4 x 2:1 multiplexer in the 74AC family — what the ratings mean for the board
The CD74AC257M is a 4-bit, 2-input multiplexer from TI's 74AC series, routing one of two 4-bit data sources to a single 4-bit output based on a common select line. The 24mA source and sink capability at both high and low output states is the figure that decides whether this mux can drive a downstream bus without a buffer. For a 50pF load at 5V, the output transitions in the low-nanosecond range; if the downstream input has a 10pF gate capacitance, the 24mA drive handles several loads in parallel before the edge rate degrades.
Package and temperature — board-fit and deployment envelope
The 16-SOIC package is widely second-sourced; if the BOM calls for a 74AC257 in this footprint, the CD74AC257M is the TI order code, but the same die in an SOIC-16 from other logic vendors (e.g., Nexperia, ON Semiconductor) is a pin-compatible drop-in. No board spin needed.