SNVAA87 august   2023 LMR38020

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Micro Inverter System
    2. 1.2 Typical Power Tree and Design Requirements
  5. 2Conventional Flyback Design Challenges
    1. 2.1 SSR Design Challenges
    2. 2.2 PSR Design Challenges
  6. 3New Fly-Buck Design
    1. 3.1 LMR38020 Overview
    2. 3.2 Comparison with Conventional Flyback
    3. 3.3 Design Considerations
    4. 3.4 LMR38020 Fly-Buck Design Example
  7. 4Bench Test and Result
    1. 4.1 Start Up
    2. 4.2 Typical Switching Waveforms Under Steady State
    3. 4.3 Efficiency
    4. 4.4 Load Regulation
    5. 4.5 Short Circuit
    6. 4.6 Thermal Performance
  8. 5Summary
  9. 6References

3.4 LMR38020 Fly-Buck Design Example

Figure 3-2 shows a typical application circuit for LMR38020 Fly-Buck™ with one non-isolated primary side output and dual secondary isolated outputs.

GUID-20230807-SS0I-DKXN-R79C-8JFXTWFZ7P54-low.svgFigure 3-2 LMR38020 Fly-Buck Application Circuit Example

Referring to the design requirements of the 7-watts auxiliary power example in Table 1-1, the detailed design parameters of LMR38020 Fly-Buck™ for micro inverter application are listed in Table 3-2. The detailed design procedure are not discussed in this application note, please refer to Designing an Isolated Buck (Fly-BuckTM) Converter using the LMR38020 for more details.

Table 3-2 Detailed Design Parameters
Design Parameter Example Value
Input voltage range (VIN) 16 V to 60 V
Primary output voltage (VOUT1) 12.6 V
Primary load current (IOUT1) 0.4 A
Isolated output voltage (VOUT2) 12 V
Isolated load current (IOUT2) 0.1 A
Isolated output voltage (VOUT3) 12 V
Isolated load current (IOUT3) 0.1 A
Switching frequency (fsw) 250 kHz