Forum Discussion
New ContributorWill a Cyclone IV be damaged if a a 3.3V LVTTL output is driven high, but connected to ground?
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!
Super Contributoraccording to output characteristics documented in Ibis files, shorted output current ttl33 8mA will probably exceed absolute maximum ratings for pin current. Damage possible.
New ContributorThank 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.
