Littelfuse Inc. 2920L300DR

Product Summary Littelfuse 2920L300DR Polymeric PTC Resettable Fuse

The Littelfuse 2920L300DR is a surface-mount, polymeric positive temperature coefficient (PTC) resettable fuse designed to provide effective overcurrent protection in electronic systems. Part of the 2920L Series, it features a 2920 (7351 Metric) package with a concave profile, specifically tailored for medium-voltage (<60 V) applications demanding resettable protection. The fuse’s primary function is to safeguard sensitive circuitry by temporarily limiting current flow during a fault event, then automatically restoring normal operation after the error condition is resolved and power is cycled or the fault is cleared. This self-resetting capability significantly reduces downtime, component replacement costs, and maintenance effort in production and fielded equipment.

Main Attributes and Technology Behind the Littelfuse 2920L300DR

The 2920L300DR leverages Littelfuse's polymeric PTC (PPTC) technology, offering notable advancements in resettable circuit protection. With a fast response to overcurrent conditions, the device is rated for a maximum voltage of 6 V and a hold current (Ihold) capability of 3 A at room temperature. Its trip current is set at 5 A, ensuring reliable tripping before damage can occur to downstream circuitry. The component’s RoHS compliance—being both lead-free and halogen-free—aligns with modern environmental directives, while its low-profile surface mount design streamlines integration into dense PCB layouts. Safety certifications from cURus and TUV underline the device’s suitability for regulated end-markets.

Electrical Specifications and Performance Details

The Littelfuse 2920L300DR presents a carefully balanced set of electrical attributes, making it optimal for protecting power, signal, and data lines. Key parameters include:

Maximum voltage (Vmax): 6 V

Hold current (Ihold): 3 A at 20°C

Trip current (Itrip): 5 A at 20°C

Maximum post-trip resistance (R1max): 48 mΩ

Maximum trip time: 20 seconds (at specified overcurrent)

Moisture Sensitivity Level (MSL): 2A (4 weeks)

When subjected to fault currents exceeding the trip threshold, the device’s resistance increases dramatically, thus limiting the fault current to a safe level. The fuse resets automatically after the fault event, provided the power is cycled and the device cools. Its thermal and time-current characteristics are consistent with polymeric PTC behavior; however, application-specific verification is essential, especially in environments subject to temperature or current surges.

Application Areas for the Littelfuse 2920L300DR

The 2920L300DR finds utility across various segments that benefit from resettable overcurrent protection:

IEEE 1394 (FireWire) port protection, safeguarding high-speed data interfaces from transient faults

Powered Ethernet ports (compliant with IEEE 802.3af standards), where in-line resettable fusing mitigates risks during power or short events

Automotive electronic control units (ECUs), providing PCB-level protection to reduce service downtime

Low-voltage telecom equipment, where reliable, maintenance-free overcurrent protection is crucial for network reliability

Its design is especially beneficial in systems where quick fault isolation and minimal downtime are business-critical, or where access to the device for fuse replacement is limited.

Mechanical and Environmental Factors of the Littelfuse 2920L300DR

Physically, the 2920L300DR’s 2920 (7351 Metric) form factor provides compact coverage while accommodating sufficient thermal mass for reliable operation. Its concave profile supports automated pick-and-place assembly, and compatibility with standard tape-and-reel packaging enhances manufacturing throughput. The device exhibits robust performance within its rated environment, with an MSL classification of 2A, allowing a 4-week window in a controlled moisture environment prior to reflow soldering. It is important to note that exposure to aggressive chemicals, such as silicon oils or strong solvents, may degrade the polymeric material, impacting device performance.

Guidelines for Soldering, Assembly, and Handling of the 2920L300DR

The Littelfuse 2920L300DR is engineered for standard surface-mount processes, including infrared (IR), vapor phase, and hot air oven reflow methods, ideally in a nitrogen environment for optimal reliability. The recommended maximum solder paste thickness is 0.25 mm, ensuring strong solder joints without excess wicking or voiding. If reflow temperatures exceed recommended profiles, device characteristics may drift outside specified limits, highlighting the importance of strict thermal process control. The fuse is compatible with rework and cleaning using conventional industry methods; however, direct exposure to excessive heat or mechanical stress during assembly should be avoided to prevent damage. When integrating into space-constrained designs, allowance must be made for slight thermal expansion during fuse operation.

Design and Integration Notes for the Littelfuse 2920L300DR

Successful application of the 2920L300DR requires close attention to several engineering principles. In circuits with high inductance, fault interruption may generate voltage overshoots (L di/dt) that can exceed the device’s voltage ratings—these need to be mitigated using snubbers or clamping diodes. The device should not be used in applications with repeated or prolonged overcurrent conditions, as PPTC fuses are intended for protection against temporary anomalies rather than constant overloads. The mounting area must also account for the device’s expansion during fault events and provide appropriate isolation from sensitive components. To ensure long-term reliability, designers should individually validate the fuse’s trip/reset behavior within the system environment and account for the specific time-current and temperature derating performance as outlined in Littelfuse technical guidance.

Alternative or Equivalent Models for the Littelfuse 2920L300DR

While the Littelfuse 2920L300DR is an industry-standard solution for 6 V, 3 A SMD resettable protection, engineers may consider equivalent devices from the same series (such as other current-rated 2920L Series parts) when tailoring hold/trip current profiles for their designs. Comparable resettable PTC fuses are available from alternative manufacturers in equivalent 2920 footprints and with similar electrical characteristics, though cross-compatibility regarding precise trip times, resistance values, and package nuances should be carefully evaluated. Substitutions should always be qualified in prototype validation to verify system-level performance and ensure regulatory compliance.

Conclusion

The Littelfuse 2920L300DR Polymeric PTC Resettable Fuse offers a balanced blend of reliable resettable protection, compact SMD packaging, and robust electrical performance for a range of medium-voltage electronics. Its fast fault response, compliance credentials, and suitability for automated assembly make it a compelling choice for engineers and procurement specialists seeking dependable, low-maintenance overcurrent protection. Proper understanding of its technical capabilities, best-practice assembly guidelines, and careful consideration of integration challenges will ensure optimal use of this device in modern electronic systems.