Quad 2-input NAND — 74S family, 6 ns propagation delay
The SN74S37D is a quad 2-input NAND gate from Texas Instruments' 74S Schottky logic family, packaged in a 14-SOIC surface-mount format. It integrates four independent NAND gates, each with two inputs, on a single monolithic IC. Maximum propagation delay is 6 ns at 5 V supply with a 150 pF load — this sets the timing budget for the critical path in a 5 V TTL system. The 74S Schottky-clamped process reduces storage time compared to standard 74LS, making this a fit for faster backplane or glue-logic lanes where 10 ns gate delays would eat into setup margins.
Output drive and logic thresholds
Output current capability is asymmetric: 3 mA sourcing (logic high) and 60 mA sinking (logic low). The 60 mA sink current allows direct drive of low-power relays, LEDs, or a bus of up to 10 standard TTL loads, but the 3 mA source limits fan-out when driving CMOS inputs without a pull-up resistor. This means it interfaces cleanly with other 5 V TTL and HCT families; a 3.3 V logic output driving the input may not reach the 2 V high threshold without a level translator.