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GPIO / I2C signal voltage? 5V safe?


#1

Hello everyone,

First off, thanks for making such a great little board! I got up and running in no time and am enjoying it quite a bit :-). I’m excited to get it hooked up to some peripherals, hence the question :-).

I’m rather new to ARM processors (coming from AVR hobbyist land) and I was wondering what the signaling voltage on the GPIOs and I2C interface is. 3.3V? If so, is it 5V safe? or do I need to level shift it? My google-fu is failing me, so I thought I’d ask here (and say hi).

Thanks in advance,
-RZ


#2

If I remember right, all GPIO’S from the EMX and G120 are 5V tolerant (what ever this means in praxis). I think the brochure of the SoM says so.
Since I2C pins are also GPIO pins it should work.
But if your I2C device also needs 5V input level, it won’t work, since the SoM will only output 3V3.


#3

I’m not an expert in I2C but his is what I believe to be true…

I2C should be open-drain with external pull-up resistors to VDD. I think the high threshold should be 0.7V so anything higher than this should be Ok. Personally I think you are probably best using 3.3 as your pull-up voltage and anything you connect to should work. Most modern chips are 3.3v not anyway. 5V is increasingly rare.

According to the datasheet for the LPC11U2x the GPIO pins are 5V tolerant if needed. See page 29 http://www.nxp.com/documents/data_sheet/LPC11U2X.pdf Doing this does cause greater leakage currents etc, but the chip should survive.


#4

Awesome. Thanks. 5V only shows up in arduino-land… but that’s what I’ve been using lately, so I thought I’d check :-).

Thanks for the response.