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Altera_Forum
Honored Contributor I
734 Views

Absolute maximum I/O/Analog pin input current

Hi, 

 

For the MAX10 family, what's the absolute maximum input current? Altera gives only the absolute maximum voltage (=4.12V). 

 

In my application I'm sampling with the MAX10 ADC an analog signal which could jump up to about 10V with up to 2mA source capability (normal range is 0 to 2.5V) 

 

 

Thanks, 

 

Noam
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3 Replies
Altera_Forum
Honored Contributor I
29 Views

Hi, 

 

I assume you're looking for "DC output current per pin", which is +/-25mA. I guess you were looking for a "DC input current per pin" or so; I doubt you'll find that, as I think that the +/-25mA limit is the maximum the input protection diodes can sustain, i.e. you're in a region where the pin isn't acting as a normal input any more. 

 

Since the maximum input voltage is 5.88V below of what your application might apply, I'd suggest to use an input buffer, i.e. some simple OP-Amp. Depending on your application, a simple RIRO-OpAmp, using the same rail as your I/O bank, could already do the trick. 

 

 

Best regards, 

GooGooCluster
Altera_Forum
Honored Contributor I
29 Views

Hi, 

 

I wish I could use a buffers but the board is too crowded... 

If the maximum input current is +/-25mA and I can guarantee up to +2mA, I think I'm on the safe side, as long as the MAX10 is protected against an input latch-up... 

 

Am I right? 

 

Thanks, 

 

Noam
Altera_Forum
Honored Contributor I
29 Views

Hi, 

 

how do you limit the current to 2mA? I mean, if there's a series resistance to limit the current, the voltage will never go to 10V, as the input protection diodes of the device would surely require a lot more current to do so. Anyway, you're making assumptions about the input protection diodes, and you're trying to operate the device outside of it's operating range, so I would not count on reliability. For a hobby project I'd say it's fine, for a product I'd say it might be dangerous. Maybe you should contact Altera and ask them directly about their opinion. 

 

Do you at least have space to add some Schottky diodes? Since you're current is limited to 2mA, very small (I mean physically small) diodes would already protect the FPGA quite well, without relying on the FPGA's protection diodes. 

 

If you look at figure 3-1 in section "MAX 10 FPGA Configuration Design Guidelines" of the MAX 10 device handbook, they recommend quite rigid protection scheme of the JTAG input pins. That leads me to the conclusion that in doubt better use additional external diodes. Maybe I'm just over-cautious, though. 

 

 

Best regards, 

GooGooCluster
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