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cyclone 3 pci clamp diode - interface with 5V inputs question for intel support.


hello, my company uses the cyclone family of FPGA in many of our project.

in a current project we need to interface a cyclone 3 FPGA with a device that outputs 5V for logic high. 

our understanding is that this can be done safely once the internal pci clamp diodes are enabled as long the interfacing device can not source more then 10 ma (the diode's maximum current rating) as the diode would lower the voltage and protect the FPGA

the device interfacing with the FPGA in our project can output a maximum of 0.7 ma from a pin

are we correct that with this current limit there is no danger of damage to the FPGA as long as the pci clamp diodes are enabled?









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Hi Amir,


I don't think this is possible. The PCI Clamp is meant for 3.3V / 3.0V interfacing. Moreover, if 5V is supplied to Cyclone III, it might damage the I/O buffer as well.


The absolute maximum rating for Vin is 3.95V only.


Thank You

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