SN74LS640NS Equivalent & Substitute Parts

Part Overview

The SN74LS640NS is an inverting transceiver logic integrated circuit manufactured by Texas Instruments, designed for 8-bit data bus applications with 3-state output capability. This component operates within the 74LS logic family and is housed in a 20-pin SOIC package. The main part is currently in Last Time Buy status, indicating discontinued production with limited availability. Identifying equivalent and substitute parts is necessary to ensure continued design support, maintain supply chain continuity, and access components with active manufacturing status.

Substiute Parts

SN74LS640NS

Texas InstrumentsIn Stock: 796SN74LS640NS Datasheet

Current PartRFQ

SN74LS640-1NSR

Texas InstrumentsIn Stock: 3467SN74LS640-1NSR Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the SN74LS640NS is determined by strict equivalence across the following critical parameters:

Functional Parameters:

• Logic type must be Transceiver, Inverting
• Configuration must be 1 element with 8 bits per element
• Output type must be 3-State

Electrical Parameters:

• Supply voltage range must be 4.75V ~ 5.25V
• Operating temperature range must be 0°C ~ 70°C (TA)

Physical Parameters:

• Package must be 20-SOIC with 0.209" (5.30mm) width
• Mounting type must be Surface Mount

Compliance Parameters:

• RoHS3 compliance required
• Moisture Sensitivity Level must be 1 (Unlimited)

The SN74LS640-1NSR meets all these criteria and is identified as the manufacturer-recommended substitute. Differences in output current specifications and packaging format (Tape & Reel versus bulk) do not affect functional substitution within the specified electrical and mechanical constraints.

Parameter Comparison

Engineering Selection Recommendations

The SN74LS640-1NSR is the direct substitute for the SN74LS640NS based on functional and electrical equivalence. Selection of the substitute part is supported by the following factors:

Product Status: The SN74LS640-1NSR maintains Active product status with ongoing manufacturing support, whereas the original part is in Last Time Buy status. This ensures long-term availability and supply chain reliability.

Compliance Certification: Both parts maintain ROHS3 compliance and identical Moisture Sensitivity Level ratings, confirming suitability for current manufacturing and environmental standards.

Electrical Performance: The substitute part demonstrates equal or superior electrical characteristics. Output low current is increased to 48mA compared to 24mA in the original, providing enhanced drive capability without affecting circuit compatibility within the specified 4.75V ~ 5.25V supply range.

Physical Compatibility: Identical package specifications (20-SOIC, 0.209" width) and surface mount configuration ensure direct PCB footprint compatibility without layout modifications.

Packaging Format: The substitute is supplied in Tape & Reel format, which is standard for production environments and offers advantages in automated assembly processes compared to bulk packaging.

Frequently Asked Questions (FAQ)

Q: Can the SN74LS640-1NSR be used as a direct replacement for the SN74LS640NS on existing PCBs?

A: Yes. Both parts share identical package specifications (20-SOIC), pin configurations, and electrical operating parameters. No PCB modifications or design changes are required for substitution.

Q: What is the significance of the higher output low current (48mA vs. 24mA) in the substitute part?

A: The increased output low current in the SN74LS640-1NSR indicates greater current sinking capability. This is compatible with the original design and does not create conflicts. Circuits designed for the original 24mA specification will operate correctly with the higher capacity substitute.

Q: Why is the original SN74LS640NS listed as Last Time Buy?

A: Last Time Buy status indicates that Texas Instruments has discontinued production of this part number. The SN74LS640-1NSR represents the active production equivalent, ensuring continued availability and manufacturing support.

Q: Are there any differences in RoHS or environmental compliance between these parts?

A: No. Both parts are ROHS3 compliant and maintain identical Moisture Sensitivity Level ratings (MSL 1 - Unlimited), confirming equivalent environmental and regulatory compliance.

Q: What is the difference between the bulk packaging of SN74LS640NS and the Tape & Reel packaging of SN74LS640-1NSR?

A: Tape & Reel packaging is the standard format for automated assembly and production environments. Bulk packaging is typically used for prototype or small-quantity applications. The functional component is identical; only the delivery format differs.

Q: Can the SN74LS640-1NSR be used in new designs?

A: Yes. The SN74LS640-1NSR is the recommended part for new designs requiring an inverting 8-bit transceiver with 3-state output in the 74LS logic family. Its Active product status ensures long-term availability and manufacturing support.