SLAAEH7 February   2024 MSPM0L1306

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 System Description
    2. 1.2 Design 1: High Efficiency Design with 50kHz
    3. 1.3 Design 2: Space Optimized Design with 250kHz
    4. 1.4 Design 3: MCU Driven Design with Flexible Switching Frequency
      1. 1.4.1 Selection of MOSFETs
      2. 1.4.2 Efficiency Test
        1. 1.4.2.1 Current Consumption of PWM (Ipwm) Test
        2. 1.4.2.2 Efficiency Test Set Up
        3. 1.4.2.3 Efficiency Test Results at 50kHz Switching Frequency
        4. 1.4.2.4 Efficiency Test Results at 250kHz Switching Frequency
  5. 2Design File
    1. 2.1 Schematics
    2. 2.2 Bill of Materials
  6. 3Summary
  7. 4References

3 Summary

This application note introduces three designs regarding to isolated power supply for two-wire loop-powered 4 to 20mA field transmitter system.

Design 1 runs at a fixed switching frequency of 50kHz offers the highest efficiency at 5V input voltage, reaching 86%, and maintains a higher efficiency at lower input voltages. However, it uses a larger transformer which may not be optimal for size-constrained applications.

Design 2 with 250kHz switching frequency shows a slightly reduced efficiency compared to design 1, with the best performance of 80% at 3.6V. It benefits from a smaller transformer size, which is advantageous for compact designs.

Design 3 is the most flexible with programmable frequency up to 500kHz, allowing a small transformer, and maintaining a compact form factor. Table 3-1 gives an overview of these three designs.

Table 3-1 Comparison of Three Designs
Features Design 1 (50kHz) Design 2 (250kHz) Design 3 (up to 500kHz)
Switching Frequency Fixed 50kHz

(- 40%, +40%)

 Fixed 250kHz

(-40%, +20%)

 Programmable up 500kHz
Efficiency
  • 86%(5V)
  • 82%(3.3V)
  • 80%(3.6V)
  • 67%(1.8V)
  • 50kHz:
    • 83%(3.6V)
    • 72%(1.8V)
  • 250kHz:
    • 77%(3.6V)
    • 62%(1.8V)

Transformer Size(mm3)

Large

9.78 x 9.50 x 10.54

Small

9.60 x 5.51 x 4.83

Small

9.60 x 5.51 x 4.83

In conclusion, the selection of an appropriate design should be based on specific application requirements, considering factors like overall board size and efficiency. The design 3 is particularly suitable for systems where an MCU is already present on the non-isolated side, offering a streamlined integration with programmable flexibility.