The Texas Instruments LM2576SX-ADJ/NOPB is a SIMPLE SWITCHER® step-down buck regulator delivering 3A continuous output from a 4V to 40V input rail. The 52kHz switching frequency keeps switching losses low and simplifies PCB layout — the trade-off is a larger inductor and higher output ripple compared to modern 500kHz+ converters. The adjustable output version lets you set Vout anywhere from 1.23V to 37V with two external resistors, covering 3.3V, 5V, 12V, and other common rails from a single BOM line.
Input headroom and thermal envelope
The 40V maximum input voltage gives margin on 24V industrial buses and 12V automotive systems, though the 52kHz switching means the input filter capacitor needs to handle the ripple current. No synchronous rectifier is used internally, so the external Schottky catch diode carries the full 3A during the off-time. The diode forward voltage and its thermal coupling to the PCB copper matter more for efficiency than the regulator itself at this switching speed.
Package and mounting — DDPAK/TO-263-5
The surface-mount DDPAK/TO-263-5 package (5 leads plus tab) is the standard footprint for 3A buck converters. The exposed tab is the thermal path and the ground connection — the PCB layout must provide a copper pour area sized for the dissipation at the target output current.
The base product number LM2576 covers the fixed-output variants (3.3V, 5V, 12V, 15V) and the adjustable version in both through-hole (TO-220) and surface-mount (D²Pak) packages. The adjustable surface-mount variant is the most flexible BOM line for multi-rail designs.