Low-resistance PTC for tight current budgets
The Littelfuse 0603L175SLYR is a polymeric PTC resettable fuse from the POLY-FUSE LoRho series, designed to protect low-voltage circuits where every milliohm of series resistance matters. It holds 1.75 A continuously and trips at 3.5 A, with an initial resistance of just 5 mOhms — low enough that it won't steal voltage headroom from a 6 V rail.
Package and rework reality
Housed in a 0603 (1608 Metric) concave package, it measures 1.60 mm x 0.80 mm with a max thickness of 1.00 mm. The concave termination style means the solder fillet wicks up the side of the part — inspect the joint after reflow to confirm wetting, especially if you're hand-soldering or reworking with hot air. The part is surface-mount, so it sits flat on the pad; no lead forming needed. After a trip event, the post-trip resistance climbs to 60 mOhms max — the polymer lattice expands and the conductive filler separates. Once the fault clears and the part cools, it resets to near its original resistance, but the cycle life is finite; repeated tripping at high current (50 A max) will eventually degrade the polymer and increase the baseline resistance.
Trip behavior and thermal environment
Approvals from cURus and TUV mean the part is accepted for use in North American and European equipment without additional agency testing on the PTC itself. The 6 V max voltage rating limits it to low-voltage rails — think USB, battery packs, or logic power — not 12 V or 24 V industrial buses.