Texas Instruments SN74AS245NS

Overview

SN74AS245NS from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It operates from 4.5 V to 5.5 V, delivers max propagation delay of 7.5 ns at 5 V, supports ±64 mA low-level output drive, and features pnp input structure to reduce DC loading. It is used in industrial backplane interfaces and legacy system bus expansion.

For engineers reviewing the SN74AS245NS datasheet, SN74AS245NS pinout, SN74AS245NS application, or SN74AS245NS equivalent, key selection criteria include its 20-pin SOP (NS) package, direction-control (DIR) and output-enable (OE) logic interface, 3-state isolation capability, and compatibility with 5-V TTL signal levels in high-speed bus arbitration scenarios.

Technical Context

The SN74AS245NS implements dual 8-bit bidirectional data paths controlled by DIR and OE inputs: when OE is low, data flows from A to B if DIR = high, or from B to A if DIR = low; when OE is high, all outputs enter high-impedance state. Its AS-family silicon ensures faster switching than ALS variants, with guaranteed tPHL/tPLH ≤ 7 ns under CL = 50 pF.

It uses bipolar transistor technology with pnp input stages to minimize input current draw (IIL ≤ –0.75 mA), enabling direct connection to TTL outputs without pull-up resistors. The device requires no external timing components and supports hot-swap isolation via OE-controlled 3-state operation.

Key Specifications

Pinout & Package

SN74AS245NS is housed in a 20-pin small-outline package (SOP-NS), 7.5 mm × 5.0 mm body size, 0.65 mm lead pitch, 2.0 mm max height, with gull-wing leads and pin 1 index area marked.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AS245N and SN74ALS245ANSR, SN74AS245NS delivers optimal balance of speed (7.5 ns), drive strength (64 mA), and SMT manufacturability in a thermally efficient SOP-NS package - making it the preferred choice for new 5-V TTL bus designs requiring both performance and density.

Availability

SN74AS245NS is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus expansion, test equipment data capture, and automated manufacturing controllers requiring stable component supply and long-term obsolescence management.

Supply support for SN74AS245NS 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 devices, with decades of heritage in TTL and advanced logic families.

The SN74AS245NS belongs to TI's 74AS logic series - engineered for high-speed, high-drive 5-V TTL applications where propagation delay and output current are critical, such as industrial control backplanes and instrumentation interfaces.

FAQ

What is the maximum operating frequency supported by the SN74AS245NS?

The SN74AS245NS does not specify a maximum clock frequency, but its 7.5 ns maximum propagation delay (tPHL/tPLH) at 5 V and 50 pF load implies reliable operation up to approximately 133 MHz in synchronous bus applications. Actual usable frequency depends on system-level timing margins, trace capacitance, and termination - design validation with worst-case setup/hold analysis is recommended for each implementation of SN74AS245NS.

Can SN74AS245NS be used with 3.3-V logic systems?

No, SN74AS245NS is strictly a 5-V TTL device: its VCC range is 4.5 V to 5.5 V, VIH minimum is 2.0 V, and VOL maximum is 0.55 V at 64 mA - incompatible with 3.3-V logic thresholds. Using SN74AS245NS with 3.3-V controllers risks undriven inputs, marginal noise margins, and potential damage due to overvoltage on I/O pins. For mixed-voltage systems, use a dedicated level translator or 3.3-V–compatible transceiver instead of SN74AS245NS.

What is the thermal resistance (θJA) of the SN74AS245NS in its SOP-NS package?

The SN74AS245NS in the SOP-NS package has a specified junction-to-ambient thermal resistance (θJA) of 60°C/W, measured per JESD 51-7. This value assumes standard JEDEC high-K test board conditions. Actual thermal performance in end equipment depends on PCB copper area, airflow, and nearby heat sources - adequate copper pour under the exposed pad (if present) and thermal vias significantly improve heat dissipation for SN74AS245NS in sustained high-current operation.

How does the DIR pin function in SN74AS245NS, and what happens when OE is high?

In SN74AS245NS, the DIR pin controls data direction: DIR = high enables A→B transfer; DIR = low enables B→A transfer - but only when OE = low. When OE is high (disabled), all A and B I/O pins enter high-impedance (3-state) regardless of DIR state, electrically isolating both buses. This dual-control architecture allows independent bus arbitration and safe hot-plug operation - a core functional behavior confirmed in the SN74AS245NS function table and logic diagram.

Is SN74AS245NS RoHS compliant and lead-free?

Yes, SN74AS245NS is RoHS compliant and features lead-free (Pb-free) terminations with NiPdAu (NIPDAU) plating, as documented in TI's Package Option Addendum. It carries a Moisture Sensitivity Level (MSL) rating of Level-1-260°C-UNLIM, indicating unlimited floor life at ≤30°C/60% RH. Full compliance documentation, including material declarations and test reports, is available from TI's official product page for SN74AS245NS.