Efficient Voltage Regulators Spartan 3 Current Requirements

I assume you're going to use switching regulators to generate all voltages directly from 5 volts, this would be the most efficient way to do things. I use the Linear Technologies LTC3411 for this sort of application because it's readily available in small quantities, takes in up to 5.5 volts and outputs down to .8 volts, and it's above 90% efficient for a wide range of output currents, from 10 mA to well over 500 mA. It can supply up to 1.25 amps, though you need big tantalum caps to keep the ripple down when you get up there in current. It does have a few tradeoffs though -- it seems Linear's parts are more expensive than the big manufacturers, and this part will take up more board space than some other solutions and has a bigger BOM, adding to the cost.

Your current draw is going to vary widely depending on your design, and will always be more than the quiescent current. You can easily burn a couple watts in a medium-sized FPGA, and 5-10 watts in a bigger FPGA running at high speed.

Hi

Yaju N wrote:

Just estimate your power requirement with the on-line xilinx tools. The power requirements of FPGA vary in function of the design you load in it.

A 64bits 200Mhz DDR interface using DCI is not gonna use the same power as a a simple slow I2C interface ...

Sylvain

directly from 5 volts, this would be the most efficient way to do things. I use the Linear Technologies LTC3411 for this sort of application because it's readily available in small quantities, takes in up to 5.5 volts and outputs down to .8 volts, and it's above 90% efficient for a wide range of output currents, from 10 mA to well over 500 mA. It can supply up to 1.25 amps, though you need big tantalum caps to keep the ripple down when you get up there in current. It does have a few tradeoffs though -- it seems Linear's parts are more expensive than the big manufacturers, and this part will take up more board space than some other solutions and has a bigger BOM, adding to the cost.

will always be more than the quiescent current. You can easily burn a couple watts in a medium-sized FPGA, and 5-10 watts in a bigger FPGA running at high speed.

Besides Linear, check also the upcoming Texas TPS75003... seems good, but still preliminary announcementl.

Apart from the current requirements, it seems that I have to worry about the real estate for heat sinking. The new TI TPS75003 seems to be good device, but it basically consists of a linear regulator and not a switching one as I had thought.

I guess I will have to compromise on the real estate for heat sinking. Maybe I will include a "finned" heat sink.

The search for the best voltage regulator continues.....

Could you please be more specific on this ?

I was thinking of using it myself. I just quickly read the datasheets.

To me, it seems to have two buck regulators for core and I/O, where you usually have most of the current, and a linear regulator for VCCAUX.

Given that VCCAUX powers also DCM modules, and its quiescent current is not so big, perhaps you would have choosen an LDO in any case, to have it less noisy.

Am I missing something obvious here ?

I found a new company that is making a very advanced surface mount regulator module. They have combined everything onto the chip except for the capacitors and run it at 5 MHz. This includes the *inductor*! The module is only 0.5" x 0.32" and can provide up to 3 Amps.

I just took another look at the web site and they now also have 1 Amp and 6 Amp versions. The 6 Amp version is only 0.67" x 0.32"!

Rick Collins

snipped-for-privacy@XYarius.com

Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design

4 King Ave. 301-682-7772 Voice Frederick, MD 21701-3110 GNU tools for the ARM

I am basicaly trying to find what is the maximum current that will ever be needed for the FPGA I/0. I know it differs on application, but based on the maximum current required, I can choose the most efficient voltage regulators.

The other constraint I have is the real-estate space that would be needed for heat sinking the voltage regulators For that purpose swiching regulators would be preferred. In case of TI TPS75003, its does have buck regulators for the core and I/O but it also has (I think its "inbuilt") Linear Regulator which would need heat sinking area.

Maybe I am missing something totally obvious here as well. I dont have much experience in using Voltage Regulators. My basic constraint is of course is board space and I am trying to find ways to get around that.