Texas Instruments CD74HCT240E

Overview

CD74HCT240E from Texas Instruments is an inverting octal buffer/line driver with three-state outputs and dual active-low output enables, designed for bidirectional bus interfacing in 5-V TTL-compatible digital systems. It delivers 8ns typical propagation delay at V_CC = 5 V, CL = 15 pF, supports ±6 mA output drive, operates across –55°C to +125°C, and features buffered inputs and high-current bus-driver outputs.

For engineers reviewing the CD74HCT240E datasheet, CD74HCT240E pinout, CD74HCT240E application, or CD74HCT240E equivalent, key selection considerations include its inverting logic function, dual OE control, LSTTL input compatibility (V_IL ≤ 0.8 V, V_IH ≥ 2 V), three-state bus hold capability, and PDIP-20 package suitability for prototyping and industrial control backplanes.

Technical Context

The CD74HCT240E implements two independent 4-bit inverting buffer sections, each controlled by its own active-low output enable (1OE, 2OE). Its HCT logic family ensures direct compatibility with standard TTL voltage thresholds while maintaining CMOS power efficiency and noise immunity.

All eight outputs enter high-impedance state when either 1OE or 2OE is high; both must be low for data transmission. Input buffering prevents signal degradation during fanout, and output transition times are balanced (12–18 ns) to minimize skew in synchronous bus environments.

Key Specifications

Pinout & Package

CD74HCT240E is supplied in a 20-pin plastic dual in-line package (PDIP-N), with 25.40 mm × 6.35 mm body size and 2.54 mm lead pitch. The package is through-hole mountable, RoHS-compliant (NIPDAU finish), and rated for manual soldering and wave soldering processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT240N and 74ACT240PC, CD74HCT240E uniquely combines military-grade temperature range, ultra-low quiescent current (8 μA), and proven reliability in long-lifecycle industrial deployments-making it the preferred choice for embedded systems requiring sustained operation across extreme ambient conditions.

Availability

CD74HCT240E is available at Aetrix Electronics and suitable for industrial bus interface, microcontroller I/O expansion, legacy system emulation, and test equipment signal conditioning requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for CD74HCT240E 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 decades of heritage in high-reliability logic families.

CD74HCT240E belongs to TI's CD74HCT high-speed CMOS logic series, engineered for seamless TTL-to-CMOS migration in industrial, aerospace, and automotive control systems demanding wide temperature operation and low static power.

FAQ

What logic family does CD74HCT240E belong to, and how does it differ from CD74HC240E?

CD74HCT240E belongs to the HCT (High-Speed CMOS TTL-compatible) logic family, operating strictly from 4.5 V to 5.5 V and featuring TTL-level input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V). In contrast, CD74HC240E is HC-family, supporting 2 V–6 V operation with CMOS input thresholds (V_IL = 0.3×V_CC, V_IH = 0.7×V_CC). Both share identical pinout and inverting three-state functionality, but CD74HCT240E ensures direct compatibility with legacy TTL systems without level-shifting.

Can CD74HCT240E drive a 50-pF load while maintaining timing specifications?

Yes, CD74HCT240E is fully characterized for C_L = 50 pF in its switching characteristics table (Section 5.7), with t_PHL/t_PLH = 9 ns (typ), 22–33 ns (max) over temperature. Its ±6 mA output drive ensures stable edge rates into 50-pF loads, and the specified 12–18 ns output transition time (t_THL/t_TLH) confirms controlled slew rate without excessive ringing or EMI.

What is the maximum continuous output current rating per pin for CD74HCT240E?

The absolute maximum rating for CD74HCT240E is ±35 mA per output pin under short-circuit conditions (VO < –0.5 V or VO > V_CC + 0.5 V), but the recommended operating condition limits steady-state output current to ±6 mA per pin (I_OL/I_OH) to maintain VOL ≤ 0.4 V and VOH ≥ 3.7 V across temperature. Exceeding ±6 mA risks violating output voltage specs and increasing junction temperature beyond safe limits.

How should unused inputs on CD74HCT240E be terminated?

Unused inputs on CD74HCT240E must not be left floating. They should be tied to a defined logic level-either V_CC or GND-using a pull-up or pull-down resistor (1–10 kΩ typical) or direct connection. This prevents undefined states, increased ICC, and potential oscillation due to noise coupling. Input leakage current is ≤ ±1 μA, so termination resistors introduce negligible loading.

Does CD74HCT240E support hot insertion or live bus swapping?

CD74HCT240E supports controlled hot insertion when used with proper power sequencing and bus protection. Its three-state outputs ensure high-impedance isolation during power-up/down, and the absolute maximum ratings include VI limits (–0.5 V to V_CC + 0.5 V) compatible with live-bus conditions. However, external series resistors (22–100 Ω) and clamping diodes are recommended for robustness in frequent hot-swap scenarios.