Texas Instruments SN74AS245DB

Overview

SN74AS245DB 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 requiring robust signal integrity and bus isolation.

For engineers reviewing the SN74AS245DB datasheet, SN74AS245DB pinout, SN74AS245DB application, or SN74AS245DB equivalent, key selection considerations include its 20-pin SSOP (DB) package, direction-control (DIR) and output-enable (OE) logic interface, 3-state bus driving capability, and compatibility with legacy AS-family timing and drive requirements.

Technical Context

The SN74AS245DB implements dual 8-bit bidirectional data paths controlled by DIR (direction) and OE (output enable) inputs. Its TTL-compatible inputs use pnp structures to minimize input current draw, while its totem-pole outputs deliver high sink current (64 mA) with VOL ≤ 0.55 V at IOL = 64 mA. The device supports true 3-state isolation when OE is high, decoupling A and B buses completely.

Switching performance is characterized under CL = 50 pF, R1 = R2 = 500 Ω, with tPHL/tPLH ≤ 7 ns and enable/disable times (tPZH/tPLZ/tPHZ/tPLZ) ≤ 9.5 ns. It meets SN74AS family specifications across 0°C to 70°C ambient, with no -1 version - distinguishing it from ALS245A-1 variants offering higher IOL ratings.

Key Specifications

Pinout & Package

SN74AS245DB uses a 20-pin Small Outline Package (SSOP), 7.5 mm × 5.6 mm body, 0.65 mm lead pitch, 2.0 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1 (unlimited reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AS245N and SN74ALS245ADBR, the SN74AS245DB offers the optimal balance of high-speed 7.5 ns propagation, 64 mA drive, and compact SSOP packaging - making it preferred for space-constrained, high-density industrial PCBs requiring full AS-family performance.

Availability

SN74AS245DB is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, test equipment data acquisition, and automated test fixture control requiring stable component supply and long-term obsolescence management.

Supply support for SN74AS245DB 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 over 90 years of innovation in industrial, automotive, and communications markets.

The SN74AS245DB belongs to TI's 74AS logic family - engineered for high-speed, high-drive TTL-compatible applications where propagation delay, output current, and noise immunity are critical in industrial control and instrumentation systems.

FAQ

What is the maximum operating frequency supported by the SN74AS245DB?

The SN74AS245DB 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 with data valid windows down to ~130 MHz in synchronous bus designs. Actual usable frequency depends on system-level timing margins, including setup/hold and board trace delays - always verify with worst-case timing analysis using the device's published switching characteristics.

Does the SN74AS245DB support hot-swapping or live insertion?

The SN74AS245DB is not explicitly rated for hot-swap operation. While its 3-state outputs provide bus isolation when OE is high, it lacks built-in bus-hold, power-up/down protection, or I²C-style slew-rate control. For hot-swap applications, external current-limiting resistors, TVS diodes, and controlled power sequencing are required - consult TI's Application Report SCBA004 for safe handling of floating inputs during insertion.

Can the SN74AS245DB be used with 3.3 V logic systems?

No - the SN74AS245DB requires a 4.5–5.5 V VCC supply and has TTL input thresholds (VIH = 2.0 V, VIL = 0.8 V). Driving its inputs from 3.3 V logic may result in marginal or non-functional VIH margin. To interface with 3.3 V systems, use level translators (e.g., TXB0108) or select a 3.3 V–tolerant transceiver like SN74LVC245A, not the SN74AS245DB.

What is the thermal resistance (θJA) of the SN74AS245DB package?

The SN74AS245DB in the SSOP (DB) package has a specified junction-to-ambient thermal resistance (θJA) of 70 °C/W, measured per JESD 51-7. This value assumes standard JEDEC 2-layer board conditions. Actual thermal performance depends on PCB copper area, airflow, and nearby heat sources - derate power dissipation accordingly to maintain TJ < 125°C under worst-case ambient conditions.

Is there a pin-compatible drop-in replacement for the SN74AS245DB with lower power consumption?

No pin-compatible drop-in replacement exists that maintains identical timing and drive while reducing power. The SN74ALS245ADBR shares the same DB package and pinout but trades 64 mA IOL and 7.5 ns speed for lower ICC (max 58 mA vs. 143 mA) and slower 10 ns propagation - it is functionally compatible but not a performance-equivalent substitute. Always validate timing and drive compliance in your specific design before substitution.