"vasile" <[email protected]> wrote in message
news:[email protected] ups.com...
> 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
>
Yes, that was the problem. I had the M0, M1, and M2 pins connected to +3.3
v. As soon as they were disconnected from 3.3v and connected to 2.5v the
2.5v power supply was right on.

Dan