4 A hold, 8 A trip — the PTC that clears fast and stays low-resistance
The Littelfuse 1206L400SLWR is a polymeric PTC resettable fuse from the POLY-FUSE LoRho series, in a 1206 (3216 Metric) concave surface-mount package. It holds 4 A continuously and trips at 8 A, with a maximum interrupt rating of 50 A at 6 V. The LoRho designation means initial resistance is held to 1 mOhm minimum, with post-trip resistance capped at 14 mOhm — this keeps I²R losses negligible in the steady state and lets the PTC sit in a high-current rail without wasting thermal budget.
Time-to-trip and thermal response
At 8 A trip current the device clears in 2 seconds typical — fast enough to protect a 6 V rail feeding a USB port or a battery pack against a dead short, without nuisance tripping on inrush. Derate the hold current above 25°C per the manufacturer's curve — at 85°C ambient the 4 A hold figure drops to roughly 2.5 A.
Package and board-fit
1206 (3216 Metric) concave package, 3.25 mm x 1.65 mm body, 1.40 mm max thickness. The concave termination profile means the solder fillet wets the end cap on the bottom side — no tombstoning risk during reflow if the pad geometry matches the recommended land pattern. The low profile suits tight board stacks where a radial-lead PTC would interfere with the enclosure lid.
Approvals and compliance
cURus and TUV approved — the part carries the major North American and European safety marks for overcurrent protection components. This simplifies the certification review for the end product.