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Altera_Forum
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15 years ago

Help about the connection between IC of voltage 5V and cyclone II

Now I've got a cyclone II(3.3v in doc) device.But I've only got a 5V D-A IC.Can I connect them directly?especially output from 5V IC input foot of cyclone II(3.3V in document).I know the signal outpu...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

Hi,

I thought a serial resistor and turning the PCI clamping diode on in Quartus may worth thinking about. Searching for "Cyclone II 5V" resulted in an ALTERA desing hint

Problem

Can I turn PCI clamp diode on in Stratix®, Stratix II and Cyclone® II devices with external series resistor to make them 5V compatible?

Solution

Yes, the input path is protected by PCI Clamp diode when you turn them on. Optional PCI clamp diodes are only available in column IO pins. Protection is achieved by clamping the pin voltage to VCCIO + 0.7V which is within the absolute maximum Vi. The VCCIO will be forced to 3.3V when PCI clamp diode is enabled. The solution given in Cyclone handbook which explains the implementation of PCI clamp diode with external resistor can be applied to all the other devices which are not 5.0V tolerant. The link to Cyclone handbook chapter 11 is stated below:

This might be a solution while perhaps going for a 3V3 ADC may at least be more future-proof solution ;)