Dual 4-input NAND gate for 5V logic buses
The SN74ALS20ANSR is a dual 4-input NAND gate from the 74ALS family, a Schottky-clamped bipolar logic series that balances speed and power for 5V TTL-compatible systems. Each of the two independent gates evaluates four inputs and outputs the NAND result, making it a direct fit for address decoding, enable signal generation, or combinatorial logic consolidation on a 5V bus.
Propagation delay and output drive — the timing and fan-out limits
If the downstream register setup time is 5 ns, the combinatorial logic chain can tolerate two of these gates in series before the clock edge arrives, assuming zero interconnect delay. Output drive is specified as 400 µA sourcing and 8 mA sinking at the logic-high and logic-low levels respectively. The 8 mA sink capability drives up to ten standard LSTTL loads (each 0.36 mA typical) with margin, but the 400 µA source current limits fan-out to about four LSTTL loads on the high side — a consideration when the output feeds a bus with pull-up resistors.
Operates from a 4.5V to 5.5V supply, which covers the nominal 5V rail with ±10% tolerance — the standard margin for legacy TTL and 5V CMOS systems. Input logic thresholds are 0.8V low and 2.0V high, TTL-compatible. This means a 3.3V CMOS output driving the input through a series resistor must still swing above 2.0V at the gate pin — a 3.3V rail with a 100-ohm series termination into a 5V-tolerant input works, but a 1.8V logic output will not reach the high threshold without a level translator.
14-SOIC surface-mount package — board integration
The 14-SO footprint is shared with many 74-series logic ICs, so a single PCB land pattern serves multiple BOM positions. The supplier device package is 14-SO, which is the JEDEC MS-012 variation — confirm the land pattern matches the 5.30 mm width, not the narrower 3.90 mm SOIC-14. The reel quantity is typically 2500 pieces per reel for this package size, though the exact count depends on the reel diameter specified at order.