Second sourcing and domestic alternatives have moved quickly in recent years, but “pin-to-pin compatible” is often reduced to a marketing line. A genuinely producible substitution has to clear four gates.
First, electrical parameters — input offset, reference accuracy and quiescent current directly shift system error. Second, power-up sequencing and protection logic: a different reset threshold changes how the unit behaves at the moment of power-on. Third, firmware and configuration registers: the same address does not mean the same default value. Fourth, reliability and lot-to-lot consistency: passing on a small sample is not the same as stable in volume.
Make substitution validation a standard checklist: one sheet per candidate part, recording parameter deltas, required hardware and firmware changes, test conclusion and owner. A checklist means the next change does not start from zero, and it gives customers a documented basis for the swap.