MICROSMD450LR-2 Equivalent & Substitute Parts

Part Overview

The MICROSMD450LR-2 is a polymeric PTC resettable fuse manufactured by Littelfuse Inc., rated for 5V at 4.5A hold current in a 1210 (3225 Metric) surface mount package. This component is classified as obsolete, making identification of equivalent substitute parts essential for ongoing design support and production continuity. Substitute parts must maintain electrical compatibility across voltage, current, and thermal characteristics while accommodating the 1210 package form factor.

Substiute Parts

MICROSMD450LR-2

Littelfuse Inc.In Stock: 1030MICROSMD450LR-2 Datasheet

Current PartRFQ

1210L450SLWR

Littelfuse Inc.In Stock: 42141210L450SLWR Datasheet

MFR RecommendedRFQ

PTSLR12106V450

Eaton - Electronics DivisionIn Stock: 8612PTSLR12106V450 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the MICROSMD450LR-2 is determined by the following critical parameters:

• Voltage Rating: Substitute parts must have a maximum voltage rating equal to or greater than 5V to ensure safe operation within the original circuit design envelope.
• Current - Hold (Ih): Substitute parts must maintain a 4.5A hold current specification to preserve circuit protection characteristics.
• Current - Trip (It): Substitute parts must maintain a 9A trip current to ensure consistent fault response.
• Package / Case: All substitutes must use the 1210 (3225 Metric) surface mount package to ensure mechanical and electrical compatibility with existing PCB layouts.
• Mounting Type: Surface mount compatibility is required for direct replacement.
• Compliance: RoHS3 compliance is mandatory for regulatory alignment.

The identified substitute parts meet these criteria while offering improved product status (active vs. obsolete) and enhanced availability.

Parameter Comparison

Engineering Selection Recommendations

1210L450SLWR (Littelfuse Inc., POLY-FUSE® LoRho Series)

This part is recommended as the primary substitute. It maintains identical hold and trip current specifications (4.5A and 9A respectively) and is rated for 6V operation, which exceeds the original 5V requirement. The part is active in production with 4200 units in stock. Certifications include cURus and TUV approval, providing broader regulatory coverage than the original UL-only certification. Moisture sensitivity is improved to MSL 1 (Unlimited) compared to the original MSL 2A (4 Weeks).

PTSLR12106V450 (Eaton - Electronics Division, PTSLR1210 Series)

This part serves as a secondary substitute from an alternative manufacturer. It maintains identical hold and trip current specifications and is rated for 6V operation. The part is active in production with 8536 units in stock. Certifications include cURus and TUV approval. Initial resistance matches the original specification at 2 mOhms minimum. This option provides supply chain diversification.

Both substitutes are compatible with the original circuit design due to their higher voltage ratings, which provide additional safety margin in the 5V application. The identical current characteristics ensure equivalent protection behavior.

Frequently Asked Questions (FAQ)

Q: Can I use a 6V-rated fuse in a 5V circuit?

A: Yes. The 6V rating indicates the maximum voltage the fuse can safely interrupt. Using a higher-rated fuse in a lower-voltage application does not compromise safety or performance. The fuse will operate identically to the original 5V part in a 5V circuit.

Q: Are the hold and trip currents identical across all three parts?

A: Yes. All three parts maintain 4.5A hold current (Ih) and 9A trip current (It), ensuring identical circuit protection behavior.

Q: What is the significance of the resistance specifications?

A: Initial resistance (Ri) and post-trip resistance (R1) affect voltage drop and thermal characteristics. The substitute parts show slightly higher post-trip resistance (14 mOhms vs. 8 mOhms), which is acceptable as it remains within the polymeric PTC fuse design envelope and does not affect protection function.

Q: Does the 1210 package dimension differ between parts?

A: The package designation is identical (1210 / 3225 Metric, Concave) for all three parts. Dimensional variations in thickness (1.00mm vs. 1.20mm) are within standard PCB assembly tolerances and do not affect placement or solderability.

Q: What is the difference between MSL 2A and MSL 1?

A: MSL (Moisture Sensitivity Level) indicates storage requirements. MSL 2A requires controlled storage for 4 weeks; MSL 1 has unlimited shelf life. The substitute parts offer improved moisture tolerance, reducing storage and handling constraints.

Q: Which substitute should I select for new designs?

A: For new designs, either substitute is acceptable. 1210L450SLWR offers the same manufacturer continuity (Littelfuse); PTSLR12106V450 provides supply chain diversification through Eaton.