Dual 4-bit inverting buffer for 5 V bus isolation
The CY74FCT240TSOC is a Cypress 74FCT-series dual 4-bit inverting buffer with 3-state outputs in a 20-SOIC package. The inverting logic and output-enable control make it a direct fit for 5 V backplane buffering, memory-address isolation, or general-purpose bus gating where the data path needs to be tri-stated during idle or test modes.
64 mA sink drive — sizing the fan-out
The output drive capability is 32 mA source and 64 mA sink per channel. That sink current is the headline number for bus loading: it can drive the combined input capacitance of up to 10-15 standard 74-series loads on a backplane without signal degradation. For a 5 V TTL bus, the 64 mA sink handles the pull-down of heavily loaded lines, while the 32 mA source is adequate for driving CMOS inputs.
Surface-mount 20-SOIC with 1.27 mm pitch — a straightforward hand-solder or reflow package. The 7.50 mm body width is the wider SOIC variant (SOIC-20W), not the narrow 300 mil body. Check your PCB footprint: the narrow 20-SOIC (208 mil body) is not pin-compatible. Supply decoupling: place a 0.1 µF ceramic within 5 mm of each VCC pin; the 5 V rail sees transient draw on output switching, and the 64 mA sink edges can couple noise into adjacent traces if decoupling is skimped.