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

4.5 Short Circuit

The LMR38020 enters hiccup protection mode when the primary side output is shorted to ground, as the waveform shown in Figure 4-13. When the short condition is removed, the converter auto-recovered.

However, when the secondary side output is shorted to ground, the device does not shutdown or enter hiccup mode. Due to the negative peak current protection mode (start a new cycle when the IL_NEG is hit), the LMR38020 operates under very high fsw, the inductor and the silicon can be hot. This needs to be avoided during normal operation as hinted in Section 3.3.

GUID-20230807-SS0I-XXWC-J4DW-QX0PLX771KPS-low.pngFigure 4-13 Short Circuit- Primary Output
GUID-20230807-SS0I-ZGPH-WR1H-D5CKN0DCRDPM-low.pngFigure 4-14 Short Circuit- Secondary Output