programmable voltage control of a VCCIO Bank

[Amontec Team]

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
www.amontec.com

 

[Jonathan Bromley]

On Thu, 15 Jul 2004 13:14:33 +0200, Amontec Team
<laurent.gauch@amontecDELETEALLCAPS.com> wrote:

Laurent,

Sorry but this question is not about logic system.

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

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.

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
VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services

Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK
Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com
Fax: +44 (0)1425 471573 Web: http://www.doulos.com

The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.

 

[Nial Stewart]

"Jonathan Bromley" <jonathan.bromley@doulos.com> wrote in message
news:q8tcf05ainjeubq31cilv4ds8gapjgjdjf@4ax.com...

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.

...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
www.nialstewartdevelopments.co.uk

 

[Andrew Dyer]

On Thu, 15 Jul 2004 13:14:33 +0200, Amontec Team wrote:

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.

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