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. 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.
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.
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.