7 Long-Term Drift Estimation

A Long-Term Drift test can range from 1000 hr to much longer. The test is time consuming and can have issues in testing due to equipment calibration, equipment failures, and environmental reasons. Due to this, it is important to be able to estimate the behavior of the device over the entire lifetime of the system that can span 10 years. The difficulty comes from the nonlinear behavior of the device that is not consistent between device to device nor between products.

One common method to estimate LTD over a large period of time is from IC long term stability: The only constant is change by Marek Lis. In this article there is a Long-Term Estimation, that can be used to estimate LTD over a long period of time. Figure 7-1 shows the accuracy of the equation near 1000 hr. The main drawback of the equation is that from 4000 hr to 8760 hr the equation goes from having a typical value to a over estimation that will be growing over 10 years (87600 hr). This is due to the REF50 settling behavior that cannot be characterized. Different voltage references will have different behavior that might not match the equation due to their settling behavior. The equation is useful to get a conservative estimate of LTD but it does have its limitations.