Virtex4 Powerdown, Vcco questions

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Hi *,

I'm planning a device with a backup battery. In case of power failure,
the FPGA (a Virtex4 in this case) should be shut down to save power,
whereas other components on the board need to keep working.

So, since the PWRDWN-pin doesn't do anything what I was planning to do
is to simply turn off the regulators for Vccint and Vccaux as soon as
the power fails.
But I can't turn off Vcco, since it's used as a supply for other
components as well (unless I use a separate regulator just for Vcco).

Can I damage the FPGA if the IO-banks are powered but the core isn't?
And what will happen to the I/Os once the core supply goes away, but
Vcco stays? Will they just start floating?


Re: Virtex4 Powerdown, Vcco questions

Nothing bad happens.

The IO banks draw 2 to 8 mA from 3.3V while remaining tristate.  The
center banks are smaller and draw 2 mA, the larger banks all draw ~ 8mA


Sean Durkin wrote:

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Re: Virtex4 Powerdown, Vcco questions
austin wrote on 08.02.2006 20:04:
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OK, perfect, just as I would've expected.

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Very good to know, thanks for the info!

But, another question: What happens if I turn Vccint and Vccaux back on
again? According to the User Guide, it doesn't matter if Vcco is powered
up before Vccaux:

"The VCCAUX and VCCO power supplies can be turned on in
any sequence, though VCCAUX must powered on before or
with VCCO for the specifications shown in Table 5. Xilinx
does not specify the current when VCCAUX is not powered
on first."

But Vccint isn't mentioned at all here... So, can I just power up the
FPGA-core again and reprogram the part (assuming I don't violate Tconfig)?


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