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RC4580: Vos VS time curve

Haiwen Huang
Intellectual 1750 points
Part Number: RC4580

Dears:

when use RC4580 in sensing project, we calibrate it in the product line, but end customer found abnormal accuracy error after several weeks work. Could you please help provide VOS VS time curve to help identify the issue?

End customer thought it may caused by VOS time drift.  If you have other comment on issue is appreciated. Thanks.

  • 0
    TI__Mastermind 28766 points

    Hey Haiwen,

    Could you please provide the customer schematic? I have an idea of what it might be but need the schematic to confirm.

    Best,
    Jerry

  • 0 in reply to Jerry Madalvanos
    TI__Intellectual 1750 points

    Jerry:

    Here is customer schematic for you reference. Thanks.

  • 0 in reply to Haiwen Huang
    TI__Mastermind 28766 points

    Hey Haiwen,

    Is the amplifier at the top of the page an unused channel of the RC4580 that is left unconnected? My initial idea of what may be the issue is not something I see in the above circuit, but an improperly configured unused amplifier can cause some issues, and if it is related to the input bias or input offset current, it may take a long time (weeks) to charge a node.

    This can be tested by forcing two different input voltages (Vid) on the unused channel and seeing how this affects the other channel. Sweep your Vid over your supply range and see if you can recreate the behavior. Leaving the channel open means that the voltage of your inputs will not be in a linear voltage range, and either the charge of the input bias current or some stray noise could cause the op amp to behave unpredictably.

    On the point of Vos over time, we don't specify or characterize Vos over time because the offset should not shift significantly over the span of weeks. You may see the spec change a small amount over time, but this would be over years, not weeks.

    Best,
    Jerry