Xilinx V4 Power Calculations

JD,

I'll look into it.

Aust> I am doing some evaluation on a possible XC4VFX20 design and had a

Austin,

Thanks for looking into it; power analysis and regulator sizing are not exactly the FUN part of the design process, but they still must be done :-(

Any info appreciated.

Jim Davis JDDC

Austin,

One more thing; I noticed that the same is true for the DCM (no variance over temperature; I did not have the data for the DCM previously so I had not entered it).

Since it is about 38mW (3 for VCCINT, 5 for VCCAUX dynamic and 30 for VCCAUX standby) it could be a factor at 85 degrees C if it does indeed vary over temperature.

Thanks for any help!

JD

Jim,

The Vccaux has so little running off it, that there is hardly any significant difference in current with temperature.

The 405PPC is always there on die, so the static leakage is also there, if you use it or not. The dynamic current of the 405PPC hardly varies with temperature: the stronger and faster at cold balances with the weaker and slower at hot. Faster edges spend less time not being a 0 or a 1, slower edges spend more time between 0 and 1. Stronger transistor draw more current (but for less time). Weaker transistors draw less current (for more time).

Yes, we could be more accurate for a particular process corner, but it would not be worth it: we need to be safe for all process corners.

Aust> Austin,

Following on from Austin's i/p, I'd just like to add that our V4 concentration (in terms of what the Web Power Tool models) has been on where we have seen the greatest variation, i.e., VCCINT quiescent.

Brendan

Austin,

I guess I would expect VCCAUX power to scale at least somewhat with VCCINT power over temp since at room temp they only differ by a factor of two for current draw (since they have the same power at room temperature but different voltage).

Understood about the leakage current on the PPC; of course, if we didn't want to use it we could have looked at the LX :)

How about the DCM (I added that question in a later post)? It also doesn't vary over temperature in the calculator.

Thanks for the info,

JD

Comments below,

Austin

Vccaux uses all thick oxide transistors. Leakage varies imperceptibly with temperature compared to all the analog stuff which has a fixed bias always flowing.

It varies A LOT with frequency.

It runs (partially) from a regulator supplied by Vccaux, at a lower voltage than the core, so leakage is again something of little consequence.

The control logic runs from Vccint, but is so small in the overall scheme of things on Vccint, that again, it is lost in the Vccint leakage with temperature.

Austin,

I guess I am concerned that all of these "imperceptible" changes in power over temperature that are calculated as ZERO in the power calculator could actually add up to be something. Are you saying that the combination of VCCAUX, multiple DCMs and multiple processors will still result in zero power difference between 25 degrees C and 85 degrees C for those functions?

Thanks,

JD

JD,

It is of course not identically 0, but it is small enough that variations from part to part will mask the effect.

So the process margin is much larger than the variation, so the variation is of no importance.

Aust> Austin,

Austin,

I am probably not planning on using any of the DSP48 blocks, but I noticed the same for them (no change over temperature). Apologies for the skepticism, but it seems strange to me that I could load up my device with DCMs, DSP48s, PPC405s and measure the power at room temp and at high temp and have the difference between those two values be the same difference I would get if I were using NONE of those resources in the first place.

Anyway, is there a spreadsheet for power calculations that I can get that would allow me to both do this analysis offline?

Thanks,

JD JDDC

JD,

The only difference for power at high temp versus low temp is leakage current. All of these blocks (DCM, DSP40, PPC405) are in the silicon and whether or not you are actively using them they are sitting there and leaking current from the VCCINT supply.

Adding these into the power tool as a "used" element will change the dynamic portion of the power consumption for the device, but it won't change the leakage current component as this is function of the device that you selected which includes leakage from everything that is in the silicon.

Ed

JD_Design wrote:

JD,

As I have said before (and also explained it to you), the differences are swamped by the margin for process.

As for a local version of the predictor, we no longer support the excel spreadsheet downloaded version. We are reconsidering that decision. Initially, there was only a spreadsheet for download. Then we had both the spreadsheet and the web based spreadsheet.

How many folks out there want to have the local spreadsheet version for estimating?

Aust> Austin,

Austin,

Obviously, I vote for the spreadsheet :)

Thanks!

JD

I vote for a spreadsheet. Using the web thing to present power numbers to a customer is a real PITA.

--

--Ray Andraka, P.E. President, the Andraka Consulting Group, Inc.

"They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759

OK,

I have received three votes for the spreadsheet.

That isn't going to convince anyone!

I am sure there are more of you out there who would like the spreadsheet, but perhaps you are just not inclined to email me?

Please don't clutter up the newsgroup, mail me directly at snipped-for-privacy@xilinx.com.

Aust> Aust>