What the hold and trip currents mean for your circuit
The 1206L450SL-VYR: The 4.5 A hold current (Ih) is the continuous DC current the PTC carries without tripping at 25 °C ambient — below this threshold the internal resistance stays at its initial 1 mOhm minimum, so the voltage drop across the part is under 5 mV at rated load. When the fault current reaches 9 A (It), the polymeric element heats and transitions to a high-resistance state within 2 seconds, clamping the current to a leakage level until power is removed or the fault clears. The post-trip resistance rises to 14 mOhm maximum — this is the resistance the circuit sees after a trip event, and it resets to the initial low value only after the device cools and power is cycled.
Surface-mount termination with a concave end-cap design — the solder fillet wets the end metallization on both sides, which improves thermal coupling to the PCB copper for faster trip response under sustained overcurrent.
Lifecycle reality and sourcing path
No official successor order code is recorded from Littelfuse for this specific LoRho variant; a functional replacement requires reviewing the POLY-FUSE LoRho family for a part with matching 4.5 A hold, 6 V max, and 1206 footprint, then verifying the initial and post-trip resistance limits against the application.
Approvals and temperature envelope
Carries cURus and TUV agency approvals — the cURus mark certifies compliance with UL 1434 and CSA C22.2 No. 0.4 for polymeric PTC devices, while TUV confirms IEC 60738-1 and EN 60738-1 conformance for overcurrent protection in equipment intended for the European market.