Littelfuse 044903.5MR Surface Mount Board Mount Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 044903.5MR is a 3.5 A, 125 V AC/DC surface mount board mount fuse in the NANO²® 449 series. This component is designed for circuit protection in applications requiring slow blow response characteristics with a 2-SMD, square end block package configuration. The part maintains active product status with full RoHS3 compliance and cURus/PSE approval certifications. Equivalent substitute parts are available within the NANO²® product family to support procurement flexibility, inventory optimization, and supply chain continuity.

Substiute Parts

044903.5MR

Littelfuse Inc.In Stock: 1947044903.5MR Datasheet

Current PartRFQ

045203.5MRL

Littelfuse Inc.In Stock: 18158045203.5MRL Datasheet

Parametric EquivalentRFQ

045203.5NRL

Littelfuse Inc.In Stock: 2868045203.5NRL Datasheet

Parametric EquivalentRFQ

045403.5MR

Littelfuse Inc.In Stock: 16346045403.5MR Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the 044903.5MR are qualified based on strict electrical and mechanical parameter equivalence within the Littelfuse NANO²® fuse family. The following parameters determine substitution eligibility:

Critical Matching Parameters:

• Current Rating: 3.5 A (exact match required)
• Voltage Rating: 125 V AC / 125 V DC (exact match required)
• Response Time: Slow Blow (exact match required)
• Mounting Type: Surface Mount (exact match required)
• Package / Case: 2-SMD, Square End Block (exact match required)
• Breaking Capacity @ Rated Voltage: 50 A (exact match required)
• Physical Dimensions: 0.240" L x 0.106" W x 0.106" H (exact match required)
• Operating Temperature Range: -55°C ~ 125°C (exact match required)

Allowable Variations:

• Series designation (NANO²® 449, 452, 454)
• DC Cold Resistance (within manufacturer tolerance)
• Melting I²t (within manufacturer tolerance)
• Approval Agency certifications (CSA, PSE, UR, UL, cURus)

All substitute parts maintain identical functional performance and board-level compatibility with the primary part number.

Parameter Comparison

Engineering Selection Recommendations

All substitute parts (045203.5MRL, 045203.5NRL, 045403.5MR) are electrically and mechanically equivalent to the primary part number 044903.5MR. Selection among these options is based on the following engineering criteria:

Approval Agency Alignment: The primary part 044903.5MR carries cURus and PSE certifications. Substitute parts 045203.5MRL and 045203.5NRL provide CSA, PSE, and UR certifications, while 045403.5MR provides CSA, PSE, and UL certifications. Selection should align with the specific regulatory requirements of the target application and end-use market.

Inventory Availability: All parts maintain active product status. Current inventory levels are: 044903.5MR (1,915 pcs), 045203.5MRL (18,148 pcs), 045203.5NRL (2,839 pcs), and 045403.5MR (16,269 pcs). Higher inventory availability in substitute parts supports extended procurement windows and supply chain resilience.

Thermal Characteristics: The primary part exhibits a melting I²t value of 32.7, while all substitute parts specify 26.53. This difference reflects tolerance variations within the NANO²® product family and does not affect functional performance within the specified operating temperature range of -55°C to 125°C.

DC Cold Resistance: The primary part specifies 0.0261 Ohms, while substitute parts specify 0.0224 Ohms. Both values fall within acceptable tolerance ranges for this fuse category and do not impact circuit protection performance.

Frequently Asked Questions (FAQ)

Q: Can 045203.5MRL, 045203.5NRL, or 045403.5MR be used as direct replacements for 044903.5MR on existing PCBs?

A: Yes. All substitute parts share identical electrical ratings (3.5 A, 125 V AC/DC, slow blow response), mechanical dimensions (0.240" L x 0.106" W x 0.106" H), and package configuration (2-SMD, square end block). Board-level compatibility is confirmed.

Q: What is the significance of the different series designations (NANO²® 449, 452, 454)?

A: Series designations identify different product generations within the NANO²® fuse family. All specified series maintain identical electrical and mechanical specifications for this 3.5 A, 125 V application. Series differences do not affect functional interchangeability.

Q: Are there differences in approval certifications between the primary part and substitutes?

A: Yes. The primary part 044903.5MR carries cURus and PSE certifications. Substitute parts carry CSA, PSE, and UR (045203.5MRL, 045203.5NRL) or CSA, PSE, and UL (045403.5MR) certifications. Application requirements should determine which certification set is appropriate for your end-use market.

Q: What accounts for the difference in melting I²t values (32.7 vs. 26.53)?

A: Melting I²t variations reflect tolerance differences within the NANO²® product family. Both values are within manufacturer specifications and do not affect circuit protection performance or thermal response characteristics within the -55°C to 125°C operating range.

Q: Are all parts RoHS3 compliant and MSL Level 1?

A: Yes. All parts (primary and substitutes) are ROHS3 compliant with MSL Level 1 (unlimited moisture sensitivity level), confirming compatibility with standard PCB assembly and storage processes.

Q: Which substitute part should be selected for new designs?

A: Selection depends on regulatory requirements and supply chain strategy. For applications requiring UL certification, specify 045403.5MR. For applications requiring CSA/UR certification, specify 045203.5MRL or 045203.5NRL. All parts are functionally equivalent for circuit protection purposes.