You explained what small ternary form is (ABA’). What is large ternary form? Which I heard is used for the slow movement of a sonata.
The textbook definition is “A tripartite full-movement form consisting of a main theme, an interior theme, and a return of the main theme.” It is pretty much a slow movement interior form.
The main theme usually is a small ternary form theme.
The interior theme is also frequently small ternary form, but usually functionally deficient, and incomplete. It also tends to be in minor.
The return of the main theme is in home key.
There can also be a coda.
Here is an example: