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Message
From: John Sheahan <jrsheahan@o...>
Date: 27 Nov 2003 08:23:22 +1100
Subject: Re: [oc] OT : FPGA price
On Thu, 2003-11-27 at 02:10, Martin.J Thompson wrote:
> >On Tue, Nov 25, 2003 at 10:54:27AM +0000, Martin.J Thompson wrote:
> >> >-no 2A power up spike,
> >>
> >> None of that in V-II or Spartan-III
> >
> >the virtex's are specified to draw a big power-on surge actually.
>
> Correct Virtex, Virtex-E, Spartan-II and SpartanIIe, and probably Spartan-XL.. Not Virtex-II
> Also, All the Altera FPGAs as far as I know exhibit this behavoiur, but its less well documented.
>
I was not aware (as I didn't look) the virtex II had eliminated surge.
The VII-pro has it back again, specified only for a particular power
sequencing, although with the statement that alternate power sequencing
is not destructive. The smallest one (v2p4) was in the half amp range
from memory.. Just vague enough I had to add supply sequencing to ensure
supplies came up ordered.There was not a big margin there.
> >Thats if you bring up the supplies in the correct order.
> >No idea what happens in the 'wrong' order.
> >
>
> Tjmax is what matters to whether your design works or not. If you have a single FF toggling at 1Hz you can probably run in an ambient close to Tjmax. In a big design all clocking fast, your maximum allowable ambient temperature is lower for the same Tjmax. That's why there no point any vendor quoting me a Tambient max. They know nothing of my design.
>
This is true.
device reliability (FIT) becomes a concern too.
My response was only to emphasize although its tjmax that matters, for
timing reasons, that the ambient enters into the calculation.
Specifying max ambient would only make sense if the device power
consumption is a constant. Hey - just like those early-eighties PLDs.
> Cheers,
> Martin
--
John Sheahan <jrsheahan@o...>
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