74S Schottky hex inverter with open-collector outputs
The SN74S05D is a hex inverter from the 74S Schottky logic family, containing six independent inverter gates each with a single input. The open-collector outputs allow wired-AND connections and level shifting to higher voltages than the 5.25 V supply rail. Housed in a 14-SOIC package (0.154" width, 3.90 mm), it mounts on standard surface-mount pads and shares the footprint with other 14-pin SOIC logic devices.
Supply rails and logic thresholds
Input logic-low threshold is 0.8 V max, and logic-high threshold is 2 V min, providing direct compatibility with 5 V TTL outputs without external translation. The open-collector output sinks up to 20 mA when low (VOL), but cannot source current when high — the output floats unless pulled up externally. This is the key design constraint: a pull-up resistor to the desired output voltage is required for each gate used.
Switching speed and propagation delay
Maximum propagation delay is 7.5 ns at 5 V supply with a 50 pF load. This is the time from input crossing the threshold to output crossing the same threshold — the open-collector output's rise time is determined by the external pull-up resistor value and load capacitance, not the IC itself. For a 1 kΩ pull-up to 5 V driving 50 pF, the RC time constant adds roughly 50 ns to the rise time. Designers should budget this external delay when calculating the maximum data rate through the inverter chain.
No official successor or pin-compatible alternative is listed — the 74S family is a mature logic series. For new designs requiring open-collector inverters in SOIC-14, the 74LS05 or 74HC05 offer lower power but different switching thresholds and supply ranges.