SDAA210 November   2025 LM5125-Q1 , LM51251A-Q1 , LM5125A-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Application Implementation
  6. 3Design Considerations
  7. 4Test Results
    1. 4.1 Efficiency Measurements
    2. 4.2 Device Features
      1. 4.2.1 Soft-Start (SS)
      2. 4.2.2 Over-Voltage Protection (OVP)
      3. 4.2.3 Second phase enable (EN2)
      4. 4.2.4 Bypass mode
    3. 4.3 Load Transient
    4. 4.4 Line Transient
    5. 4.5 Temperature Measurements
    6. 4.6 Bode Plot
  8. 5Summary
  9. 6References

1 Introduction

The LM5125x operates over a wide input voltage range (up to 42V) and provides a regulated output that can be changed dynamically via the ATRK/DTRK pin. The LM5125x offers a number of different features such as: selectable switching frequency (100kHz to 2.2MHz), selectable dead time (18ns to 200ns), average inductor current monitoring, dynamically selectable switching modes (diode emulation mode (DEM) and forced pulse width modulation (FPWM)), programmable current limit and power good indicator.

[LM5125-Q1 data sheet, product information and support | TI.com]

[LM5125A-Q1 data sheet, product information and support | TI.com]

The boost controller is designed for synchronous operation, driving a high-side switch replacing the diode of the standard boost controller topology. Synchronous operation allows for lower power losses, by avoiding the forward voltage drop of the diode, hence an overall increase in efficiency. However, synchronous operation increases the BoM cost and the complexity of the design. In some applications, an asynchronous boost converter can still be a good fit, making use of a cheaper, smaller diode instead of the high-side switch.

This application note shows how to use the LM5125x in asynchronous mode while still having all the features the device offers. Test results show a decrease of only 2-3% in the overall efficiency of the converter.