On Sep 7, 7:54 pm, Peter Alfke <pe...@xilinx.com> wrote:
> Hi John.
> That's what I suggested in my posting yesterday.
> "Great minds think the same way" :-)
> Peter Alfke
>
> On Sep 7, 9:29 am, John Larkin
>
>
>
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> > On Thu, 6 Sep 2007 17:23:39 -0500, "Dan K" <danielgkNOS...@visi.com>
> > wrote:
>
> > >Using linear adjustable regulators for VCCINT (1.25v), VCCIO (3.3v), and
> > >VCCAUX (2.5v). VCCINT and VCCIO are dead on, but VCCAUX is 2.72v, 2.88v,
> > >and 2.92v on the 3 boards I grabbed and measured. All boards seem to work
> > >just fine.
>
> > >The regulator output voltage is controlled by just 2 resistors. When I
> > >changed one of the resistors to lover the voltage a bit, VCCAUX did not
> > >change. This leads me to believe that VCCAUX is somehow being "back"
> > >powered from the Xilinx chip. These voltages are present like this before
> > >the Xilinx chip has been programmed. I have not removed the regulator to
> > >measure current yet. Another thought was to put a shotkey diode between the
> > >regulator output and the load to see if the Xilinx really is powering
> > >VCCAUX, but I thought I'd post and see if anyone else has come across this
> > >issue. Half the I/O banks are 2.5v and half are 3.3v if that makes any
> > >difference.
>
> > >Thanks - Dan
>
> > Try adding a "dump" resistor from Vccaux to ground, and see if that
> > pulls the voltage down.
>
> > John- Hide quoted text -
>
> - Show quoted text -

I'm curious if the original poster has solved the problem in the
indicated way above.
I have a design with Stratix II which has the same behaviour.

thx,
Vasile