3A fixed-rail LDO for post-regulator and point-of-load duty
The LP3963ESX-2.5: Maximum dropout is 1.2V at full load, so the input rail needs at least 3.7V to hold regulation across load and temperature; a 5V bus gives roughly 1.8V of headroom, which is comfortable.
Package, thermal path, and board-fit realities
The enable pin lets a supervisor or GPIO sequence this rail on after the input bus is stable, which avoids inrush glitches on the upstream supply. Protection is built in: over-current, over-temperature, and short-circuit shutdown keep the regulator from self-destructing if the load faults or the ambient spikes during a stalled fan event.
Quiescent draw and supply current — always-on rail budget
Quiescent current is 9 mA typical, and the maximum supply current is 15 mA — not a micropower LDO, but acceptable for a 3A-rated part where the load current dominates the power budget. The 15 mA supply max means the regulator's own dissipation at 5V input is under 75 mW, negligible next to the 3A load dissipation.
Lifecycle and sourcing — active, but watch the RoHS flag
That is a flag for new designs targeting RoHS-10/REACH compliance; legacy BOMs that already have an exemption or a Pb-free waiver can proceed.