Re: Datasheets and probability

On 15/12/2024 01:50, John S wrote:

Hi, men -
 There are sometimes 3 columns on a datasheet which may contain min, nom, and max values. Like Vds for example.
 Is there any probability tacitly assigned to the values? I know that nominal is the average, and I assume that the value lies between the two middle one standard deviation points.
 1. Is that a valid assumption?
 2. Is the min between one and two standard deviations down from the mean?
 Thanks and I apologize for asking such a basic question in this professional group.

It is actually a rather deep and difficult to answer question in general because for some components the answer can be "it depends".
Semiconductors I generally take it to mean ~3 sigma either side of the mean but design with a bit of extra margin so the 0.5% tail doesn't cause trouble.
But for some components like resistors and capacitors that may be obtained in 10%, 5%, 2%, 1%, 0.1% tolerances you can find that the frequency distribution of the components in the wider tolerance bins consists of values that are almost *never* inside the narrower ones.
IOW you are guaranteed at least 2% error in the 5% parts.
It is a bit better today than it used to be when they made batches and then selected from the process output. These days it is all a lot more reproducible and laser trimmed for precision parts.
--
Martin Brown