Virtex "Virtual VCC"

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Hi !

I have a PCI Mezzanine Card (PMC) with a Virtex 400 and a front panel
connector. The Virtex is connected to the SCSI-2 style front panel
connector with 68 pins.These pins are interleaved signal and ground
pairs.So, I have 34 free I/O at the front panel connector.
  
I would like to connect a little add-on board to this front panel
connector. This board will be populated with a Gigabit Ethernet
Controller (PMC-Sierra PM3387). Besides data and control signals I
have to provide power to the add-on board.

I am planning to connect the add-on board VCC plane with the I/O pins
at the front panel connector. Then the Virtex will drive '1' at the
front panel connector I/O. The add-on board ground plane will be
connected with the ground pins at the front panel connector.

Can this provide sufficient power to the add-on board ?
Is there a better way to provide power ?

Thanks in advance.

Mark Lenz

Re: Virtex "Virtual VCC"
Mark, your question cannot be answered without knowing the Icc
consumption of that extra board.
If it is <10 mA and not too picky about low Vcc, this might work if you
select the strongest Output drive for the pin ( or do you intend to use
multiple pins?)

Once you know the current, you can experiment with a simple resistive
load. :-)

Peter Alfke, Xilinx
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lenz wrote:
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Re: Virtex "Virtual VCC"
Hi Peter,

thank you for your response.

The datasheet of the chip which is on the add-on board states a DC
Input Current of +/- 20mA. I have a total of 4 pins to provide power
to the add-on board.
The Virtex datsheet states a output current for one pin of +/- 24mA
for LVTTL. As a novice I would expect that one pin with +/- 24mA would
be sufficient to source the add-on board which requires +/- 20mA. Is
this correct ?

How can I determine the value of the experiment resistor. I assume
Vcc/Icc. Is this correct ?

Regards,
Mark Lenz


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Re: Virtex "Virtual VCC"
Yes, that's what I would use as resistor value.. I would use all 4 pins
in parallel, and configure them such that they can only pull High ( the
mirror image of opencollector ) which means:
 output a permanent High level
and keep the outputs permanently active (Tristate control input = Low).
Viel Erfolg!
Peter Alfke
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