FSAT66P5X Equivalent & Substitute Parts

Part Overview

The FSAT66P5X is a single-circuit SPST-NO (Normally Open) analog switch manufactured by onsemi, housed in a 5-TSSOP (SC-70-5) package. This component features a 15Ohm on-state resistance and operates across a 1.65V to 5.5V supply range with a -3dB bandwidth of 250MHz. The part is currently classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity.

Key Parameters

Parameter	FSAT66P5X
Manufacturer	onsemi
Switch Circuit Type	SPST - NO
Multiplexer/Demultiplexer Circuit	1:1
Number of Circuits	1
On-State Resistance (Max)	15Ohm
Voltage - Supply, Single (V+)	1.65V ~ 5.5V
Switch Time (Ton, Toff) (Max)	4.5ns, 5.5ns
-3dB Bandwidth	250MHz
Charge Injection	0.05pC
Channel Capacitance (CS(off), CD(off))	6pF
Current - Leakage (IS(off)) (Max)	10µA
Operating Temperature	-40°C ~ 85°C (TA)
Package / Case	5-TSSOP, SC-70-5, SOT-353
Product Status	Obsolete
RoHS Status	Not specified
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the FSAT66P5X is determined by the following critical parameters:

Switch Circuit Type: SPST-NO topology (Normally Open configuration)
Package Compatibility: 5-TSSOP / SC-70-5 / SOT-353 form factor
Supply Voltage Range: Minimum 1.65V operation required
On-State Resistance: Maximum 15Ohm specification
Operating Temperature Range: -40°C to 85°C minimum
Switching Speed: Ton/Toff performance within 4.5ns/5.5ns envelope
Bandwidth: -3dB bandwidth of 250MHz or higher

Substitute parts are grouped into two categories:

Category A - Direct Functional Equivalents (SPST-NO, 10Ohm Ron, SC-70-5 Package) These parts maintain identical circuit topology, package form factor, and superior electrical performance characteristics.

Category B - Compatible Alternatives (SPST-NO, Higher Ron or Different Package) These parts satisfy the core SPST-NO topology and voltage requirements but feature higher on-state resistance or alternative package options, suitable for applications with relaxed impedance requirements.

Parameter Comparison

Part Number	Manufacturer	Switch Circuit	Ron (Max)	V+ Range	Ton/Toff (Max)	-3dB BW	Package	Status	Temp Range
FSAT66P5X	onsemi	SPST-NO	15Ohm	1.65V~5.5V	4.5ns/5.5ns	250MHz	SC-70-5	Obsolete	-40°C~85°C
SN74LVC1G66DCKT	Texas Instruments	SPST-NO	10Ohm	1.65V~5.5V	4.2ns/5ns	300MHz	SC-70-5	Last Time Buy	-40°C~85°C
SN74LVC1G66DCKR	Texas Instruments	SPST-NO	10Ohm	1.65V~5.5V	4.2ns/5ns	300MHz	SC-70-5	Active	-40°C~85°C
74LVC1G66GW,125	Nexperia USA Inc.	SPST-NO	10Ohm	1.65V~5.5V	4.2ns/5ns	500MHz	5-TSSOP	Active	-40°C~125°C
74LVC1G66GV,125	Nexperia USA Inc.	SPST-NO	10Ohm	1.65V~5.5V	4.2ns/5ns	500MHz	SC-74A	Active	-40°C~125°C
74AHC1G66GW-Q100H	Nexperia USA Inc.	SPST-NO	22Ohm	2V~5.5V	11ns/11ns	280MHz	5-TSSOP	Active	-40°C~125°C
74HCT1G66GW-Q100H	Nexperia USA Inc.	SPST-NO	95Ohm	4.5V~5.5V	30ns/44ns	200MHz	5-TSSOP	Active	-40°C~125°C
TS5A3166DCKR	Texas Instruments	SPST-NO	900mOhm	1.65V~5.5V	7ns/11.5ns	200MHz	SC-70-5	Active	-40°C~85°C
ISL43L110IHZ-T	Renesas Electronics Corporation	SPST-NO	220mOhm (Typ)	1.1V~4.5V	15ns/10ns	Not specified	SC-70-5	Active	-40°C~85°C
74LVC1G384GW,125	Nexperia USA Inc.	SPST-NC	10Ohm	1.65V~5.5V	4.2ns/5ns	500MHz	5-TSSOP	Active	-40°C~125°C
74LVC1G384GV,125	Nexperia USA Inc.	SPST-NC	10Ohm	1.65V~5.5V	4.2ns/5ns	500MHz	SC-74A	Active	-40°C~125°C

Engineering Selection Recommendations

Primary Substitutes (Highest Compatibility)

SN74LVC1G66DCKR and SN74LVC1G66DCKT from Texas Instruments are the most direct substitutes. Both maintain SPST-NO topology, SC-70-5 package, 1.65V to 5.5V supply range, and -40°C to 85°C operating temperature. The 10Ohm on-state resistance is lower than the FSAT66P5X specification, providing improved performance margin. SN74LVC1G66DCKR is currently in active production status, while SN74LVC1G66DCKT is designated Last Time Buy. Both are RoHS3 compliant with MSL 1 rating.

Secondary Substitutes (Extended Temperature Range)

74LVC1G66GW,125 and 74LVC1G66GV,125 from Nexperia USA Inc. offer identical electrical specifications to the Texas Instruments parts with extended operating temperature range (-40°C to 125°C). Both are active products with RoHS3 compliance. 74LVC1G66GW,125 is packaged in 5-TSSOP, while 74LVC1G66GV,125 uses SC-74A form factor. These are suitable for applications requiring wider temperature operation.

Alternative Substitutes (Relaxed Impedance Requirements)

74AHC1G66GW-Q100H features 22Ohm on-state resistance with automotive qualification (AEC-Q100) and extended temperature range. Suitable for applications where higher impedance is acceptable. Minimum supply voltage is 2V, which may limit use in ultra-low-voltage designs.

74HCT1G66GW-Q100H provides 95Ohm on-state resistance with automotive qualification. Applicable only to applications with minimal impedance sensitivity. Minimum supply voltage is 4.5V, restricting use to standard 5V logic systems.

Specialized Alternatives (High-Impedance Applications)

TS5A3166DCKR and ISL43L110IHZ-T feature significantly higher on-state resistance (900mOhm and 220mOhm respectively) and are suitable only for applications where impedance is not a critical parameter. Both maintain SC-70-5 packaging and 1.65V to 5.5V supply compatibility.

Not Recommended for Direct Substitution

74LVC1G384GW,125 and 74LVC1G384GV,125 implement SPST-NC (Normally Closed) topology, which is functionally incompatible with the FSAT66P5X SPST-NO requirement.

Frequently Asked Questions (FAQ)

Q: Can I use SN74LVC1G66DCKR as a direct replacement for FSAT66P5X?

A: Yes. Both parts maintain SPST-NO topology, SC-70-5 package, 1.65V to 5.5V supply range, and -40°C to 85°C operating temperature. The SN74LVC1G66DCKR features 10Ohm on-state resistance compared to FSAT66P5X's 15Ohm, providing superior electrical performance. The part is currently in active production status.

Q: What is the difference between 74LVC1G66GW,125 and SN74LVC1G66DCKR?

A: Both parts share identical electrical specifications (10Ohm Ron, 1.65V to 5.5V supply, 4.2ns/5ns switching time). The primary differences are manufacturer (Nexperia vs. Texas Instruments), operating temperature range (74LVC1G66GW,125 extends to 125°C), and packaging options. 74LVC1G66GW,125 is available in 5-TSSOP form factor.

Q: Can I use 74HCT1G66GW-Q100H as a substitute?

A: 74HCT1G66GW-Q100H maintains SPST-NO topology and SC-70-5 package compatibility but features 95Ohm on-state resistance and requires minimum 4.5V supply voltage. This part is suitable only for applications where impedance is not performance-critical and operation is restricted to 4.5V to 5.5V supply range.

Q: What does "Last Time Buy" status mean for SN74LVC1G66DCKT?

A: Last Time Buy designation indicates that Texas Instruments will accept orders for a limited period before discontinuing the part. Existing inventory remains available, but long-term availability is not guaranteed. SN74LVC1G66DCKR, which is in active production status, is recommended for new designs requiring extended supply assurance.

Q: Are 74LVC1G384GW,125 and 74LVC1G384GV,125 compatible with FSAT66P5X?

A: No. These parts implement SPST-NC (Normally Closed) topology, which is functionally opposite to the FSAT66P5X SPST-NO (Normally Open) configuration. They are not suitable substitutes for this application.

Q: What is the significance of MSL 1 (Unlimited) rating?

A: MSL 1 indicates Moisture Sensitivity Level 1, meaning the component has unlimited shelf life without special moisture control measures. This simplifies inventory management and reduces handling requirements compared to higher MSL ratings.

Q: Can I use ISL43L110IHZ-T for low-impedance switching applications?

A: ISL43L110IHZ-T features 220mOhm typical on-state resistance, which is significantly higher than FSAT66P5X's 15Ohm specification. This part is suitable only for applications where impedance is not a critical design parameter, such as high-impedance signal routing or logic-level switching with minimal current requirements.

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