FST3125QSC Bus Switch 1 x 1:1 Equivalent & Substitute Parts

Part Overview

The FST3125QSC is a bus switch IC manufactured by onsemi, configured as a 1 x 1:1 logic switch in a 16-QSOP package. This component functions as a single-pole, single-throw (SPST) electronic switch for bus isolation and multiplexing applications. The FST3125QSC is classified as obsolete, making equivalent substitute parts necessary for new designs and ongoing production requirements. Substitute parts must maintain identical circuit configuration, package compatibility, and electrical operating parameters to ensure direct replacement capability.

Substiute Parts

FST3125QSC

onsemiIn Stock: 1509FST3125QSC Datasheet

Current PartRFQ

SN74CBT3125DBQR

Texas InstrumentsIn Stock: 3870SN74CBT3125DBQR Datasheet

DirectRFQ

PI5C3125QE

Diodes IncorporatedIn Stock: 7405PI5C3125QE Datasheet

SimilarRFQ

PI5C3125QEX

Diodes IncorporatedIn Stock: 17979PI5C3125QEX Datasheet

SimilarRFQ

QS3125QG

Renesas Electronics CorporationIn Stock: 1392QS3125QG Datasheet

SimilarRFQ

QS3125QG8

Renesas Electronics CorporationIn Stock: 19276QS3125QG8 Datasheet

SimilarRFQ

SN74CBT3125CDBQR

Texas InstrumentsIn Stock: 806SN74CBT3125CDBQR Datasheet

SimilarRFQ

SN74CBTLV3125DBQR

Texas InstrumentsIn Stock: 2390SN74CBTLV3125DBQR Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the FST3125QSC are qualified based on the following criteria:

Mandatory Compatibility Parameters:

• Circuit type: Bus Switch with 1 x 1:1 configuration
• Independent circuits: 4
• Mounting type: Surface Mount
• Package width: 16-pin with 0.154" (3.90mm) width
• Operating temperature range: -40°C ~ 85°C minimum
• Voltage supply compatibility: Overlapping or encompassing supply voltage range

Substitution Categories:

Direct substitutes maintain identical electrical specifications and package form factor, allowing pin-for-pin replacement without design modification.

Similar substitutes share the same circuit configuration and operating temperature range but may have different voltage supply specifications or packaging variants (Tape & Reel vs. Tube). These require verification of voltage compatibility within the application circuit.

Parameter Comparison

Engineering Selection Recommendations

Recommended Primary Substitutes (Active Product Status):

QS3125QG and QS3125QG8 from Renesas Electronics are the preferred substitutes. Both maintain active product status, ensuring long-term availability and supply chain stability. These parts operate within a narrower voltage range (4.75V ~ 5.25V) compared to the FST3125QSC (4V ~ 5.5V), but this range is fully compatible with standard 5V logic supply applications. Both achieve ROHS3 compliance and feature MSL 1 rating, matching the moisture sensitivity profile of the original part.

SN74CBT3125CDBQR from Texas Instruments provides an alternative with active status and ROHS3 compliance. This part operates at 4.5V ~ 5.5V, providing broader low-voltage tolerance than the Renesas options while maintaining compatibility with the FST3125QSC's upper voltage limit.

Secondary Substitutes (Last Time Buy Status):

PI5C3125QEX and PI5C3125QE from Diodes Incorporated are available in higher inventory quantities (17,920 and 7,300 units respectively) but carry Last Time Buy status. These parts are suitable for immediate production needs where supply is critical. Both operate at 4.5V ~ 5.5V and achieve ROHS3 compliance with MSL 1 rating.

SN74CBT3125DBQR from Texas Instruments also carries Last Time Buy status but remains a viable option for applications requiring the 4.5V ~ 5.5V supply range.

Not Recommended for Direct Substitution:

SN74CBTLV3125DBQR operates at 2.3V ~ 3.6V and is unsuitable for applications designed for 5V logic levels. This part is appropriate only for low-voltage designs and cannot serve as a direct replacement for the FST3125QSC.

Frequently Asked Questions (FAQ)

Q: Can QS3125QG replace FST3125QSC in a 5V application?

A: Yes. The QS3125QG operates at 4.75V ~ 5.25V, which encompasses standard 5V supply voltages (typically 5.0V ±5%). The narrower voltage range does not restrict operation in standard 5V logic circuits.

Q: What is the difference between PI5C3125QE and PI5C3125QEX?

A: Both parts are functionally identical with matching electrical specifications. The primary difference is packaging: PI5C3125QE is supplied in Tube format, while PI5C3125QEX is supplied in Tape & Reel (TR) format. Selection depends on assembly process requirements and inventory management preferences.

Q: Why does the FST3125QSC specify 4V minimum supply while most substitutes specify 4.5V?

A: The FST3125QSC supports a broader supply voltage range (4V ~ 5.5V) than most modern substitutes. However, standard 5V logic applications operate at 5.0V ±5%, which falls within all substitute part specifications. Applications requiring operation below 4.5V are not compatible with the listed substitutes.

Q: Are there package compatibility concerns between 16-LSSOP and 16-SSOP?

A: Both packages maintain 0.154" (3.90mm) width and 16-pin configuration. Pin pitch and spacing are identical, allowing direct PCB footprint compatibility. The designations reflect minor manufacturing process differences that do not affect electrical performance or mechanical fit.

Q: Which substitute offers the longest product lifecycle?

A: QS3125QG and QS3125QG8 from Renesas Electronics carry Active product status, indicating ongoing production and support. These parts provide the most stable long-term supply availability compared to Last Time Buy alternatives.

Q: Is ROHS3 compliance mandatory for substitution?

A: ROHS3 compliance is a regulatory requirement for most applications in regulated markets. All recommended substitutes achieve ROHS3 compliance. The original FST3125QSC does not specify ROHS status due to its obsolete classification.

Q: Can SN74CBTLV3125DBQR be used as a substitute?

A: No. The SN74CBTLV3125DBQR operates at 2.3V ~ 3.6V and is designed for low-voltage applications. It is not compatible with 5V logic circuits and cannot serve as a direct replacement for the FST3125QSC.