1.5 A adjustable LDO for post-regulation rails
The LD39150PT-R is a positive adjustable LDO regulator from STMicroelectronics, delivering up to 1.5 A continuous output with a maximum dropout voltage of 0.4 V at full load — meaning the input rail needs to stay at least 400 mV above the programmed output voltage to maintain regulation. The output is adjustable from a 1.22 V reference up to 5 V, set by an external resistor divider. A single regulator in a TO-252-5 PPAK package, it is suited for point-of-load post-regulation where a clean, low-noise rail is needed downstream of a switching converter.
PSRR profile and noise rejection across frequency
Power supply rejection ratio is specified at 65 dB at 120 Hz, dropping to 55 dB at 1 kHz — this tells you the regulator attenuates 120 Hz ripple from a full-wave rectifier by a factor of ~1800, but at 1 kHz the attenuation drops to ~560. Upstream switching noise above a few kilohertz will pass through with less rejection, so a pre-filter or a second-stage LC filter ahead of this LDO is worth considering if the switching frequency is in the 100 kHz+ range.
Thermal and protection features for industrial duty
Operating junction temperature range is -40 to +125 °C, covering industrial and automotive under-hood environments. The PPAK package's exposed pad must be soldered to a sufficient copper area on the PCB to keep the junction below the thermal shutdown threshold at 1.5 A output. Built-in over-current and over-temperature protection means the regulator folds back or shuts down under fault conditions without external protection diodes — the load is protected and the regulator survives a sustained short on the output. Quiescent current is 2.5 mA typical — modest for a 1.5 A LDO, but worth budgeting in always-on or battery-backed rails where every milliamp of overhead matters.