Texas Instruments CD74AC240E

Overview

CD74AC240E from Texas Instruments is an octal 3-state inverting buffer/line driver in PDIP-20 package, operating from 1.5 V to 5.5 V, delivering ±24 mA output drive per channel, with balanced propagation delays (e.g., 6.5 ns max tPHL at 5 V), and designed for bus interface and data routing in industrial control backplanes.

For engineers reviewing the CD74AC240E datasheet, CD74AC240E pinout, CD74AC240E application, or CD74AC240E equivalent, key selection criteria include dual active-low output enables (1OE, 2OE), 50-Ω transmission-line drive capability, SCR-latch-up resistance, and compatibility with FAST logic fanout requirements.

Technical Context

The CD74AC240E implements two independent 4-bit inverting buffer banks, each controlled by its own active-low output enable (1OE for Bank 1, 2OE for Bank 2). Its RCA Advanced CMOS process ensures latch-up immunity and operation across −40°C to +85°C.

It features balanced AC switching characteristics: tPLH/tPHL ≤ 9.2 ns (3.3 V), ≤ 7.2 ns (5 V); tPZL/tPLZ ≤ 18 ns (3.3 V), ≤ 12 ns (5 V); and low dynamic power via CPD = 65 pF - enabling high-speed, low-noise bus buffering without external termination.

Key Specifications

Pinout & Package

CD74AC240E uses a 20-pin plastic dual in-line package (PDIP-N), body size 24.33 mm × 6.35 mm, with through-hole mounting and industry-standard pin pitch (2.54 mm).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74ACT240E and SN74AC240N, the CD74AC240E offers optimal balance of wide supply range, low static power (<80 µA ICC), and industrial temperature support - making it the most versatile choice for modern embedded bus interfaces.

Availability

CD74AC240E is available at Aetrix Electronics and suitable for industrial automation, test equipment, and legacy system upgrades requiring stable component supply, long-term obsolescence management, and RoHS-compliant through-hole packaging.

Supply support for CD74AC240E 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 industry-standard logic families.

The CD74AC240E belongs to TI's legacy CD74AC high-speed CMOS logic portfolio, engineered for robustness, wide-voltage operation, and seamless replacement of bipolar TTL in industrial and instrumentation applications.

FAQ

What is the maximum clock frequency supported by CD74AC240E in a bus application?

The CD74AC240E does not operate on a clock; it is an asynchronous buffer. Its usable data rate depends on propagation delay and system timing margins. With tPHL ≤ 7.2 ns (5 V) and tPLZ ≤ 12 ns, it reliably supports bus toggle rates up to 70 MHz in well-terminated 50 Ω environments - confirmed by transmission-line drive testing per datasheet Section 4.4.

Can CD74AC240E be used with a 3.3 V supply while driving 5 V-tolerant inputs?

Yes. The CD74AC240E operates down to 1.5 V and its VOH reaches ≥2.58 V (min) at 3.3 V supply with −4 mA load, meeting typical 5 V TTL VIH (≥2.0 V). Its outputs are not 5 V-tolerant, but the driven devices must only interpret the 3.3 V logic-high as valid - which is standard for mixed-voltage interconnects.

Does CD74AC240E require external pull-up or pull-down resistors on unused inputs?

Yes. Per TI's layout guidelines (Section 7.2), all unused inputs must be terminated to VCC or GND to prevent floating states and undefined operation. For CD74AC240E, tie unused A-inputs (e.g., 1A2, 2A3) to GND if inactive, or to VCC if logic-high default is preferred - never leave open.

How does the dual output-enable architecture of CD74AC240E improve system design?

The independent 1OE and 2OE pins let designers isolate two 4-bit data paths on a single device - e.g., using Bank 1 for address latching and Bank 2 for data strobing. This eliminates need for two separate buffers, reduces PCB footprint, and enables precise timing control without cross-talk or enable skew between banks.

Is CD74AC240E pin-compatible with older 74LS240 devices?

Yes - CD74AC240E shares identical PDIP-20 pinout, function table, and DC electrical behavior (e.g., inverting 3-state buffer) with 74LS240. However, CD74AC240E draws significantly less supply current, operates over wider voltage range, and offers superior noise immunity - making it a direct drop-in upgrade.