Texas Instruments SN74ALS29821DWR

Overview

SN74ALS29821 from Texas Instruments is a 10-bit edge-triggered D-type flip-flop with 3-state outputs, designed for driving highly capacitive or low-impedance bus loads. It operates from 0°C to 70°C, supports 5-V supply (4.75–5.25 V), delivers ±24 mA/48 mA output drive, features power-up high-impedance state, and is packaged in 24-pin SOIC (DW). It is used in wide address/data buffers, I/O ports, and parity-enabled bidirectional bus drivers.

For engineers reviewing the SN74ALS29821 datasheet, SN74ALS29821 pinout, SN74ALS29821 application, or SN74ALS29821 equivalent, key selection criteria include 10-bit synchronous latch behavior, 3-state OE control timing (tPZH/tPLZ ≤14 ns @50 pF), undershoot-protection circuitry, buffered inputs for reduced DC loading, and compatibility with ALS logic family voltage thresholds.

Technical Context

This device implements ten independent D-type latches triggered on the rising edge of CLK, each with dedicated D input and Q output. The OE input controls all ten outputs simultaneously into high-impedance or active logic states without affecting internal latch operation - enabling data retention during bus isolation.

It uses bipolar ALS (Advanced Low-Power Schottky) technology, delivering higher speed than standard LS while maintaining lower power. Input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive (IOH = −24 mA, IOL = 48 mA) are specified across full temperature range, with propagation delays tPLH/tPHL ≤10 ns (CL = 50 pF) and enable/disable times tPZH/tPLZ ≤14 ns under same conditions.

Key Specifications

Pinout & Package

SN74ALS29821 is housed in a 24-pin plastic small-outline integrated circuit (SOIC) package (DW), 300-mil width, with standard pin pitch of 1.27 mm. The package is RoHS-compliant, moisture sensitivity level 1, and rated for surface-mount reflow up to 260°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 10-bit 3-state D-type latch applications.

Compared with SN74ALS29821N and AM29821, the SN74ALS29821 offers identical logic behavior and timing but provides surface-mount compatibility via DW package - critical for space-constrained industrial controllers and modernized avionics modules where DIP sockets are obsolete.

Availability

SN74ALS29821 is available at Aetrix Electronics and suitable for industrial bus interface, legacy computing memory buffer, test equipment data capture, and avionics I/O expansion requiring stable component supply across extended product lifecycles.

Supply support for SN74ALS29821 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 ICs for industrial, automotive, and communications markets.

The SN74ALS29821 belongs to TI's legacy ALS logic family, engineered for high-speed, low-power bus interfacing in 1980s–1990s computing and control systems - emphasizing robustness, timing predictability, and backward compatibility.

FAQ

What is the operating voltage range for SN74ALS29821?

The SN74ALS29821 operates over a supply voltage range of 4.75 V to 5.25 V, as specified in its recommended operating conditions. This tight tolerance ensures compatibility with regulated 5-V ALS/TTL systems and avoids marginal behavior seen at wider VCC ranges. Operation outside this window may cause timing violations or output instability in the SN74ALS29821.

Does SN74ALS29821 support hot insertion or live bus connection?

The SN74ALS29821 features undershoot-protection circuitry and a power-up high-impedance state, which collectively mitigate transient faults during live insertion. However, it lacks explicit hot-swap qualification per JEDEC standards. For controlled hot-plug applications, external series resistors and slew-rate limiting remain advisable when integrating the SN74ALS29821 into backplane systems.

How does the OE pin behave relative to internal latch operation in SN74ALS29821?

In the SN74ALS29821, the OE pin affects only output driver state - not internal flip-flop operation. When OE is deasserted (high), all Q outputs enter high-impedance mode while internal latched data remains intact and continues to update on subsequent CLK edges. This allows seamless data staging and bus arbitration without disrupting register contents in the SN74ALS29821.

What is the maximum capacitive load the SN74ALS29821 can drive reliably?

The SN74ALS29821 is characterized for CL = 50 pF and CL = 300 pF in its switching characteristics table, with tPLH/tPHL ≤21 ns at 300 pF. Its 48 mA output sink capability supports heavier loads than standard LS devices. For reliable operation beyond 300 pF, external buffering or reduced clock edge rates are recommended - especially in long-trace industrial bus implementations using the SN74ALS29821.

Is SN74ALS29821 pin-compatible with SN74LS29821 or other 29821 variants?

No - SN74ALS29821 is not pin-compatible with SN74LS29821. While both share identical pin count and function mapping, ALS and LS families differ in input thresholds, output drive strength, and timing. Substituting LS for ALS risks setup/hold violations and insufficient drive. Always verify logic family compatibility before replacing any variant of the 29821 in an existing design containing SN74ALS29821.