What the 15 mA / 64 mA drive means on a real board
The SN74BCT125AD: This is a quad non-inverting buffer with 3-state outputs — four independent single-bit channels, each able to source 15 mA and sink 64 mA at 5 V. The asymmetric drive (weak source, strong sink) is characteristic of TTL-compatible logic: the output can pull a bus line low through a 50 Ω termination but needs a pull-up resistor to drive a high-impedance load high. On a 5 V backplane with 4.7 kΩ pull-ups, the 15 mA source margin is comfortable; driving a 50 Ω transmission line directly is outside its capability.
Supply rail and temperature — 5 V only, indoor use
No industrial or automotive temperature rating is available in this variant.
Package and footprint — narrow SOIC, easy rework
Housed in a 14-SOIC narrow body (3.90 mm width, 0.154" pitch), the SN74BCT125AD uses a standard JEDEC footprint shared with hundreds of other 14-pin SOIC logic parts. The 1.27 mm lead pitch is hand-solderable and rework-friendly under a hot-air station. No exposed pad or thermal slug — power dissipation is handled through the leads and the FR-4 board copper.