Re: explaination of table 3 of appnote 447

Altera_Forum · ‎04-25-2007

I dont understand table 3 of appnote 447. The 3.3v row and 3.3v TTL column... The table says that if the driver is capable of 30mA or less at Voh of 2.4v then all is good. How does this relate back to the original requirement that the V input max is 3.95 and the pci diode current is < 10mA?

Also why is the row with a 3.0 Vccio receiver all listed as "No max limit". It appears that this table is the result of some modeling and assumptions but the details are missing.

Also page 4 has a note that implies that the 10mA limit is only when vccio is 2.5V and the driver is 3.0 or 3.3? How can that be? Does that mean when I have Vccio = 3.0/3.3v I can put more current into the pci diode?

Altera_Forum · ‎04-26-2007

The answer to your second question is that the input buffer powered by VCCIO = 2.5V is 3.3V tolerant. And coupled with the information below

Also, re-read the text in the first paragraph "When the bank supply

voltage (VCCIO) is 2.5-V or 3.0-V, the diode can sufficiently clamp

overshoot voltage to within the DC and AC input voltage specification.

As for 3.3-V VCCIO, voltage may be clamped to a level exceeding the DC

and AC input voltage specification considering the ± 5% supply voltage

tolerance."

Altera_Forum · ‎05-04-2007

Justin,

Could you please explain how the max. current (for example 30mA) at V0H=2.4V relates to the VI max spec? I don't understand how the max. current figures were obtained.

Thanks.

--jmv