3 A hold, 6 V max — the LoRho advantage
This Littelfuse 0603L300SLYR is a Polymeric PTC resettable fuse from the POLY-FUSE LoRho series, rated for 3 A hold current (Ih) at 6 V max. The LoRho designation means the initial resistance is just 3 mOhms minimum — that is low enough to keep voltage drop negligible in a 3 A power rail, so the fuse does not steal headroom from the load. When a fault pushes current past the 6 A trip threshold, the PTC element heats and latches into a high-resistance state within 5 seconds, limiting the fault to 50 A max.
What the resistance numbers mean for your rail
The 3 mOhm minimum initial resistance (Ri) is the cold-state value. At 3 A continuous, that is only 9 mV drop — irrelevant for a 6 V rail. The 30 mOhm maximum post-trip resistance (R1) is what the PTC settles to after it trips and cools; that is the resistance the circuit sees when the fault is gone but the fuse has not yet been power-cycled to reset. At 85°C the 3 A rating drops to roughly 70% of the 25°C value, so a rail that must hold 3 A at the top of the temperature range needs a higher-rated fuse or active cooling.
Active production, approvals on file
The 0603 concave package (1.60 mm x 0.80 mm footprint, 1.00 mm max thickness) is a standard surface-mount form factor. Tape-and-reel or cut-tape packaging is available, matching standard pick-and-place feeders.