Absolute maximum rating

A damage threshold. The vendor is saying that beyond this point the part may be destroyed, and that none of its other promises were evaluated up there. Exceeding it is not “using the full range”.

The recommended operating condition says where a part still works, and it is always the lower of the two. Between them sits a band where the part is probably not damaged and nothing at all is guaranteed about what it does.

Three voltage bands: recommended operating below 15 V, an unpromised band from 15 to 20 V, and damage above the 20 V absolute maximum 20 V 15 V 0 V Damage the part may not survive this Works, but nothing is promised no specification was evaluated here Recommended operating where the datasheet's other numbers hold absolute maximum recommended max a supply pin

The two get confused because they are printed in adjacent tables in the same units. If a design mistakes one for the other, it looks fine until a part fails in the field. So the layer keeps them as separate LimitKind values (ABSOLUTE_MAX and RECOMMENDED_OPERATING) rather than one number, and a rule declares which it means.

Two rules read it. supply-exceeds-abs-max compares a supply pin’s rail against the part’s rating, and pin-out-of-recommended catches the quieter case of a pin sitting in the middle band.

A rating is only meaningful next to the conditions it was measured under, so a value carried without them is treated as under-specified rather than compared. The datasheet layer applies the same discipline to every parameter.

The course teaches it in chapter 7, a whole chapter about it. That chapter’s section Two numbers that look alike covers the distinction on its own.