Will a Cyclone IV be damaged if a a 3.3V LVTTL output is driven high, but connected to ground?

[BWalker]

Will a Cyclone IV be damaged if a 3.3V LVTTL output is driven high, but connected to ground?

The pin has the current strength set to 8 mA.

I'm working on an old design where the original designer added a switch to ground on an output pin that may get set high by the FPGA logic.  I'm trying to determine if this is a risk to the FPGA.

[FvM]

Hi,
according to output characteristics documented in Ibis files, shorted output current ttl33 8mA will probably exceed absolute maximum ratings for pin current. Damage possible.

[BWalker · Accepted solution]

Thank you for answering my question!

However, I'm still misunderstanding something.

I thought it would be safe, because this pin has the "CURRENT_STRENGTH_NEW 8MA" assignment set.  I thought this meant there was an internal current limiting feature to limit the output current to 8 mA under any situation, including when shorted to ground.

8 mA is well below the Absolute Maximum Rating of 40 mA for the DC output current per pin.

Would you please confirm I misinterpreted how this works?

Thank you!

[FvM]

Hi,
you are misunderstanding the meaning of 8 mA spec. It tells that the output voltage drop is keeping the LVTTL limits, e.g. 0.4V. Short circuit current can be as high as 40 or 50 mA.
As mentioned, Ibis files contain a full set of static output characteristics with min, typ and max current for all IO standards.

Here's the respective 8 mA pull-up curve

If I understand the datasheet correctly, the absolute maximum sink current per pin is 25 mA, already exceeded by typical GND short current.