Peter Alfke wrote:
>>
>>>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
>
> I would load the Vccaux pin with a 100 Ohm resistor to ground. That
> adds 25 mA to the regulated current.
> Normall, this should hardly change the voltage, but if the regulator
> is back-fed, there will be a big voltage drop.
> Parallel resistors to ground are nice and easy, and do not cuase any
> irrepairable tdamage.

You can also drop the values of the two SET resistors, then you do not
need to change the PCB design.

-jg