MICROSMD350LR-2 Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The MICROSMD350LR-2 is a polymeric PTC resettable fuse manufactured by Littelfuse Inc., rated for 6V at 4.6A hold current in a 1210 (3225 Metric) surface mount package. This component is classified as obsolete product status. Identifying equivalent and substitute parts is necessary due to discontinued availability and the need for active, in-stock alternatives that maintain electrical and mechanical compatibility within specified parameter tolerances.

Key Parameters

Parameter	MICROSMD350LR-2
Manufacturer	Littelfuse Inc.
Voltage - Max	6V
Current - Hold (Ih) (Max)	4.6 A
Current - Trip (It)	9 A
Current - Max	50 A
Time to Trip	10 s
Resistance - Initial (Ri) (Min)	2.5 mOhms
Mounting Type	Surface Mount
Package / Case	1210 (3225 Metric)
Size / Dimension	0.127" L x 0.102" W (3.22mm x 2.58mm)
Thickness (Max)	0.039" (1.00mm)
RoHS Status	ROHS3 Compliant
Approval Agency	CSA, UL
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the MICROSMD350LR-2 is determined by the following critical parameters:

Voltage Rating: All substitute parts must maintain 6V maximum voltage rating to ensure safe operation within the original circuit design.

Current - Hold (Ih): The hold current rating determines the maximum continuous current the fuse can carry without tripping. Substitute parts are grouped by current rating: 350mA, 500mA, 750mA, 1A, 1.1A, 1.5A, and 1.75A. The original part's 4.6A hold current is matched by the 0603L175SLYR and 0805L175SLYR parts, both rated at 1.75A Ih with 4.6A trip current.

Package / Case: The original 1210 (3225 Metric) package is not available in the active substitute lineup. Substitute parts are available in smaller packages: 0402 (1005 Metric), 0603 (1608 Metric), and 0805 (2012 Metric). Package selection depends on PCB space constraints and thermal management requirements.

Product Status: All substitute parts listed are Active status, ensuring continued availability and manufacturing support.

Compliance & Certifications: All substitutes maintain ROHS3 compliance and carry cURus/TUV certifications, meeting the original part's regulatory requirements.

Parameter Comparison

Part Number	Voltage - Max	Current - Hold (Ih) (Max)	Current - Trip (It)	Resistance - Initial (Ri) (Min)	Package / Case	Size / Dimension	Product Status	RoHS Status
MICROSMD350LR-2	6V	4.6 A	9 A	2.5 mOhms	1210 (3225 Metric)	0.127" L x 0.102" W	Obsolete	ROHS3 Compliant
0603L175SLYR	6V	1.75 A	4.6 A	5 mOhms	0603 (1608 Metric)	0.063" L x 0.032" W	Active	ROHS3 Compliant
0805L175SLYR	6V	1.75 A	4.6 A	5 mOhms	0805 (2012 Metric)	0.083" L x 0.053" W	Active	ROHS3 Compliant
0603L150SLYR	6V	1.5 A	3 A	7 mOhms	0603 (1608 Metric)	0.063" L x 0.032" W	Active	ROHS3 Compliant
0805L150SLYR	6V	1.5 A	3 A	15 mOhms	0805 (2012 Metric)	0.083" L x 0.053" W	Active	ROHS3 Compliant
0603L100SLYR	6V	1 A	1.8 A	40 mOhms	0603 (1608 Metric)	0.063" L x 0.032" W	Active	ROHS3 Compliant
0805L110SLYR	6V	1.1 A	1.8 A	30 mOhms	0805 (2012 Metric)	0.083" L x 0.053" W	Active	ROHS3 Compliant
0603L075SLYR	6V	750 mA	1.5 A	20 mOhms	0603 (1608 Metric)	0.063" L x 0.032" W	Active	ROHS3 Compliant
0603L050SLYR	6V	500 mA	1 A	70 mOhms	0603 (1608 Metric)	0.063" L x 0.032" W	Active	ROHS3 Compliant
0402L050SLKR	6V	500 mA	1 A	40 mOhms	0402 (1005 Metric)	0.039" L x 0.020" W	Active	ROHS3 Compliant
0402L035SLKR	6V	350 mA	700 mA	50 mOhms	0402 (1005 Metric)	0.039" L x 0.020" W	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Substitutes (Matched Trip Current):

The 0603L175SLYR and 0805L175SLYR are the closest electrical equivalents, both rated at 1.75A hold current with 4.6A trip current, matching the original part's trip specification. Both parts are Active status with cURus/TUV certifications and ROHS3 compliance. Selection between 0603 and 0805 packages depends on available PCB footprint space; the 0805 package provides larger contact area for improved thermal dissipation if needed.

Secondary Substitutes (Lower Current Ratings):

The 0603L150SLYR and 0805L150SLYR are rated at 1.5A hold current with 3A trip current. These parts are suitable for applications where the circuit load does not require the full 4.6A hold current specification. Both maintain Active status and full compliance certifications.

Space-Constrained Applications:

The 0402L050SLKR and 0402L035SLKR provide the smallest footprint (0402 package) for designs with severe PCB space limitations. These parts carry lower current ratings and are suitable only for circuits designed for 500mA or 350mA operation respectively.

All substitute parts maintain 6V voltage rating, ROHS3 compliance, and regulatory certifications required for direct substitution in the original circuit design.

Frequently Asked Questions (FAQ)

Q: Can the 0603L175SLYR directly replace the MICROSMD350LR-2?

A: The 0603L175SLYR matches the electrical specifications (6V, 1.75A hold, 4.6A trip) but uses a different package footprint (0603 vs. 1210). PCB layout modification is required. Verify that the smaller 0603 package dimensions (0.063" L x 0.032" W) fit within the available space on your circuit board.

Q: What is the difference between the 0603L175SLYR and 0805L175SLYR?

A: Both parts have identical electrical ratings (6V, 1.75A hold, 4.6A trip). The difference is package size: 0603 (1608 Metric) measures 0.063" x 0.032", while 0805 (2012 Metric) measures 0.083" x 0.053". The 0805 package provides a larger footprint and may offer improved thermal characteristics in high-current applications.

Q: Can I use a lower current-rated part like the 0603L150SLYR?

A: The 0603L150SLYR (1.5A hold, 3A trip) can be used only if your circuit design operates below 1.5A continuous current. Using an undersized fuse will cause nuisance tripping. Verify circuit current requirements before substitution.

Q: Are all substitute parts RoHS compliant?

A: Yes. All listed substitute parts are ROHS3 compliant and carry cURus/TUV certifications, meeting the regulatory requirements of the original MICROSMD350LR-2.

Q: What is the significance of the Resistance - Initial (Ri) parameter?

A: Initial resistance affects voltage drop across the fuse during normal operation. Lower Ri values (5 mOhms for 0603L175SLYR and 0805L175SLYR) result in minimal voltage loss compared to the original part's 2.5 mOhms. Verify that circuit voltage margins accommodate the substitute part's resistance specification.

Q: Why is the MICROSMD350LR-2 listed as obsolete?

A: Obsolete status indicates the manufacturer has discontinued production. Active substitute parts listed provide equivalent or compatible functionality with continued manufacturing support and availability.

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