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OPA347: Aging effect of Offset voltage

Kuramochi Tadahiko
Guru 28715 points
Part Number: OPA347

Hi,

I received the following question from my customer.

Do you have any data of aging effect of offset voltage on the following condition?

Condition 1

・Ta = room temperature or +85℃

・Term：1000/2000/3000 hour

・Energization statement

Condition2

・Ta = -55℃/+85℃(Temperature cycle)

・Energization statement

They may allow a little different condition.

Best Regards,

Kuramochi

  • 0
    TI__Mastermind 25795 points
    Hello Tadahiko-san,

    What is "Energization statement"?
  • 0 in reply to Pete%20Semig
    Guru 28715 points

    Pete-san,

    Thank you for your help.

    How is "operation statement"?

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Mastermind 25795 points

    Hello Tadahiko-san,

    For amplifiers, the main criteria of passing the life test is to make sure that lifetest shift is no greater than the max/min specified Vos. A life test represents operating the device for 10 years at room temperature. Having said that, Vos shift during the lifetest is typically much smaller than max/min Vos. We do not have data for amplifier specifications at particular times (e.g. 1000/2000/3000 hours).

    Over a 10 year period the device's offset voltage may shift by as much as the maximum specification (in addition to the initial offset). Such a shifting event, however, is rare. One standard deviation is approximately +/-1.25mV ((7.5 mV)/(6 sigma)) according to the offset voltage distribution histogram on page 5 of the data sheet. The maximum offset specification of +/-6mV represents approximately +/-4.8sigma, which is approximately 1 in 630,000. Note that shift is not a linear function. Most offset shift is within the first few months of operation.

    We can calculate the approximate offset voltage drift with temperature. Given the temperature range -55C to 85C the largest change in temperature with respect to room temperature is 80C (25C-(-55C)). The typical drift specification is listed as +/-3uV/C, which equates to a shift of +/-240uV (typical). There is no maximum drift specification listed, but you can use the Offset Voltage Drift Magnitude vs. Production Distribution histogram on page 5 similar to how we used the offset voltage distribution histogram previously. In order to increase the confidence level you must increase the drift value. For example, the typical drift is +/-3uV/C which represents approximately 1 standard deviation (sigma). If we multiply this by 4 (+/-12uV/C) we have a 4 sigma value, which represents 1 out-of-spec unit for every ~15,000 units. We can then calculate the corresponding offset due to temperature as follows:

    Vos_max_drift_80C=+/-sqrt(6mV^2+(80C*12uV/C)^2)=+/-6076uV

    Notice I combined the errors using RSS (root-sum-square) as opposed to simple addition. Such a method yields a more realistic result.