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ADC08D1000: Noise is severe at high temperatures

Ryu Yamashita
Genius 4485 points

Part Number: ADC08D1000

Hi team,

Our tests verify that the AD converter functions normally in high-temperature environments.
We understand that this device exhibits reduced SNR under high temperatures.
However, starting from a certain lot, abnormal noise began occurring during high-temperature operation.
Since cooling resolves the noise, we believe this device is the cause.
We have no specific PCN and do not believe the device has changed. Is there any possible cause?

Best Regards,
Ryu.

  • 0
    TI__Mastermind 45670 points

    Hi Ryu,

    Please send us some specific FFT plots so we can quantify both good and bad parts across your temperature range use case.

    This will help us understand better what the issue might be. There a no PCNs on this device in regards to your issue.

    Is the ADC isolated when subjected to high temperature? Or the entire board?

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Genius 4485 points

    Hi Rob,

    Thank you for your reply.
    I apologize for the poor explanation.
    By “noise,” I mean fluctuations in the output values.
    I will show the relationship between OK and NG outputs and time.

    Best Regards,
    Ryu.

  • 0 in reply to Ryu Yamashita
    TI__Mastermind 45670 points

    Hi Ryu,

    One thing that could be happening is the ADC and or any surrounding circuitry might be affecting the ADC performance.

    When you subject the board to extreme temperatures, sometimes poor soldering or assembly can show intermittent connections.

    If you think this is still related to the ADC, then please review and ensure the epad in the center of the device has a robust connection.

    if you want to send over some gerber files for me to review please do. 

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Genius 4485 points

    Hi Rob,

    Thank you for your reply.

    Could you please clarify the following points regarding the surface finish change from lead-free solder leveler to OSP (water‑soluble pre‑flux)?
    1. When switching to OSP, is it possible that changes in characteristics could lead to symptoms such as the ones we are observing?
    2. Is the lead‑free solder leveler considered the recommended surface finish in this case?
    3. If you have any comments, observations, or recommendations, we would greatly appreciate your feedback.

    Best Regards,
    Ryu.

  • 0 in reply to Ryu Yamashita
    TI__Mastermind 45670 points

    Hi Ryu,

    Are you suspecting the lead free finish on the ADC device is the issue?

    Some other questions:

    Does this issue happen on all board/devices?

    Have you x-rayed the board at the assembly house to make sure all the parts are put down appropriately?

    There is a large ground pad under the ADC device. If this is not connecting to the pcb in a robust manner than this could also be the cause as the part experiences different temperatures. If you want us to review the layout please send over the gerber files or some screen snapshots.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Genius 4485 points

    Hi Rob,

    When we reviewed the assembly, it appeared that the solder volume was insufficient. Therefore, we would like to ask a few questions.

    Is there a guideline or criterion for acceptable solder wettability?
    To what extent of electrical/mechanical connection is considered acceptable without causing issues?
    Additionally, what is the allowable temperature range for the die?

    Best Regards,
    Ryu.

  • 0 in reply to Ryu Yamashita
    TI__Mastermind 45670 points

    Hi Ryu,

    For the first question, this would be determined by your assembly house.

    For the second question, you definitely need to make sure the center epad/ground is soldered robustly to the pcb. Your assembly house should be able to xray the device once it is soldered to the pcb to see if there are any voids.

    For the third question, this information is in the datasheet.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Genius 4485 points

    Hi Rob,

    Thank you for your reply.

    Regarding the soldering of the center ePad/ground, I would like to better understand the acceptance criteria.
    Could you please advise what level of solder wettability or voiding would be considered acceptable and unlikely to cause issues? We have checked the solder joints by X-ray, but it is difficult for us to judge whether the observed condition is at a problematic level or not. If there are any general guidelines or criteria, we would appreciate your guidance.

    Additionally, regarding die temperature, could you let us know the temperature level at which functional issues may start to occur (not the absolute failure level)?
    The datasheet specifies maximum ratings, but we assume those represent damage or failure limits. We would like to understand the recommended or safe operating range from a reliability standpoint.

    Best regards,
    Ryu

  • 0 in reply to Ryu Yamashita
    TI__Mastermind 45670 points

    Hi Ryu,

    #1: please see the following attached article for epad recommendations, see pages 1-3.

    6661.AN-1142-HSLayout.pdf

    #2: please see the pic below for the ADCs operational rating as shown in the datasheet.

    Regards,

    Rob