Dual 1:4 decoder/demux in a 16-SOIC footprint
The SN74LS156NSR is a dual 1:4 decoder/demultiplexer from the 74LS series, packing two independent 1:4 demux circuits into a single 16-SOIC package. Each section selects one of four outputs based on two address lines, with a common enable per section.
Output drive and what it means for bus loading
The outputs source 100 µA and sink 8 mA — the sink current is the figure that matters when driving TTL inputs or LED indicators. A standard LS TTL input requires about 0.4 mA at logic low, so one output can drive up to 20 such loads without exceeding the sink rating. The high-level output current is only 100 µA, which means the part is not designed to source significant current — it pulls outputs low to sink load current, typical for open-collector or totem-pole LS logic driving into a pull-up or a CMOS input with high impedance.
Package and board-fit for the pick-and-place line
Housed in a 16-SOIC (0.209", 5.30 mm width) with a supplier device package of 16-SO, the footprint is standard for SOIC-16 wide-body. The 1.27 mm pitch and gull-wing leads place well on standard reflow profiles with no tombstoning risk if the pad geometry follows the IPC-7351 standard.
Lifecycle and compliance documentation
RoHS3 compliance (2011/65/EU + 2015/863) means the part is free of the ten restricted substances including the four phthalates — no exemption expiry to track for EU-market equipment.