FSA266K8X Equivalent & Substitute Parts

Part Overview

The FSA266K8X is a 2-circuit SPST-NO IC switch manufactured by onsemi, housed in an 8-VFSOP package with 10Ohm on-state resistance. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The device operates across a supply voltage range of 1.65V to 5.5V with a maximum switch time of 3.2ns (Ton) and 4.1ns (Toff), delivering 300MHz bandwidth performance suitable for high-speed switching applications.

Key Parameters

Parameter	FSA266K8X
Manufacturer	onsemi
Switch Circuit	SPST - NO
Number of Circuits	2
Multiplexer/Demultiplexer Circuit	1:1
On-State Resistance (Max)	10Ohm
Channel-to-Channel Matching (ΔRon)	200mOhm
Voltage - Supply, Single (V+)	1.65V ~ 5.5V
Switch Time (Ton, Toff) (Max)	3.2ns, 4.1ns
-3dB Bandwidth	300MHz
Channel Capacitance (CS(off), CD(off))	5pF
Current - Leakage (IS(off)) (Max)	100nA
Crosstalk	-70dB @ 10MHz
Operating Temperature	-40°C ~ 85°C (TA)
Package / Case	8-VFSOP (0.091", 2.30mm Width)
Product Status	Obsolete
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution eligibility for the FSA266K8X is determined by the following critical parameters:

Switch circuit topology: SPST - NO configuration
Circuit count and multiplexing ratio: 2 circuits, 1:1 multiplexer/demultiplexer
On-state resistance: 10Ohm maximum
Supply voltage compatibility: 1.65V ~ 5.5V single supply
Package compatibility: 8-VFSOP form factor
Operating temperature range: -40°C ~ 85°C minimum

Substitute parts are grouped into three categories based on parameter alignment:

Parametric Equivalents maintain identical electrical specifications including on-state resistance, switch timing, bandwidth, and leakage characteristics. These parts are direct functional replacements with no design modifications required.

Direct Substitutes meet all critical parameters but may exhibit variations in secondary characteristics such as channel-to-channel matching, charge injection, or crosstalk performance. These parts are suitable for applications where the primary switching function is the design constraint.

Similar Substitutes share the same package, circuit topology, and supply voltage range but may differ in on-state resistance or operating temperature range. These parts require application-level evaluation to confirm suitability.

Parameter Comparison

Parameter	FSA266K8X (onsemi)	NL7WB66USG (onsemi)	NC7WB66K8X (Fairchild)	SN74LVC2G66DCUR (TI)	74LVC2G66DC,125 (Nexperia)	SN74LVC2G66DCUT (TI)	TS5A21366DCUR (TI)	TS5A23166DCUR (TI)
Switch Circuit	SPST - NO	SPST - NO	SPST - NO	SPST - NO	SPST - NO	SPST - NO	SPST - NO	SPST - NO
Number of Circuits	2	2	2	2	2	2	2	2
Multiplexer/Demultiplexer	1:1	1:1	1:1	1:1	1:1	1:1	1:1	1:1
On-State Resistance (Max)	10Ohm	10Ohm	10Ohm	10Ohm	10Ohm	10Ohm	1Ohm	900mOhm
Channel-to-Channel Matching (ΔRon)	200mOhm	15Ohm	200mOhm	2Ohm (Max)	Not specified	2Ohm (Max)	40mOhm	40mOhm
Voltage - Supply, Single (V+)	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V	1.65V ~ 5.5V
Switch Time (Ton, Toff) (Max)	3.2ns, 4.1ns	3.9ns, 6.3ns	3.2ns, 4.1ns	3.9ns, 6.3ns	3.9ns, 5ns	3.9ns, 6.3ns	72ns, 318ns	7.5ns, 11ns
-3dB Bandwidth	300MHz	186MHz	300MHz	300MHz	500MHz	300MHz	260MHz	150MHz
Channel Capacitance (CS(off), CD(off))	5pF	10pF, 10pF	5pF	6pF	5pF	6pF	19pF, 17pF	19pF, 18pF
Current - Leakage (IS(off)) (Max)	100nA	1nA	100nA	100nA	5µA	100nA	10nA	20nA
Crosstalk	-70dB @ 10MHz	Not specified	-70dB @ 10MHz	-58dB @ 1MHz	-56dB @ 1MHz	-58dB @ 1MHz	-98dB @ 1MHz	-85dB @ 1MHz
Operating Temperature	-40°C ~ 85°C	-55°C ~ 125°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 125°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	8-VFSOP	8-VFSOP	8-VFSOP	8-VFSOP	8-VFSOP	8-VFSOP	8-VFSOP	8-VFSOP
Product Status	Obsolete	Obsolete	Active	Active	Active	Last Time Buy	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

NC7WB66K8X (Fairchild Semiconductor) is the parametric equivalent, delivering identical on-state resistance, switch timing, bandwidth, and leakage specifications. This part maintains active product status and is the preferred direct replacement for the obsolete FSA266K8X.

SN74LVC2G66DCUR (Texas Instruments) and SN74LVC2G66DCUT (Texas Instruments) are direct substitutes with matching on-state resistance and supply voltage range. Both maintain 300MHz bandwidth and 100nA maximum leakage. SN74LVC2G66DCUR is in active production, while SN74LVC2G66DCUT is designated Last Time Buy. Both are ROHS3 compliant.

74LVC2G66DC,125 (Nexperia USA Inc.) meets all critical switching parameters with enhanced 500MHz bandwidth capability. This part supports extended operating temperature range (-40°C to 125°C) and is in active production with ROHS3 compliance.

NL7WB66USG (onsemi) maintains the same manufacturer lineage as the original part with identical on-state resistance and supply voltage specifications. Extended operating temperature range (-55°C to 125°C) provides thermal margin. Product status is obsolete; use only if existing inventory is available.

TS5A21366DCUR (Texas Instruments) offers superior on-state resistance (1Ohm) and exceptional crosstalk performance (-98dB @ 1MHz). Switch timing is significantly slower (72ns, 318ns). This part is suitable for applications prioritizing low resistance over speed.

TS5A23166DCUR (Texas Instruments) provides intermediate on-state resistance (900mOhm) with improved crosstalk (-85dB @ 1MHz) and faster switching than TS5A21366DCUR. Bandwidth is reduced to 150MHz. This part balances resistance and speed characteristics.

SN74CB3Q3306ADCUR (Texas Instruments) is a bus switch variant with different electrical classification. Restricted supply voltage range (2.3V to 3.6V) limits compatibility with the original 1.65V to 5.5V specification. This part is not recommended as a direct substitute.

Frequently Asked Questions (FAQ)

Q: Can NC7WB66K8X directly replace FSA266K8X without design changes?

A: Yes. NC7WB66K8X is a parametric equivalent with identical on-state resistance (10Ohm), switch timing (3.2ns, 4.1ns), bandwidth (300MHz), and leakage current (100nA). The 8-VFSOP package is mechanically and electrically compatible. No design modifications are required.

Q: What is the difference between the Texas Instruments 74LVC2G66 variants?

A: SN74LVC2G66DCUR and SN74LVC2G66DCUT are electrically identical with matching 10Ohm on-state resistance and 300MHz bandwidth. SN74LVC2G66DCUR is supplied in Cut Tape packaging and maintains active production status. SN74LVC2G66DCUT is supplied in Tape & Reel packaging and is designated Last Time Buy. Both are ROHS3 compliant.

Q: Why does 74LVC2G66DC,125 specify 500MHz bandwidth when the original FSA266K8X is 300MHz?

A: 74LVC2G66DC,125 is manufactured by Nexperia with enhanced bandwidth performance. The higher bandwidth does not affect compatibility; it represents improved frequency response capability. All critical switching parameters (on-state resistance, supply voltage, package) remain compatible.

Q: Are TS5A21366DCUR and TS5A23166DCUR suitable substitutes?

A: These parts share the same 2-circuit SPST-NO topology and 8-VFSOP package but differ significantly in on-state resistance and switching speed. TS5A21366DCUR (1Ohm) and TS5A23166DCUR (900mOhm) are suitable only for applications where lower resistance is prioritized over the original 10Ohm specification. Verify application requirements before selection.

Q: What is the significance of the NL7WB66USG extended temperature range?

A: NL7WB66USG operates from -55°C to 125°C compared to FSA266K8X at -40°C to 85°C. The extended range provides thermal margin for high-temperature environments. However, NL7WB66USG is obsolete; procurement may be limited. NC7WB66K8X is the recommended active-status alternative.

Q: Why is SN74CB3Q3306ADCUR not recommended as a substitute?

A: SN74CB3Q3306ADCUR is classified as a bus switch rather than an IC switch and operates at a restricted supply voltage range of 2.3V to 3.6V. The original FSA266K8X requires 1.65V to 5.5V compatibility. This voltage incompatibility makes it unsuitable for direct substitution.

Q: Can I use 74LVC2G66DC,125 in applications requiring the original -40°C to 85°C temperature range?

A: Yes. 74LVC2G66DC,125 supports -40°C to 125°C operation, which encompasses the original -40°C to 85°C range. The extended upper temperature limit does not restrict use in narrower temperature specifications.

Q: What packaging considerations apply to these substitutes?

A: All substitute parts use the 8-VFSOP (0.091", 2.30mm Width) package, maintaining mechanical and electrical compatibility with FSA266K8X. Packaging variants (Cut Tape, Tape & Reel) affect procurement and handling but not circuit performance.

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