Are there a few “goto” external ADC’s that are typically used with the IMP or is it “horses for courses?”
There’s an amazing number of ADC parts on Digikey; too much of a good thing!
yes, tons of choices and as you hint it depends on what you are doing. I like the MCP3424. You could search for development kits or breakout boards or arduino shields and choose an ADC that is easy to buy.
MCP3424 has it’s own internal reference and it can operate from a supply of 2.7 to 4.5. An easy way to filter out some ADCs is to limit those that will not operate at 3.3V and work with 3.3V logic levels.
I also prefer the MCP342x. First because it’s got differential inputs (although all inputs have to lie above GND+0,3V), but also because they come in 1, 2 and 4 channels that operate the same way from a programming perspective and have a built in very accurate Programmable Gain of 1x - 8x (next to the built in reference).
When used with proper input filtering, the accuracy is very good.