FSA1256L8X Equivalent & Substitute Parts

Part Overview

The FSA1256L8X is a 2-circuit IC switch manufactured by onsemi, featuring SPST-NO (Single Pole Single Throw - Normally Open) configuration with 1.15Ohm on-state resistance. This component is classified as obsolete, making identification of suitable substitute parts essential for ongoing design support and production continuity. The part operates across a supply voltage range of 1.65V to 5.5V and is housed in an 8-MicroPak™ surface mount package.

Key Parameters

Parameter	Value
Manufacturer Part Number	FSA1256L8X
Manufacturer	onsemi
Category	Interface
Switch Circuit	SPST - NO
Number of Circuits	2
On-State Resistance (Max)	1.15Ohm
Voltage - Supply, Single (V+)	1.65V ~ 5.5V
Switch Time (Ton, Toff) (Max)	35ns, 15ns
-3dB Bandwidth	300MHz
Operating Temperature	-40°C ~ 85°C
Package / Case	8-UFQFN
Product Status	Obsolete
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution of the FSA1256L8X is determined by the following critical parameters:

Switch Configuration: SPST - NO topology with 2 circuits
Supply Voltage Compatibility: Operating range must encompass or overlap with 1.65V ~ 5.5V
On-State Resistance: Maximum resistance value determines signal integrity and power dissipation characteristics
Bandwidth Performance: -3dB bandwidth of 300MHz establishes high-frequency signal handling capability
Package Type: Surface mount configuration with compatible footprint dimensions
Temperature Range: Operating temperature must support -40°C ~ 85°C minimum

Two substitute parts meet these criteria: the NX3L2T66GM,125 from NXP Semiconductors and the TS5A2066DCTR from Texas Instruments. Both maintain SPST-NO 2-circuit topology and surface mount packaging, though with differing electrical characteristics and product status classifications.

Parameter Comparison

Parameter	FSA1256L8X (onsemi)	NX3L2T66GM,125 (NXP)	TS5A2066DCTR (TI)
Switch Circuit	SPST - NO	SPST - NO	SPST - NO
Number of Circuits	2	2	2
On-State Resistance (Max)	1.15Ohm	750mOhm	10Ohm
Voltage - Supply, Single (V+)	1.65V ~ 5.5V	1.4V ~ 4.3V	1.65V ~ 5.5V
Switch Time (Ton, Toff) (Max)	35ns, 15ns	28ns, 20ns	5.8ns, 3.6ns
-3dB Bandwidth	300MHz	60MHz	300MHz
Charge Injection	20pC	6pC	1pC
Channel Capacitance (CS(off), CD(off))	11.5pF	35pF	5.5pF, 5.5pF
Current - Leakage (IS(off)) (Max)	2nA (Typ)	10nA	30nA
Operating Temperature	-40°C ~ 85°C	-40°C ~ 125°C	-40°C ~ 85°C
Mounting Type	Surface Mount	Surface Mount	Surface Mount
Package / Case	8-UFQFN	8-XFQFN Exposed Pad	8-LSSOP, 8-MSOP
Product Status	Obsolete	Discontinued at DiGi Electronics	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

TS5A2066DCTR (Texas Instruments) is the primary substitute option. This part maintains active product status, ensuring long-term availability and manufacturing support. It provides identical supply voltage range (1.65V ~ 5.5V) and superior switching performance with faster transition times (5.8ns, 3.6ns) and lower charge injection (1pC). The 8-LSSOP/8-MSOP package differs from the original 8-UFQFN, requiring PCB layout modification. On-state resistance of 10Ohm is higher than the original 1.15Ohm, which may impact applications with strict power dissipation or signal attenuation requirements.

NX3L2T66GM,125 (NXP Semiconductors) serves as a secondary option for applications requiring lower on-state resistance (750mOhm). This part offers extended operating temperature range (-40°C ~ 125°C) and lower charge injection (6pC). However, the supply voltage range (1.4V ~ 4.3V) does not fully encompass the original specification, and the -3dB bandwidth (60MHz) is significantly reduced. Product status is discontinued at DiGi Electronics, limiting future procurement availability. The 8-XFQFN package with exposed pad differs from the original footprint.

Both substitute parts maintain ROHS3 compliance and 2-circuit SPST-NO configuration. Selection depends on application-specific requirements for resistance characteristics, bandwidth performance, and supply voltage constraints.

Frequently Asked Questions (FAQ)

Q: Can the TS5A2066DCTR directly replace the FSA1256L8X without PCB modifications?

A: No. The TS5A2066DCTR uses an 8-LSSOP/8-MSOP package (0.110", 2.80mm width) versus the original 8-UFQFN package. PCB footprint redesign is required. Pin configuration compatibility must be verified against application schematics.

Q: What is the impact of the higher on-state resistance in the TS5A2066DCTR?

A: The TS5A2066DCTR on-state resistance of 10Ohm is approximately 8.7 times higher than the FSA1256L8X (1.15Ohm). This increases signal attenuation and power dissipation. Applications with low-impedance signal paths or strict insertion loss requirements may require circuit redesign or alternative parts.

Q: Why does the NX3L2T66GM,125 have a reduced supply voltage range?

A: The NX3L2T66GM,125 operates at 1.4V ~ 4.3V, which does not cover the upper 5.5V specification of the original part. This part is unsuitable for applications requiring 5V supply operation without additional voltage regulation.

Q: Is the reduced -3dB bandwidth of the NX3L2T66GM,125 a concern?

A: The NX3L2T66GM,125 provides 60MHz bandwidth versus the original 300MHz. This represents a 5-fold reduction and may limit high-frequency signal integrity. Applications operating above 60MHz require the TS5A2066DCTR or continued sourcing of FSA1256L8X inventory.

Q: Are both substitute parts RoHS compliant?

A: Yes. Both the TS5A2066DCTR and NX3L2T66GM,125 are ROHS3 compliant, matching the original FSA1256L8X compliance status.

Q: What is the lead time impact of selecting an active versus discontinued product?

A: The TS5A2066DCTR maintains active status with Texas Instruments, ensuring standard lead times and continuous manufacturing. The NX3L2T66GM,125 is discontinued at DiGi Electronics, restricting procurement to remaining inventory channels and potentially extending acquisition timelines.

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