SNVA790A October   2020  – July 2022 LMR36520

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2 Fly-Buck Converter Device Operation
    1. 2.1 Output Current Equations and Considerations
  5. 3LMR36520 Fly-Buck Converter Design
    1. 3.1 Coupled Inductor
    2. 3.2 Primary Output Capacitor
    3. 3.3 Rectifying Diode
    4. 3.4 Secondary Output Capacitor
    5. 3.5 Preload Resistor
    6. 3.6 Zener Diode
    7. 3.7 Snubber Circuit
  6. 4Experimental Results
    1. 4.1 Steady State
    2. 4.2 Secondary Output Voltage
    3. 4.3 Load Transient
    4. 4.4 Start-up
    5. 4.5 Output Current
  7. 5Conclusion
  8. 6References
  9. 7Revision History

3 LMR36520 Fly-Buck Converter Design

GUID-20201218-CA0I-GC1D-CCRS-K3ZLLPMQNBDG-low.gifFigure 3-1 Fly-Buck™ Converter Schematic
Table 3-1 Fly-Buck™ Converter Design Input and Output Parameters
VIN minimum 10 V
VIN maximum 36 V
Vout1 5 V
Iout1 500 mA
Vout2 3.3 V
Iout2 500 mA
Switching frequency 400 kHz

In order to operate as a Fly-Buck™ converter, an IC that offers Forced Pulse Width Modulation (FPWM) must be selected to ensure that the part can handle negative inductor current. In this case, the LMR36520FADDA is selected for this reason.

The LMR36520 data sheet should be consulted for recommended values and equations for components such as input capacitor, feedback resistors, EMI filter, feedforward capacitor, CVCC, and bootstrap capacitor. The following design example will focus on calculating component values for Fly-Buck™ converter components specifically.