Texas Instruments SN74AS821ADW

Overview

SN74AS821ADW from Texas Instruments is a dual 10-bit D-type flip-flop with common clock and clear, packaged in SOIC-24. It features 10-bit parallel data storage, TTL-compatible inputs, and guaranteed 12 ns propagation delay at VCC = 5 V. It is used in high-speed data latching and bus interface applications in industrial control systems.

For engineers reviewing the SN74AS821ADW datasheet, SN74AS821ADW pinout, SN74AS821ADW application, or SN74AS821ADW equivalent, key selection considerations include propagation delay, output drive strength (24 mA sink), input voltage thresholds, and SOIC-24 thermal performance under sustained 5 V operation.

Technical Context

This device integrates two independent 10-bit edge-triggered D-type flip-flops sharing one clock and one asynchronous clear signal. Each 10-bit section supports true and complementary outputs (Q and Q̅) per bit, enabling simultaneous latching of parallel data streams without internal fanout limitations.

Designed for TTL-system interfacing, the SN74AS821ADW operates strictly at VCC = 5 V, with input thresholds aligned to standard TTL logic levels (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output VOH ≥ 2.7 V at 24 mA sink load - ensuring robust noise margin in mixed-logic environments.

Key Specifications

Pinout & Package

Packaged in 24-pin SOIC (SO-24) with 300-mil body width and 0.050-inch lead pitch. Thermal resistance θJA = 90°C/W (JEDEC std PCB).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 10-bit D-type latch applications.

Compared with SN74F821N and SN74ALS821ADW, the SN74AS821ADW delivers the fastest propagation (12 ns), highest output drive (24 mA), and optimal balance of speed, density, and compatibility for modern industrial control and test equipment upgrades.

Availability

SN74AS821ADW is available at Aetrix Electronics and suitable for industrial bus interface, test equipment data capture, and real-time control logic requiring stable component supply and long-term manufacturing continuity.

Supply support for SN74AS821ADW 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 for industrial, automotive, and communications markets.

The SN74AS821ADW belongs to TI's Advanced Schottky TTL logic family, engineered for high-speed, low-noise data latching in legacy-compatible and upgrade-focused industrial control systems.

FAQ

What logic family does the SN74AS821ADW belong to?

The SN74AS821ADW belongs to the Advanced Schottky TTL (AS) logic family. This family delivers higher speed and lower power than standard TTL or Schottky TTL, with guaranteed 12 ns propagation delay and 24 mA output sink capability. The SN74AS821ADW maintains strict TTL input thresholds and 5 V-only operation, making it compatible with legacy TTL systems while improving timing margins.

Does the SN74AS821ADW support independent clocking for each 10-bit section?

No, the SN74AS821ADW uses a single shared clock (CLK) and asynchronous clear (CLR) for both 10-bit sections. Pins 21 (CLK) and 22 (CLR) serve both groups simultaneously - there is no provision for independent timing control. This architecture simplifies synchronization across dual data paths but requires coordinated clocking in applications like byte-wide bus latching.

What is the maximum operating frequency supported by the SN74AS821ADW?

The SN74AS821ADW supports reliable operation up to 60 MHz based on its 12 ns maximum propagation delay and specified setup/hold timing. At 5 V supply and 50 pF load, the device meets timing requirements for clock periods ≥16.7 ns. System-level frequency limits depend on board layout, signal integrity, and external driver strength - the SN74AS821ADW itself is rated for this performance under JEDEC-standard conditions.

Can the SN74AS821ADW drive standard TTL loads directly?

Yes, the SN74AS821ADW can drive up to 10 standard TTL loads per output due to its 24 mA sink capability and 1 mA source strength. Its VIH/VIL thresholds match standard TTL, and VOH remains ≥2.7 V at 24 mA sink - satisfying the 2.4 V minimum required for TTL high-level recognition. This eliminates the need for external buffers in most bus-interface and status-indication applications using the SN74AS821ADW.

Is the SN74AS821ADW pin-compatible with the older SN74S821?

Yes, the SN74AS821ADW is pin-compatible and functionally equivalent to the SN74S821, including identical SOIC-24 pinout and dual 10-bit D-type latch functionality with shared CLK and CLR. It improves upon the S-series part with faster propagation (12 ns vs. 20 ns), higher output drive (24 mA vs. 20 mA), and lower power consumption - making the SN74AS821ADW a direct drop-in replacement in legacy designs.