ADS7953: EMI throws off reference?

Hi Joshua,

Between the output of the REF5025 and ref input of the ADS7953, what passive components (resistors and/or capacitors) do you have connected?

Can you confirm that the REF5025 is providing a solid 2.5V during testing? Does the entire system work post failure (after being reset and while not be subjected to EMI)?

How much is the offset? Is it possible that the inputs are shifting during testing?

Hi Evan,

I have a 10uF, 6.3V X7R ceramic and a 22uF 10V X7R ceramic to ground.  I could not check the 2.5V while it was in the chamber, however post test the 2.5V is solid.  However the entire system is permanently "offset" on all of its values.  It appears to be off by about 50%.  And when I replace the ADS7953, everything is back to normal.

Also note that +Vbd = 5V.

Here is the schematic:

Here is the layout:

Thank you!

Josh

Hi Joshua,

It looks like your schematic and layout were not successfully uploaded. Can you please try to attached them again?

Hi Evan,

Copy and paste into this webform appeared to not work, so I tried using the attach button.  Let me know if they come through.

Thanks!

Josh

Hi Josh,

Thanks for your patience. I'm working with a couple of colleagues, and we have a couple of questions to ask to help us clarify the source of the issue:

1) Is the failure permanent and only fixed with a part replacement (as opposed to power cycling the part)?
2) Does the problem go away after rewriting to the range selection register bit?

Hi Evan,

The failure is permanent, as in only fixed with a part replacement.  So when I replace the part, everything comes up fine.  But I am worried about the susceptibility that the part appears to have.

Thank you,

Josh

Hi Evan,

Do you have any advice?  We go back into the chamber in 2 weeks, so the only thing I can think of is grounding the floating pins, because if they were not grounded, they could be susceptible to bulk current injection (acting like antennas)?

Thank you!

Josh

Hi Josh,

Thanks for your patience, I've been speaking with several colleagues about possible reasons for the chip to fail BCI. It is possible that something in the device is causing the range to be set to 2*Vref, which would look like a 50% offset.

- When testing the device after BCI and when you noticed the 50% 'offset,' do you recall if the conversions were all in the range of 0-2.5V or in the range of 2.5-5V?
- When testing the reference after BCI and you noticed that it still output 2.5V, was the ADC still connected while measuring the reference output?

Regarding the floating pins, it is a good idea to ground these. I don't believe this will make a difference though.