

The output voltage is set with a resistive divider network. In this case, the top feedback resistor (RFBT) is chose to be 51.1 k. The output voltage is expressed in the equation below, where VREF is a parameter that can be found in the data sheet of the selected IC:

Equation 17. V L O A D = V R E F × R F B T R F B B + 1

Therefore, the bottom resistor (RFBB) can be calculated as follows:

Equation 18. R F B B = R F B T V L O A D V R E F - 1