StabilityAnalysis Tool User's Guide For use with Board Mounted DC-DC converters V1.
Copyright *************************************************************************** * COPYRIGHT 2001, TYCO ELECTRONICS POWER SYSTEMS, INC. * * ALL INTERNATIONAL RIGHTS RESERVED * *************************************************************************** !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! BY USING THE INFORMATION CONTAINED HEREIN, YOU ARE AGREEING TO BE BOUND BY THE TERMS OF THIS AGREEMENT.
No oral or written information or advice given by Tyco Electronics or its distributors, agents or employees will operate to create any warranty or guarantee or vary any provision or information herein, and you may not rely on any such information or advice. Tyco Electronics reserves the right to change any portion of this data, and to change the Information, at any time without notice.
1 Introduction The Stability Analysis Tool (SAT) is a Microsoft Excel-based program that provides a Bode plot of the voltage loop gain of a DC-DC converter for a variety of external loads. From this plot, information such as crossover frequency and gain and phase margins can be obtained. In classical control theory, the stability of a feedback system is assessed by evaluating its gain and phase margin which are read directly from the Bode plot of the loop gain.
Installation and Usage You should first read and accept the terms of the SAT usage. Download the file SAT_v1.3.xls from the Tyco Electronics Power Systems web site (given below) to a directory on your computer. Download one or more module data file(s) to the same directory. You can start up the tool by following the usual procedures to open an Excel Worksheet and follow the directions on the screen. Make sure that the Analysis Toolpak Add-ins are enabled in Excel.
2 Using SAT When you start SAT, you will see the window shown in Figure 1. Fig. 1.
There are two sheets, "Module Selection" and "Configuration Menu" shown initially at the bottom left-hand section of the Excel spreadsheet. Each session should start at the "Module Selection" sheet. Click on the button Load Module Data File This will bring the module data file import window as shown below in Figure 2. Note that all module data files have .pwr extensions.
If you want to choose a different module data file, you can always go back to the Module Selection sheet to change it. The Configuration Menu lists five choices for representing the load circuit topology. The first configuration is a simple one where the output voltage is sensed directly at the output pins of the module. The capacitor is modeled as a series combination of equivalent series resistance (ESR) and equivalent series inductance (ESL). If all the capacitors are the same type (e.g.
model of the capacitor bank. The load is modeled by the resistance RL. The second configuration is similar to the first one except that the voltage sense location is moved from the output pins of the module to the load. In this case, the voltage sensed and regulated is not the module output voltage but the voltage across the load, a situation commonly referred to as "remote sensing".
SAT draws the Bode plot of the voltage loop gain on the right half of the page as shown in Figure 5. The phase margin, which is a measure of stability, and the gain crossover frequency, which is a measure of fast transient response, are also calculated and presented below the Bode plot. You can enter your notes under the "Notepad Area for JFW050A Module" section in the left lower corner of the page.
Stability Analysis Tool L S1 RS1 LS2 SENSE RS2 Magnitude of the Loop Gain R a2 Ra 3 Rb1 Rb2 Ca 1 C a2 Ca 3 C b1 C b2 Lb1 Lb2 La 1 L a2 L a3 40 RL 20 Gain (dB) DC /DC C O NVERTER Ra 1 Please enter the circuit parameters below Rload = 0.
To analyze a different module, you should select the Module Selection tab at the bottom of the Excel Worksheet to go back to the first page and load the data file for the new module. Note that the new data file will overwrite the old one belonging to the JFW050A. If you want to keep your analysis results for the JFW050A module, you should save SAT_v1.3.xls under a different name, e.g. JFW050A.xls.
customer application. SAT can be used to assess the common-mode stability characteristics of a paralleled converter system by analyzing an equivalent single-module system. The single-module equivalent is obtained by scaling the load by the number of paralleled modules. For example, in a two module parallel system, the load is scaled by a factor of two by doubling the load resistance, ESR’s and ESLs, and reducing the capacitances by half.
3 Limitations of SAT Although SAT is a powerful tool, please keep in mind the following : 1. The loop gain Bode plot and phase margin predicted by SAT are valid when the module is operating in continuous conduction mode (CCM). Therefore, make sure that RL is sufficiently low enough to guarantee a load current that leads to CCM operation. Modules with synchronous rectifier based output stages operate in CCM throughout the entire load current range. 2.
4 Troubleshooting If you encounter the following message when running SAT, there are two possibilities for the error message. 1. Some of the parameters you entered for your network are nonnumeric. 2. You have not enabled the Analysis Toolpack and Analysis Toolpack – VBA in your Excel environment as desribed in page 5 of this document under “Installation and Usage”.
