What this buffer does that a plain HC240 won't
The SN74AC240PW is a dual 4-bit inverting buffer with 3-state outputs from TI's 74AC family. The inverting path cleans up a signal polarity issue in a single package, and the 3-state outputs let you share a bus without contention. Each output can sink or source 24mA, enough to drive a handful of CMOS inputs or a small relay coil through a resistor.
Supply voltage — why 2V to 6V matters on a mixed-voltage board
If your design has a 3.3V microcontroller talking to a 5V peripheral, the SN74AC240PW can sit on either rail and still meet the input thresholds. The AC family's faster edge rates compared to HC logic also help when you are pushing clock or data lines above 20 MHz.
Package and rework — 20-TSSOP on a field swap
The 20-TSSOP package (0.173" body width, 4.40mm) is a fine-pitch surface-mount part. On a field repair, you will want a hot-air station with a fine nozzle and a steady hand — the 0.65mm lead pitch does not forgive a soldering iron slip. The part is marked with TI logo and date code, so orientation is clear from the pin-1 dot. No ESD-sensitive handling beyond the usual CMOS precautions.