Protection diode for FPGA IO pins

[CLa_R]

Hi to all.

For my project I am using a Cyclone IV-E FPGA.

The lowest input voltage on its IO pins is -0.5V (as showed on Altera datasheet).

I have many input that can be lower that -0.5v (around -3v beacause its come from analog comparator) but for me their value condsidered as 0V.

Can I use a diode as protection of FPGA IO pins and to interpreted the negative voltage values as 0/GND?

[AnandRaj_S_Intel]

Hi,

Yes, We can use external diode so that we can meet the devices absolute maximum DC input voltage and maximum allowed overshoot/ undershoot voltage requirements.

Regards

Anand

[CLa_R]

Thank you.

Even if it's not properly referring to FPGAs, could you tell me a suitable diode?

In the meantime, I have come up with another solution, which uses a transistor and which should be both faster and safer than the diode. I enclose the scheme. What do you think?

[AnandRaj_S_Intel]

Hi,

Even if it's not properly referring to FPGAs, could you tell me a suitable diode?

 >>Sorry we can'l recommend any part number However you can refer development kit schematics for it.

In the meantime, I have come up with another solution, which uses a transistor and which should be both faster and safer than the diode. I enclose the scheme. What do you think?

>>Yes, Design with MOSFE looks good, Even i have used it in my first project.

Regards

Anand

[CLa_R]

I'm also trying this scheme, which uses a N type MOSFET.

Which is the best solution?

Also, what is the input impedance of IO PINs of the FPGA?

[AnandRaj_S_Intel · Accepted solution]

​Hi,

Both scheme holds good for your design.

Refer table 6-2 for impedance details.

https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyclone-iv/cyiv-51006.pdf

Regards

Anand

[CLa_R]

Thanks for the reply.

I still have some doubts concerning the input impedance, in my case, I use a 3.3V LVTTL level, but in table 6.2 I don't see any value of the input resistance.

How should I interpret?

[AnandRaj_S_Intel]

​Hi,

similar question

https://forums.intel.com/s/question/0D50P00003yyGwmSAE/cyclone-iii-33v-lvttllvcmos-input-impedance?language=en_US