weird behaviour of ADR550BRTZ

Hi all.

   we are using ADR550BRTZ as reference in our AD system. currently we meet a weird phenomenon in 8 PCBA among 50 PCBA total. the output value does not meet spec, sometimes it fluctuates at a rough 1mv range, sometimes it not only fluctuate, but also keep decrease. i attach some picture to show the abnormal output, and i also attach the relevant schematics. we have suspect the design, so i cut the trace which connects post-stage circuit, but the problem is still there. 

    when we resolder these defect chip, the problem would disappeare for a while or permenantly on different PCBA (we have 8 defect PCBA total). and when we use cleaning agents to clean the PCBA, it would also make the problem disappeare for a while or permenantly on different PCA.

    we have a similiar design on the same PCBA using the same ADR550BRTZ, but in layout it's in other place. but the problem never happened at there. 

    sometimes i found some chip would self-recover to normal without i do something to it, but it would go back to abnormal after some time, and the situation could happen repeatly.

    could someone give me some suggestion? you can find the weird output waveform and design schematics in attachment.

attachments.zip
  • 0
    •  Analog Employees 
    on Jul 20, 2018 5:31 AM

    Hi Summer,

    Is ADR550BRTZ trim pin 3 connected to any potentiometer to fine trim output? If not, can you please check if there is any potential due to static effect on pin 3?

    When you state ADR550BRTZ is working fine without any problem on different DUT location. Can you please share any PCB differences between two DUT locations? Difference in terms of surrounding components, layout layer mismatch, ground plane etc.

    If applicable, can you please share PCB gerber files?

     

    Regards,

    Anshul

  • hello Anshul

        i did a test that i physically cut the trim pin and the result shows the output is still abnormal. 

        now our sourcing engineer found that the date code for these chips is in year 2010, maybe the part deteriorate for some reason in these years. 

        as for why the component works well in other location, now i think maybe it doesn't work that well like we suggest before, because in other location the circuit is used to measure a small signal with x4000 amplified. the front-end signal we computed is very hard to show some abnormal fluctuate. i put a bad chip to the other location, but the front-end signal isn't abnormal when the bad reference chip output is fluctuate.

        thank you!

  • 0
    •  Analog Employees 
    on Jul 31, 2018 2:11 AM

    Hi Summer,

    To debug further can you please share following DMM plot:

    1) Supply Voltage

    2) Trim Pin 3 voltage

    3) Output Voltage

    Repeat the same measurement plot with 100pF connected to trim pin 3.

    What is supply current limit set to?

    To understand better, can you please provide information about application that is driven by ADR550BRTZ?

    If applicable, can you please share PCB gerber files or picture of layout?

    Regards,

    Anshul