SN74ALS138AD Equivalent & Substitute Parts

Part Overview

The SN74ALS138AD is a Decoder/Demultiplexer logic integrated circuit manufactured by Texas Instruments, featuring a 1 x 3:8 configuration in a 16-SOIC surface mount package. This component is classified as Last Time Buy, indicating limited availability and the necessity to identify suitable alternatives for ongoing design requirements and production planning.

The SN74ALS138AD operates with a single supply voltage between 4.5V and 5.5V, making it suitable for standard TTL logic applications requiring address decoding or demultiplexing functions. Identifying equivalent and substitute parts ensures design continuity and supply chain resilience.

Substiute Parts

SN74ALS138AD

Texas InstrumentsIn Stock: 2021SN74ALS138AD Datasheet

Current PartRFQ

SN74ALS138ADR

Texas InstrumentsIn Stock: 1934SN74ALS138ADR Datasheet

MFR RecommendedRFQ

SN74ALS137AD

Texas InstrumentsIn Stock: 783SN74ALS137AD Datasheet

Parametric EquivalentRFQ

SN74AS138D

Texas InstrumentsIn Stock: 1175SN74AS138D Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the SN74ALS138AD are qualified based on the following critical parameters that determine functional and mechanical compatibility:

Functional Equivalence Criteria:

• Decoder/Demultiplexer type with 1 x 3:8 circuit configuration
• Output current specifications: 400µA (high), 8mA (low)
• Single supply voltage range: 4.5V ~ 5.5V
• Operating temperature range: 0°C ~ 70°C

Mechanical Compatibility Criteria:

• 16-SOIC surface mount package with 0.154" (3.90mm) width
• RoHS3 compliance
• Moisture Sensitivity Level 1

Substitution Categories:

1. MFR Recommended Equivalent (Packaging Variant): SN74ALS138ADR differs only in packaging format (Cut Tape & Digi-Reel versus Tube) while maintaining identical electrical specifications and Active product status.

2. Parametric Equivalents (Same Series): SN74ALS137AD maintains all electrical and mechanical parameters within the 74ALS logic family, though classified as Last Time Buy.

3. Parametric Equivalents (Alternative Series): SN74AS138D provides identical functional and mechanical specifications within the 74AS logic family with Active product status, representing a cross-series alternative.

Parameter Comparison

Engineering Selection Recommendations

Primary Recommendation: SN74ALS138ADR

The SN74ALS138ADR is the preferred substitute for the SN74ALS138AD. Both parts are manufactured by Texas Instruments with identical electrical and mechanical specifications. The SN74ALS138ADR maintains Active product status, ensuring long-term availability and supply chain stability. The only distinction is packaging format (Cut Tape & Digi-Reel versus Tube), which does not affect functional performance or PCB integration. This part is suitable for direct replacement in new designs and production runs.

Secondary Recommendation: SN74AS138D

The SN74AS138D provides a cross-series alternative within the 74AS logic family. All electrical parameters, mechanical specifications, and compliance certifications are identical to the SN74ALS138AD. The SN74AS138D maintains Active product status. Selection of this part may be appropriate when 74AS series components are preferred for system-level consistency or when supply availability of 74ALS variants is constrained.

Alternative: SN74ALS137AD

The SN74ALS137AD remains within the 74ALS series and meets all functional and mechanical requirements. However, this part shares Last Time Buy status with the original SN74ALS138AD, limiting its suitability for long-term production planning. This part may be considered only when Active alternatives are unavailable and existing inventory is sufficient for project requirements.

Frequently Asked Questions (FAQ)

Q: Can SN74ALS138ADR be used as a direct replacement for SN74ALS138AD?

A: Yes. The SN74ALS138ADR is functionally and electrically identical to the SN74ALS138AD. The difference is packaging format: SN74ALS138ADR is supplied in Cut Tape & Digi-Reel format, while SN74ALS138AD is supplied in Tube format. Both are 16-SOIC surface mount packages with identical pinout and electrical characteristics. No circuit modifications are required.

Q: What is the difference between 74ALS and 74AS logic families?

A: Both 74ALS and 74AS are TTL-compatible logic families manufactured by Texas Instruments. For the decoder/demultiplexer function specified, the SN74ALS138AD and SN74AS138D have identical electrical specifications, including voltage supply, output current, and operating temperature range. The primary distinction is the logic family designation, which may affect propagation delay characteristics not specified in the provided parameters. Both are suitable for standard TTL applications.

Q: Why is the SN74ALS138AD classified as Last Time Buy?

A: Last Time Buy status indicates that Texas Instruments has discontinued or is discontinuing production of this specific part number. This classification necessitates identifying and qualifying substitute parts to ensure design continuity and supply chain resilience. The SN74ALS138ADR (Active status) is the recommended alternative.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All substitute parts listed—SN74ALS138ADR, SN74ALS137AD, and SN74AS138D—are RoHS3 compliant with Moisture Sensitivity Level 1 (Unlimited). They meet the same environmental and regulatory requirements as the original SN74ALS138AD.

Q: Can these parts be used interchangeably in existing PCB designs?

A: Yes, provided the PCB footprint accommodates the 16-SOIC (0.154", 3.90mm width) surface mount package. All substitute parts use identical pinout and package dimensions. No PCB layout modifications are required for functional substitution.

Q: What inventory levels are available for each substitute part?

A: Current inventory levels are: SN74ALS138ADR (1900 Pcs), SN74ALS137AD (719 Pcs), and SN74AS138D (1156 Pcs). Inventory availability may change; verification with the supplier is recommended for production quantities.