Texas Instruments SN74ACT240RKSR

Overview

SN74ACT240RKSR from Texas Instruments is an octal buffer/driver with 3-state outputs, designed for bus-oriented receivers and transmitters in memory address and clock distribution systems. It operates at 4.5V–5.5V V_CC, supports TTL-compatible inputs up to 5.5V, delivers ≤8.5ns propagation delay at 5V, and features dual independent output-enable controls (1OE, 2OE) for flexible bus management in high-density digital systems.

For engineers reviewing the SN74ACT240RKSR datasheet, SN74ACT240RKSR pinout, SN74ACT240RKSR application, or SN74ACT240RKSR equivalent, this device is selected for its balanced CMOS push-pull drive strength (±24 mA), low-output-impedance 3-state control, and VQFN-20 thermal pad support-key considerations for compact, thermally constrained logic interface designs in smartphones, network switches, and wearables.

Technical Context

The SN74ACT240RKSR implements two independent 4-bit inverting buffers, each controlled by a dedicated output-enable input (1OE for Y1–Y4; 2OE for Y1–Y4). Its logic function follows positive-logic enable: outputs are active-low when OE is low, and enter high-impedance state when OE is high.

It uses balanced CMOS push-pull output stages capable of sourcing and sinking equal current (±24 mA), enabling fast edge rates into light loads. The RKS package includes an exposed thermal pad that may be connected to GND for improved thermal performance-critical for sustained operation at 125°C ambient.

Key Specifications

Pinout & Package

VQFN-20 (RKS) package with 0.4-mm pitch, 4.5 mm × 2.5 mm body size, and exposed thermal pad (connected to GND or left floating per design requirements).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC240APWR and SN74ACT541RKR, the SN74ACT240RKSR uniquely combines 5-V tolerance, inverting logic, and thermal-pad-enabled thermal performance-making it optimal for industrial 5-V bus expansion where signal inversion is acceptable and thermal headroom is constrained.

Availability

SN74ACT240RKSR is available at Aetrix Electronics and suitable for smartphone baseband interfaces, industrial network switch backplanes, and wearable sensor hub designs requiring stable component supply, extended temperature operation, and compact VQFN packaging.

Supply support for SN74ACT240RKSR 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 expertise in high-reliability interface ICs.

The SNx4ACT240 family was engineered to deliver high-speed, low-skew 3-state buffering for memory, clock, and bus systems-addressing density, timing, and thermal challenges in industrial, telecom, and consumer electronics.

FAQ

What is the maximum operating temperature for SN74ACT240RKSR?

The SN74ACT240RKSR is rated for operation from –40 °C to +125 °C. This extended temperature range is validated per TI's industrial qualification standards and supported by its VQFN-20 thermal pad, which achieves a junction-to-ambient thermal resistance of 68 °C/W-enabling reliable use in hot environments like network switch chassis or automotive engine compartments.

Does SN74ACT240RKSR require external pull-up resistors on its OE pins?

Yes-TI recommends connecting both 1OE and 2OE to V_CC via pull-up resistors to ensure outputs remain in high-impedance state during power-up and power-down sequences. The minimum resistor value depends on the current-sinking capability of the driving source; typical values range from 4.7 kΩ to 10 kΩ for robust noise immunity and fast enable timing.

Can SN74ACT240RKSR interface directly with 3.3-V logic inputs?

No-SN74ACT240RKSR inputs are TTL-compatible (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) but require a minimum V_CC of 4.5 V. While 3.3-V logic outputs may meet the V_IH threshold, they risk violating the absolute maximum input voltage rating (V_I ≤ V_CC + 0.5 V) if V_CC = 5.5 V. A level-shifter or voltage translator is required for safe 3.3-V to 5-V interfacing.

What is the purpose of the thermal pad on the SN74ACT240RKSR package?

The exposed thermal pad on the SN74ACT240RKSR (RKS package) serves dual purposes: thermal conduction to the PCB ground plane to reduce junction temperature, and EMI suppression via low-inductance grounding. TI specifies it may be connected to GND or left floating-but grounding is strongly recommended to achieve the published R_θJA of 68 °C/W and maintain reliability under continuous load.

How does the inverting logic function of SN74ACT240RKSR affect system design?

The SN74ACT240RKSR performs true inverting logic: when OE is low, Y = NOT(A). This must be accounted for in signal path design-e.g., if used for address line buffering, the MCU must invert addresses before driving A inputs, or compensate in firmware. For non-inverting behavior, TI's SN74ACT541RKR is the functional counterpart in the same RKS package.