ADS1258-EP: MUXOUT Isolation

Hi Anant Kanungo,

I am not too sure what you are trying to do here.

Anant Kanungo said:

the first way to approach this would be to operate the device in Auto-Scan mode but not put any of the inputs into the input list register.

For example, what would this accomplish? You are not reading any inputs in this case, so why do you want to isolate MUXOUT? And what do you want to isolate the MUXOUT from? Do you have components connected to MUXOUT?

Maybe providing a quick drawing of what you want to do will help

-Bryan

Hey Bryan,

Thanks for the quick reply! I probably should have contextualized what I was doing in my post. Basically, I have a signal conditioning circuit which involves an op amp between MUXOUT and ADCIN. Because of precision requirements, I would like to periodically measure the offset voltage caused by the signal conditioning circuit and calibrate my measurements based on that. Below is a picture of the very rough circuit I have in mind.

Basically, I want to every once in a while tie the input pins of the signal conditioning circuit together (or to ground) so I can measure just the offset voltage on the ADC pins. I can do this by using an analog switch and the GPIOs of the ADS to control the analog switch. I don't want to tie pins together on sensors though so i would like to isolate the mux output from the mux input. I know I could do this by adding two more analog switches controlled by GPIOs, but am hoping the ADS1258 has this capability to reduce part count and complexity of the circuit. I additionally am locked into using the ADS1258 for external reasons.

Unfortunately I don't have any unused channels, I planned on using all as differential pairs to read 8 per ADC. If I couldn't figure out a way to do the isolation on the ADS my plan was to either add analog switches in the signal conditioning block (and use ADS GPIOs to control them) or to sacrifice a channel and figure out what to do with my unmapped sensors.