LTC2485 Analog-to-Digital Converter

LTC2485 Linear Technologies Analog-to-Digital Converter

Goal is to add support for the LTC2485 to Linux IIO subsystem.

This is new territory for me so it begins with more than the usual research.   Alas, it only took a few keystrokes and a lot of reading to get some initial bearings on this project.

Aside: If you google "Linear Technology" today, you'll see the news that Analog Devices Inc. has announced that it is acquiring Linear Technology.  The Linux IIO subsystem currently supports an abundance of Analog Devices sensors.   Additionally, Analog Devices "library" is the main resource I used for ramping up on ADC's.

Analog Devices Library  <-----GREAT RESOURCE!!!

Apparently there are thousands of converters to choose from, and companies like Analog Devices aims to make that choice simpler by offering parametric search engines. Here's where Delta-Sigma ADC's (like the LTC2485) fit into the market.  (this was dated 2005 - perhaps very outdated, but you get the idea.) It basically matches the applications that Linear Technology is suggesting on it's data sheet.

Courtesy of Analog Devices Library

The big picture of an ADC:  It's a quantizer, mapping a large set of input values to a countable smaller set.

Courtesy of Analog Devices Library

Highlights from the LTC2485 DataSheet:

Beyond the DataSheet:

One of the first things I was on the look out for was whether this device already had some sort of support in the IIO subsystem.  I know the quick answer is no, that's why my mentor has selected this sensor, but it's not necessarily clear cut.  I'm also looking for leverage!

I saw that a set of LTC Digital->Analog Converters were recently added to dac/ad5064.  So, that had me on alert that there might be a similar relationship between the ADC's of Analog Devices and Linear Technologies sensors.  So far, I haven't found any direct connections.   I'll need to learn more about the sensor and driver requirements before I can intelligently spot any connections.

If the architecture matters, which I think it does, then there are a couple of Analog Devices drivers (ad7791 and ad7793) that use sigma_delta architecture. They are SPI devices, not I2C.  So, maybe a sigma-delta reference, but not something to share.

I also see this chart below offered on Linear Technologies, and don't find any of these comparable devices supported in IIO.

So, onward with this.  Next actions: look at some code and ponder how these are tested.