Texas Instruments SN74S240NG4

Overview

SN74S240NG4 from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for memory address and bus driving applications in TTL-compatible systems. It features dual 4-bit independent channels, 7 ns typical propagation delay at 5 V, ±64 mA output drive capability, and operates across 0°C to 70°C. It is used in server memory subsystems to isolate and strengthen address signals between CPU and DRAM modules.

For engineers reviewing the SN74S240NG4 datasheet, SN74S240NG4 pinout, SN74S240NG4 application, or SN74S240NG4 equivalent, key selection criteria include 3-state enable timing (tPZH/tPZL), high-current sinking capability (IOL = 64 mA), input hysteresis for noise immunity, PNP input structure for reduced DC loading, and compatibility with both 5-V TTL and mixed-voltage 3.3-V logic interfaces.

Technical Context

The SN74S240NG4 implements two independent 4-bit inverting buffer sections, each controlled by a dedicated active-low output-enable (G) input. Its Schottky-clamped TTL architecture delivers fast switching (tPLH/tPHL ≤ 7 ns) into 90 Ω loads with 50 pF capacitance, enabling reliable signal integrity on terminated backplanes and long PCB traces.

Each channel supports bidirectional bus isolation via high-impedance output states, with hysteresis (0.2–0.4 V) on all inputs to reject noise in electrically noisy environments. The PNP input stage reduces input current draw (IIL = –400 µA per A-input), minimizing loading on upstream drivers and improving fan-out capacity.

Key Specifications

Pinout & Package

SN74S240NG4 is supplied in a 20-pin plastic DIP (PDIP-N) package measuring 24.33 mm × 6.35 mm, with through-hole mounting and 0.3-inch row spacing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS240N and SN74ALS240N, SN74S240NG4 provides superior noise immunity (hysteresis + PNP inputs), higher drive strength (64 mA), and faster edge rates - making it the preferred choice for industrial backplanes, LED displays, and memory subsystems where signal integrity is critical.

Availability

SN74S240NG4 is available at Aetrix Electronics and suitable for memory address buffering, LED display multiplexing, network switch backplane interfacing, and industrial I/O expansion requiring stable component supply across extended production lifecycles.

Supply support for SN74S240NG4 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions with over 50 years of innovation in industrial, automotive, and communications markets.

SN74S240NG4 belongs to TI's legacy TTL logic portfolio, engineered specifically for high-reliability bus driving, memory addressing, and level translation in commercial-grade systems where robustness and long-term availability are essential.

FAQ

What is the maximum operating temperature range for SN74S240NG4?

The SN74S240NG4 is rated for commercial operation from 0°C to 70°C ambient temperature. This range is defined under Recommended Operating Conditions in the datasheet and applies to all electrical specifications including propagation delay, output drive, and noise margin. Operation outside this range may result in parametric degradation or functional failure. For extended temperature applications, consider the military-grade SN54S240J variant.

Does SN74S240NG4 support 3.3-V logic inputs?

Yes, SN74S240NG4 supports 3.3-V logic inputs. Its input voltage thresholds (VIH = 2 V min, VIL = 0.8 V max) and input hysteresis ensure reliable recognition of 3.3-V CMOS logic levels while operating from a 5-V supply. This makes SN74S240NG4 suitable as a level translator in mixed-voltage systems without external resistors or level-shifters.

How does the PNP input structure in SN74S240NG4 improve system performance?

The PNP input structure in SN74S240NG4 reduces input current draw to –400 µA per A-input (vs. –2 mA typical for standard TTL), significantly lowering DC loading on upstream drivers. This increases fan-out capability, reduces power dissipation in dense bus architectures, and minimizes voltage droop on shared signal lines - especially beneficial in memory address distribution networks.

Can SN74S240NG4 drive a 133-Ω terminated line?

Yes, SN74S240NG4 is explicitly characterized to drive terminated lines down to 133 Ω, as confirmed in the device description and switching characteristics section. Its 64 mA sink capability and fast edge rates (7 ns) maintain signal integrity on properly terminated transmission lines, making it suitable for backplane and long-trace applications where impedance matching is critical.

What is the purpose of input hysteresis in SN74S240NG4?

The input hysteresis (0.2–0.4 V) in SN74S240NG4 widens the voltage difference between logic-high and logic-low transition thresholds, increasing immunity to noise-induced glitches on slow-rising or electrically noisy signals. This is especially valuable in industrial I/O expansion and telecom infrastructure where EMI from motors, relays, or RF sources could otherwise cause false triggering.