1-of-8 decoder with enable — 3:8 demultiplexer in SOIC-16
The 74FCT138ASO is a single 3:8 decoder/demultiplexer from Renesas, implementing a 1-of-8 output decode with an active-low enable input. It takes a three-bit binary address and asserts one of eight active-low outputs, making it a standard building block for memory-mapped I/O selection, chip-enable generation, and address decoding in 5V logic systems. The industrial temperature range spans -40°C to +85°C, covering factory-floor and outdoor telecom enclosures.
Supply voltage, output drive, and temperature grade
Rated for 4.5V to 5.5V single-supply operation, the 74FCT138ASO is a 5V-logic part that sits comfortably on a regulated 5V rail. The 15 mA high-level and 48 mA low-level output currents mean it can fan out to multiple CMOS or TTL loads without adding line drivers — useful when the decode output must enable several memory or peripheral chips simultaneously. In a control cabinet near a motor drive or a base-station radio head, the 85°C ceiling provides thermal margin above the 70°C commercial limit.
The wide-body variant offers better thermal dissipation than the narrow SOIC for the same pin count — the extra copper area under the package helps sink heat from the output drivers when several channels are active. Surface-mount assembly with a standard reflow profile; no exposed pad or special thermal management required. The 1.27 mm pitch is readily inspectable and reworkable with basic hot-air tools.
Lifecycle, compliance, and sourcing
Sourced through independent distribution channels with full lot traceability.