Texas Instruments CD74HC240M

Overview

CD74HC240M from Texas Instruments is an inverting octal buffer/line driver with three-state outputs and dual active-low output enables, operating across 2 V to 6 V. It delivers 8 ns typical propagation delay at 5 V/15 pF, supports ±25 mA bus-driver output current, and functions reliably from –55°C to +125°C - used in bidirectional data bus isolation for industrial control backplanes.

For engineers reviewing the CD74HC240M datasheet, CD74HC240M pinout, CD74HC240M application, or CD74HC240M equivalent, key selection criteria include its inverting logic polarity, dual OE control architecture, HC-series CMOS voltage range, high-noise-immunity input thresholds, and compatibility with LSTTL-loaded buses requiring three-state bus arbitration.

Technical Context

The CD74HC240M implements eight independent inverting buffer channels, each with buffered inputs and high-current three-state outputs. Its dual active-low output enable (1OE, 2OE) allows grouped control of two sets of four outputs - enabling selective bus driving without contention.

It uses standard silicon-gate CMOS technology with rail-to-rail output swing, balanced rise/fall times, and no internal latch-up risk under recommended conditions. Input thresholds scale with VCC (VIH = 70% VCC, VIL = 30% VCC), ensuring robust noise margins across the full 2–6 V supply range.

Key Specifications

Pinout & Package

CD74HC240M is supplied in a 20-pin SOIC (Small Outline Integrated Circuit) package measuring 12.80 mm × 7.50 mm, with standard 0.050″ (1.27 mm) lead pitch and gull-wing surface-mount leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC240N and CD74HCT240M, CD74HC240M provides broader supply flexibility (2–6 V), superior thermal resistance in SOIC packaging, and CMOS-input noise immunity - making it optimal for new industrial and automotive PCB designs prioritizing layout density and voltage scalability.

Availability

CD74HC240M is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and test instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC240M 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 delivering analog and embedded processing solutions, with decades of expertise in logic IC design, reliability qualification, and high-volume manufacturing.

CD74HC240M belongs to TI's CD74HC high-speed CMOS logic family, engineered for low-power, wide-voltage, and high-noise-immunity operation in harsh-environment industrial and automotive control systems.

FAQ

What logic polarity does CD74HC240M implement?

CD74HC240M implements inverting logic: each of its eight buffer channels outputs the logical complement of its input signal (Y = NOT A). This behavior is fixed and cannot be configured. The device maintains this inversion regardless of output enable state - when outputs are disabled (high-impedance), no logic level is driven, but the internal gate still computes the inverted value.

Can CD74HC240M operate at 3.3 V supply voltage?

Yes, CD74HC240M is fully specified to operate at 3.3 V, as part of its 2 V to 6 V supply range. At 3.3 V, input thresholds scale to VIH ≈ 2.31 V and VIL ≈ 0.99 V, providing 0.99 V noise margin. Output VOH exceeds 3.2 V and VOL remains below 0.33 V at 6 mA load - meeting standard 3.3 V LVTTL interface requirements without level shifters.

How are the two output enables (1OE and 2OE) used in CD74HC240M?

In CD74HC240M, 1OE controls outputs Y1–Y4 and 2OE controls Y5–Y8; both are active-low. To drive all eight outputs, both 1OE and 2OE must be held low. Asserting either enable high places its associated four outputs in high-impedance state - enabling independent gating of two 4-bit data groups, such as separating address and data lines on a shared bus.

Does CD74HC240M require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs on CD74HC240M must be terminated to a defined logic level - either VCC or GND - to prevent floating nodes that cause increased ICC, erratic output states, or ESD susceptibility. TI recommends tying unused A1–A8 inputs directly to VCC or GND using short traces; no resistor is needed unless current limiting is required for fault tolerance.

What is the maximum capacitive load CD74HC240M can drive while maintaining 8 ns propagation delay?

The 8 ns typical propagation delay for CD74HC240M is specified at CL = 15 pF and VCC = 5 V. As load capacitance increases, delay increases linearly: at CL = 50 pF, tPD rises to 20 ns (max) over temperature. For designs requiring ≤10 ns delay, total load (including trace and receiver input capacitance) must remain ≤25 pF - achievable with short traces and low-Ci receivers.