FSA1258AL8X Equivalent & Substitute Parts

Part Overview

The FSA1258AL8X is a 2-circuit IC switch manufactured by onsemi, featuring SPST (Single Pole Single Throw) NO/NC configuration with 1.15Ohm on-state resistance in an 8-MicroPak™ surface mount package. This component is classified as obsolete, making identification of suitable substitute parts essential for ongoing design support and production continuity. The low on-state resistance and high-speed switching characteristics position this device for signal routing and analog switching applications requiring minimal signal distortion.

Substiute Parts

FSA1258AL8X

onsemiIn Stock: 4401FSA1258AL8X Datasheet

Current PartRFQ

DG2739DN-T1-E4

Vishay SiliconixIn Stock: 1531DG2739DN-T1-E4 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the FSA1258AL8X is determined by the following critical parameters:

• Switch Configuration: SPST - NO/NC with 2 circuits (1:1 multiplexer/demultiplexer)
• On-State Resistance: Maximum 1.15Ohm for signal integrity in low-impedance applications
• Supply Voltage Range: 2.7V ~ 5.5V single supply operation
• Switching Speed: Ton/Toff specifications of 35ns/15ns maximum
• Bandwidth: 300MHz minimum for high-frequency signal routing
• Package Type: 8-UFQFN surface mount form factor
• Operating Temperature: -40°C ~ 85°C range

The DG2739DN-T1-E4 from Vishay Siliconix shares the same switch circuit topology, number of circuits, package footprint, and operating temperature range. However, this substitute exhibits different electrical characteristics in on-state resistance, supply voltage range, and switching speed, requiring circuit-level evaluation for compatibility.

Parameter Comparison

Engineering Selection Recommendations

The DG2739DN-T1-E4 is an active product with ROHS3 compliance, providing long-term availability and regulatory alignment compared to the obsolete FSA1258AL8X. Both devices share identical package footprints (8-UFQFN) and operating temperature ranges, enabling direct PCB-level substitution without layout modifications.

Substitution feasibility depends on application-specific tolerance to the following differences:

• On-State Resistance: The DG2739DN-T1-E4 exhibits 8Ohm maximum resistance versus 1.15Ohm for the FSA1258AL8X. Applications sensitive to signal attenuation or requiring minimal impedance must evaluate this 7x increase in on-state resistance.
• Supply Voltage Range: The DG2739DN-T1-E4 operates within 2.3V ~ 4.3V, which is narrower than the FSA1258AL8X range of 2.7V ~ 5.5V. Systems requiring 5V operation or extended low-voltage support may require circuit redesign.
• Switching Speed: The DG2739DN-T1-E4 exhibits longer switching times (60ns Ton, 50ns Toff) compared to the FSA1258AL8X (35ns, 15ns). Time-critical applications must verify compatibility with system timing margins.
• Leakage Current: The DG2739DN-T1-E4 specifies 10nA maximum leakage versus 2nA for the FSA1258AL8X, which may impact low-power or precision analog applications.

The DG2739DN-T1-E4 offers superior bandwidth (720MHz versus 300MHz) and lower charge injection (10.4pC versus 20pC), providing advantages in high-frequency signal routing applications.

Frequently Asked Questions (FAQ)

Q: Can the DG2739DN-T1-E4 be used as a direct replacement for the FSA1258AL8X?

A: Direct PCB substitution is possible due to identical 8-UFQFN package footprints. However, circuit-level compatibility must be verified due to significant differences in on-state resistance, supply voltage range, and switching speed. Applications with tight impedance or timing specifications require detailed electrical analysis.

Q: What is the primary limitation of using the DG2739DN-T1-E4 as a substitute?

A: The on-state resistance of 8Ohm is substantially higher than the FSA1258AL8X specification of 1.15Ohm. This increase may cause unacceptable signal attenuation in low-impedance signal routing applications or introduce additional power dissipation in switching circuits.

Q: Does the DG2739DN-T1-E4 support 5V operation?

A: No. The DG2739DN-T1-E4 is specified for 2.3V ~ 4.3V single supply operation, which does not include 5V. The FSA1258AL8X supports 2.7V ~ 5.5V. Systems requiring 5V operation cannot use the DG2739DN-T1-E4 without external level shifting or voltage regulation.

Q: Are there packaging considerations for substitution?

A: Both devices use 8-UFQFN surface mount packages with identical footprints. No PCB layout modifications are required for physical substitution. Moisture sensitivity levels are identical (MSL 1, Unlimited), so storage and handling procedures remain unchanged.

Q: What is the compliance status difference between these parts?

A: The FSA1258AL8X is obsolete with unspecified RoHS status. The DG2739DN-T1-E4 is an active product with ROHS3 compliance, ensuring regulatory alignment with current environmental standards and long-term supply availability.

Q: How do the switching speed differences affect application compatibility?

A: The DG2739DN-T1-E4 exhibits 25ns longer turn-on time and 35ns longer turn-off time compared to the FSA1258AL8X. Applications with timing-critical signal switching or high-frequency multiplexing must verify that these delays do not violate system timing requirements or introduce unacceptable signal distortion.