Fixed 5V, 3A buck — the workhorse rail
The Texas Instruments LM2576S-5.0/NOPB is a SIMPLE SWITCHER® step-down regulator that delivers a fixed 5V output at up to 3A from a 4V to 40V input bus. It uses a 52kHz buck topology with no synchronous rectifier — the catch diode is external.
52 kHz switching — inductor size vs. ripple trade-off
The 52 kHz switching frequency is low by modern standards — it calls for a physically larger inductor (typically 100 µH to 330 µH for a 3A design) but keeps switching losses low and radiated EMI easier to filter. The fixed 5V output means no feedback divider resistors on the board; the internal reference and error amp set the regulation point. The 3A output is continuous, not peak — budget derating for ambient temperature and input voltage near the 40V maximum.
For the storeroom keeper: this part is still a standard catalog item, not a scavenge part. The DDPAK-5 reels store well if kept dry — the MSL level is typically Level 3 (168-hour floor life), so a dry cabinet or sealed bag with desiccant is the safe bet for inventory beyond a few months.
Input range and thermal envelope
The 4V minimum input means it can run from a 5V rail with headroom, but the dropout at 52 kHz is about 2V — below 6V input the output may not regulate cleanly at full load. The 40V maximum input covers 24V industrial buses and 12V/24V automotive systems with margin.