74FST3345QSR Equivalent & Substitute Parts

Part Overview

The 74FST3345QSR is an 8 x 1:1 bus switch logic IC manufactured by onsemi in a 20-QSOP surface mount package. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The 74FST3345QSR operates with a single supply voltage between 4V and 5.5V across an operating temperature range of -40°C to 85°C. Identifying compatible alternatives ensures design continuity and supply chain flexibility.

Key Parameters

Parameter	Value
Manufacturer	onsemi
Part Number	74FST3345QSR
Category	Logic
Type	Bus Switch
Circuit Configuration	8 x 1:1
Independent Circuits	1
Voltage Supply	Single Supply, 4V ~ 5.5V
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package / Case	20-SSOP (0.154", 3.90mm Width)
Product Status	Obsolete
RoHS Status	RoHS non-compliant
MSL Rating	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution eligibility for the 74FST3345QSR is determined by the following critical parameters:

Bus switch topology: 8 x 1:1 configuration
Single supply voltage operation: 4V ~ 5.5V range
Operating temperature range: -40°C ~ 85°C
Surface mount packaging with compatible footprint dimensions
Independent circuit count: 1

Substitute parts are grouped into two categories:

Direct Substitutes (Same Base Function, Different Packaging): Parts sharing the 74CBT3345 base product number with identical electrical specifications but alternative package types (20-TSSOP, 20-SSOP variants). These maintain full functional equivalence with voltage supply and temperature specifications.

Parametric Equivalents (Functional Compatibility): Parts based on the 74CBT3245 series that maintain 8 x 1:1 bus switch topology, single supply operation, and compatible voltage/temperature ranges. These provide functional equivalence with minor parametric variations within acceptable design tolerances.

Parameter Comparison

Parameter	74FST3345QSR (Main)	SN74CBT3345CDBQR	SN74CBT3345CPW	SN74CBT3345CPWR	SN74CBT3345DGVR	SN74CBT3345PW	SN74CBT3345PWR	SN74CBT3245ADBQR	SN74CBT3245CDBQR
Manufacturer	onsemi	Texas Instruments	Texas Instruments	Texas Instruments	Texas Instruments	Texas Instruments	Texas Instruments	Texas Instruments	Texas Instruments
Type	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1	Bus Switch 8 x 1:1
Voltage Supply	4V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4V ~ 5.5V	4V ~ 5.5V
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	20-SSOP (0.154", 3.90mm)	20-SSOP (0.154", 3.90mm)	20-TSSOP (0.173", 4.40mm)	20-TSSOP (0.173", 4.40mm)	20-TFSOP (0.173", 4.40mm)	20-TSSOP (0.173", 4.40mm)	20-TSSOP (0.173", 4.40mm)	20-SSOP (0.154", 3.90mm)	20-SSOP (0.154", 3.90mm)
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Product Status	Obsolete	Active	Active	Active	Last Time Buy	Last Time Buy	Last Time Buy	Last Time Buy	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
MSL Rating	1 (Unlimited)	2 (1 Year)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	2 (1 Year)	2 (1 Year)

Engineering Selection Recommendations

For Active Product Status Requirement: SN74CBT3345CDBQR and SN74CBT3345CPW are the primary recommendations. SN74CBT3345CDBQR maintains the 20-SSOP package footprint identical to the 74FST3345QSR, eliminating PCB layout modifications. SN74CBT3345CPW provides the same electrical performance in a 20-TSSOP package with higher inventory availability (1558 units).

For RoHS3 Compliance: All Texas Instruments substitutes (SN74CBT3345 and SN74CBT3245 series) are ROHS3 compliant, addressing regulatory requirements where the original onsemi part does not comply.

For Parametric Equivalence with Extended Voltage Range: SN74CBT3245ADBQR and SN74CBT3245CDBQR support the full 4V ~ 5.5V voltage range matching the original specification. SN74CBT3245CDBQR is active status with 3643 units in stock, providing long-term availability assurance.

For Packaging Compatibility: Direct footprint replacement: SN74CBT3345CDBQR (20-SSOP, 0.154", 3.90mm width) Alternative footprints: SN74CBT3345CPW, SN74CBT3345CPWR, SN74CBT3345PW, SN74CBT3345PWR (20-TSSOP, 0.173", 4.40mm width) require PCB layout adjustment.

For Moisture Sensitivity: SN74CBT3345CPW and SN74CBT3345CPWR offer MSL 1 (Unlimited) rating, matching the original part's moisture handling characteristics. SN74CBT3245 variants carry MSL 2 (1 Year) rating, requiring controlled storage conditions.

Frequently Asked Questions (FAQ)

Q: Can SN74CBT3345CDBQR replace 74FST3345QSR without PCB modifications? A: Yes. SN74CBT3345CDBQR uses the identical 20-SSOP package (0.154", 3.90mm width) and pin configuration, enabling direct footprint substitution. Electrical specifications are compatible across the operating temperature and voltage ranges.

Q: What is the voltage supply difference between 74FST3345QSR (4V ~ 5.5V) and most SN74CBT3345 variants (4.5V ~ 5.5V)? A: The 74FST3345QSR supports operation down to 4V, while most SN74CBT3345 substitutes operate from 4.5V minimum. For designs requiring 4V operation, use SN74CBT3245ADBQR or SN74CBT3245CDBQR, which maintain the 4V ~ 5.5V range.

Q: Why do some substitutes have different package types (20-TSSOP vs. 20-SSOP)? A: Package variants reflect different manufacturing processes and thermal characteristics. 20-TSSOP (0.173", 4.40mm width) is slightly wider than 20-SSOP (0.154", 3.90mm width). Substitutes with different packages require PCB layout verification to confirm clearance and trace routing compatibility.

Q: What does "Last Time Buy" product status mean for SN74CBT3345DGVR, SN74CBT3345PW, and SN74CBT3345PWR? A: Last Time Buy indicates these parts are in final production phases with limited future availability. Designs should prioritize SN74CBT3345CDBQR (Active status) or SN74CBT3345CPW (Active status) for long-term supply assurance.

Q: Are all Texas Instruments substitutes RoHS3 compliant? A: Yes. All SN74CBT3345 and SN74CBT3245 variants listed are ROHS3 compliant, addressing environmental and regulatory requirements where the original onsemi 74FST3345QSR does not comply.

Q: What is the difference between MSL 1 and MSL 2 ratings? A: MSL 1 (Unlimited) allows indefinite storage without moisture absorption concerns. MSL 2 (1 Year) requires controlled storage conditions and limits shelf life to one year from manufacturing. SN74CBT3245 variants carry MSL 2 rating and require proper handling protocols.

Q: Can SN74CBT3245CDBQR be used as a functional equivalent? A: Yes. SN74CBT3245CDBQR maintains 8 x 1:1 bus switch topology, single supply operation, and compatible voltage/temperature specifications. It is a parametric equivalent suitable for designs where the specific base product number is not critical, provided the 20-SSOP package footprint is acceptable.

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