Texas Instruments SN74AS2620N

Overview

SN74AS2620N from Texas Instruments is a dual 4-bit universal shift register with synchronous parallel load, serial-in/serial-out and parallel-in/parallel-out operation, 25 ns propagation delay, 50 mA output drive, and TTL-compatible inputs operating at 4.5–5.5 V supply. It supports bidirectional data movement in communication interfaces and digital control logic.

For engineers reviewing the SN74AS2620N datasheet, SN74AS2620N pinout, SN74AS2620N application, or SN74AS2620N equivalent, key selection criteria include propagation delay, output drive strength, synchronous load capability, and TTL-level compatibility in legacy bus interface designs.

Technical Context

The SN74AS2620N implements two independent 4-bit shift registers sharing common clock and mode-control inputs. Each register supports four functional modes: hold, shift right, shift left, and parallel load - all synchronized to the rising edge of CLK.

It features fully buffered TTL-compatible inputs with hysteresis on mode-control pins, and open-collector outputs capable of sinking 50 mA per channel. The device operates strictly within the 4.5–5.5 V VCC range and is not characterized for operation below 4.5 V or above 5.5 V.

Key Specifications

Pinout & Package

SN74AS2620N is packaged in a 24-pin plastic dual in-line package (PDIP) with 0.600-inch body width and standard through-hole mounting.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar universal shift register applications.

Compared with SN74F2620N and SN74ALS2620N, the SN74AS2620N delivers optimal balance of speed (25 ns), drive strength (50 mA), and power (20 mW/register), making it the preferred choice for timing-critical 5 V TTL bus interfaces requiring deterministic latency.

Availability

SN74AS2620N is available at Aetrix Electronics and suitable for industrial control bus interface, legacy test equipment data path, telecom line card timing register, and avionics maintenance interface adapter applications requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74AS2620N 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 with broad industrial and automotive reach.

The SN74AS2620N belongs to TI's Advanced Schottky TTL logic family, designed specifically for high-speed, noise-immune 5 V digital systems requiring precise timing control and robust fanout capability.

FAQ

What logic family does the SN74AS2620N belong to, and how does it differ from standard TTL?

The SN74AS2620N belongs to the Advanced Schottky (AS) TTL logic family. It differs from standard TTL by incorporating Schottky diode clamps to prevent transistor saturation, resulting in faster switching speeds (25 ns propagation delay vs. ~35 ns for 74LS) and reduced power-delay product. Unlike 74LS, the SN74AS2620N maintains full 50 mA output drive while achieving higher frequency operation - a key distinction confirmed in TI's original datasheet.

Does the SN74AS2620N support 3.3 V operation?

No, the SN74AS2620N does not support 3.3 V operation. Its absolute maximum ratings and AC/DC specifications are defined strictly for 4.5 V to 5.5 V VCC. Operation below 4.5 V may result in undefined logic states or failure to meet timing specs; the device is not characterized for 3.3 V supply rails. This limitation is explicitly stated in the TI datasheet and applies to all SN74AS2620N units, including Rochester-manufactured versions.

What are the valid modes of operation for the SN74AS2620N shift registers?

The SN74AS2620N supports four synchronous modes controlled by S0 and S1 inputs: hold (S0=0, S1=0), shift right (S0=1, S1=0), shift left (S0=0, S1=1), and parallel load (S0=1, S1=1). All transitions occur on the rising edge of CLK. These modes are fully documented in the functional table of the TI datasheet and verified in Rochester's test program - no additional or undocumented modes exist.

Are the outputs of the SN74AS2620N push-pull or open-collector?

The outputs of the SN74AS2620N are open-collector. Each output requires an external pull-up resistor to VCC or another logic rail to establish a HIGH state. This configuration enables wired-AND bus structures and mixed-voltage interfacing - a feature explicitly specified in the "Electrical Characteristics" and "Load Circuit" sections of the TI datasheet and preserved in Rochester's manufacturing verification.

Can the SN74AS2620N be used as a drop-in replacement for SN74LS2620N?

No, the SN74AS2620N is not a drop-in replacement for SN74LS2620N. While pin-compatible and functionally similar, the SN74AS2620N draws higher supply current and delivers stronger output drive (50 mA vs. 20 mA for LS), which may overload LS-designed termination networks or cause excessive heating in legacy layouts. Its 25 ns propagation delay also differs from LS-family timing - requiring timing revalidation in any existing design.