SNVAA84 October   2023 LMR36506

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Topology Selection
    2. 1.2 From Buck to Fly-Buck-Boost Converter
  5. 2Specific Implementation of the Fly-Buck-Boost Converter
    1. 2.1 Schematic
    2. 2.2 Bill of Materials
  6. 3Test Results
    1. 3.1 Start-up Behavior
    2. 3.2 System Loop Stability
    3. 3.3 Thermal Behavior
    4. 3.4 VOUT Ripple and SW Node Waveforms
    5. 3.5 Efficiency Data
      1. 3.5.1 Efficiency Data for Balanced Loads
      2. 3.5.2 Efficiency Data for Unbalanced Loads
    6. 3.6 Load Regulation
      1. 3.6.1 Load Regulation for Balanced Loads
      2. 3.6.2 Load Regulation for Unbalanced Loads
  7. 4Summary
  8. 5References

Abstract

This application brief describes a bi-polar (split-rail) ±15-V and 125-mA output power design usable in analog output modules of PLCs (Programmable Logic Controllers). The input voltage range of the design is 16 V to 35 V to address the standard 24-V rail which typically can be found in PLC applications. A Fly Buck-Boost (FBB) topology with an off-the shelf 1:1 coupled inductor driven by a single DC/DC converter is selected. This selection makes sure that the switching frequency for the positive and the negative output is identical to avoid beat frequencies and support the wide input voltage range. Operation at 1 MHz enables the use of a small coupled inductor and provides low-output ripple voltage of around 40 mVp-p. The selected LMR36506RFRPER forced PWM synchronous buck converter warrants accurate output voltage under symmetrical, as well as under non-symmetrical, loading of the positive and negative output rails.