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Altera_Forum
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14 years ago

What's the maximum input current of 3.3V LVTTL for Cyclone4?

Hi, AN447 mentions "The PCI-clamp diode in Cyclone III and Cyclone IV devices can support a maximum of 10-mA DC current" at page 3, but Table 3 tell us the Maximum Allowed Current from driver ...
Altera_Forum's avatar
Altera_Forum
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14 years ago

Thanks for your reply, FvM.

May be we can define the maximum FPGA input current rating for dynamical overshoots, with PCI diode, is 10 mA, that's right? If so, we should limit the driver maximum output current the same as this value, without series termination.

But, in AN447 Table 3, give the Maximum Allowed Current from driver is 30-mA for a 3.3V to 3.3V interface without series termination, this value is much more than the allowed 10 mA PCI diode current limit.

So mysterious extra current! May be it's to control the overshoot voltage at the FPGA input pin not exceed the PCI diode's foward voltage condition when driver a 50ohm transmission line, if so, there is no need to enable the FPGA input pin's PCI diode, that's right?