0467.375NR

FAQFrequently Asked Questions

• What are the key differences between the Littelfuse 0467.375NR and its substitute part numbers 0494.375NR and 0434.375NRP when designing a new board? The 0467.375NR is a fast-blow 375mA fuse in 0603 surface mount package with 50A breaking capacity at 32V. The 0494.375NR and 0494.375NRHF are direct electrical equivalents in the same package; however, the 0494 series may have different lead finishes and moisture sensitivity profiles depending on manufacturing date. The 0434.375NRP uses a different package geometry and footprint, requiring PCB redesign if substitution is necessary. When migrating designs, verify the actual footprint dimensions and thermal characteristics, as the 0467.375NR has a DC cold resistance of 0.3 Ohms which affects power dissipation calculations in your circuit topology.
• Can the Littelfuse 0467.375NR be used in automotive or industrial applications operating continuously at the upper temperature limit? The 0467.375NR is rated for -55°C to 90°C operation, which covers industrial and some automotive environments. However, at sustained 90°C ambient with internal self-heating from the 0.3 Ohm cold resistance, fuse response time may shift toward the slower end of the fast-blow specification. For automotive Grade 0 or Grade 1 reliability requirements, thermal modeling of the PCB layout around the 0467.375NR is necessary to ensure the fuse trips predictably at fault current levels without nuisance blows during normal operation. Additionally, confirm that your application's inrush current profile does not approach the melting I²t threshold of 0.0035.
• How does the 0467.375NR's 0603 surface mount package affect PCB thermal design compared to larger cartridge fuses? The 0467.375NR in 0603 metric (1.60mm L × 0.81mm W × 0.31mm H) has minimal thermal mass and dissipates self-heating rapidly into the PCB copper. This compact form factor allows dense board layouts but requires careful copper area planning beneath and around the fuse to avoid localized hotspots that could trigger premature nuisance trips. Cartridge-style alternatives dissipate heat more gradually due to their larger volume; the 0467.375NR's small size means thermal coupling to neighboring components is tighter, so isolating high-current switching circuits or power supplies feeding the protected rail is advisable.
• What design considerations apply when the 0467.375NR is protecting a circuit with high inrush current at startup? The 0467.375NR is a fast-blow fuse with a melting I²t of 0.0035, which is sensitive to current spikes. High inrush events—such as transformer energization, capacitor bank charging, or motor soft-start transients—can trigger the fuse even if steady-state current is well below 375mA. During design, calculate the inrush energy (I²t) over the transient duration and compare it to the fuse's melting threshold; if inrush exceeds this limit, either add series inductance or resistance to slow the current rise, or select a slower-blow fuse variant. The 0467.375NR's fast response is ideal for semiconductor protection but may cause nuisance failures in circuits with unavoidable inrush.
• Is the Littelfuse 0467.375NR suitable as a replacement in existing designs that currently use cartridge-style 375mA fuses? Direct replacement of cartridge fuses with the 0467.375NR requires PCB redesign because the 0603 surface mount footprint is incompatible with cartridge holders. Additionally, verify that the original circuit was designed for the 0467.375NR's fast-blow characteristic; older designs may have used medium or slow-blow cartridge fuses with different melting I²t curves. The 0467.375NR's 50A breaking capacity at 32V must also meet your fault current level. If the cartridge fuse was oversized for thermal or mechanical reasons, the transition to 0603 SMD may require re-evaluation of thermal management and protective relay coordination.
• What are the voltage and current stress considerations when the 0467.375NR operates at its rated 32V AC / 32V DC limits? The 0467.375NR is rated symmetrically for 32V AC and 32V DC, meaning AC and DC applications see the same voltage stress. However, DC circuits experience no zero-crossing recovery, so arcing during fault interruption is more sustained; the fuse's 50A breaking capacity at rated voltage assumes AC fault current. In DC applications approaching 32V, confirm that the arc energy during a 375mA+ fault does not exceed the fuse element's thermal budget, especially in high-frequency switching contexts. Operating above 32V voids the UL/CSA approval, and at voltages near the limit with elevated ambient temperature, the margin for nuisance trips shrinks.
• How does the 0467.375NR's RoHS3 compliance and MSL 1 rating affect supply chain and assembly planning? The 0467.375NR is RoHS3 compliant and carries MSL (Moisture Sensitivity Level) 1, indicating unlimited shelf life without desiccant storage. This simplifies procurement and reduces lead time risk compared to higher MSL components. However, verify your manufacturing partner's solder reflow profile; even MSL 1 components can degrade if exposed to thermal shock during wave or reflow soldering in high-humidity conditions. The REACH Unaffected status ensures no additional restricted substance documentation is required, reducing regulatory complexity in EU and international supply chains.
• What is the expected fuse response behavior of the 0467.375NR in a 32VDC circuit protecting a low-impedance short-circuit fault? In a 32VDC system with a low-impedance short (fault current >> 375mA), the 0467.375NR's fast-blow response is determined by its 0.0035 I²t melting threshold and the 50A breaking capacity. At maximum breaking capacity (50A at 32V), the fuse element vaporizes within microseconds, creating an arc that must be extinguished by the fuse's internal design. The 0603 SMD package provides minimal arc chamber volume, so confirm that PCB trace geometry, via placement, and solder joint integrity can withstand the arc pressure without delamination. DC arcing is more aggressive than AC, so thermal and mechanical stress analysis of the fuse and surrounding PCB structure is necessary for high-reliability applications.
• Can the 0467.375NR be paralleled with other fuses or resistors to reduce total I²t or adjust trip threshold? Paralleling the 0467.375NR with other fuses or resistors is not recommended. Fuses in parallel create unpredictable current sharing due to variation in cold resistance and melting point; this leads to unequal stress distribution and potential nuisance trips in one fuse while others remain intact, leaving the circuit partially unprotected. The 0467.375NR's 0.0035 I²t is already optimized for its 375mA rating; adding parallel elements invalidates the CSA and UL approvals. If the circuit requires lower I²t or adjustable protection, select an alternate fuse series designed for that characteristic or incorporate a supplementary active protection circuit.
• What thermal and electrical performance differences exist between the 0467.375NR and medium or slow-blow alternatives in the same package? The 0467.375NR is fast-blow, characterized by low melting I²t (0.0035) and rapid response to overload. Slower-blow variants have higher I²t thresholds, allowing brief current spikes to pass without nuisance trips but taking longer to interrupt sustained faults. In the 0603 package, the trade-off is that slower-blow fuses generate more self-heating during the transition to open circuit, potentially raising PCB temperature by 10–20°C above the 0467.375NR during a marginal overload condition. For semiconductor protection (MOSFETs, op-amps), the 0467.375NR's fast response minimizes damage; for motor or inductive load circuits, a slower variant may reduce false trips. Verify the application's fault tolerance before selecting fuse speed.
• How does DC cold resistance of 0.3 Ohms in the 0467.375NR affect power dissipation in a continuous 375mA load? At the rated 375mA continuous current, the 0467.375NR dissipates P = I²R = (0.375)² × 0.3 ≈ 0.042 Watts. In a compact 0603 SMD footprint on a FR-4 PCB with standard copper trace widths, this self-heating raises local board temperature by roughly 5–15°C above ambient, depending on copper area and air circulation. In a 25°C ambient, this places the fuse at approximately 35–40°C under continuous full load. This is well within the -55°C to 90°C rating, but in high-ambient industrial environments (80°C+) or in thermally congested layouts, cumulative heating may approach the upper operating limit, narrowing the margin before fuse response shifts.
• What is the breaking capacity of the 0467.375NR at voltages below the rated 32V, and how does this affect circuit protection architecture? The 0467.375NR's 50A breaking capacity is specified at the rated 32V (AC and DC). Breaking capacity typically decreases at lower voltages because the fuse element vaporizes more slowly at reduced voltage stress; however, Littelfuse datasheets for the 467 series generally maintain breaking capacity down to approximately 16V. Below that threshold, breaking capacity may degrade, and fault interruption may not be reliable at high short-circuit currents. For circuits operating at 12V or lower, verify the actual breaking capacity curve in the detailed datasheet or request application notes from Littelfuse; if breaking capacity is insufficient, a higher-rated fuse (e.g., 500mA or 750mA in the same package) may be required to ensure safe fault interruption despite not protecting as tightly at nominal current.
• Is the Littelfuse 0467.375NR approved for safety-critical applications such as medical devices or functional safety systems? The 0467.375NR carries CSA and UL approvals, indicating it meets recognized safety standards for general electrical protection. However, CSA and UL approvals do not automatically qualify the fuse for functional safety (IEC 61508) or medical device (IEC 60601) applications without additional qualification. Safety-critical designs require Design Failure Mode and Effects Analysis (DFMEA), fault tree analysis, and documented test data demonstrating that the 0467.375NR's failure modes (open circuit, latent defect, slow response under marginal conditions) are acceptable within the system's safety architecture. Contact Littelfuse directly for safety-critical application support and request relevant certifications (e.g., ISO 13849 PLd, SIL 2) if your application demands them.
• How should the 0467.375NR be handled and stored to maintain CSA and UL certification compliance? The 0467.375NR is MSL 1 (Unlimited) and ROHS3 compliant, meaning it requires no special desiccant storage and tolerates standard warehouse conditions indefinitely. However, to maintain CSA and UL certification validity, the component must remain in original packaging (Tape & Reel, TR) until assembly and must not be subjected to mechanical damage, corrosion, or exposure to contaminants that could degrade solder joints or internal fuse elements. Upon receipt, inspect for any visible damage to the component or tape packaging; if damage is detected, return to supplier rather than risk failure in service. During PCB assembly, use standard solder reflow parameters (per IPC-A-610) to avoid thermal shock or cold solder joints that could impair fuse performance and void warranty.