Protection diode for FPGA IO pins - Protection diode for FPGA IO pins 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? Replies: Re: Protection diode for FPGA IO pins Hi, similar question https://forums.intel.com/s/question/0D50P00003yyGwmSAE/cyclone-iii-33v-lvttllvcmos-input-impedance?language=en_US Replies: Re: Protection diode for FPGA IO pins 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? Replies: Re: Protection diode for FPGA IO pins 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 Replies: Re: Protection diode for FPGA IO pins 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? Replies: Re: Protection diode for FPGA IO pins 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 Replies: Re: Protection diode for FPGA IO pins 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? Replies: Re: Protection diode for FPGA IO pins 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