4 x 2:1 multiplexer in the 74AC family — what it is and where it fits
The CD74AC257E is a 4 x 2:1 multiplexer from the 74AC series, a high-speed CMOS logic family that combines the low power of CMOS with the speed of advanced CMOS. It selects one of two 4-bit data inputs based on a single select line, routing the chosen nibble to the output. The part operates from a 1.5V to 5.5V supply, making it suitable for mixed-voltage systems where a 3.3V core interfaces with 5V peripherals. With a military temperature range of -55°C to 125°C, it is rated for avionics, satellite, downhole drilling, and other environments where the board sees extreme thermal cycling. The 16-pin DIP package (0.300" body width) is a through-hole footprint that suits prototyping, legacy board repairs, and designs where vibration resistance or manual rework is a priority.
Supply range and output drive — what the ratings mean for your BOM
The 1.5V to 5.5V supply range is wide enough to cover standard logic rails from 1.8V through 5V. In a 3.3V system the part runs without a level translator when the select and data inputs are also 3.3V; at 5V it can directly drive legacy TTL inputs. The 24mA output sink and source capability at both logic levels means the multiplexer can drive a bus line or a bank of LEDs without a buffer — useful in panel indicator or status-latch applications. The 24mA figure is symmetrical, so the output high and low levels stay balanced under load, which simplifies timing analysis in synchronous designs.
Active lifecycle — no last-time-buy pressure
The CD74AC257E carries an Active product status per the manufacturer, with ROHS3 compliance. The 74AC family is broadly second-sourced; if dual-sourcing is required, the standard 74AC257 in a DIP-16 package from other vendors is a direct form-fit-function alternate — verify the exact order code for your preferred supplier's inventory.