Octal inverting buffer with 64 mA sink — the bus-driving workhorse
The Fairchild 74F240SCX is an octal inverting buffer with 3-state outputs, organized as two independent 4-bit elements. The headline spec is the asymmetric output drive: 3 mA source and 64 mA sink per output. That 64 mA sink capability is what sets this part apart — it can directly drive terminated backplane traces, relay coils, or LED arrays without an external transistor buffer. The inverting logic means a high on the input produces a low on the output, which matters when you are matching polarity to the downstream load.
The 64 mA low-level output current handles terminated backplane traces with margin.
5 V only — no mixed-voltage trickery
There is no 3.3 V operation, no 5 V tolerant inputs. If your system has a 3.3 V microcontroller talking to this buffer, you need a level translator on the input side. The 3-state outputs are controlled by two active-low output enable pins (one per 4-bit bank), which lets you tristate the bus during power sequencing or when another driver takes control.
Commercial temperature, wide-body SOIC
Package is 20-SOIC with 7.50 mm width.
Lifecycle and compliance
RoHS non-compliant (leaded solder finish).