IO Expansion?

[Will Reeve]

I've always used the MCP23017 but end up adding a TVS diode and current limit resistor when the outputs / inputs are going off board. I was thinking if anyone knows of a expansion IC which has built in protection and also interfaces via I2C or SPI. A sort of world facing I/O IC. The MCP23017 data-sheets makes no mention of any clamp diodes internally (I assume there are otherwise they would be a little fragile).

[Ttelmah]

The pins on the MCP23017, are clamped exactly like those on a PIC. In the data sheet, +/-20mA.
However no normal 'IC', is really going to give you good protection if you are talking spikes from ESD etc.. The problem is that the physical structure used inside the IC, isn't capable of handling the sort of voltages involved. The 'best protected' IC's, are ones using much larger gate structures, designed specifically for this (things like RS232 drivers), but these have very low gate counts inside the chip, because of this....
Consider though, switching to using protection that is cheaper in bulk, like the TPD4E001 from Texas. These have a small SMD package, carrying four protectors in one package, and offering 8Kv contact protection, in a package that is probably smaller than a single TVS...
It is really down to you deciding the level of protection you need. For local connections inside a conduit, this sort of protection would be entirely adequate, but if the connections are going any significant distance, and you want reliability, you should consider alternatives like opto-coupling, or even fibre optics...

Best Wishes