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Xilinx Coolrunner II CPLD power-down input characteristics?

S

Spehro Pefhany

Jan 1, 1970
0
Hi, all:-

A bit of a long shot here, but does anyone know whether the inputs
will float on the Xilinx CPLD parts will float when power is not
applied or do they have a nasty protection structure to a supply pin?

And if so, what if I float the related Vccio pin-- will that allow the
input current to be reduced to just leakage current?

I don't see any info in what appears to be the relevant document:
http://direct.xilinx.com/bvdocs/appnotes/xapp382.pdf


Best regards,
Spehro Pefhany
 
U

Uwe Bonnes

Jan 1, 1970
0
Spehro Pefhany said:
Hi, all:-
A bit of a long shot here, but does anyone know whether the inputs
will float on the Xilinx CPLD parts will float when power is not
applied or do they have a nasty protection structure to a supply pin?
And if so, what if I float the related Vccio pin-- will that allow the
input current to be reduced to just leakage current?
I don't see any info in what appears to be the relevant document:
http://direct.xilinx.com/bvdocs/appnotes/xapp382.pdf

Some more words are said in the datasheet ds090.pdf, page 11,
Power-Up Characteristics

For the protection structure, perhaps check with an ohmmeter/conduction
tester on an unpowered board...
 
S

Spehro Pefhany

Jan 1, 1970
0
Some more words are said in the datasheet ds090.pdf, page 11,
Power-Up Characteristics

For the protection structure, perhaps check with an ohmmeter/conduction
tester on an unpowered board...

Thanks.

I would in a NY minute, if I had one..


Best regards,
Spehro Pefhany
 
K

Ken Smith

Jan 1, 1970
0
Hi, all:-

A bit of a long shot here, but does anyone know whether the inputs
will float on the Xilinx CPLD parts will float when power is not
applied or do they have a nasty protection structure to a supply pin?

And if so, what if I float the related Vccio pin-- will that allow the
input current to be reduced to just leakage current?

I don't see any info in what appears to be the relevant document:
http://direct.xilinx.com/bvdocs/appnotes/xapp382.pdf

I can't say for sure about the 3.3V version of the Coolrunner but I do
know that there was no diode to the Vdd rail on the 5V parts. They seemed
to have zener/thick-oxide like protection. The input didn't hit a hard
limit as it passed Vcc+0.7 as a diode would. This doesn't mean your idea
will work however. The input leakage current may rise quite a bit before
the hard limit is hit.
 
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