3 A adjustable LDO — dropout and output range
The LP3966ES-ADJ/NOPB is a single-output positive adjustable LDO regulator from Texas Instruments, delivering up to 3 A continuous current. Its output voltage is set by an external resistor divider between 1.216 V (the internal reference) and a maximum of 5.1 V, making it a fit for powering low-voltage cores, I/O rails, or post-regulation stages that need a clean, adjustable rail from a 7 V max input. Maximum dropout voltage is 1.2 V at the full 3 A load — the headroom between the input rail and the set output must stay above this across all load and temperature conditions, or the output falls out of regulation. For a 3.3 V output, the input should be at least 4.5 V to guarantee regulation at full current.
Thermal and protection envelope
The TO-263-5 (DDPAK) package has an exposed pad on the bottom — the PCB copper area under the tab sets the junction-to-ambient thermal resistance; a solid thermal via array to an inner-layer plane is expected for 3 A continuous operation at high ambient. Built-in protection includes over-current limiting, over-temperature shutdown, and short-circuit current foldback — the regulator survives a sustained output short without damage, though the junction temperature may cycle near the thermal limit. An Enable pin (active-high) allows the output to be gated by a logic signal, dropping quiescent current to near zero when the rail is not needed.
Quiescent current and supply budget
Quiescent current (Iq) is 9 mA typical, with a maximum supply current of 15 mA — this is the regulator's own draw from the input rail, independent of load. For battery-powered designs, the 9 mA Iq is non-negligible; a load switch ahead of the LDO or using the Enable pin to power-cycle the regulator when the load is idle can extend standby time.