8-bit bus transceiver for 5V backplanes
The CY74FCT646TSOC is an 8-bit non-inverting transceiver from the 74FCT logic family, packaged in a 24-SOIC (7.50mm wide) for surface-mount assembly. It provides bidirectional data flow between two buses, with direction and output-enable controls, and 3-state outputs so multiple devices can share the same bus lines without contention. The 74FCT series is a faster, lower-power evolution of the original 74F logic — expect propagation delays in the 4-6 ns range, which keeps bus timing margins healthy on 5V backplanes running at 20-33 MHz.
The 4.75V to 5.25V supply range means this part runs on a standard 5V rail with ±5% tolerance — no need for a separate regulator if your board already has a clean 5V bus. If your repair bench is pulling a dead board from a rooftop enclosure, this part can handle the environment.
Output drive — sizing the bus load
With 32mA source and 64mA sink capability per output, this transceiver can drive a moderately loaded backplane or a bank of CMOS/TTL inputs without external line drivers. The asymmetric sink/source ratio is typical for bipolar logic — the stronger sink handles capacitive discharge on the falling edge, which matters for signal integrity on long traces. If your bus has more than 8-10 loads per line, budget for a buffer or check the total capacitive loading against the datasheet derating.
RoHS compliance — lead-free assembly ready
This part is ROHS3 compliant, meaning it meets the EU Restriction of Hazardous Substances directive including the exemption for lead in solder. It is compatible with lead-free reflow profiles (260°C peak typical) and can be used in RoHS-compliant production without a waiver.