Device function and supply rail fit
The SN74LS138DR is a 3-to-8 line decoder/demultiplexer from the 74LS Schottky-clamped TTL family, decoding one 3-bit binary input into eight mutually exclusive active-low outputs. The 400 µA output high and 8 mA output low current ratings set the fan-out limit: each output can drive up to 10 standard 74LS loads, but driving a heavier bus or LED requires a buffer stage.
Package and board integration
The 1.27 mm pin pitch of the SOIC-16 body is layout-friendly — two-layer boards with 0.25 mm traces can route the eight outputs and three enable inputs without a via farm.