onsemi 74F240SC

Overview

74F240SC from Fairchild Semiconductor is an octal inverting buffer/line driver with dual active-Low 3-STATE outputs, designed for memory and address bus driving, clock distribution, and bidirectional bus interfacing in TTL-compatible systems. It operates at 4.5–5.5 V, delivers 64 mA sink current per output, supports 7 ns max propagation delay (tPLH/tPHL), and features input clamp diodes for high-speed termination control.

For engineers reviewing the 74F240SC datasheet, pinout, applications, or equivalent options, key selection criteria include its dual enable architecture (OE1/OE2 active-Low), inverting logic function, SOIC-20 package compatibility, and verified 3-STATE bus-driving capability under industrial temperature range (0°C to +70°C).

Technical Context

The 74F240SC implements two independent 4-bit inverting buffer sections, each controlled by a dedicated active-Low 3-STATE enable input (OE1 and OE2). Its outputs enter high-impedance state when either enable is HIGH, enabling bidirectional bus arbitration without external logic.

It uses standard F-series TTL circuitry with Schottky-clamped transistors, delivering 64 mA sink (48 mA min) and −12 mA source drive while maintaining VIH ≥ 2.0 V and VIL ≤ 0.8 V for reliable TTL-level interfacing. Input clamp diodes suppress ringing on fast edges, critical for stable operation on long PCB traces or unterminated buses.

Key Specifications

Pinout & Package

74F240SC is housed in a 20-lead Small Outline Integrated Circuit (SOIC) package per JEDEC MS-013, 0.300" wide (Package Code M20B), with 1.27 mm lead pitch and surface-mount footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal inverting buffer applications.

Compared with SN74F240N and 74ACT240SC, the 74F240SC uniquely balances legacy TTL interoperability, SOIC surface-mount readiness, and robust 64 mA bus-driving capability-making it optimal for cost-sensitive, volume-manufactured 5 V digital systems requiring proven reliability.

Availability

74F240SC is available at Aetrix Electronics and suitable for memory address buffering, clock distribution networks, and parallel bus transceiver interfaces requiring stable component supply and long-term industrial availability.

Supply support for 74F240SC includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and discrete power products, acquired by ON Semiconductor in 2016; its legacy logic portfolio remains widely deployed in industrial and computing infrastructure.

The 74F240SC belongs to Fairchild's F-series TTL logic family, engineered specifically for high-density memory and bus interface applications where speed, drive strength, and 3-STATE controllability were critical design requirements.

FAQ

What is the logic function of the 74F240SC?

The 74F240SC implements two independent groups of four inverting buffers, each with active-Low 3-STATE enable control (OE1 and OE2). When enabled, inputs I0–I3 and I4–I7 are inverted and driven onto outputs O0–O3 and O4–O7 respectively; when disabled, all outputs enter high-impedance state. This behavior is confirmed in the truth table and logic symbol of the official Fairchild DS009501 datasheet for the 74F240SC.

Does the 74F240SC support 3.3 V operation?

No, the 74F240SC is specified only for 4.5 V to 5.5 V supply operation and is not rated for 3.3 V use. Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output drive characteristics assume a nominal 5 V rail. Attempting 3.3 V operation may result in marginal noise margins or failure to meet AC timing specifications. The 74F240SC must be used within its documented VCC range to guarantee functionality.

What is the maximum capacitive load the 74F240SC can drive reliably?

The 74F240SC is characterized for CL = 50 pF in AC timing tests, with 7.0 ns max propagation delay under those conditions. While it can drive higher capacitance, performance degrades linearly: at 100 pF, delay increases ~20–30%, and output rise/fall times widen. For reliable operation beyond 50 pF, verify timing margins in-system and consider adding series termination or reducing trace length. This behavior is consistent across all 74F240SC units per DS009501.

Is the 74F240SC pin-compatible with the 74F244SC?

No, the 74F240SC is not pin-compatible with the 74F244SC. Although both are 20-pin SOIC octal buffers, the 74F240SC has inverting outputs and dual active-Low enables (OE1/OE2), whereas the 74F244SC provides non-inverting outputs with one active-Low and one active-High enable. Their pin assignments differ: for example, 74F240SC places OE1 at pin 1 and OE2 at pin 19, while 74F244SC assigns OE1 to pin 1 and OE2 to pin 19 but maps inputs/outputs differently. Substitution requires PCB redesign.

What thermal considerations apply to the 74F240SC in continuous operation?

The 74F240SC has a maximum junction temperature of +150°C and is rated for ambient operation from 0°C to +70°C. Under worst-case conditions (all outputs sinking 64 mA), total power dissipation reaches ~375 mW (ICCL × VCC). Adequate PCB copper area (≥1 cm² per side under the package) and airflow prevent exceeding Tj. Derating is required above +50°C ambient; thermal data in DS009501 confirms θJA ≈ 90°C/W for SOIC-20, so the 74F240SC must be thermally managed accordingly.