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CLa_R
Novice
683 Views

Protection diode for FPGA IO pins

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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?

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1 Solution
AnandRaj_S_Intel
Employee
318 Views

​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.pd...

 

Regards

Anand

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7 Replies
AnandRaj_S_Intel
Employee
318 Views

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
Novice
318 Views

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?

 

T2B v4.jpg

AnandRaj_S_Intel
Employee
318 Views

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
Novice
318 Views

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?

 

Annotazione 2019-07-09 210314.png

 

AnandRaj_S_Intel
Employee
319 Views

​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.pd...

 

Regards

Anand

View solution in original post

CLa_R
Novice
318 Views

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?

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