Texas Instruments SN74BCT240DW

Overview

SN74BCT240DW from Texas Instruments is an octal noninverting buffer/driver with 3-state outputs, designed for memory address and bus driving in 5-V TTL-compatible systems. It operates from 4.5 V to 5.5 V, delivers ±64 mA output drive (IOL/IOH), supports 3.5 ns typical propagation delay (tPHL), and features BiCMOS architecture for low ICCZ quiescent current (6–9 mA).

For engineers reviewing the SN74BCT240DW datasheet, SN74BCT240DW pinout, SN74BCT240DW application, or SN74BCT240DW equivalent, this page provides verified pin mapping, real-world timing behavior, bus-driving capability metrics, thermal performance (θJA = 58°C/W), and validated alternatives for legacy 5-V system upgrades and industrial control backplanes.

Technical Context

The SN74BCT240DW implements two independent 4-bit noninverting buffer sections, each with active-low 3-state enable (1OE, 2OE). Its BiCMOS design combines bipolar input stages for TTL-level compatibility and CMOS output stages for high current drive and reduced power consumption during output disable.

Each output supports true 3-state operation with guaranteed high-impedance states under power-up/down conditions when OE is pulled up to VCC. Input thresholds meet standard TTL levels (VIL = 0.8 V, VIH = 2.0 V), and outputs are specified for 50-pF capacitive loads at 5 V with 500-Ω source/sink termination per JEDEC test conditions.

Key Specifications

Pinout & Package

SN74BCT240DW uses a 20-pin SOIC (DW) package, 7.5 mm wide, 2.65 mm max height, with 1.27 mm pitch and RoHS-compliant NiPdAu lead finish. Pin 1 is marked by a beveled corner or notch; device orientation follows JEDEC MS-013 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT240N and SN74LS240N, the SN74BCT240DW uniquely balances 64 mA drive, 4 ns timing, and 9 mA ICCZ-making it the optimal choice for upgrading industrial 5-V backplanes requiring both speed and robustness without redesigning power or layout.

Availability

SN74BCT240DW is available at Aetrix Electronics and suitable for memory interface design, industrial bus conditioning, and legacy system upgrade projects requiring stable component supply and long-term obsolescence management.

Supply support for SN74BCT240DW 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 for industrial, automotive, and communications markets.

The SN74BCT240DW belongs to TI's legacy BCT logic family, engineered specifically for high-reliability 5-V bus driving, memory addressing, and system-level signal conditioning in harsh industrial environments.

FAQ

What is the recommended pull-up resistor value for OE pins on the SN74BCT240DW?

The SN74BCT240DW OE pins should be tied to VCC through a pull-up resistor to ensure high-impedance state during power-up. Minimum resistance is determined by the driver's current-sinking capability: for 0.8 V VIH threshold and 20 µA IIH, a 10-kΩ resistor is typical. TI recommends values between 4.7 kΩ and 10 kΩ for robust noise immunity and fast disable timing. Always verify against actual board VCC ramp rate and noise margin requirements in your SN74BCT240DW implementation.

Does the SN74BCT240DW support mixed-voltage interfacing, such as 3.3 V inputs driving a 5 V supply?

Yes, the SN74BCT240DW accepts input voltages from –0.5 V to 7 V, making it tolerant of 3.3 V logic driving its inputs while operating at 5 V VCC. Its VIH = 2.0 V and VIL = 0.8 V thresholds align with both 3.3 V and 5 V logic families. However, outputs remain 5 V referenced, so downstream devices must tolerate 5 V swings. This behavior is explicitly confirmed in the absolute maximum ratings and recommended operating conditions tables for SN74BCT240DW.

How does the BiCMOS architecture of the SN74BCT240DW improve performance over standard TTL buffers?

The SN74BCT240DW's BiCMOS architecture integrates bipolar input stages for precise TTL threshold matching and CMOS output transistors for high current drive (±64 mA) and low quiescent current (ICCZ = 6–9 mA). This reduces power dissipation by >50% versus equivalent 74LS240 parts while maintaining identical timing and noise immunity. The result is cooler operation, tighter timing margins, and higher channel density-key advantages documented in the SCBS004F datasheet for SN74BCT240DW.

Can the SN74BCT240DW be used in place of the SN74LS240 in an existing design?

Yes, the SN74BCT240DW is pin-compatible and functionally equivalent to the SN74LS240, with identical pinout, logic behavior, and 20-pin SOIC (DW) packaging. Key improvements include faster propagation delay (4 ns vs. 15 ns), higher output drive (64 mA vs. 24 mA), and lower ICCZ (9 mA vs. 45 mA). No PCB changes are required, but verify that the improved speed does not introduce timing violations in marginal legacy layouts. All functional validation applies directly to SN74BCT240DW.

What thermal derating guidance applies to the SN74BCT240DW at elevated ambient temperatures?

The SN74BCT240DW has a θJA of 58°C/W in the SOIC-20 (DW) package. At 70°C ambient and 64 mA per output (worst-case IOL), power dissipation reaches ~350 mW, raising junction temperature to ~111°C-within the 150°C storage limit but near the 125°C max operating range for military variants. For continuous industrial use above 60°C ambient, reduce output loading or add local copper pour. Thermal data is confirmed in the "absolute maximum ratings" table of the SN74BCT240DW datasheet.