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FST3257QSCX Equivalent & Substitute Parts
Part Overview
The FST3257QSCX is a 4 x 2:1 Multiplexer/Demultiplexer logic IC manufactured by onsemi in a 16-QSOP surface mount package. This component is classified as Obsolete, making equivalent substitute parts necessary for new designs and ongoing production support. The FST3257QSCX operates across a single supply voltage range of 3V to 5.5V with an operating temperature range of -40°C to 85°C, serving applications requiring signal multiplexing and demultiplexing functions in logic circuits.
Substiute Parts
Key Parameters
| Parameter | Value |
|---|---|
| Manufacturer Part Number | FST3257QSCX |
| Manufacturer | onsemi |
| Category | Logic |
| Type | Multiplexer/Demultiplexer |
| Circuit Configuration | 4 x 2:1 |
| Independent Circuits | 1 |
| Voltage Supply Source | Single Supply |
| Voltage - Supply Range | 3V ~ 5.5V |
| Operating Temperature Range | -40°C ~ 85°C |
| Mounting Type | Surface Mount |
| Package / Case | 16-LSSOP (0.154", 3.90mm Width) |
| Supplier Device Package | 16-QSOP |
| Product Status | Obsolete |
| Moisture Sensitivity Level (MSL) | 1 (Unlimited) |
| REACH Status | REACH Unaffected |
Substitute Part Grouping Explanation
Substitution of the FST3257QSCX is determined by strict adherence to the following electrical and mechanical parameters:
Critical Substitution Parameters:
- Circuit configuration: 4 x 2:1 multiplexer/demultiplexer topology
- Voltage supply range compatibility: Substitute must operate within or encompass the 3V to 5.5V range
- Operating temperature range: -40°C to 85°C minimum
- Package type: 16-pin surface mount packages (QSOP, TSSOP, or SSOP variants)
- Single supply operation requirement
Acceptable Package Variants: Substitutes may use 16-QSOP, 16-TSSOP, or 16-SSOP packages, as these are mechanically and electrically compatible pinout configurations for this device class.
Voltage Range Considerations: The FST3257QSCX operates from 3V to 5.5V. Substitute parts with narrower voltage ranges (such as 4V to 5.5V, 4.5V to 5.5V, or 4.75V to 5.25V) are acceptable for applications operating within those narrower ranges but may not be suitable for designs requiring the full 3V minimum specification.
Parameter Comparison
| Part Number | Manufacturer | Circuit | Voltage Supply (V) | Temp Range (°C) | Package | Product Status | RoHS Status |
|---|---|---|---|---|---|---|---|
| FST3257QSCX | onsemi | 4 x 2:1 | 3.0 ~ 5.5 | -40 ~ 85 | 16-QSOP | Obsolete | Not Specified |
| 74FST3257DTR2G | onsemi | 4 x 2:1 | 4.0 ~ 5.5 | -40 ~ 85 | 16-TSSOP | Last Time Buy | ROHS3 Compliant |
| CBT3257ADS,118 | Nexperia USA Inc. | 4 x 2:1 | 4.5 ~ 5.5 | -40 ~ 85 | 16-SSOP | Active | ROHS3 Compliant |
| CBT3257APW,118 | Nexperia USA Inc. | 4 x 2:1 | 4.5 ~ 5.5 | -40 ~ 85 | 16-TSSOP | Active | ROHS3 Compliant |
| PI5C3257LE | Diodes Incorporated | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-TSSOP | Last Time Buy | ROHS3 Compliant |
| PI5C3257LEX | Diodes Incorporated | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-TSSOP | Last Time Buy | ROHS3 Compliant |
| PI5C3257QE | Diodes Incorporated | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-QSOP | Active | ROHS3 Compliant |
| PI5C3257QEX | Diodes Incorporated | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-QSOP | Active | ROHS3 Compliant |
| QS3257QG | Renesas Electronics Corporation | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-QSOP | Active | ROHS3 Compliant |
| QS3257QG8 | Renesas Electronics Corporation | 4 x 2:1 | 4.75 ~ 5.25 | -40 ~ 85 | 16-QSOP | Active | ROHS3 Compliant |
| SN74CBT3257CDBQR | Texas Instruments | 4 x 2:1 | 4.5 ~ 5.5 | -40 ~ 85 | 16-SSOP | Active | ROHS3 Compliant |
Engineering Selection Recommendations
For Active Product Status Priority: PI5C3257QE, PI5C3257QEX, QS3257QG, QS3257QG8, CBT3257ADS,118, CBT3257APW,118, and SN74CBT3257CDBQR are all currently Active products. These parts provide ongoing manufacturer support and are recommended for new designs requiring long-term availability.
For Package Compatibility with FST3257QSCX: PI5C3257QE and PI5C3257QEX maintain the same 16-QSOP package as the original FST3257QSCX, minimizing PCB layout modifications. QS3257QG and QS3257QG8 also use 16-QSOP packaging. These options are preferred when PCB redesign must be minimized.
For Full Voltage Range Coverage: 74FST3257DTR2G (onsemi, 4V to 5.5V) and CBT3257ADS,118 or CBT3257APW,118 (Nexperia, 4.5V to 5.5V) provide the widest voltage ranges among available substitutes. However, applications requiring operation below 4V will require PI5C3257 or QS3257 series parts operating at 4.75V to 5.25V, or the original FST3257QSCX specification of 3V to 5.5V.
For RoHS3 Compliance: All listed substitute parts carry ROHS3 Compliant certification. The original FST3257QSCX does not specify RoHS status.
For Moisture Sensitivity: The FST3257QSCX specifies MSL 1 (Unlimited). SN74CBT3257CDBQR specifies MSL 2 (1 Year), which represents a more stringent moisture handling requirement. All other substitutes specify MSL 1 (Unlimited), matching the original part.
Frequently Asked Questions (FAQ)
Q: Can I use PI5C3257QE as a direct replacement for FST3257QSCX?
A: PI5C3257QE is electrically and mechanically compatible for applications operating within the 4.75V to 5.25V supply range. Both parts use 16-QSOP packaging and implement the same 4 x 2:1 multiplexer/demultiplexer circuit. However, if your application requires operation at 3V or 4V, PI5C3257QE is not suitable. Verify your circuit's actual operating voltage before substitution.
Q: What is the difference between 16-QSOP, 16-TSSOP, and 16-SSOP packages?
A: These are all 16-pin surface mount packages with identical pinouts for this device class. The primary differences are physical dimensions: 16-QSOP measures 0.154" width (3.90mm), 16-TSSOP measures 0.173" width (4.40mm), and 16-SSOP measures 0.154" width (3.90mm). Package selection depends on PCB layout constraints and available footprint space. Substitution between these packages requires PCB layout verification.
Q: Why is FST3257QSCX marked as Obsolete?
A: Obsolete status indicates the manufacturer has discontinued production and will not accept new orders. Active substitute parts from other manufacturers provide equivalent functionality and are recommended for new designs and production continuity.
Q: Can I substitute a part with a narrower voltage range than the original?
A: Only if your application operates entirely within that narrower range. For example, if your circuit operates at 5V nominal with ±5% tolerance (4.75V to 5.25V), then PI5C3257QE is acceptable. If your circuit requires operation at 3V or 4V, you must select a part with a voltage range that includes those values.
Q: Which substitute offers the best long-term availability?
A: Active status parts (PI5C3257QE, PI5C3257QEX, QS3257QG, QS3257QG8, CBT3257ADS,118, CBT3257APW,118, and SN74CBT3257CDBQR) are currently in production and offer the best long-term availability. Last Time Buy parts (74FST3257DTR2G, PI5C3257LE, PI5C3257LEX) have limited remaining inventory and will eventually become obsolete.
Q: Does moisture sensitivity level affect my selection?
A: MSL rating determines storage and handling requirements. FST3257QSCX and most substitutes specify MSL 1 (Unlimited), meaning no special moisture control is required. SN74CBT3257CDBQR specifies MSL 2 (1 Year), requiring baking before reflow if the part has been stored in humid conditions for extended periods. Select based on your manufacturing process capabilities.
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