Maximum Current utilized by Spartan-3

I am trying to use a Spartan 3 in my design.

The power requirements and current requirement are going to vary according to applications. According to a TI website for Sparatan 3, the VCCINT (1.5v) has the current range from 300mA to 10A, and for VCCO(3.3V) the current range is from 50mA to 3A. For VCCAUX(2.5V) the current is maxed at 300mA.

Has anyone used such high currents when using a Spartan 3.

I will be implementing soft-cores and will be utilizing most of the core. So I am expecting a heavy load on the FPGA. I just wanted to be able to estimate the current that would be required, so I can choose the correct Voltage Regulators. Many of the voltage regulator specify the current limits as 1-2.5A, which may not meet the requirement for upper limit of the current requirement for Spartan -3.

I did post a previous topic regarding chossing a voltage regulator,but I wanted to be more specific on the issue at large.

Thanks for your help.

-Yaju

Reply to
Yaju N
Loading thread data ...

Yaju,

Use our Power Prediction web tool to esitmate your actual power.

The 'problem' with FPGAs, is that they will use whatever power you tell them to: so we (and TI) have no idea how much power they will need to do your job (after all, it is your job to do, and we don't know what that is).

formatting link

Aust> I am trying to use a Spartan 3 in my design.

Reply to
Austin Lesea

Which Spartan-3? A -1500 part will consume a lot more current than the

-200 part for designs which use "most of the core."

What clock frequency? Check out the Xilinx power utility (online). What type of utilization? SRL functionality consumes more power than standard LUT.

2.5v rail should be easier to estimate if you're only using it for VCCAUX. (I think) it's only used for the DCMs and configuration logic.

Play with the power utility to determine ballpark figures or even upper bounds. It'll give you a general feel for how the thing will be sucking down current.

Jake

Reply to
Jake Janovetz

Yaju, remember, this is CMOS which (until recently) consumed no static power at all. The size of the chip and the size of the design does not matter, the power comes from clocking the logic. And the current or power is proportional to the clock rate.

Things have become more complicated in 130 and 90 nm technology, where we have a significant amount of leakage current and power that is independent of utiliation and clock frequency, but increases very much with higher teperature.

Except for the leakage current, the power is design-dependent, i.e. your design! Peter Alfke, Xilinx Applications

Reply to
Peter Alfke

I am using a Spartan 3 the PQ 208 package. The maximum input current available to the board is going to be 2.5A. I am just concerned whether that will be good enough. I am planning on using a 50Mhz oscillator on the board, similar to the one one the Spartan 3 demo board.

I am not sure what my application is going to be. I am currently developing the board as a part of my Master's research. So I will be experiementing with different designs on the board. I just wanted to finalise the board so that the FPGA would be a ready to go product, without having to worry about the power and current.

The online estimation tool requires some very specific information about the prospective design or application which I may not be able to accurately predict at this point. But I guess I will give it a try.

I guess what I would be looking for if I have missed an "CRITICAL" current or power specs, which might render my board useless if I implement some amazingly futuristic design or application.

Is power and current specification a very important issue at all, as I feel I might be speding too much time on something trivial? I am planning on just throwing in the new TPS7xxx buck regulator hoping it will work fine. Other than that I guess my advisor suggests sticking to the Linear Dropout Regulators as used in those Demo Board, since they have been in use for a while and hopefully they work fine.

Yaju y a j u at b y u edu

Reply to
Yaju N

The easiest for you would be to "play" with an existing evaluation board, where you can easily find out the power consumption of different designs. Implement a long shift register with a toggling first flip-flop ( relatively high power) or a counter ( less power per bit). You should be able to do a lot of logic with 2.5 A and 50 MHz... Peter Alfke

Reply to
Peter Alfke

If this is just a one-off or very low volume device that doesn't require a high-efficiency power source, why wouldn't you use an LDO? They're easy! Although switchers, etc, are getting easier and more reliable, they're more complicated -- just in component count alone.

Also-- what's wrong with off-the-shelf eval boards?

Jake

Reply to
Jake Janovetz

Beware. Modern LDO regulators have restrictions on the ESR of the filter caps. Too low or too high and they oscillate.

I'm far from a wizard on this topic. But I got burned several years ago so it's on my hot-list of things to check carefully and then still be suspicious.

I think older non-LDO type linear regulators are easier to work with. But they often don't go down to 1.2V.

--
The suespammers.org mail server is located in California.  So are all my
other mailboxes.  Please do not send unsolicited bulk e-mail or unsolicited
 Click to see the full signature
Reply to
Hal Murray

Also, bear in mind that older devices may not have the load-transient response performance that modern high-speed logic may need.

Reply to
Mike Harrison

[...]

Even LDOs that go to 1.2V are fairly uncommon. National has one, the LP3881ES-1.2 ($2.58 from Digikey in quantity 100). That seems quite expensive, but it is well documented. The typical application shows

4.7uF tantalums for the input and output filters, says that 4.7uF is the recommended minimum for both the input and output filter capacitors, and gives a range of output capacitor ESRs for which it is stable (dependent on load current). They point out that aluminum electrolytics have high ESR below 10C, and often have their ESR specified only at low frequencies. Ceramic capacitors have too low an ESR for stability.

Someone else in this newsgroup brought to my attention the very inexpensive Sharp 1.2V LDO, PQ012FZ ($0.66 from Digikey in quantity

100), but the data sheet doesn't describe the requirements for the capacitance and ESR of the filter caps. The test circuit shown in the data sheet has a 0.33uF on the input, and a 100uF 50V on the output, but no ESR or specific capacitor type is mentioned.

Eric

Reply to
Eric Smith

The simple designs are working fine on the evaluation board, and not big power consumers.

What if I want to use all the logic that is available to me on the Spartan -3 FPGA (PQ 208). For now, I have a 50Mhz oscillator on board, so the application would run at a maximum of 50Mhz. The FPGA board derives its power from another board, which can provide upto a maximum of 2.5A.

I am basically looking for the worst case power or current requirements for the FPGA. As this is part of my research, I would be creating designs which put the FPGA to its limit, basically using as much as the FPGA can offer. It would not be impressive, if I my board burns up because of the high power application I implement on the FPGA. Its interesting that I have been unable to find any documentation on this topic online.

Thanks for any help,

Yaju N y a j u attherate b Y u eD u Peter Alfke wrote:

different

bit).

Reply to
Yaju N

Actually there are DCMs in a Spartan-3 that allow you to run your design on much higher frequencies, even if there is only a 50 MHz oscillator present.

Kolja Sulimma

Reply to
Kolja Sulimma

But 1.25V are extremly common. They call it "adjustable" ;-)

Kolja Sulimma

Reply to
Kolja Sulimma

Yeah, but what about tolerances? The 1,25V reference of the good ole LM317 ist exactly 1,25V. Are the tolerances within the +/-5 % of the 1,2V for the core?

Regards Falk

Reply to
Falk Brunner

Yes, but for most of them 1.25V is the maximum spec for the reference voltage, so they're not guaranteeed to be adjustable below that. Since

1.26V is the maximum Vint for Spartan 3, that's cutting it too close. Better to use a regulator for which 1.2V is actually within the rated specifications.
Reply to
Eric Smith

No. The reference voltage specification for the LM317 is min 1.20V, max

1.30V (page 5 of data sheet from National, dated July 2004). So for any given LM317, you *might* be able to adjust to within the rating of an XC3S (1.14V to 1.26V), or you might not. The LM317A has a tighter range, 1.225V to 1.270V, which is still potentially out of spec.

The only linear regulators I've found that meet the spec are either 1.2V fixed LDO, or special low voltage LDO.

Reply to
Eric Smith

From the above, -50mv on the reference pin would bring the LM317 into spec...

- Brian

Reply to
Brian Drummond

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.