Obsolete — sourcing the LM2596SX-12 for sustainment
This is not a part you can pull from standard distributor stock for a new production run — it is a last-time-buy or surplus-channel item. For sustainment of existing boards, the key question is whether you have enough inventory to cover the remaining build, or whether a form-fit-function replacement is acceptable.
3 A buck regulator with a fixed 12 V rail
The LM2596SX-12 is a SIMPLE SWITCHER® step-down (buck) regulator from Texas Instruments, delivering a fixed 12 V output at up to 3 A from an input range of 4.5 V to 40 V. The 150 kHz fixed switching frequency is low enough to keep inductor losses manageable and EMI predictable, but it does mean the output ripple is higher than a modern 500 kHz+ switcher — plan for a larger LC filter if the load is noise-sensitive.
The TO-263-5 (DDPAK) surface-mount package has a large exposed tab on the bottom — the PCB copper area under that tab sets the thermal resistance. For 3 A continuous at high ambient, a 2 oz copper pour of at least 6 cm² is typical.
No synchronous rectifier — external diode required
The LM2596SX-12 does not integrate a synchronous rectifier. A Schottky catch diode (rated for at least 3 A and 40 V reverse) must be added externally. This is typical for the SIMPLE SWITCHER generation — it keeps the BOM simple but means the diode conduction loss adds to the thermal budget, especially at high duty cycles near 12 V output from a low input rail.