MF-USML300-2 PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The MF-USML300-2 is a Polymeric PTC Resettable Fuse manufactured by Bourns Inc., rated for 6V at 3A hold current in a 1210 (3225 Metric) surface mount package. This part is classified as Obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and procurement planning. The Multifuse® MF-USML series provides polymeric PTC protection suitable for circuit protection applications requiring automatic reset capability after fault conditions are cleared.

Key Parameters

Parameter	Value
Voltage - Max	6V
Current - Hold (Ih) (Max)	3 A
Current - Trip (It)	6 A
Current - Max	50 A
Mounting Type	Surface Mount
Package / Case	1210 (3225 Metric), Concave
Operating Temperature	-40°C ~ 85°C
Type	Polymeric
RoHS Status	ROHS3 Compliant
Approval Agency	cURus, TUV

Substitute Part Grouping Explanation

Substitution eligibility for the MF-USML300-2 is determined by the following critical parameters:

Voltage rating: 6V maximum
Current hold (Ih): 3A maximum
Current trip (It): 6A
Package type: 1210 (3225 Metric), Concave surface mount
Polymeric PTC type classification
Operating temperature range: -40°C to 85°C
Regulatory compliance: cURus and TUV approval

The substitute part MF-USML300/6-2 meets all primary electrical and mechanical requirements. Variations in secondary parameters such as time to trip (4s vs. 5s), initial resistance (4 mOhms vs. 3 mOhms), and post-trip resistance (18 mOhms vs. 24 mOhms) remain within acceptable tolerance ranges for polymeric PTC fuse operation. Packaging format differs (loose vs. Tape & Reel), but the component footprint and electrical interface remain identical.

Parameter Comparison

Parameter	MF-USML300-2 (Main)	MF-USML300/6-2 (Substitute)
Manufacturer	Bourns Inc.	Bourns Inc.
Series	Multifuse®, MF-USML	Multifuse®, MF-USML/X
Product Status	Obsolete	Active
Type	Polymeric	Polymeric
Voltage - Max	6V	6V
Current - Hold (Ih) (Max)	3 A	3 A
Current - Trip (It)	6 A	6 A
Current - Max	50 A	50 A
Time to Trip	4 s	5 s
Resistance - Initial (Ri) (Min)	4 mOhms	3 mOhms
Resistance - Post Trip (R1) (Max)	18 mOhms	24 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C
Mounting Type	Surface Mount	Surface Mount
Package / Case	1210 (3225 Metric), Concave	1210 (3225 Metric), Concave
Size / Dimension	0.127" L x 0.102" W (3.22mm x 2.58mm)	0.127" L x 0.101" W (3.22mm x 2.58mm)
Thickness (Max)	0.024" (0.60mm)	0.047" (1.20mm)
Approval Agency	cURus, TUV	cURus, TUV
RoHS Status	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	2A (4 Weeks)	2A (4 Weeks)
REACH Status	REACH Unaffected	REACH Unaffected
ECCN	EAR99	EAR99
HTSUS	8533.40.8070	8533.40.8070

Engineering Selection Recommendations

The MF-USML300/6-2 is the direct functional equivalent for the obsolete MF-USML300-2. Both components carry identical regulatory certifications (cURus, TUV) and comply with ROHS3 and REACH requirements. The substitute part is currently in active production status, ensuring long-term availability and supply chain continuity.

The MF-USML300/6-2 is supplied in Tape & Reel (TR) packaging format, whereas the original part number references loose packaging. This distinction affects procurement and assembly processes but does not alter electrical or mechanical compatibility. The substitute maintains the same 1210 (3225 Metric) footprint and concave surface mount configuration.

Minor variations in secondary electrical parameters (time to trip, initial resistance, and post-trip resistance) fall within normal manufacturing tolerances for polymeric PTC fuse technology and do not compromise circuit protection performance in equivalent applications.

Frequently Asked Questions (FAQ)

Q: Can MF-USML300/6-2 be used as a direct replacement for MF-USML300-2 on existing PCBs?

A: Yes. Both parts share identical voltage ratings (6V), current hold specifications (3A), current trip values (6A), and 1210 (3225 Metric) surface mount package geometry. PCB footprints are compatible without modification.

Q: What is the significance of the packaging difference (loose vs. Tape & Reel)?

A: Packaging format affects procurement and assembly logistics only. The MF-USML300/6-2 Tape & Reel format is standard for high-volume manufacturing and provides improved handling efficiency. The electrical and mechanical component specifications remain unchanged.

Q: Why does the substitute part have a different thickness specification (0.047" vs. 0.024")?

A: The thickness variation reflects manufacturing tolerance ranges within the polymeric PTC fuse product line. Both values remain within acceptable limits for 1210 package class components and do not affect PCB assembly clearance or electrical performance.

Q: Are regulatory certifications equivalent between the two parts?

A: Yes. Both MF-USML300-2 and MF-USML300/6-2 carry cURus and TUV approvals, maintain ROHS3 compliance, and are classified as REACH Unaffected. Regulatory status is identical.

Q: What is the impact of the 1-second difference in time to trip (4s vs. 5s)?

A: Time to trip variation is a normal characteristic of polymeric PTC fuse technology and reflects manufacturing process tolerances. Both specifications remain within the Multifuse® series design parameters and do not alter the protective function in equivalent circuit applications.

Q: Is the MF-USML300/6-2 suitable for new designs?

A: Yes. The MF-USML300/6-2 is classified as Active product status with current manufacturing availability, making it appropriate for both replacement and new design applications requiring 6V, 3A hold current PTC resettable fuse protection in 1210 surface mount packages.

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