Texas Instruments SN74BCT2245NS

Overview

SN74BCT2245NS from Texas Instruments is an octal transceiver and line/MOS driver with 3-state outputs, designed for asynchronous bidirectional data bus communication between A and B buses. It operates at 4.5 V to 5.5 V, features BiCMOS design, integrates 33-Ω series resistors on B-port outputs, and supports ±12 mA B-port drive capability - used in legacy industrial backplane interfaces and TTL-to-MOS level translation.

For engineers reviewing the SN74BCT2245NS datasheet, SN74BCT2245NS pinout, SN74BCT2245NS application, or SN74BCT2245NS equivalent, key selection criteria include direction-control (DIR) and output-enable (OE) logic behavior, 3-state isolation timing (tPZH/tPLZ), B-port integrated termination, and compatibility with 5-V TTL/CMOS systems requiring bus contention avoidance.

Technical Context

The SN74BCT2245NS implements dual-directional 8-bit data flow controlled by DIR (L = B→A, H = A→B) and OE (L = active, H = high-Z). Its BiCMOS architecture reduces ICCZ quiescent current while enabling robust 12-mA sink/source on B ports and 24-mA sink on A ports.

B-port outputs integrate nominal 33-Ω series resistors to suppress overshoot/undershoot without external components; A-port outputs lack internal termination and require external design attention for signal integrity. Propagation delays range from 1.7 ns (tPLH B→A) to 7.8 ns (tPHL A→B) under CL = 50 pF conditions.

Key Specifications

Pinout & Package

SN74BCT2245NS uses a 20-pin SO (Small Outline) package with 0.300-inch body width and gull-wing leads, compliant with JEDEC MS-012 (NS drawing). Pin 1 is located at top-left corner with notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N and SN74LVC245APW, the SN74BCT2245NS uniquely delivers 5-V operation with integrated B-port termination and BiCMOS low-ICCZ performance - making it the only option among the three that simultaneously satisfies legacy bus voltage, signal integrity, and power constraints.

Availability

SN74BCT2245NS is available at Aetrix Electronics and suitable for industrial backplane interfaces, TTL-to-MOS level translation, and legacy system bus isolation requiring stable component supply across extended production lifecycles.

Supply support for SN74BCT2245NS 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74BCT2245NS belongs to TI's legacy BCT logic family, engineered specifically for high-drive, low-noise bidirectional bus interfacing in 5-V systems where signal integrity and bus contention avoidance are critical.

FAQ

What is the recommended power-up sequence for SN74BCT2245NS to ensure high-impedance state at startup?

To guarantee high-impedance outputs during power-up, OE must be held HIGH before VCC reaches valid operating range. TI recommends tying OE to VCC through a pullup resistor - minimum value determined by the current-sinking capability of the driving control signal. This prevents bus contention during system initialization. The SN74BCT2245NS does not include internal power-on reset, so external OE control is essential for deterministic startup behavior in the SN74BCT2245NS.

Does SN74BCT2245NS support hot-swapping, and what design considerations apply?

The SN74BCT2245NS supports hot-swapping only when OE is actively controlled to HIGH before insertion and held until after VCC stabilizes. Its absolute maximum ratings allow VI and VO up to 7 V during transitional states, but sustained operation outside 4.5–5.5 V violates recommended conditions. The SN74BCT2245NS requires external sequencing logic or RC delay on OE to enforce safe isolation windows - it does not autonomously enter high-Z on undervoltage.

How do the integrated 33-Ω resistors on SN74BCT2245NS B-port outputs affect signal integrity?

The nominal 33-Ω series resistors on each SN74BCT2245NS B-port output dampen edge-induced reflections on PCB traces with characteristic impedance near 50 Ω, reducing overshoot and undershoot by ~40% versus unterminated outputs. These resistors are internal to the die and cannot be disabled; they apply only to B1–B8. The SN74BCT2245NS A-port outputs lack this feature and require external termination if used on transmission lines.

Can SN74BCT2245NS operate reliably at 4.5 V supply, and how does performance change versus 5 V?

Yes, SN74BCT2245NS is fully specified from 4.5 V to 5.5 V. At 4.5 V, VOH drops to 2.4 V (min) for B-port at −12 mA, and VOL rises to 0.8 V (max) under same load - still within TTL VIH/VIL margins. Propagation delays increase by ≤15% versus 5 V operation, and ICCZ remains within 8–14 mA. All timing and DC parameters in the SN74BCT2245NS datasheet include 4.5-V test conditions.

What is the function of the DIR pin in SN74BCT2245NS, and how does it interact with OE?

DIR controls data direction: LOW enables B→A transfer; HIGH enables A→B transfer. OE independently enables/disables all outputs - when HIGH, both A and B ports enter high-impedance regardless of DIR state. DIR has no effect unless OE is LOW. This dual-control architecture allows independent management of bus ownership (DIR) and electrical isolation (OE) in the SN74BCT2245NS, supporting complex arbitration protocols.