Dual 4-input AND gate in 14-SOIC — 74ALS logic for 5 V bus glue
The Texas Instruments SN74ALS21AD is a dual 4-input AND gate from the 74ALS family, packaged in a 14-SOIC (0.154", 3.90 mm width) for surface-mount assembly. It operates from a 4.5 V to 5.5 V supply and is specified over the commercial temperature range of 0°C to 70°C. Typical applications include address decoding, clock gating, and general-purpose combinatorial logic in 5 V TTL systems where propagation delay and output drive matter.
The 15 ns max propagation delay at 5 V and 50 pF load sets the timing budget for address decode or control signal paths. At 5 V nominal, this gate keeps combinatorial delays under 15 ns.
There is no last-time-buy or obsolescence notice on record. The SN74HC21N is a 74HC-series dual 4-input AND gate in a through-hole package, but its 2 V to 6 V supply range and wider temperature grade (-40°C to 85°C) make it a different fit for a pure 5 V TTL design.