Texas Instruments SN74BCT240DBR

Overview

SN74BCT240DBR from Texas Instruments is an octal noninverting buffer/driver with 3-state outputs, designed for memory address driving and bus interfacing in 5-V TTL-compatible systems. It operates from 4.5 V to 5.5 V, delivers ±64 mA output drive, supports 3.5 ns typical propagation delay (tPHL), and features BiCMOS architecture for low ICCZ (6–9 mA) and high noise immunity.

For engineers reviewing the SN74BCT240DBR datasheet, SN74BCT240DBR pinout, SN74BCT240DBR application, or SN74BCT240DBR equivalent, key selection criteria include 3-state bus contention control, TTL-level input compatibility, 20-pin SSOP package constraints, and verified 5-V system timing margins in memory and address buffering roles.

Technical Context

This device integrates eight independent noninverting buffers, each with active-low 3-state enable (1OE, 2OE), enabling bidirectional bus control without external logic. Its BiCMOS design combines bipolar input stages for TTL threshold compatibility and CMOS output stages for reduced power consumption during high-impedance states.

Each buffer pair shares a dedicated OE input (1OE controls Y1–Y4; 2OE controls Y1'–Y4'), supporting split-bus enable schemes. The 3-state outputs meet JESD22-A114A ESD rating (>2000 V HBM) and tolerate –0.5 V to 5.5 V off-state voltage, ensuring robustness in hot-swap and mixed-voltage environments.

Key Specifications

Pinout & Package

SN74BCT240DBR uses a 20-pin SSOP (Shrink Small Outline Package) with 0.65 mm lead pitch, 7.2 mm × 5.3 mm body size, and exposed pad-less construction suitable for automated surface-mount assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74BCT240DBR, SN74LS240N trades speed and efficiency for broad TTL ecosystem compatibility, while SN74ACT240DBR prioritizes ultra-low ICCZ over drive strength-making SN74BCT240DBR optimal for high-fan-out, 5-V bus buffering where both performance and robustness are required.

Availability

SN74BCT240DBR is available at Aetrix Electronics and suitable for memory subsystem design, industrial backplane interfacing, and legacy system upgrades requiring stable component supply and long-term obsolescence management.

Supply support for SN74BCT240DBR 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 U.S.-based semiconductor company specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74BCT240DBR belongs to TI's 'BCT logic family, engineered specifically for high-speed, high-drive 5-V bus buffering in memory and address-path applications where TTL compatibility and 3-state control are essential.

FAQ

What is the recommended power-up sequence for SN74BCT240DBR to avoid bus contention?

TI specifies that OE inputs must be held high (via pull-up resistors to VCC) during power-up to guarantee all outputs start in high-impedance state. For SN74BCT240DBR, use ≥10 kΩ pull-ups on pins 1 (1OE) and 19 (2OE); this prevents unintended low-impedance outputs before system initialization completes. This requirement applies regardless of VCC ramp rate or sequencing with other logic devices.

Can SN74BCT240DBR drive a 100-pF bus load while maintaining timing specifications?

No-SN74BCT240DBR's switching characteristics (tPLH/tPHL) are characterized at CL = 50 pF. At 100 pF, propagation delay increases beyond the 5.6 ns max (tPLH) and 4 ns max (tPHL) specified in the datasheet. For 100-pF loads, derate timing by ~30% or add series termination; alternatively, consider dual-driver configurations or lower-capacitance layout practices to stay within SN74BCT240DBR's validated operating window.

Does SN74BCT240DBR support hot-swap insertion into a live 5-V bus?

SN74BCT240DBR tolerates –0.5 V to 5.5 V on outputs in disabled state and includes 2000 V HBM ESD protection, making it more robust than standard TTL buffers-but it lacks explicit hot-swap circuitry (e.g., slew-rate limiting or current limiting). TI does not qualify SN74BCT240DBR for live insertion; use external current-limiting resistors or dedicated hot-swap controllers if bus activity cannot be halted during module replacement.

What is the maximum continuous output current per pin for SN74BCT240DBR at 25°C ambient?

The absolute maximum rating for SN74BCT240DBR is 128 mA per output in the low state (IOL) and –15 mA in the high state (IOH), but these are stress limits-not operational ratings. For reliable continuous operation at 25°C, TI recommends limiting IOL to 64 mA and IOH to –12 mA, as validated in the recommended operating conditions table. Exceeding these degrades timing and increases junction temperature beyond safe limits.

How does the BiCMOS architecture of SN74BCT240DBR reduce power consumption compared to bipolar-only equivalents?

SN74BCT240DBR's BiCMOS design replaces the bipolar output stage with a CMOS totem-pole structure, cutting ICCZ (quiescent supply current during 3-state) from ~30 mA in LS variants to just 6–9 mA. This occurs because CMOS outputs draw near-zero static current when idle, whereas bipolar drivers require base current even in high-impedance mode-directly improving power efficiency in bus-hold or standby states without sacrificing drive strength.