MICROSMD035-2 Equivalent & Substitute Parts

Part Overview

The MICROSMD035-2 is a Polymeric PTC Resettable Fuse manufactured by Littelfuse Inc., rated for 6V at 350 mA hold current in a 1210 (3225 Metric) surface mount package. This component is classified as Obsolete, making substitute parts necessary for new designs and ongoing production requirements. The part provides overcurrent protection through polymeric PTC technology with a trip current of 750 mA and rapid response time of 200 ms.

Key Parameters

Parameter	Value
Voltage - Max	6V
Current - Hold (Ih) (Max)	350 mA
Current - Trip (It)	750 mA
Current - Max	40 A
Time to Trip	200 ms
Resistance - Initial (Ri) (Min)	320 mOhms
Resistance - Post Trip (R1) (Max)	1.3 Ohms
Operating Temperature	-40°C ~ 85°C
Package / Case	1210 (3225 Metric), Concave
Mounting Type	Surface Mount
Approval Agency	CSA, TUV, UL

Substitute Part Grouping Explanation

Substitution for the MICROSMD035-2 is determined by the following critical parameters: voltage rating (6V maximum), current hold rating (350 mA), current trip rating (750 mA), package form factor (1210 surface mount), and thermal operating range (-40°C to 85°C). Substitute parts are grouped into two categories:

Category 1: Direct Functional Equivalents (Same Package, Same Current Rating) Parts that maintain identical electrical specifications and package dimensions, differing only in product status or packaging format.

Category 2: Alternative Current Ratings (Different Package, Different Current Rating) Parts that operate at the same voltage and temperature range but with reduced current hold ratings and different package sizes. These require circuit-level evaluation for compatibility.

Parameter Comparison

Parameter	MICROSMD035-2	MICROSMD035F-2	MF-USMF035-2	0402L020SLKR	0402L010SLKR
Manufacturer	Littelfuse Inc.	Littelfuse Inc.	Bourns Inc.	Littelfuse Inc.	Littelfuse Inc.
Product Status	Obsolete	Active	Active	Active	Active
Voltage - Max	6V	6V	6V	6V	6V
Current - Hold (Ih) (Max)	350 mA	350 mA	350 mA	200 mA	100 mA
Current - Trip (It)	750 mA	750 mA	750 mA	500 mA	300 mA
Resistance - Initial (Ri) (Min)	320 mOhms	320 mOhms	200 mOhms	100 mOhms	150 mOhms
Resistance - Post Trip (R1) (Max)	1.3 Ohms	1.3 Ohms	1.3 Ohms	1.25 Ohms	2 Ohms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	1210 (3225 Metric)	1210 (3225 Metric)	1210 (3225 Metric)	0402 (1005 Metric)	0402 (1005 Metric)
Time to Trip	200 ms	200 ms	200 ms	1 s	1 s
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Approval Agency	CSA, TUV, UL	CSA, TUV, UL	cURus, TUV	cURus, TUV	cURus, TUV

Engineering Selection Recommendations

MICROSMD035F-2 is the primary direct substitute for MICROSMD035-2. Both parts maintain identical electrical specifications (6V, 350 mA hold current, 750 mA trip current, 200 ms response time) and package form factor (1210 surface mount). MICROSMD035F-2 is Active status with ROHS3 compliance, addressing the obsolescence of the original part. Packaging differs (Tape & Reel versus unspecified), but electrical performance is equivalent.

MF-USMF035-2 (Bourns Inc.) provides an alternative direct equivalent with matching voltage, current hold, and trip specifications in the same 1210 package. Initial resistance is lower (200 mOhms minimum versus 320 mOhms), resulting in reduced voltage drop during normal operation. This part carries AEC-Q200 automotive qualification and ROHS3 compliance. Thickness specification differs (0.033" versus 0.024"), requiring PCB layout verification for height-constrained applications.

0402L020SLKR and 0402L010SLKR are alternative current ratings in smaller 0402 packages. These parts operate at reduced hold currents (200 mA and 100 mA respectively) with extended trip times (1 s versus 200 ms). Selection requires circuit-level analysis to confirm current protection thresholds are appropriate for the application. Package size reduction may enable board space optimization but requires design re-evaluation.

Frequently Asked Questions (FAQ)

Q: Can MICROSMD035F-2 directly replace MICROSMD035-2 without circuit modification?

A: Yes. MICROSMD035F-2 maintains identical electrical specifications and package dimensions. The only differences are product status (Active versus Obsolete) and packaging format (Tape & Reel). No circuit changes are required.

Q: What is the primary reason to substitute MICROSMD035-2?

A: MICROSMD035-2 is classified as Obsolete. MICROSMD035F-2 is the direct Active equivalent from the same manufacturer and series, ensuring continued supply and ROHS3 compliance for new production.

Q: Can MF-USMF035-2 be used as a drop-in replacement?

A: MF-USMF035-2 provides electrical equivalence with identical voltage and current ratings. However, thickness differs (0.033" versus 0.024"), requiring verification that PCB assembly height tolerances accommodate the increased thickness. Initial resistance is lower, which may reduce voltage drop in the protected circuit.

Q: When would 0402L020SLKR or 0402L010SLKR be appropriate substitutes?

A: These parts are suitable only when circuit requirements permit reduced hold current ratings (200 mA or 100 mA respectively) and extended trip response times (1 s). The smaller 0402 package enables board space reduction. Circuit analysis must confirm that the lower current thresholds provide adequate protection for the application.

Q: What compliance differences exist between substitute options?

A: MICROSMD035-2 is RoHS non-compliant. All substitute parts (MICROSMD035F-2, MF-USMF035-2, 0402L020SLKR, 0402L010SLKR) are ROHS3 compliant. MF-USMF035-2 additionally carries AEC-Q200 automotive qualification.

Q: Are there package compatibility considerations for PCB assembly?

A: Yes. MICROSMD035F-2 and MF-USMF035-2 use the same 1210 footprint as the original part. The 0402 alternatives (0402L020SLKR, 0402L010SLKR) require different PCB footprints and assembly processes. Thickness variations (0.024" to 0.033") may affect reflow profiles and component placement clearances.

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