Help with Virtex II and 5v TTL

Help, I've been trying to find a definitive answer to this question. Can I connect Virtex II pins configured as pure outputs (LVCMOS33 or LVTTL) directly to 5v LSTTL, ACT, or FCT INPUTS without any resistors and not risk any damage ?

I've used the quickswitch design from the appnotes for my bidirectional pins, and 175 ohm series resistors for 5v TTL inputs to the Virtex II, but I tied the fpga outputs directly to 5v input logic pins and now I think I have a Virtex II part failure.

Any feedback greatly appreciated.

Thanks Jim

Reply to
Jim
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Jim,

See below,

Aust> Help,

Yes (you can connect directly a 3.3V output to a 5V input). It is the reverse that you can not do without a resistor.

Unlikely this is the cause. Unless the inputs can behave as outputs? Check during power ON? power OFF?

When you say a "part failure" what kind of failure?

Reply to
Austin Lesea

Part failure as in 3.3v sucking mucho current > 5 amps, when normally the module takes less than 100ma idle. When problems began, measured 2 ohms from

3.3v to gnd. 30ohm from 1.5v to gnd.

Haven't done a full analysis yet, but the only active 3.3v parts on the board are the virtexII xc2v40, xcf02s, 2 quickswitch idtqs3r861

Thanks for replying, will post more when more info is available. Jim

connect

to 5v

?

but I

Reply to
Jim

Jim,

That sounds like a complete electrical overstress of Vcco (basically, complete oxide and/or junction failure).

That is usually something caused by a power supply grossly overshooting on turn on (as in way beyond the abs max ratings), or momentary negative voltage being forced on the IO pins, or the Vcco supply (as in a momentary short to -48V -- always sure and sudden death!).

Aust> Part failure as in 3.3v sucking mucho current > 5 amps, when normally the

Reply to
Austin Lesea

Thanks Austin, will check the power supplies more carefully and post back when I have more info.

Jim

Reply to
gja

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