Octal inverting buffer with 3‑state outputs – what it is and where it fits
The Texas Instruments SN74HC240N is an octal inverting buffer with 3‑state outputs from the 74HC logic family. It operates from a 2V to 6V supply rail, making it compatible with both 3.3V and 5V logic systems. The two elements each handle four bits, giving eight total channels of inverting buffering with independent output enable control. The 3‑state outputs allow multiple devices to share a common bus – the outputs go high‑impedance when disabled, which is standard for memory address lines, data buses, and multiplexed I/O in industrial controllers and telecom line cards. The industrial temperature range (-40°C to 85°C) suits it for factory automation, outdoor networking gear, and HVAC panels where the ambient can swing well past commercial limits.
Supply voltage and output drive – what the ratings mean for the BOM
The 2V to 6V supply range is the key selection parameter. At 5V the part runs directly off a standard logic rail; at 3.3V it interfaces with lower‑voltage FPGAs or MCUs without a level shifter. The symmetric 7.8 mA high/low output current is modest – enough to drive one or two CMOS inputs or a low‑power LED indicator, but not a relay coil or a long backplane trace. For bus‑driving applications with higher fan‑out, a 74ABT or 74LVTH part (like the SN74ABT2245DW with 32 mA drive) would be the next tier up. The inverting output means this is not a drop‑in for a non‑inverting buffer – verify the logic sense in the schematic before ordering.