ASMD250F-2 Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The ASMD250F-2 is an active polymeric PTC resettable fuse manufactured by Littelfuse Inc. in the PolySwitch® ASMD series. This surface mount 2-SMD component is rated for 16V maximum voltage with a 1.97A hold current and 5A trip current. The device is designed for overcurrent protection in electronic circuits and is AEC-Q200 rated for automotive applications. Substitute parts are identified when equivalent electrical and mechanical parameters align within the allowed specifications for this product category.

Key Parameters

Parameter	Value	Unit
Voltage - Max	16	V
Current - Hold (Ih) (Max)	1.97	A
Current - Trip (It)	5	A
Current - Max	40	A
Time to Trip	30	s
Resistance - Initial (Ri) (Min)	35	mOhms
Resistance - Post Trip (R1) (Max)	85	mOhms
Operating Temperature	-40 to 85	°C
Mounting Type	Surface Mount	—
Package / Case	2-SMD	—
Size / Dimension	8.70 x 6.36	mm
Thickness (Max)	3.00	mm
RoHS Status	ROHS3 Compliant	—
Ratings	AEC-Q200	—

Substitute Part Grouping Explanation

Substitution of the ASMD250F-2 is determined by the following critical parameters:

Voltage rating must be equal to or greater than 16V maximum
Current hold (Ih) rating must accommodate the 1.97A specification
Current trip (It) must match or exceed 5A
Mounting type must be Surface Mount with 2-SMD package configuration
Physical dimensions must be compatible with PCB layout constraints
Operating temperature range must cover -40°C to 85°C
Post-trip resistance (R1) must not exceed 85 mOhms
RoHS3 compliance and AEC-Q200 rating are required for automotive applications

The MF-SM250-2 from Bourns Inc. meets these substitution criteria within the allowed parameter tolerances for polymeric PTC resettable fuses in this category.

Parameter Comparison

Parameter	ASMD250F-2 (Littelfuse)	MF-SM250-2 (Bourns)	Compatibility
Voltage - Max	16V	15V	ASMD250F-2 rated higher
Current - Hold (Ih) (Max)	1.97A	2.5A	MF-SM250-2 rated higher
Current - Trip (It)	5A	5A	Equal
Current - Max	40A	100A	MF-SM250-2 rated higher
Time to Trip	30s	25s	MF-SM250-2 faster
Resistance - Initial (Ri) (Min)	35 mOhms	24 mOhms	MF-SM250-2 lower
Resistance - Post Trip (R1) (Max)	85 mOhms	85 mOhms	Equal
Operating Temperature	-40 to 85°C	-40 to 85°C	Equal
Mounting Type	Surface Mount	Surface Mount	Equal
Package / Case	2-SMD	2-SMD	Equal
Size / Dimension	8.70 x 6.36 mm	8.75 x 6.71 mm	Dimensionally similar
Thickness (Max)	3.00 mm	3.00 mm	Equal
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Equal
Ratings	AEC-Q200	AEC-Q200	Equal

Engineering Selection Recommendations

Both the ASMD250F-2 and MF-SM250-2 are active products with AEC-Q200 automotive qualification and ROHS3 compliance. The MF-SM250-2 substitute part demonstrates higher current handling capacity (100A maximum versus 40A) and lower initial resistance (24 mOhms versus 35 mOhms), which may provide improved thermal performance in certain circuit configurations. The MF-SM250-2 features faster trip time (25 seconds versus 30 seconds) and higher hold current rating (2.5A versus 1.97A). Both devices maintain identical post-trip resistance limits and operating temperature ranges. Physical dimensions are compatible within standard PCB layout tolerances. Selection between these parts should be based on specific circuit requirements for voltage headroom, current handling, and response time characteristics.

Frequently Asked Questions (FAQ)

Q: Can the MF-SM250-2 directly replace the ASMD250F-2 in all applications?

A: The MF-SM250-2 is dimensionally and electrically compatible for surface mount 2-SMD applications. However, the lower maximum voltage rating (15V versus 16V) must be evaluated against your circuit's maximum operating voltage. Both parts share identical post-trip resistance and operating temperature specifications.

Q: What is the significance of the different hold current ratings?

A: The ASMD250F-2 has a 1.97A hold current while the MF-SM250-2 is rated at 2.5A. This means the MF-SM250-2 allows higher continuous current before triggering. Selection depends on your circuit's normal operating current and desired protection threshold.

Q: Are there packaging differences between these parts?

A: Both parts are supplied in 2-SMD surface mount packages. The ASMD250F-2 is available in Tape & Reel (TR) packaging with 2623 pieces in stock. The MF-SM250-2 is available in Cut Tape (CT) & Digi-Reel® packaging with 2622 pieces in stock. Physical dimensions are nearly identical (8.70 x 6.36 mm versus 8.75 x 6.71 mm) and compatible with standard PCB layouts.

Q: Do both parts meet automotive qualification standards?

A: Yes. Both the ASMD250F-2 and MF-SM250-2 carry AEC-Q200 ratings and are ROHS3 compliant, meeting automotive industry requirements for reliability and environmental compliance.

Q: What is the difference in trip time between these parts?

A: The ASMD250F-2 has a 30-second trip time while the MF-SM250-2 trips in 25 seconds. The faster response of the MF-SM250-2 may provide more aggressive overcurrent protection in sensitive circuits.

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