8-bit bidirectional bus buffer for 5 V TTL backplanes
The SN74LS645N3 is an 8-bit non-inverting transceiver from TI's 74LS low-power Schottky TTL family, with 3-state outputs on both the A and B ports. It buffers bidirectional data between two 8-bit buses under direction (DIR) and output-enable (OE) control. Output drive is rated 15 mA source and 24 mA sink per channel — enough to drive a standard TTL load or a short backplane trace, but not a heavily loaded parallel bus without external buffers. The 3-state outputs let multiple transceivers share the same bus lines without contention.
Supply rail and temperature grade
No wide-VIN flexibility; a regulated 5 V supply is required. This limits deployment to indoor, temperature-controlled equipment — not suitable for industrial enclosures, automotive, or outdoor use without environmental mitigation.
Housed in a 20-pin plastic DIP (0.300" wide, 7.62 mm body), through-hole mounting. The supplier device package is 20-PDIP. This is a legacy footprint — no SMD rework possible; the part inserts into a socket or solders into plated through-holes on a 100-mil pitch grid. Supplied in bulk packaging (loose tubes or bags), not tape-and-reel. For high-volume pick-and-place, the tube-packed SN74LS645-1N is the same die in the same package but shipped in tubes.
RoHS non-compliant. The part uses a tin-lead (SnPb) finish on the leads. This is acceptable for RoHS-exempt applications (military, aerospace, medical implants, some industrial spares) and for prototypes where leaded solder is still used. For RoHS-required builds, a lead-free alternative from the 74LS family (e.g., SN74LS645N) should be verified for pin-compatibility.