RUSBF155-2 Circuit Protection

Resistance - Initial (Ri) (Min):	40 mOhms
Approvals:	CSA, TUV, UL
Lead Spacing:	0.201" (5.10mm)
Thickness (Max):	--
Height - Seated (Max):	0.461" (11.70mm)
Size / Dimension:	0.272" Dia x 0.122" W (6.90mm x 3.10mm)
Package / Case:	Radial
Mounting Type:	Through Hole
Ratings:	--
Operating Temperature:	-40°C ~ 85°C
Resistance - Post Trip (R1) (Max):	100 mOhms
Series:	PolySwitch®, RUSBF
Time to Trip:	2.2s
Current - Trip (It):	2.65A
Current - Hold (Ih) (Max):	1.55A
Current - Max:	40A
Voltage - Max:	6V
Type:	Polymeric
Moisture Sensitivity Level (MSL):	--
Part Status:	Active
Lead Free Status / RoHS Status:	--
Packaging:	Tape & Reel (TR)

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Introduction of PTC Resettable Fuses

PTC Resettable Fuses are an emerging type of current protection technology which allows for automatic re-setting of the fuse after it has tripped due to an over current. Unlike conventional fuses that require replacement after tripping, PTC resettable fuses do not. Instead, the resettable fuse can reset itself quickly, allowing the circuit to remain powered. There are multiple advantages that can be associated with these types of protection devices, with carefully selected ones able to provide a wide variety of applications.

RUSBF155-2 Application Field and Working Principle

The RUSBF155-2 is an SMD resettable fuse which is an ideal choice as a primary board level circuit protection device. It has an operating temperature range of 0°C to +85°C and a working current of 4A and working voltage of 32V. The PTC action will provide high temperature protection to reduce the risk of molten solder contamination in the event of an Over-Current Condition (OCC).The RUSBF155-2 measures approximately 2.5mm in length and 0.8mm in width not including the terminals. The device employs fuse action featuring a metal oxide varistor (MOV), a thermistor, resistors, and transistors. Due to its size, the RUSBF155-2 is typically used in surface mount applications and is ideal for a variety of automotive, consumer, and industrial applications. The working principle of the RUSBF155-2 works by reducing the load current below a certain threshold to reset the device. This is achieved by using the device’s PTC action which includes a thermistor that increases its resistance with temperature. The increased temperature from the load current creates a higher resistance across the thermistor, which prevents the current level from increasing past a specific level. Once the current is reduced, the internal thermistor can cool and return to its original resistance, thus allowing the current flow again.Besides providing the basic fuse action, the RUSBF155-2 also offers a low holding current modification. This modification consists of any additional resistors placed in parallel with the device’s sensing element which causes the current at which the device will re-set to be adjusted. This feature is commonly used in applications where the current may need to be adjusted depending on the application. The advantage of the RUSBF155-2 over other PTC resettable fuse technologies is that it can reset at lower temperatures then other devices or technologies can, while still achieving the same type of fuse action.

Conclusion

Through its PTC action featuring the metal oxide varistor, thermistor, and resistors, the RUSBF155-2 is an ideal current protection device in a wide variety of applications, and is able to provide its users remarkable current protection in a small package. With its re-settable action, increased temperature protection, and ability to be adjusted to the required application’s requirements, the RUSBF155-2 is an ideal choice of SMD resettable fuse for any board application. In conclusion, the RUSBF155-2 is the perfect choice of PTC resettable fuse to provide users with protection from any potential over current condition, while also being able to re-set itself in a fast time frame when necessary.

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