250 mA fixed 5V LDO — DDPAK thermal story
The LP2957ISX/NOPB is a single-output positive LDO regulator from Texas Instruments, delivering a fixed 5V rail at up to 250 mA. The DDPAK/TO-263-5 package (5 leads plus exposed tab) is the surface-mount version of the TO-220 power footprint. For 250 mA at 12V in, the regulator dissipates about 1.75W; a 1-inch-square copper pour on the bottom layer keeps the junction below 125°C in still air.
Temperature grade and protection — survives harsh environments
The 30V maximum input voltage gives margin on a nominal 24V rail that can spike to 28V during a load transient. On-chip protection circuits cover over-current (foldback current limit), over-temperature (thermal shutdown with hysteresis), and reverse polarity — the regulator survives a reversed battery connection without external diode protection on the input. The Enable pin lets a system controller shut down the 5V rail to save power, dropping the quiescent current from 200 µA to near zero.