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ADS1217 - reset due external interference

Jiri Antos
Prodigy 180 points
Other Parts Discussed in Thread: ADS1217, TPD4E001

Hello,

I have fully insulated analog input with ADS1217. It is measuring very precise, but I have problem with disturbances.

If I make a burst test - ADS is reseted. I have RESET input directly connected to output of Si8462AB.

Circuit is supplied by DC/DC converter 5V/5V with in/out capacitance 60 pF.

How do interference immunity increase?

Best regards

Jiri Antos

  • 0
    TI__Guru** 113765 points

    Hi Jiri,

    Usually these types of problems on not specifically related to the RESET pin, but the burst getting into the ADS1217 through power supply or analog input pins which cause the device to go into a reset condition.  You did not specify whether the bursts are ESD (high voltage) or EMI/RFI.  Extra ESD protection diodes can be added if needed, or additional filtering is also possible if related to EMI/RFI. Sometimes these problems can be improved with PCB layout changes.

    Please let me know the specifics of the tests and send me your schematic and layout and I can help identify areas of concern.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 180 points

    Hi Bob,

    I make burst test by IEC 61000-4-4. I am adding circuit diagram and layouts.

    I have problems with interferences from both sides - through power suply and through input too.

    Best regards

    Jiri A.

    2311.omc802uni_07_11 bot.pdf
    1273.omc802uni_07_11 top.pdf
    7534.omc802uni_07_11 sch.pdf

  • 0 in reply to Jiri Antos
    TI__Guru** 113765 points

    Hi Jiri,

    Can I assume that you have inner layers to your board?  Can you send me the inner layer plots too? Were you able to pass any levels of the IEC61000-4-4 (like threat level 1, 2 or 3)? For the test, did the cabling all connect to X12, or were other points to other connectors tested as well?

    I would try to isolate the power problem first.  You may want to add some TVS diodes to the input side of the supply (U20) and the digital isolator (U16). You may need some protection on your input signal lines too.  Devices like the TPD4E001 also provide enhanced ESD protection.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 180 points

    Hi Bob.

    I had a short vacation. There are a inner layers and pictures of testing table with our instrument.

    Card OMC802UNI is on bottom bord as piggiback card. Connected is power supply and one voltage input. Input wire is put to the capacitive bridge, which is disconnect from testing maschine. I want imunity for the highest level - 4 kV to power supply and 2 kV to inputs.

    Best regards

    Jiri

    1273.OMC802UNI_IN1.pdf

    3247.OMC802UNI_IN2.pdf

  • 0 in reply to Jiri Antos
    TI__Guru** 113765 points

    Hi Jiri,

    If you apply 4kV to the supply, you will need extra protection for U20 as it is limited to 3kV isolation.

    You may find that you will have better success if AGND and DGND have a low impedance connection under the ADS1217. You might consider making this a solid ground plane area. Some of the analog return paths crosses ground splits.  You need to make sure that all return paths are as optimal as possible and no analog signals cross out of the analog plane.

    The connections to R32 and R42 in the thin board area will act like antenna. 

    Best regards,

    Bob B