FST3125MX Equivalent & Substitute Parts

Part Overview

The FST3125MX is a Bus Switch IC manufactured by onsemi in a 14-SOIC package configuration. This component functions as a 1 x 1:1 logic bus switch with 4 independent circuits, designed for single supply voltage operation. The FST3125MX carries an Obsolete product status, making identification of functionally equivalent alternatives essential for ongoing design support and production continuity.

Substiute Parts

FST3125MX

onsemiIn Stock: 9938FST3125MX Datasheet

Current PartRFQ

FST3125DR2G

onsemiIn Stock: 1993FST3125DR2G Datasheet

UpgradeRFQ

FST3125MTCX

onsemiIn Stock: 37870FST3125MTCX Datasheet

SimilarRFQ

SN74CBT3125D

Texas InstrumentsIn Stock: 2536SN74CBT3125D Datasheet

DirectRFQ

SN74CBT3125DR

Texas InstrumentsIn Stock: 2896SN74CBT3125DR Datasheet

DirectRFQ

SN74CBT3125CD

Texas InstrumentsIn Stock: 1731SN74CBT3125CD Datasheet

SimilarRFQ

SN74CBT3125CDR

Texas InstrumentsIn Stock: 3518SN74CBT3125CDR Datasheet

SimilarRFQ

SN74CBTLV3125DR

Texas InstrumentsIn Stock: 2246SN74CBTLV3125DR Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the FST3125MX is determined by the following critical parameters:

• Circuit Configuration: Must be 1 x 1:1 with 4 independent circuits
• Package Type: Must be 14-SOIC (0.154", 3.90mm Width) for direct pin-compatible replacement
• Voltage Supply Range: Must support the required 4V ~ 5.5V operating window
• Operating Temperature Range: Must encompass or exceed -40°C ~ 85°C
• Mounting Type: Must be Surface Mount
• Compliance: Must maintain ROHS3 compliance

Substitute parts are categorized as follows:

Upgrade Substitutes (Enhanced specifications within same package):

• FST3125DR2G (onsemi) — Extended temperature range (-55°C ~ 125°C), same 14-SOIC package

Similar Substitutes (Alternative package, same base functionality):

• FST3125MTCX (onsemi) — 14-TSSOP package, Tape & Reel packaging
• SN74CBT3125CD (Texas Instruments) — 14-SOIC package, Active status
• SN74CBT3125CDR (Texas Instruments) — 14-SOIC package, Tape & Reel, Active status
• SN74CBTLV3125DR (Texas Instruments) — 14-SOIC package, lower voltage range (2.3V ~ 3.6V)

Direct Substitutes (Same package, same manufacturer series):

• SN74CBT3125D (Texas Instruments) — 14-SOIC package, Tube packaging, Last Time Buy status
• SN74CBT3125DR (Texas Instruments) — 14-SOIC package, Cut Tape, Last Time Buy status

Parameter Comparison

Engineering Selection Recommendations

For Direct Pin-Compatible Replacement (14-SOIC Package):

SN74CBT3125CD and SN74CBT3125CDR (Texas Instruments) are the preferred substitutes. Both maintain Active product status, ensuring long-term availability and supply chain stability. These parts are functionally equivalent to FST3125MX with identical circuit configuration, package geometry, and operating temperature range. The voltage supply range (4.5V ~ 5.5V) is compatible with applications designed for the FST3125MX (4V ~ 5.5V). Both parts maintain ROHS3 compliance and MSL Level 1 rating.

For Extended Temperature Operation:

FST3125DR2G (onsemi) provides an upgrade path with extended operating temperature range (-55°C ~ 125°C) while maintaining the same 14-SOIC package footprint. This option is suitable for applications requiring broader thermal performance specifications.

For Alternative Package Consideration:

FST3125MTCX (onsemi) offers the same functional specification in a 14-TSSOP package with higher inventory availability (37,800 units). This option requires PCB layout modification but maintains onsemi sourcing continuity.

Not Recommended for Standard Applications:

SN74CBTLV3125DR operates at a reduced voltage range (2.3V ~ 3.6V) and is suitable only for low-voltage applications. This part is not compatible with standard 4V ~ 5.5V supply designs without circuit modification.

Frequently Asked Questions (FAQ)

Q: Can SN74CBT3125D or SN74CBT3125DR be used as direct replacements for FST3125MX?

A: Yes. Both parts share identical 14-SOIC package geometry, circuit configuration (1 x 1:1 with 4 independent circuits), and operating temperature range (-40°C ~ 85°C). The voltage supply range difference (4.5V ~ 5.5V vs. 4V ~ 5.5V) is not a functional barrier for applications operating above 4.5V. Both maintain ROHS3 compliance.

Q: What is the difference between FST3125DR2G and FST3125MX?

A: FST3125DR2G extends the operating temperature range to -55°C ~ 125°C compared to FST3125MX (-40°C ~ 85°C). Both use the same 14-SOIC package and voltage supply range. FST3125DR2G is suitable for industrial or extended-temperature applications.

Q: Why is SN74CBTLV3125DR listed but not recommended?

A: SN74CBTLV3125DR operates at 2.3V ~ 3.6V supply voltage, which does not overlap with the FST3125MX specification (4V ~ 5.5V). This part is only suitable for low-voltage designs and requires circuit redesign for compatibility.

Q: Does package type affect substitution eligibility?

A: Package type affects PCB layout compatibility. FST3125MTCX uses 14-TSSOP instead of 14-SOIC, requiring PCB footprint modification. All other listed substitutes use 14-SOIC and are pin-compatible without layout changes.

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

A: SN74CBT3125CD and SN74CBT3125CDR (Texas Instruments) carry Active product status, indicating ongoing production and supply chain support. Parts with Obsolete or Last Time Buy status have limited future availability.