Texas Instruments SN74ACT240PW

Overview

SN74ACT240PW from Texas Instruments is an octal 3-state inverting buffer/driver IC operating at 4.5V–5.5V V_CC, with TTL-compatible inputs, 8.5ns max propagation delay at 5V, and dual independent output-enable controls. It serves as a bus-oriented transceiver in memory address buffering and clock distribution circuits within industrial control and telecom infrastructure.

For engineers reviewing the SN74ACT240PW datasheet, SN74ACT240PW pinout, SN74ACT240PW application, or SN74ACT240PW equivalent, key selection criteria include its TSSOP-20 package footprint, 24mA drive strength per output, high-impedance state control via separate OE pins, and compatibility with 5V logic systems requiring bidirectional bus isolation.

Technical Context

The SN74ACT240PW implements two independent 4-bit inverting buffer sections, each with dedicated output-enable (OE) inputs. Its CMOS push-pull outputs provide balanced sourcing and sinking capability up to ±24mA, enabling robust driving of capacitive loads without external termination.

Logic operation follows positive-logic enable: when OE is low, inverted data passes from A inputs to Y outputs; when OE is high, outputs enter high-impedance state. Input voltage tolerance extends to 5.5V regardless of V_CC, supporting mixed-voltage interface scenarios.

Key Specifications

Pinout & Package

TSSOP-20 package: 6.5mm × 6.4mm body size, 1.2mm max height, 0.65mm lead pitch, exposed pad optional for thermal relief (not electrically connected).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal 3-state buffer applications.

Compared with SN74ACT240PW, SN74ACT244PW offers identical form-factor and electrical specs except output polarity, making it a drop-in replacement where inversion is irrelevant; SN74LVC244APW reduces power and cost in 3.3V-native systems but sacrifices 5V interface capability and backward compatibility.

Availability

SN74ACT240PW is available at Aetrix Electronics and suitable for industrial control systems, telecom infrastructure equipment, and consumer electronics requiring stable component supply with long-term lifecycle support.

Supply support for SN74ACT240PW 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 90 years of innovation in industrial, automotive, and communications markets.

The SNx4ACT240 family was designed for high-density, high-speed bus interface applications-including memory addressing, clock distribution, and data path isolation-in systems demanding robust 5V logic performance and wide temperature operation.

FAQ

What is the function of the two OE pins on the SN74ACT240PW?

The SN74ACT240PW features two independent output-enable (OE) inputs: 1OE controls the first four buffers (1A1–1A4 → 1Y1–1Y4), and 2OE controls the second set (2A1–2A4 → 2Y1–2Y4). When an OE pin is low, its associated outputs pass inverted input data; when high, those outputs enter high-impedance state. This enables selective bus segmentation without affecting other channels, which is essential for multi-master arbitration and partial bus isolation in the SN74ACT240PW.

Does the SN74ACT240PW support 3.3V input signals while operating at 5V V_CC?

Yes, the SN74ACT240PW accepts input voltages up to V_CC+0.5V (i.e., 5.5V), so 3.3V logic levels fall well within its valid VIH/VIL thresholds (VIH ≥ 2V, VIL ≤ 0.8V). This makes the SN74ACT240PW suitable for interfacing 3.3V microcontrollers with 5V peripherals without level shifters-provided all inputs remain within absolute maximum ratings and current limits specified in the SN74ACT240PW datasheet.

Can the SN74ACT240PW drive a 50pF load at 10MHz without signal degradation?

Yes-the SN74ACT240PW's 24mA output drive and 8.5ns propagation delay are characterized into 50pF loads at 5V, ensuring clean edges and adequate timing margins for 10MHz bus operation. Its C_pd of 45pF per buffer also indicates predictable dynamic power draw under these conditions, confirming suitability for sustained 10MHz switching in the SN74ACT240PW's recommended operating range.

Is the thermal pad on the SN74ACT240PW's TSSOP package required to be connected?

No-the thermal pad on the SN74ACT240PW's TSSOP-20 package is optional and may be left floating or connected to GND for improved thermal dissipation. It is not electrically functional and must never be tied to V_CC or signal nets. TI recommends grounding it for better junction-to-board thermal resistance, especially in high-duty-cycle applications where the SN74ACT240PW may dissipate >100mW continuously.

How does the SN74ACT240PW handle power-up sequencing to avoid bus contention?

The SN74ACT240PW enters high-impedance state when OE is high. To prevent contention during power-up, tie both 1OE and 2OE to V_CC via pull-up resistors-ensuring outputs remain in high-Z until firmware actively drives OE low. This behavior is explicitly documented in the SN74ACT240PW functional description and eliminates need for external reset supervision in most applications.