Texas Instruments SN74AHCT240NSR

Overview

SN74AHCT240NSR from Texas Instruments is an octal inverting buffer/driver with tri-state outputs, designed for memory-address, clock, and bus-oriented signal routing in 5-V systems. It features TTL-compatible inputs (VIH = 2 V, VIL = 0.8 V), ±8 mA output drive, 9.5 ns max propagation delay at 5 V/50 pF, and operates from –40°C to +125°C. It enables bidirectional bus isolation in industrial control backplanes.

For engineers reviewing the SN74AHCT240NSR datasheet, SN74AHCT240NSR pinout, SN74AHCT240NSR application, or SN74AHCT240NSR equivalent, key selection criteria include its 5-V-only supply operation, inverting logic function per channel, dual independent output-enable controls (1OE, 2OE), and SOP-20 package compatibility with legacy 5-V board layouts.

Technical Context

The SN74AHCT240NSR implements two independent 4-bit inverting buffer sections, each with dedicated output-enable (OE) inputs controlling high-impedance state entry/exit. Its CMOS design with TTL-level input thresholds allows direct interfacing with 3.3-V logic while driving 5-V buses.

Propagation delays are specified at 5 V ±0.5 V with CL = 15 pF and CL = 50 pF loads; disable times (tPHZ/tPLZ) and enable times (tPZH/tPZL) are matched within 1 ns skew across outputs. Input clamp current exceeds ±20 mA, and latch-up performance meets JESD17 (>250 mA).

Key Specifications

Pinout & Package

SOP-20 (NS) package: 12.60 mm × 7.80 mm body size, 20-pin surface-mount, RoHS-compliant, NIPDAU lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AHCT240NSR, the DWR offers mechanical compatibility with legacy SOIC footprints but larger size, while the PW provides miniaturization at the cost of thermal headroom and active production status - making NS the optimal balance of manufacturability, thermal performance, and long-term supply assurance.

Availability

SN74AHCT240NSR is available at Aetrix Electronics and suitable for industrial PLC backplanes, automotive body control modules, test equipment signal routing, and legacy display interfaces requiring stable component supply across extended temperature ranges.

Supply support for SN74AHCT240NSR 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 industrial-grade product validation.

The SN74AHCT240NSR belongs to TI's AHCT logic family, engineered for robust 5-V bus interfacing in harsh environments - emphasizing TTL compatibility, ESD resilience, and extended-temperature operation.

FAQ

What is the maximum operating frequency supported by SN74AHCT240NSR?

The SN74AHCT240NSR does not specify a maximum clock frequency, but its 9.5 ns maximum propagation delay (A-to-Y, CL = 50 pF) implies reliable operation up to ~50 MHz for single-edge-triggered paths. System-level timing must account for enable/disable delays (up to 13 ns) and board trace effects. For synchronous bus applications, validate setup/hold margins using the device's tPLH/tPHL and tPZH/tPZL values at actual load conditions.

Can SN74AHCT240NSR operate with a 3.3-V supply?

No, SN74AHCT240NSR requires a 4.5 V to 5.5 V supply and is not rated for 3.3-V operation. Its internal circuitry is optimized for 5-V CMOS logic levels, and VIH/VIL thresholds (2.0 V/0.8 V) assume VCC ≥ 4.5 V. Using 3.3 V risks undefined output states, excessive ICC, and potential damage. For 3.3-V systems, consider the SN74LVC240A instead.

How should unused inputs be handled on SN74AHCT240NSR?

All unused inputs on SN74AHCT240NSR must be tied to either VCC or GND to prevent floating nodes that cause increased ICC, oscillation, or ESD susceptibility. Inputs tied to VCC disable their associated outputs (via OE logic), while tying to GND enables inversion but leaves outputs active. TI recommends connecting unused OE pins to VCC via a pull-up resistor to ensure default high-impedance state during power-up.

Is SN74AHCT240NSR pin-compatible with older SN74LS240 devices?

Yes, SN74AHCT240NSR shares identical pinout and function mapping with SN74LS240 in SOP-20 (NS) packaging, including 1OE, 1A1–1A4, 1Y1–1Y4, GND, VCC, 2A1–2A4, 2Y1–2Y4, and 2OE. However, it replaces bipolar LS logic with CMOS AHCT technology - delivering lower power, higher noise immunity, and TTL-compatible inputs without requiring external pull-ups.

What thermal considerations apply to SN74AHCT240NSR in continuous operation?

SN74AHCT240NSR has a junction-to-ambient thermal resistance (RθJA) of 80.4°C/W in SOP-20. At maximum rated output current (±8 mA per output, 8 outputs), worst-case power dissipation is ~15 mW. With 25°C ambient, junction temperature remains below 40°C - well within the 125°C limit. No heatsink is needed, but ensure ≥100 mm² copper pour under the package for optimal conduction cooling in high-density layouts.