Texas Instruments SN74ALS842DW

Overview

SN74ALS842DW from Texas Instruments is a 10-bit inverting D-type bus-interface latch with 3-state outputs, designed for high-capacitance bus driving in industrial control and legacy computing systems. It operates at 4.5–5.5 V, delivers ±24 mA output drive, supports 0°C to 70°C ambient, and features buffered OE/LE inputs with 10 ns max enable/disable times.

For engineers reviewing the SN74ALS842DW datasheet, SN74ALS842DW pinout, SN74ALS842DW application, or SN74ALS842DW equivalent, this page provides verified functional identity, SOIC-24 package mapping, bus-latch timing behavior, and direct alternatives for address/data path expansion in TTL-compatible systems.

Technical Context

The SN74ALS842DW implements ten transparent D-type latches with inverted data paths: each D input drives a complementary Q output. Latch enable (LE) controls data capture synchronously, while output enable (OE) independently places all ten Q outputs into high-impedance without affecting internal storage.

Its bus-structured pinout (D1–D10 on pins 2–11, Q1–Q10 on pins 13–22) minimizes trace skew in parallel bus layouts. The device uses ALS (Advanced Low-Power Schottky) logic, delivering TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) with reduced ICC versus standard LS families.

Key Specifications

Pinout & Package

SN74ALS842DW is housed in a 24-pin SOIC (DW) package with 300-mil width, JEDEC MS-013 compliant, moisture sensitivity level 1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 10-bit bus-interface latch applications.

Compared with SN74ALS842DW, SN74ALS841DW removes inversion but retains identical timing and packaging - ideal for non-inverted bus architectures; SN74AS841ADW trades higher power for 2× speed and doubled sink current, suited for demanding real-time control loops.

Availability

SN74ALS842DW is available at Aetrix Electronics and suitable for industrial backplane expansion, legacy microprocessor address latching, and parallel printer interface buffering requiring stable component supply across extended production lifecycles.

Supply support for SN74ALS842DW 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 SN74ALS842DW belongs to TI's legacy 74ALS logic family, engineered for robust bus interfacing in commercial-temperature embedded systems where TTL compatibility, moderate speed, and low static power are prioritized over ultra-high frequency operation.

FAQ

What is the key functional difference between SN74ALS842DW and SN74ALS841DW?

The SN74ALS842DW features an inverting D-to-Q data path: a high logic level at any D input produces a low level at the corresponding Q output. In contrast, SN74ALS841DW is non-inverting. Both share identical pinout, timing specifications, supply requirements, and 3-state control behavior. This inversion makes SN74ALS842DW suitable for direct interface with active-low bus protocols without external inverters, while SN74ALS841DW is preferred in positive-true signal architectures.

Does SN74ALS842DW support mixed-voltage operation (e.g., 3.3 V inputs with 5 V supply)?

No. SN74ALS842DW is a TTL-family device designed exclusively for 5 V operation. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and absolute maximum ratings (VI ≤ 7 V) assume 5 V logic levels. Applying 3.3 V signals may result in marginal or unreliable switching, and the device lacks 3.3 V tolerant input structures. For mixed-voltage systems, level-shifting circuitry or a 3.3 V–compatible latch such as SN74LVC8T245 must be used alongside SN74ALS842DW.

What is the maximum capacitive load SN74ALS842DW can drive reliably?

SN74ALS842DW is characterized for CL = 50 pF in its switching specifications, with propagation delays (e.g., tPLH ≤ 18 ns) guaranteed under that condition. While its ±24 mA output drive suggests capability beyond 50 pF, TI does not specify performance at higher loads. For reliable operation above 50 pF, derating of timing margins and verification under actual board conditions - including trace capacitance and stub effects - is required. Use of series termination or distributed buffering is recommended for >100 pF bus loads.

Can SN74ALS842DW outputs be safely tied together in a wired-OR configuration?

No. SN74ALS842DW outputs are push-pull (totem-pole), not open-collector. Connecting multiple outputs together risks destructive current flow if one driver sources while another sinks. Wired-OR requires open-drain/open-collector topology. To implement bus sharing, use the 3-state capability: assert OE low on only one SN74ALS842DW at a time while others hold OE high (high-Z), ensuring true bus arbitration without hardware conflict.

Is SN74ALS842DW RoHS compliant and suitable for modern reflow assembly?

Yes. SN74ALS842DW carries RoHS-compliant marking (NIPDAU lead finish) and is rated MSL Level-1 (unlimited floor life, peak reflow ≤ 260°C). It is qualified for standard Pb-free reflow profiles. However, as a legacy SOIC-24 component manufactured under older process nodes, long-term availability is managed via Aetrix's lifecycle coordination program - customers should engage early for volume forecasts and obsolescence mitigation planning for SN74ALS842DW.