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Web-based SMPS Design Programs Evaluation:Intersil
August 16, 2004
6 Min Read
Key Items for Evaluating the Web Design Tools:
I assumed that the majority of users would be relative novices in the field of switching power supply design. I noted the difficulties I had encountered during the process of evaluating these sites.
Some of the factors I looked for are:
1. Ease of navigation.
2. Understandability of terminology used.
3. Usefulness of information presented.
4. Detailed documentation of results -paper copies.
5. User computer revisions of SW needed to interface to the Web application
6. Ease of building first prototype
7. Comparing the design with classic approaches and to other simulation programs.
INTERSIL Web-based Design Program:
The system I ran was:
800 MHz P2, w/ explorer 6.0 & latest JAVA.
Minimum System Requirements are:
MAC System OS X with JAVA version 1.4.2.
Earlier systems are not supported by Apple and Sun Microsystems.
PC: System 98, ME, XP, and 2000.
Must download most recent JAVA tools to your system (free).
The Intersil Web-based tools were obviously designed by only IT people. There is no latitude for older operating systems or JAVA tools. This is a PC tool only. Although MAC OSX is somewhat supported, it is an Apple-only supported JAVA plug-in.
From The Home Page: http://www.intersil.com.
There are many choices that look like the choice you may want to choose for the simulation program. But only one choice leads you to the actual simulation tools. Select "Design iSIM Design Simulation Tool" or go directly to: http://www.intersil.com/isim/
Here you are presented with several 2 to 4 Phase VRM buck converters that are meant for the Pentium or Power PC applications. However, there are five choices that involve other ICs and topologies.
Select the power topology desired: Click on button "iS" adjacent to the desired design.
You are presented with a list of suggested component values that can be changed.
IF you were to select "view schematic", it presents a schematic that can be blown-up to fit the screen. BUT, if one wants to print the entire schematic, it cannot be done. The INTERSIL pop-up page set-up is for portrait, but their typical schematic should be printed in landscape-mode. From schematic window, there is no way to select the "page Set-up," unless the "print" window of your particular print driver includes the print orientation buttons for the printer. Otherwise, there is no way to print the right part of the schematic. Reducing the scale will make no change in the printout content. (Apparently a bug or an oversight in the program).
I would suggest printing the datasheet out before this point, which may include this schematic (with the same component designation numbers).
Select "Run Simulation":
This produces two Bode plots of the "open-loop" (control-to-output) and the closed loop Bode plots of the final circuit elements. The units are in the proper units but difficult to understand because of the presentation. They do not include the -180 degrees of phase lag added by the inverting (negative feedback) amplifier. So the user must add this -180-degree phase lag to the closed-loop phase plot to view the actual point where the closed loop approaches -360 degrees.
There is no print utility included on Bode plot screens, so it cannot be printed or saved to the local computer for future design documentation. Only the "print screen" utility can be used in this option.
Comparing the simulation results against other methods:
When comparing the component values presented in the feedback loop compensation against those derived from my book (Power Supply Cookbook) and from Ridley Engineering's POWER456, the values were within 10 percent of each other. Therefore, the INTERSIL simulation program uses the straightforward method of determining open-loop poles and zeros and for placing the compensating poles and zeros for making the relative optimum closed-loop compensation.
The INTERSIL ISIM tools cover less than 30 percent of the power management parts in INTERSIL's product portfolio. I would recommend that the user select the part that he wants to use first, printout the datasheet, implement the design using the datasheet guidelines, then proceed into the iSim utility. The designs offered by the simulation program are for one output voltage, output current and input power system (not directly changeable). It is good for verifying stability, but not as a design tool. The user must still design the end-circuit manually.
The presented designs only present the individual component values. So to change the operation of the selected switching power supply, such as the output voltage, frequency of operation, overcurrent settings, etc, the user must still manually perform the design equations or refer to the datasheet graphs for determining the new values.
The feedback compensation presents the straightforward approach of assigning the locations of the compensating poles and zeros within the error amplifier. If you want to change the location of these poles and zeros, the user must almost start from the beginning in determining the open-loop pole/zero characteristics. (you can get the main output filter pole from the open-loop plot ("power train transfer function)). The zero related to the output filter capacitor cannot be determined from the open-loop plot. Then the user must relocate the pole/zero frequencies, then run the classic equations for the actual compensation component values, which can then be placed within the simulator.
In short, if the user desires any changes to what was initially presented, the process is completely manual. Without the needed literary references on-hand, the effort would be a blind shot in the dark and be very iterative.
It is also very inconvenient because the user cannot properly print out the schematic and feedback simulator results. This makes it very inconvenient to document the design for the user's internal design reviews, if the part were to be included in an actual product.
I encountered some JAVA errors when running the simulations that had to be re-run to finally get the desired results. This was more a factor of the server loading than not having the actual required JAVA within my desktop computer.
This web tool is for the seasoned power engineer since the design must be completed before the user can derive any useful information from the simulation tools. Also an accompanying design resource, such as the "Power Supply Cookbook" might be in order, to quickly refer to the various design areas within a switching power supply.
There needs to be some additional work on these tools. They are not very useful for the occasional power supply designer. Perhaps having a design team that not only includes the IT department, but also some savvy applications engineers might be in order.
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