Long Term Drift and Arrhenius - Page 1
Forum section: electronics / general

author: 16bitanalogue
author_rank: Regular Contributor
timestamp: February 21, 2022, 11:38:55 pm
content: I need a greybeard to help regarding Long Term Drift. If this is the wrong forum, I apologize, since using my Google-Fu I found the below topic:https://www.eevblog.com/forum/metrology/ltc6655b-long-term-drift/The papers below make a very explicit statement that the Arrhenius Equation cannot be used to extrapolate Long Term Drift of a voltage reference. This is a little unsatisfying, as I would like to knowwhythis is the case. The reasoning in the papers below is that the Arrhenius Equation provides erroneous results, "results are too good and not possible."https://www.maximintegrated.com/en/design/technical-documents/app-notes/7/7009.htmlhttps://www.analog.com/media/en/reference-design-documentation/design-notes/dn229f.pdfhttps://www.analog.com/media/en/technical-documentation/tech-articles/lt-journal-article/LT1461_1199_Mag.pdfTI's paper continues with discussing the actual setup, but does not outright state the Arrhenius Equation is erroneous.https://www.ti.com/lit/pdf/sbaa436A blog post from TI discusses references, but clearly states the use of the Arrhenius Equation:https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/ic-long-term-stability-the-only-constant-is-changeI do not doubt the wisdom of the ancients with the greyest of beards; however, can someone help provide additional insight? Extrapolating ignores package curing effects? Package stress on the die? Electromigration (doubtful)? I will leave my questions, somewhat open ended.1. Does LTD only apply to voltage references? Does it matter if it's a bandgap, buried zener?2. If we have more complicated circuits like op-amps, integrated window-comparators, DCDC voltage specs that will drift over time, is the Arrhenius Equation still not applicable?3. Why does there appear to be an inconsistency (especially from TI) where the Arrhenius Equation can be applied?4. STFU, kid. Go back to your VR Chat.

author: KT88
author_rank: Frequent Contributor
timestamp: February 22, 2022, 10:31:46 am
content: The Arrhenius Effect describes the dependancy of chemical prcesses on temperature. There are some other effects that look like Arrhenius like leakage currents in CMOS - but it's a different effect. Same with LTD - it is not related to ion mobility or somethiong like that....Estimating LTD is a tricky business - it is somewhat possible but it requires thorough characterisation of a large lot of preconditioned parts. The result would still be not very satisfying...

author: Kleinstein
author_rank: Super Contributor
timestamp: February 22, 2022, 11:03:49 am
content: The long term dirft has multiple contributions and not all have the same temperature dependence. The can also be oppsing effects, so that a relatively small error in one contribution can cause a large error in the final sum. Quite often one of the porcesses dominates, but this does not mean that the slower processes are not happening and get relevant for the really long time scale. The relative relevance can change with time (aging) and temperature.One sometimes sees this on the short time scale with the drift rate even changing the sign.The Arrhenius type thermal activation with processes speeding up exponential is just one possible describtion. Even here there can be different activation energies and thus a different temperature difference to cause a doubling in the speed. For interpolation over a small temperature range this may still be OK, but with a larger temperature step this can cause significant errors.An important type of aging that often follows a different equation is the relaxation of mechnical stress: there the creep rate also depends some power of the stress and the stress from thermal mismatch changes with temperature. There is often still an exponential factor from thermal activation, but only as one part of the quation.Also glassy materials (e.g. epoxy) relatively close to the glass transition are known to behave different: there sturcture changes with temperature and this can effects the speed of other processes, like diffusion of oxigen and stress relaxation.Another formular used that is not necessary correct is the square root time dependence. This is valid for a simple diffusion processes and random walk like processes, but not necessary all aging processes. Other effects can follow a simple exponential decay or stretched exponential with a power different from 2.