What this PTC resettable fuse does on the board
The 1206L400SLTH-VYR is a polymeric PTC resettable fuse from Littelfuse's POLY-FUSE LoRho series, designed for overcurrent protection in low-voltage circuits where low series resistance matters. It holds 4 A continuously (Ih) and trips at 8 A (It), with a maximum interrupt rating of 50 A at 6 V — sized for USB, battery, or low-voltage DC rail protection where the fault current is limited by the supply impedance. The initial resistance is 1 mOhm minimum, rising to 16 mOhm maximum after a trip event — the LoRho construction keeps I²R losses low during normal operation, which matters for power-sensitive designs.
Obsolete — sourcing through independent channels
No pin-compatible drop-in replacement is listed by Littelfuse, so a BOM position using this part requires sourcing existing inventory or qualifying a parametric substitute.