Hold current and trip behaviour
The 1206L450/12SLWR is a Littelfuse Lo Rho polymeric PTC resettable fuse, rated to hold 4.5 A continuously at 12 V. When a fault pushes current past the 9 A trip threshold, the PTC element heats and its resistance jumps, limiting the fault to 50 A max. The trip time is 2 s at the rated fault current — fast enough to protect a 12 V rail feeding a USB port or a sensor cluster without nuisance tripping on inrush.
Low-resistance Lo Rho series
The Lo Rho series is built for low internal resistance: initial resistance is 3 mOhms minimum, and post-trip resistance stays at 14 mOhms maximum. That sub-10 mOhm typical path means the fuse drops under 50 mV at 4.5 A continuous load — negligible for a 12 V bus and critical for keeping the downstream regulator input voltage above dropout.
1206 SMD footprint and approvals
The concave termination profile suits standard reflow profiles and allows visual inspection of the solder joint. cURus and TUV approvals cover the safety certification for the end equipment.
Littelfuse lists the 1206L450/12SLWR as Active in its product lifecycle.