FST3257MX Equivalent & Substitute Parts

Part Overview

The FST3257MX is a 4 x 2:1 Multiplexer/Demultiplexer logic IC manufactured by onsemi in a 16-SOIC package. This component is classified as obsolete, which necessitates identifying functionally equivalent alternatives for new designs or component replacement in existing applications. The FST3257MX operates across a 3V to 5.5V supply range with a single supply configuration and supports operating temperatures from -40°C to 85°C.

Substiute Parts

FST3257MX

onsemiIn Stock: 80344FST3257MX Datasheet

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74FST3257DR2G

onsemiIn Stock: 443774FST3257DR2G Datasheet

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FST3257MTCX

onsemiIn Stock: 55297FST3257MTCX Datasheet

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74CBTLV3257D,118

NXP SemiconductorsIn Stock: 1045574CBTLV3257D,118 Datasheet

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CBT3257AD,118

NXP SemiconductorsIn Stock: 46189CBT3257AD,118 Datasheet

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SN74CBT3257CD

Texas InstrumentsIn Stock: 1107SN74CBT3257CD Datasheet

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SN74CBT3257CDR

Texas InstrumentsIn Stock: 2314SN74CBT3257CDR Datasheet

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SN74CBT3257D

Texas InstrumentsIn Stock: 2177SN74CBT3257D Datasheet

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SN74CBT3257DR

Texas InstrumentsIn Stock: 2629SN74CBT3257DR Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the FST3257MX is determined by the following critical parameters:

• Circuit Configuration: Must be 4 x 2:1 Multiplexer/Demultiplexer topology
• Package Type: 16-SOIC form factor with 0.154" (3.90mm) width for direct PCB compatibility
• Voltage Supply Range: Must encompass or be compatible with 3V ~ 5.5V operation
• Operating Temperature Range: Must support -40°C ~ 85°C minimum
• Mounting Type: Surface mount technology required
• Independent Circuits: Single circuit configuration

Substitute parts are grouped into two categories based on package compatibility:

Category 1: 16-SOIC Package (Direct Pin-Compatible) Parts maintaining the identical 16-SOIC package enable direct PCB replacement without layout modifications.

Category 2: Alternative Packages (Functional Equivalents) Parts with different packages (16-TSSOP) provide equivalent functionality but require PCB layout adaptation.

Parameter Comparison

Engineering Selection Recommendations

For Direct PCB Replacement (16-SOIC Package):

Active product status parts are preferred for new designs and long-term availability:

• SN74CBT3257CD (Texas Instruments, Active) and SN74CBT3257CDR (Texas Instruments, Active) provide the most stable long-term supply. Both operate within 4.5V ~ 5.5V and maintain full temperature range compatibility.
• CBT3257AD,118 (NXP Semiconductors, Active) offers equivalent functionality with active product status and identical package footprint.

Last Time Buy alternatives:

• 74FST3257DR2G (onsemi, Last Time Buy) maintains onsemi manufacturing continuity with 4V ~ 5.5V operation.
• SN74CBT3257D and SN74CBT3257DR (Texas Instruments, Last Time Buy) are available but subject to end-of-life constraints.

For Alternative Package Consideration (16-TSSOP):

• FST3257MTCX (onsemi, Obsolete) provides identical voltage range (3V ~ 5.5V) in 16-TSSOP package but requires PCB layout modification.

Voltage Supply Consideration:

The FST3257MX operates from 3V minimum. Most active substitutes (CBT3257AD,118 and SN74CBT3257 variants) require 4.5V minimum. Verify system supply voltage compatibility before selection. The 74CBTLV3257D,118 operates at lower voltage (2.3V ~ 3.6V) and is not compatible with the original 3V ~ 5.5V specification.

Frequently Asked Questions (FAQ)

Q: Can SN74CBT3257CD directly replace FST3257MX on the PCB?

A: Yes, for PCB layout purposes. Both use 16-SOIC packaging with identical 0.154" (3.90mm) width and pin configuration. However, verify that your system supply voltage meets the 4.5V ~ 5.5V requirement of the SN74CBT3257CD, as the FST3257MX supports operation down to 3V.

Q: What is the difference between SN74CBT3257CD and SN74CBT3257CDR?

A: Both parts are functionally identical with the same electrical specifications. The difference is packaging format: SN74CBT3257CD is supplied in Tube packaging, while SN74CBT3257CDR is supplied in Cut Tape (CT) & Digi-Reel format. Select based on your procurement and assembly requirements.

Q: Why is 74CBTLV3257D,118 listed but not recommended as a direct substitute?

A: While 74CBTLV3257D,118 shares the 16-SOIC package and active product status, it operates at 2.3V ~ 3.6V supply voltage, which does not overlap with the FST3257MX specification of 3V ~ 5.5V. Additionally, it implements a 4 x 1:2 circuit configuration rather than 4 x 2:1, making it functionally incompatible.

Q: Is FST3257MTCX a viable alternative if I can modify the PCB layout?

A: FST3257MTCX provides identical electrical specifications (3V ~ 5.5V, 4 x 2:1 configuration, -40°C ~ 85°C) but uses 16-TSSOP packaging instead of 16-SOIC. PCB layout modification is required. However, both FST3257MX and FST3257MTCX are obsolete products, so active alternatives are preferred for new designs.

Q: Which substitute offers the best long-term availability?

A: Active product status parts offer the most stable supply: SN74CBT3257CD and SN74CBT3257CDR (Texas Instruments) and CBT3257AD,118 (NXP Semiconductors). All three maintain 4 x 2:1 configuration and 16-SOIC packaging. Verify 4.5V ~ 5.5V supply voltage compatibility with your system design.

Q: Are all listed substitutes RoHS3 compliant?

A: RoHS3 compliance is confirmed for FST3257MX, 74FST3257DR2G, SN74CBT3257CD, SN74CBT3257CDR, SN74CBT3257D, and SN74CBT3257DR. Compliance status for CBT3257AD,118 and 74CBTLV3257D,118 is not specified in the provided data.