Adjustable 1.5 A regulator in a rework-friendly D²Pak
The Texas Instruments LM317KTTRG3 is a classic adjustable positive voltage regulator in a TO-263-4 (D²Pak) surface-mount package. It delivers up to 1.5 A output current from a 40 V maximum input, with an adjustable output range from 1.25 V to 37 V set by two external resistors. The 1.5 A rating covers most board-level loads up to about 7 W before the thermal limit of the D²Pak tab becomes the constraint.
PSRR and ripple rejection at line frequency
The LM317KTTRG3 specifies a PSRR of 80 dB to 65 dB at 120 Hz — that is the full-wave-rectified ripple frequency from a 60 Hz mains supply. 80 dB means the ripple on the output is about 10,000 times smaller than the ripple on the input. At the lower end of the range, 65 dB still knocks down 120 Hz ripple by a factor of roughly 1,800. This matters when the regulator feeds a sensitive analog stage like an op-amp front-end or a VCO.
Built-in fault survival
On-chip protection covers over-current, over-temperature, and short-circuit conditions. That means the regulator shuts itself down before the bond wires fuse or the die cracks under a sustained overload. For a board-level repair tech, this is the difference between a part that can be reworked after a fault and one that has to be replaced along with the load it took out.
Package and thermal reality for the rework bench
The TO-263-4 (D²Pak) has a large copper tab that is electrically the output pin (Vout). The tab is also the primary heat path — a hot-air rework station set to 300 °C to 350 °C on the tab side will lift the part cleanly if the board has been preheated. The three leads are on a 2.54 mm pitch, easy to inspect and touch up with a fine iron.