RUSBF120-AP Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUSBF120-AP is a polymeric PTC resettable fuse manufactured by Littelfuse Inc. in the PolySwitch® RUSBF series. This component provides overcurrent protection with a 6V maximum voltage rating and 1.2A hold current specification. The part is currently listed as obsolete, which necessitates identification of active equivalent alternatives for ongoing design support and procurement.

Key Parameters

Parameter	Value
Voltage - Max	6V
Current - Hold (Ih) (Max)	1.2 A
Current - Trip (It)	2 A
Current - Max	40 A
Time to Trip	500 ms
Resistance - Initial (Ri) (Min)	70 mOhms
Resistance - Post Trip (R1) (Max)	140 mOhms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Lead Spacing	0.201" (5.10mm)

Substitute Part Grouping Explanation

Substitution eligibility for the RUSBF120-AP is determined by strict equivalence across the following critical parameters:

Voltage rating: 6V maximum
Current hold specification: 1.2A maximum
Current trip specification: 2A
Maximum current capacity: 40A
Time to trip: 500 milliseconds
Initial resistance: 70 mOhms minimum
Post-trip resistance: 140 mOhms maximum
Operating temperature range: -40°C to 85°C
Mounting configuration: Through hole radial disc package
Lead spacing tolerance: 5.10mm nominal

The RUSBF120-2 meets all specified electrical and mechanical parameters and represents the active production equivalent within the PolySwitch® RUSBF series.

Parameter Comparison

Parameter	RUSBF120-AP (Main)	RUSBF120-2 (Substitute)
Manufacturer	Littelfuse Inc.	Littelfuse Inc.
Series	PolySwitch®, RUSBF	PolySwitch®, RUSBF
Product Status	Obsolete	Active
Type	Polymeric	Polymeric
Voltage - Max	6V	6V
Current - Hold (Ih) (Max)	1.2 A	1.2 A
Current - Trip (It)	2 A	2 A
Current - Max	40 A	40 A
Time to Trip	500 ms	500 ms
Resistance - Initial (Ri) (Min)	70 mOhms	70 mOhms
Resistance - Post Trip (R1) (Max)	140 mOhms	140 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C
Mounting Type	Through Hole	Through Hole
Package / Case	Radial, Disc	Radial, Disc
Size / Dimension	0.272" L x 0.122" W (6.90mm x 3.10mm)	0.272" L x 0.122" W (6.90mm x 3.10mm)
Height - Seated (Max)	0.461" (11.70mm)	0.461" (11.70mm)
Lead Spacing	0.201" (5.10mm)	0.200" (5.08mm)
Approval Agency	CSA, TUV, UL	CSA, TUV, UL
RoHS Status	ROHS3 Compliant	ROHS3 Compliant
REACH Status	REACH Unaffected	REACH Unaffected
ECCN	EAR99	EAR99
HTSUS	8533.40.8070	8533.40.8070

Engineering Selection Recommendations

The RUSBF120-2 is the direct active equivalent for the obsolete RUSBF120-AP. Both components share identical electrical specifications, thermal operating range, and mechanical form factor. The RUSBF120-2 maintains full compliance with CSA, TUV, and UL certifications, as well as RoHS3 and REACH regulatory requirements.

Lead spacing differs by 0.02mm (5.10mm versus 5.08mm), which falls within standard PCB tolerance for through-hole radial component placement and does not constitute a functional incompatibility.

The RUSBF120-2 is available in cut tape packaging with significantly higher inventory availability (3990 units) compared to the obsolete RUSBF120-AP, supporting both new design implementation and legacy system maintenance.

Frequently Asked Questions (FAQ)

Q: Can RUSBF120-2 be used as a direct replacement for RUSBF120-AP in existing designs?

A: Yes. The RUSBF120-2 is electrically and mechanically equivalent. All protection characteristics, voltage ratings, current thresholds, and thermal specifications are identical. The minor lead spacing variance (0.02mm) is within standard PCB manufacturing tolerances for through-hole components.

Q: What is the difference between the two part numbers?

A: The RUSBF120-AP is an obsolete variant. The RUSBF120-2 is the active production equivalent from Littelfuse Inc. Both are PolySwitch® RUSBF series polymeric PTC resettable fuses with identical electrical and mechanical characteristics.

Q: Are there packaging differences between these parts?

A: The RUSBF120-AP was supplied in standard packaging. The RUSBF120-2 is available in cut tape (CT) packaging, which is standard for high-volume procurement and automated assembly processes.

Q: Do both parts meet the same regulatory and compliance standards?

A: Yes. Both the RUSBF120-AP and RUSBF120-2 carry CSA, TUV, and UL approvals. Both are ROHS3 compliant and REACH unaffected, with identical ECCN (EAR99) and HTSUS (8533.40.8070) classifications.

Q: What are the key electrical parameters that define substitution compatibility?

A: Substitution is based on matching voltage rating (6V), hold current (1.2A), trip current (2A), maximum current (40A), time to trip (500ms), initial resistance (70 mOhms minimum), and post-trip resistance (140 mOhms maximum). The RUSBF120-2 meets all these specifications.

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