SST 375/5K Equivalent & Substitute Parts

Part Overview

The SST 375/5K is a 375 mA surface mount board mount fuse manufactured by Bel Fuse Inc., rated for 125 V AC/DC operation with slow blow response characteristics. This part is classified as obsolete, making identification of functionally equivalent active alternatives essential for ongoing design support and procurement continuity. The SST 375/5K operates across the industrial temperature range of -55°C to 125°C and meets multiple international compliance standards including AEC-Q200, CE, and CSA certifications.

Key Parameters

Parameter	Value
Current Rating	375 mA
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Slow Blow
Mounting Type	Surface Mount
Package / Case	2-SMD, Square End Block
Operating Temperature Range	-55°C to 125°C
Size / Dimension	0.240" L x 0.100" W x 0.100" H (6.10mm x 2.54mm x 2.54mm)
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution eligibility for the SST 375/5K is determined by strict equivalence across the following critical parameters:

Mandatory Matching Parameters:

Current Rating: 375 mA (exact match required)
Voltage Rating AC: 125 V (exact match required)
Voltage Rating DC: 125 V (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)
Operating Temperature Range: -55°C to 125°C (minimum requirement)

Allowable Variation Parameters:

Breaking Capacity @ Rated Voltage: Variations permitted (50A to 100A DC acceptable)
Melting I²t: Variations permitted within thermal design tolerance (0.088 to 0.15 range)
DC Cold Resistance: Variations permitted (0.72 to 1.513 Ohms acceptable)
Physical Dimensions: Minor variations permitted (width/height up to 0.106" acceptable for 2-SMD form factor)
Approval Agencies: Subset of original certifications acceptable if core compliance maintained

Substitute parts are grouped into two categories: Bel Fuse 0680L series (active status, direct lineage) and Littelfuse NANO² series (active status, cross-manufacturer equivalents).

Parameter Comparison

Part Number	Manufacturer	Current Rating	Voltage AC/DC	Response Time	Breaking Capacity	Melting I²t	DC Cold Resistance	Product Status	Packaging
SST 375/5K	Bel Fuse Inc.	375 mA	125V / 125V	Slow Blow	50A	0.15	0.72 Ω	Obsolete	Bulk
0680L0375-01	Bel Fuse	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0680L0375-05	Bel Fuse Inc.	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0680L0375-11	Bel Fuse	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0680L0375-15	Bel Fuse Inc.	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0680L0375-21	Bel Fuse	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0680L0375-25	Bel Fuse	375 mA	125V / 125V	Slow Blow	50A AC, 100A DC	0.14	0.93 Ω	Active	Tape & Reel
0449.375MR	Littelfuse	375 mA	125V / 125V	Slow Blow	50A	0.088	1.513 Ω	Active	Tape & Reel
0452.375MRL	Littelfuse Inc.	375 mA	125V / 125V	Slow Blow	50A	0.101	1.2 Ω	Active	Tape & Reel
0452.375NRL	Littelfuse Inc.	375 mA	125V / 125V	Slow Blow	50A	0.101	1.2 Ω	Active	Tape & Reel
0454.375MR	Littelfuse	375 mA	125V / 125V	Slow Blow	50A	0.101	1.2 Ω	Active	Tape & Reel

Engineering Selection Recommendations

Bel Fuse 0680L Series (0680L0375-01, 0680L0375-05, 0680L0375-11, 0680L0375-15, 0680L0375-21, 0680L0375-25)

These parts represent the direct active-status successor line to the obsolete SST 375/5K. All variants maintain identical electrical specifications (375 mA, 125V AC/DC, slow blow response) and are manufactured by the original supplier. The 0680L series carries AEC-Q200, CE, and cURus certifications, providing continuity with automotive and industrial compliance requirements. These parts are supplied in Tape & Reel packaging, standard for high-volume production environments. The variants differ in internal construction or tape configuration only; electrical performance is equivalent across all 0680L0375 designations.

Littelfuse NANO² Series (0449.375MR, 0452.375MRL, 0452.375NRL, 0454.375MR)

These cross-manufacturer alternatives meet all mandatory electrical parameters and maintain the same 2-SMD form factor. The NANO² series operates within the same temperature range and achieves ROHS3 compliance. Littelfuse parts carry CSA and UR certifications. Physical dimensions vary slightly (0.106" width/height versus 0.100"), remaining within acceptable 2-SMD board mount tolerances. Melting I²t values range from 0.088 to 0.101, representing tighter thermal response compared to the original SST 375/5K (0.15). DC cold resistance values are higher (1.2 to 1.513 Ohms) than the original part.

Selection Basis:

For direct replacement requiring minimal design validation, select from the Bel Fuse 0680L series. For cross-manufacturer sourcing or supply chain diversification, Littelfuse NANO² parts are electrically equivalent. All substitute parts are active-status components with current manufacturing support and established supply chains.

Frequently Asked Questions (FAQ)

Q: Can I substitute a Littelfuse NANO² part for the original SST 375/5K without circuit modification?

A: Yes. All NANO² variants (0449.375MR, 0452.375MRL, 0452.375NRL, 0454.375MR) meet the mandatory electrical specifications: 375 mA current rating, 125V AC/DC voltage rating, and slow blow response. Physical dimensions vary slightly (width/height 0.106" versus 0.100"), but both conform to 2-SMD board mount standards. The higher DC cold resistance (1.2-1.513 Ohms versus 0.72 Ohms) and lower melting I²t (0.088-0.101 versus 0.15) represent tighter thermal characteristics, which are acceptable for the same circuit application.

Q: What is the difference between the various Bel Fuse 0680L0375 part numbers?

A: All 0680L0375 variants (01, 05, 11, 15, 21, 25) are electrically identical. They differ in tape configuration, reel size, or internal construction specifications. Selection among these variants depends on your procurement and assembly equipment compatibility, not electrical performance.

Q: Is the SST 375/5K still available for purchase?

A: The SST 375/5K is classified as obsolete. However, 881 pieces remain in current inventory. For new designs or long-term production, transition to active-status alternatives: Bel Fuse 0680L series (22,784 pieces of 0680L0375-05 available) or Littelfuse NANO² series (15,400 pieces of 0452.375MRL available).

Q: Do all substitute parts carry the same certifications as the original SST 375/5K?

A: The original SST 375/5K carries AEC-Q200, CE, CSA, and cULus certifications. Bel Fuse 0680L series carries AEC-Q200, CE, and cURus certifications. Littelfuse NANO² series carries CSA and UR certifications. All parts maintain ROHS3 compliance and unlimited moisture sensitivity level (MSL 1). Verify specific certification requirements for your application before final selection.

Q: What is the impact of different melting I²t values on circuit protection?

A: Melting I²t determines the thermal energy required to melt the fuse element. The original SST 375/5K has I²t of 0.15, while Littelfuse NANO² parts range from 0.088 to 0.101. Lower I²t values indicate faster thermal response to overcurrent conditions. For the same 375 mA current rating and slow blow response classification, these variations remain within acceptable protection characteristics for standard circuit applications.

Q: Can I mix Bel Fuse and Littelfuse parts in the same production batch?

A: Yes, provided your circuit design and compliance documentation account for the physical dimension variation (0.100" versus 0.106" width/height) and the different DC cold resistance values. Both manufacturers' parts meet the mandatory electrical specifications and operate identically from a circuit protection standpoint. Verify PCB footprint compatibility and thermal design margins before implementation.

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