programmable voltage control of a VCCIO Bank

Hi all,

Sorry but this question is not about logic system.

I have to control the VCCO of one bank of a SPARTAN-3. I need to be able to control the drive of 3.3V, 2.5V, 1.8V, 1.5V, 1.2V to VCCO.

The main control would be in the FPGA itself. I have to add an external electronic to switch between the different voltage sources.

Do you have any circuit example to do a controllable voltage switch or to do an controllable DC/DC regulator.

Price and dimension are very important for this design.

THANKS Laurent Gauch

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Amontec Team
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Laurent,

Yes, it is. In most systems it's these "peripheral" issues that cause the most trouble...

I suggest you trawl through Maxim, Linear Technology and all the usual power-supply suspects. For some while now, Pentium-class CPUs have had a digital output (5 bits, I think) that sends to the power supply a value indicating what Vcc(core) voltage is required. The standard CPU power regulator solutions interpret this value and change their output appropriately. They are far too powerful for your needs, but that should not be a problem - it simply means that you should be able to use smaller external components (L, C). They all provide excellent application notes and example circuits.

Alternatively, if the current requirements are fairly low, you may find that the good old LM317-class regulators will do what you need. You can build a simple resistive-ladder DAC on one set of FPGA outputs, and use it to set the tail voltage for the LM317 device.

There is a truly huge selection of power regulator devices available today. Their performance is much better than the older parts, they are available in tiny surface-mount packages, they are cheap (because they're used in high volume applications) and, for the switch-mode parts, they now use very high switching frequencies so that the external passive components can be quite small. It's just a question of raking through the websites until you find a part that meets all your criteria *and is freely available*. To be sure that your chosen part is available, it's often a good idea to begin your search at one of the "supermarket" distributors such as Newark/Farnell, RS, Digi-Key or whatever. Anything in their catalogues is probably a popular part with good availability.

If you can cope with the flames and aggression, you might get a good response if you post on sci.electronics.design as well.

If you need the design doing for you, we could probably help on a consultancy basis.

--
Jonathan Bromley, Consultant

DOULOS - Developing Design Know-how
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Reply to
Jonathan Bromley

..or use a single pin to generate the PWM output for a PWM DAC.

There's an app note on the Xilinx web site on this.

Nial

------------------------------------------------ Nial Stewart Developments Ltd FPGA and High Speed Digital Design Cyclone Based 'Easy PCI' proto board

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Nial Stewart

How about a digital pot (Xicor or similar) in the feedback for an adjustable linear regulator?

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Andrew Dyer

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