2V to 5.5V supply — the mixed-voltage bridge
The SN74LV138ADR is a single 3:8 decoder/demultiplexer from TI's 74LV low-voltage logic family. Its 2V to 5.5V supply range lets it sit between a 3.3V MCU and a 5V peripheral without a level shifter — the inputs are 5V-tolerant when running at 3.3V, and the outputs drive 12mA high or low across the full voltage range. That 12mA symmetric drive is enough to fan out to eight CMOS loads or switch a small LED directly.
Memory decoding — the classic job
A 3:8 decoder like this one is the standard way to generate chip-select signals from three address lines. With one active-low enable and two active-high enables (the 74LV138 has three enable inputs), you can cascade multiple decoders for larger address spaces without extra glue logic. The 74LV family's propagation delay is fast enough for most 8-bit and 16-bit bus cycles at 5V; at 3.3V budget an extra 2-3 ns per the family typicals.
Package and footprint
Supplied in a 16-SOIC body (3.90mm width, 0.154" pitch) — a standard footprint shared by hundreds of logic ICs. The Tape & Reel option (SN74LV138ADR) feeds pick-and-place lines directly; Cut Tape is also available for bench prototypes. Surface-mount only, no through-hole variant in this suffix.