Dual 4-input AND gate in 74HCT — what it is and where it fits
The CD74HCT21M is a dual 4-input AND gate from the 74HCT logic family, in a 14-SOIC surface-mount package. It implements two independent AND functions, each with four inputs, and operates from a 4.5V to 5.5V supply. The 74HCT series uses TTL-compatible input thresholds (0.8V low, 2V high) while running on a 5V CMOS rail, making it a direct drop-in for 5V TTL legacy designs or mixed-logic boards that need CMOS output drive with TTL-level signaling.
-55°C to 125°C — military temperature range for harsh environments
Rated for -55°C to 125°C operating temperature, this part covers military, avionics, downhole, and outdoor telecom applications where the board sees extreme thermal cycling. The 27ns max propagation delay at 4.5V and 50pF load is the timing spec to close in your bus-margin analysis — it's the worst-case delay across temperature and voltage, so your setup/hold budget needs to accommodate it. Quiescent current maxes at 2 µA, which keeps the power rail draw negligible in standby or battery-backed sections.
Sourcing and lifecycle — active, no LTB risk
The CD74HCT21M carries an Active product status and is ROHS3 compliant.