I’ve wondered about this, too. The thing that makes sense to me is that the designation is done AFTER post-manufacturing testing. It does not make sense to make a second line. Those are expensive! What makes economic sense is to find the best or most consistent ones and sell them at a premium. But this is just what’s inside my jumbled, lunatic brain.
Yes, I see now that "A" has a guaranteed max noise voltage. But what's the difference between P and PE4? The datasheet indicates these are physically identical. Digikey sells both from TI with slightly different pricing.
The "P" and "PE4" (not "APE4") are close together in price at Digikey. That's why I was hoping to understand what the differences might be. News Flash! I found a TI FAQ this morning that states "E4" and "G4" suffixes designate lead-free construction. It goes on to say that part numbers without this suffix are also lead-free now, but the older numbers have been retained so customers will have a consistent orderable part number. Mystery solved.
I used to test AD797 opamps in a circuit I designed before retiring. About 5%-10% of the chips would fall outside the noise voltage spec and would have to be replaced in order to ship our product. The difference was always very small, just enough to make me believe these failures had simply slipped by during the manufacturer's final test. In the case of the AD797, there's no lesser-guaranteed part number. This all strongly implies the process being used at the factory is one of selecting better performing individual examples from batches that are all intended to be as performant as possible.
