Texas Instruments SN74AS756DWE4

Overview

SN74AS756DWE4 from Texas Instruments is a dual 4-bit noninverting open-collector buffer/line driver IC designed for memory address bus driving and clock distribution in TTL-compatible systems. It features two independent 4-bit channels (1A–1Y and 2A–2Y), symmetrical active-low output-enable inputs (1OE, 2OE), and delivers 64 mA sink current per output at VCC = 4.5 V. It operates from 0°C to 70°C and eliminates 3-state overlap timing constraints in high-density bus architectures.

For engineers reviewing the SN74AS756DWE4 datasheet, SN74AS756DWE4 pinout, SN74AS756DWE4 application, or SN74AS756DWE4 equivalent, key selection criteria include open-collector drive capability, propagation delay (tPLH/tPHL ≤ 19.5 ns), fan-out compatibility with AS-family logic, and SOIC-20 package suitability for space-constrained board layouts.

Technical Context

This device implements two independent 4-bit noninverting buffer sections with open-collector outputs, enabling wired-OR bus configurations and direct interface to memory address registers or clock distribution networks. Each channel has dedicated active-low output-enable control (1OE, 2OE) and pnp input structure to reduce DC loading on upstream drivers.

It belongs to the 74AS logic family and is electrically compatible with 74AS240A/241 but optimized for bus driving via open-collector outputs. Its design eliminates need for external 3-state overlap protection circuitry by ensuring clean enable/disable transitions with tPLZ/tPZH < 8.5 ns under CL = 50 pF conditions.

Key Specifications

Pinout & Package

SN74AS756DWE4 is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, with 1.27 mm pitch and 2.65 mm maximum height. Pin 1 is located at the top-left corner with notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal open-collector buffer applications.

Compared with SN74AS756DWE4, SN74AS240N offers 3-state control instead of open-collector outputs - useful for bidirectional buses but requiring additional timing coordination. SN74ALS244N trades 2.7× lower sink current and slower edges for broader legacy compatibility and lower unit cost in non-critical timing paths.

Availability

SN74AS756DWE4 is available at Aetrix Electronics and suitable for industrial control systems, legacy computer refurbishment, and embedded bus interface designs requiring stable component supply and long-term obsolescence management.

Supply support for SN74AS756DWE4 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 SN74AS756DWE4 belongs to TI's 74AS advanced Schottky logic product line, engineered for high-speed memory addressing, clock distribution, and bus driving in systems where timing precision and drive strength outweigh power efficiency concerns.

FAQ

What is the maximum sink current per output of the SN74AS756DWE4?

The SN74AS756DWE4 guarantees a minimum sink current of 48 mA and a typical value of 64 mA per open-collector output at VCC = 4.5 V and TA = 25°C. This specification ensures robust driving of multiple TTL loads or long PCB traces without signal degradation. The absolute maximum rating for output current is not specified, but operation beyond 64 mA may affect VOL compliance and thermal performance. Always verify load conditions using the recommended operating conditions table in the SN74AS756DWE4 datasheet.

Is SN74AS756DWE4 pin-compatible with SN74AS240 or SN74AS241?

Yes, SN74AS756DWE4 is an open-collector version of SN74AS240A and SN74AS241, sharing identical pinout and package dimensions in SOIC-20 (DW) form. All three devices use the same 20-pin layout with matching 1A–1Y and 2A–2Y signal assignments and OE control placement. However, SN74AS240A/241 feature 3-state outputs rather than open-collector, so external pull-up resistors are required only when using SN74AS756DWE4 in wired-OR configurations - not for basic unidirectional buffering.

Can SN74AS756DWE4 operate at 3.3 V supply voltage?

No, SN74AS756DWE4 is not rated for 3.3 V operation. Its recommended supply voltage range is strictly 4.5 V to 5.5 V, and absolute maximum VCC is 7 V. Applying 3.3 V will result in undefined logic thresholds, excessive propagation delay, and potential failure to meet VOL/VOL specifications. For 3.3 V systems, consider TI's 74LVC244A or 74LVCH244A as functional alternatives with compatible pinouts and open-drain variants.

What is the purpose of the pnp input structure in SN74AS756DWE4?

The pnp input structure in SN74AS756DWE4 reduces DC input loading by limiting IIL to −0.5 mA maximum and IIH to 20 µA maximum at VCC = 5.5 V. This design lowers fan-out burden on upstream drivers, improves noise margin, and enables higher input fan-in without signal degradation. It also contributes to faster switching by minimizing input capacitance and charge storage effects - a key advantage over standard TTL inputs in high-speed bus applications involving SN74AS756DWE4.

Does SN74AS756DWE4 support hot-swap or live-insertion?

No, SN74AS756DWE4 does not support hot-swap or live-insertion. It lacks built-in power-up/down sequencing protection, bus-hold circuitry, or Ioff partial-power-down capability. Applying VCC while inputs are driven or removing power with active outputs can cause latch-up or excessive current flow. For hot-swap applications, use TI's SN74CBT3244 or SN74AVC24T244, which provide powered-off protection and controlled turn-on characteristics not present in the SN74AS756DWE4.