Hold current and trip point for a 4.5 A rail
The Littelfuse 1206L450SLWR is a polymeric PTC resettable fuse from the POLY-FUSE LoRho series, designed to protect a 4.5 A continuous current rail at up to 6 V. It trips at 9 A, meaning the PTC element switches from low resistance to a high-impedance state when the load current exceeds the trip threshold, clearing the fault. The time to trip is 2 seconds at the rated fault current — fast enough to protect downstream components from sustained overcurrent without nuisance tripping on inrush.
Package and rework considerations for the 1206 footprint
The concave termination style is common for PTCs in this footprint — the part sits flat on the pad and the concave ends wick solder during reflow, giving a visible fillet on inspection. The PTC body is epoxy-encapsulated and survives a standard rework cycle without cracking — just lift the part, not the pad.
Initial resistance (Ri) is a minimum of 1 mOhm — this is the cold resistance before any fault event. Post-trip resistance (R1) rises to a maximum of 14 mOhm, which is the resistance after the PTC has tripped and reset. The low Ri means minimal I²R loss at 4.5 A: about 20 mW dissipated in the part during normal operation. The 50 A maximum interrupt rating means the PTC can handle a dead short up to 50 A at 6 V without rupturing — the device limits the fault current by heating up and increasing its resistance.
Temperature range and approvals for global deployment
The part carries cURus and TUV approvals, certifying compliance with UL 1434 (PTC thermistor standard) and IEC 60738-1 for overcurrent protection. These marks are accepted in North American and European equipment without additional safety agency review.