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Original question:

ADS1158: ADS1158IRTC

ADS1158: AinCom mystery pulse

Arshia Dabiran
Prodigy 10 points
Part Number: ADS1158

Hello!

I'm using the ADS1158 for  measuring some analog values, however I see that frequently the measurements will be completely wrong. I have seen this issue on 3 boards now and I believe I traced the issue down to the fact that AinCom is not a steady GND as expected from our schematics. The GND going into the GND selector MUX is about ~0V, however I see that the AinCom pin seems to have a pulse every few ms, which would explain why the measurements are incorrect. 

I disconnected most circuitry from this pin(U26), and still see the pulses so I'm pretty sure they are coming from the ADC. I checked the MuxOutN in comparision to AinCom and see that the AinCom pulse is seen, as well as some other signals which I am unable to explain. This ADC is run differentially with all measurements referenced to AinCom so I don't see how there can be any other pulses outside of those seen on AinCom. My assumption is the ADC internal mux has been damaged, however I am unsure what might cause this issue as I've seen this happen on 3 boards already. Does the issue require me to replace the ADC, or is there some other reason AinCom could be pulsing like this? Any help/info is apprecaited!

MuxOutN(Blue) vs AinCom(Yellow)

  • 0
    TI__Mastermind 45731 points

    Hi Arshia Dabiran,

    Can you provide some more information about what are you doing and what you have tried:

    • All of your inputs have large resistor dividers on them, which implies you are measuring high voltage signals. Is it possible that you applied voltages to the inputs >absolute maximum which damaged the device?
    • What is the AVDD voltage? It's cut off in the image you sent
    • Why do you have the RESET pin pulled low using a pulldown? This will hold the device in RESET when that pin is not actively driven. I would have expected you to pull this up to DVDD, similar to PWDN
    • When you said you disconnected most circuitry from the AINCOM pin, what exactly did you disconnect? You just show red X's on your schematic, so did you only remove the OPA?
      • In the second scope shot, is MUXOUTN connected to anything at this point, assuming the OPAs have been removed? It is not clear the order in which you took measurements, removed components, etc.
    • It looks like you have a switch to enable multiple options for AINCOM: one goes to GND, one goes to a resistor divider from one of your input signals. Does this issue occur only in one mode of operation, or both?

    Let me know

    -Bryan