SN74LS155AD Equivalent & Substitute Parts

Part Overview

The SN74LS155AD is a decoder/demultiplexer logic integrated circuit manufactured by Texas Instruments in the 74LS series. This component features a 1 x 2:4 decoder configuration in a 16-SOIC surface mount package. The SN74LS155AD is currently designated as Last Time Buy, indicating limited availability and the necessity to identify equivalent substitute components for ongoing design requirements and production planning.

Substiute Parts

SN74LS155AD

Texas InstrumentsIn Stock: 1120SN74LS155AD Datasheet

Current PartRFQ

SN74LS155ADR

Texas InstrumentsIn Stock: 5970SN74LS155ADR Datasheet

MFR RecommendedRFQ

SN74LS139AD

Texas InstrumentsIn Stock: 1441SN74LS139AD Datasheet

Parametric EquivalentRFQ

SN74S139AD

Texas InstrumentsIn Stock: 1207SN74S139AD Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the SN74LS155AD are qualified based on the following critical parameters that determine functional and mechanical compatibility:

Electrical Parameters:

• Decoder/Demultiplexer type with 1 x 2:4 circuit configuration
• 2 independent circuits
• Output current specifications: 400µA (high), 8mA (low)
• Single supply voltage range: 4.75V ~ 5.25V
• Operating temperature range: 0°C ~ 70°C

Mechanical Parameters:

• 16-SOIC surface mount package (0.154", 3.90mm width)
• Supplier device package: 16-SOIC

Compliance Parameters:

• ROHS3 compliance
• REACH unaffected status
• MSL rating: 1 (Unlimited)

Substitutes are grouped into two categories: manufacturer-recommended direct substitutes (packaging variant) and parametric equivalents (functional equivalents with different series designations).

Parameter Comparison

Engineering Selection Recommendations

SN74LS155ADR (Manufacturer-Recommended Substitute)

The SN74LS155ADR is the primary recommended substitute for the SN74LS155AD. This part maintains identical electrical specifications and 16-SOIC package configuration. The sole difference is packaging format: SN74LS155ADR is supplied in Tape & Reel (TR) format versus Tube format for the original part. The SN74LS155ADR carries Active product status, ensuring continued availability and supply chain stability. This substitute is suitable for direct replacement in production environments where tape and reel packaging is compatible with assembly processes.

SN74LS139AD (Parametric Equivalent - 74LS Series)

The SN74LS139AD is a parametric equivalent within the 74LS logic series. All electrical parameters, voltage supply specifications, output current ratings, operating temperature range, and package dimensions are identical to the SN74LS155AD. The SN74LS139AD is packaged in Tube format matching the original part. However, this part is listed as Discontinued at DiGi Electronics, which may impact long-term availability. Selection of this substitute should account for supply chain considerations.

SN74S139AD (Parametric Equivalent - 74S Series)

The SN74S139AD is a parametric equivalent from the faster 74S logic series. Electrical parameters, voltage supply range, output current specifications, operating temperature, and 16-SOIC package configuration are identical to the SN74LS155AD. The SN74S139AD maintains Active product status, supporting ongoing availability. This substitute is suitable for applications where the 74S series performance characteristics are acceptable within the design requirements.

All substitute parts maintain ROHS3 compliance, REACH unaffected status, and MSL rating of 1 (Unlimited), ensuring compatibility with modern manufacturing and environmental standards.

Frequently Asked Questions (FAQ)

Q: Can SN74LS155ADR be used as a direct replacement for SN74LS155AD?

A: Yes. The SN74LS155ADR is electrically and mechanically identical to the SN74LS155AD. The only difference is packaging format: SN74LS155ADR is supplied in Tape & Reel format while SN74LS155AD is supplied in Tube format. Both use the same 16-SOIC package. Compatibility depends on whether your assembly process can accommodate tape and reel packaging.

Q: What is the difference between 74LS and 74S series logic?

A: Both series meet the same electrical specifications for the decoder/demultiplexer function, including voltage supply (4.75V ~ 5.25V), output current (400µA, 8mA), and operating temperature (0°C ~ 70°C). The 74S series represents a faster logic family. Selection between 74LS and 74S depends on timing requirements within your specific application.

Q: Why is SN74LS155AD marked as Last Time Buy?

A: Last Time Buy status indicates that the manufacturer has discontinued or is discontinuing production of this part number. This designation signals the need to identify and qualify substitute components for future production requirements. The recommended substitute SN74LS155ADR maintains Active status and ensures continued supply availability.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All substitute parts listed (SN74LS155ADR, SN74LS139AD, SN74S139AD) are ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements.

Q: What does MSL rating 1 (Unlimited) mean?

A: MSL (Moisture Sensitivity Level) rating of 1 indicates the lowest moisture sensitivity classification. Parts with this rating have unlimited shelf life and do not require special moisture control handling during storage or assembly, simplifying logistics and manufacturing processes.

Q: Can I use SN74LS139AD if it is discontinued at DiGi Electronics?

A: SN74LS139AD is listed as discontinued at DiGi Electronics, which may limit availability through that specific distributor. However, availability through other authorized distributors should be verified. For long-term production planning, the Active status parts (SN74LS155ADR or SN74S139AD) are recommended to ensure supply chain continuity.