package choice, temperature and obsolesence issues with a xilinx fpga

Hi,

I am involved in a project dealing with fpgas and the pcb may only be used on one side for component placement (actives an passives). Therefore I am considering using a QFP package instead of a BGA package for decoupling purposes mainly. My application runs at 40 MHz and the IO need is small (about 100 IOs). I am considering either a 208 QFP or a 256 FBGA for a Xilinx part like spartan IIE. The other issue is about obsolescence. I noticed the QFP package is still available for Spartan III. Is it a good indicator for the life of this package for Spartan IIE or is this idea irrelevant ? Finally, the temperature of the environment will border 85°C so I believe the regular industrial grade parts we use may be out of our specs. What is the rule for Xilinx parts like spartan IIE or else ? Since the junction temperature is 100°C what happens if the part is in an ambient temperature above 85°C ? Will it keep working or will performance be degraded ? Does it depend on the process of the FPGA for a same grade ? Is there a derating one can apply if the FPGA is out of specs but not about to be destoyed because junction temperature was not reached ? Any idea is welcome !!!

JF

Reply to
jean-francois hasson
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JF,

Wow. Not enough questions?

See below, I will try to do my best.

Aust> Hi,

A QFP package has significantly more inductance, and is harder to get a good decoupling design done right. A fgXXX package (fg256) is a much lower inductance value package, and with all components on top, is not impossible at all to do a power distribution decoupling scheme well. You may need two more layers in the pcb stackup to do it right (in either case). If you are having problems with your layout, you may send it into the Hotline, and someone will look at it for you, and advise you. My Lab gets invovled in many pcb cases. I would prefer you learn how to do it right and succeed the first time!

My application runs at 40 MHz and the IO need is small

The QFP will be around for quite awhile. It is too popular, and too high a seller. For extreme SI applications, it is not used, however.

Finally, the temperature of the environment will border 85°C so

85C to 100C is 15C junction to ambient. In a QFP package, that might limit you to about 1 watt of power dissipation in the part! This will be tough.

The 'rule' is that above 85C for commercial, and above 100C for Industrial, the device is not expected to meet specifications (but it will still function up to 125C).

Since the

Specifications may not be met.

Will it keep working or will performance be

Functionality will continue to ~125C junction, and beyond that we make no statements or assurances.

Does it depend on the process of the FPGA for a same grade ?

No.

Is

In the old days, when everything was simple, simple derating formulas could be applied to the CLB, routing, etc. With DCMs, BRAMs, etc. this no longer works at all. Perhaps you need the automotive version of the parts which is characterized (has a speeds file) for 125C abs max? Contact your disti or Xilinx FAE.

Contact your disti or Xilinx FAE. They can be more helpful than I.

Reply to
Austin Lesea

Is there an appnote with recommendations and/or examples? That would be really useful!

Reply to
Eric Smith

Eric, try XAPP623. Cheers, Syms.

Reply to
Symon

Eric,

The SI webpage on support.xilinx.com lists all of the collateral material that we can provide (and there is a lot). There are a couple of app notes that cover this topic.

Aust> Aust>

Reply to
Austin Lesea

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