■ Overview

This article explains why power supplies include regulation loops and how to optimize these loops to achieve optimal performance.

In order to verify whether the design process was actually carried out accurately, performance testing must be conducted in a laboratory.

This laboratory work is time-consuming because it involves the procedure of soldering capacitors and resistors of different values to adjust the compensation components.

Using a software-controlled compensation probe card allows these soldering tasks to be replaced with a mouse click, reducing the workload and shortening evaluation time.

■ Preface

Power supplies are generally designed to generate a fixed output voltage.

This output voltage must not oscillate and must remain constant despite load transient response or fluctuations in input voltage.

To optimize the control loop of a switch-mode power supply (SMPS), many power supply ICs include a compensation pin.

These pins allow for the optimization of the control loop by connecting appropriate compensation components, namely capacitors and resistors, enabling the achievement of the highest possible control bandwidth while maintaining loop stability.

The reason for allowing the control loop to be adjusted is due to operating conditions and power consumption.This is because the compensation method must vary depending on the selection of external components used in the furnace.

Figure 1 shows a buck (step-down) regulator with a compensation pin VC.


The selection of compensation parts can be performed using appropriate calculation and simulation programs such as LTpowerCAD® or LTspice®.

However, parasitic effects of the circuit board layout also have a certain impact. Therefore, power supplies must always be verified in actual hardware, and during this process, the selection of compensation components is ultimately confirmed and verified.

These steps take a lot of time during the power supply design process.

For example, you need to perform Bode diagrams or load transient response measurements using LTpowerAnalyzer.

If the obtained results do not meet the design goals, they must be optimized.

To do this, the existing compensation parts must be removed and replaced with parts of different values, but this process is labor-intensive and time-consuming.


Figure 2 is an evaluation board provided by Analog Devices, called a compensation probe.

This card can be connected to any power supply's compensation pin or ground pin via the solder contact on the right.

This board replaces the compensation part indicated in the red square of Figure 1.

The left side of the board connects to the PC via a USB cable. Once the hardware connection is complete, run the free software for LTpowerAnalyzer.

By utilizing this software, you can very quickly switch between parts with various compensation values using a graphical user interface (GUI).

You can also generate Bode diagrams using LTpowerAnalyzer and perform load transient tests at different compensation settings.


Figure 3 shows the software interface of the EVAL-LTPA-COMPRB (compensation probe) board.

Here, you can select resistance values from 511Ω to 100kΩ and capacitor values from 5pF to 39nF.

In addition, the internal series resistance of the capacitor is also indicated and can be considered together.

By connecting this compensation board to the ground terminal and compensation pin of the power converter IC to be tested with short connection leads, various compensation component values can be selected accurately, simply, and quickly.

■ Conclusion

Using a compensation probe such as the EVAL-LTPA-COMPRB allows for very easy and efficient verification and optimization of power supply control loop stability.

Various compensation settings can be tested in a very short time, which not only enables superior power supply designs but also contributes to reducing design time.

※ Author Introduction
Frederik Dostal is a power management expert with over 20 years of experience. After majoring in microelectronics at the University of Erlangen in Germany, he joined National Semiconductor in 2001 as a field application engineer, gaining experience in implementing power management solutions for customer projects. During his four years at NS, he worked in Phoenix, Arizona, where he was responsible for Switch Mode Power Supplies (SMPS) as an application engineer. Since joining Analog Devices in 2009, he has performed various roles, including product lines and European technical support, and currently serves as a power management expert based on his extensive design and application experience. He is currently working at the Analog Devices Munich office.