The Texas Instruments SN74ALS644AN is a bus driver/transceiver from the ALS (Advanced Low-Power Schottky) logic family. It provides bidirectional data transfer between two buses, with the direction controlled by a separate enable input. This part is designed for high-capacitance backplane or memory-bus driving, where the ALS series offers a balance of speed and power dissipation.
Lifecycle and RoHS compliance
However, it is RoHS non-compliant, which is a critical factor for designs targeting environmental compliance exemptions or legacy maintenance. No successor has been officially designated, so the part is the direct choice for new builds where lead-bearing solder is permitted.
This device is, typically a 20-pin DIP package (the 'N' suffix indicates a plastic DIP). It operates from a standard 5 V supply rail, compatible with TTL thresholds. For a BOM review, the key check is the supply voltage tolerance and the output drive capability relative to the bus load — the ALS family is specified for ±24 mA output drive at 5 V, which suits most parallel bus interfaces.