Spartan 3 Power Supply Design

Jakob,

scroll down to "Power Partner Websites"

All of these excellent vendors products have been reviewed for use for Virtex, and Spartan products. They have fully integrated packaged solutions (for example, TI POLA series which we use on our ML series of boards), or components, and most have eval pcb's, too.

My lab has tested many of these to be sure they work (such as the advanced Bellnix super fast point of load supplies which don't require any high value capacitors, and one uses fewer bypass caps -- really!), and all have been thoroughly reviewed.

Any questions or comments on any power supply information should be directed BOTH to the vendor directly, and please cc me.

Vendors have their own FAEs and engineers who will supply you with complete designs, layouts, and a bill of materials.

I started this service, and I take it very seriously that we recommend only those products that will work without any difficulties.

Aust> Hello Everyone,

Austin,

thank you very much for your swift reply. The reason for my initial post was, that I already had a look at the Power Central page and also at all of the Power Partner Websites. As you say there are a number of example designs and products that I could choose from. The difficulties I am having is that there are so many different designs, and I know too little about power supplies in order to make an educated judgement on whats best for me. I am currently in the process of trying to understand some of the designs.

Most of the example designs are based on 5V or 3.3V Vin. If I have

11.6V as my main power source, should I step down to 5V first, and use one of the example designs, or would it be better to go from 11.6V to the individual rails directly?

Also, is it correct, that with increasing current requirement, there needs to be an inductor? I figured the inductors are the largest parts in the design.

thanks greatly for your help.

Jakob

Jakob,

I would suggest you intially buy a module, or a complete power supply for each required voltage (least expensive option).

There are standard modules that take a 12V input.

6, 5, and 3.3 V inputs are more common, however.

If you were an experienced power supply designer, I would suggest a fairly standard synchronous rectifier flyback design, with a tapped inductor to provide all your supply voltages at the same time... basically what PC power supplies look like.

The power supply is often left for last, and is the most often source of problems, as there are very few individuals left in the world who can actually design switching power supplies.

Linear power supplies are completely out of the question for the low core voltages today, as they would be just horribly inefficient.

If you want to design power supplies, first read the four or five textbooks out there on designing switching regulators, then get the evaluation kits for a half dowzen different parts. Then learn how to design inductors and power transformers by reading the ferrite core manufacturers guides to using their products.

For most engineers, v = -l di/dt is a complete and utter mystery.

It is a long road, and you will have many failures (or else you are not learning).

If you just wish to use an existing design from a vendor, get their layout for their pcb, and their bill of materials, and copy it exactly on your pcb. And then hope you didn't make any mistakes.

Aust> Austin,

Austin's suggestions were great.

I'd add that if you want to build only a few, the 12V compliant switcher modules for each rail (and a linear for the VCCaux) is a great suggestion. If you want to put together enough devices that 1) you don't want the expense of the modules and 2) you don't want to bring in the expertise for the multi-rail, 12V tolerant optimized design selection then your idea of regulating to 5V and then further to the rails would work nicely; the efficiencies are poorer than direct conversion but there's "ease versus specs" to consider in your situation.

The TPS75003 was listed at $25 for an eval board. When I went to buy one, it was $10. So I bought three. You should be able to prototype things pretty quickly.

Hi Jakob,

You *must* use a switching supply if you are to avoid a heatsink given the constraints you mention.

IMO, the physically smallest solution will have one switching DC/DC converter and a linear reg for each rail.

If you are a "software engineer gone electronics" then I recommend buying a DC/DC converter module instead of rolling your own with a controller chip, mosfets, inductors, low ESR caps and so forth. The disadvantage is that it costs more. The advantage is that you can get it to work. You should be able to find a few dozen modules that would meet your requirements here:

Regards, Allan