What the 1.6 A rating means on the bench
The Littelfuse 045101.6MR is a NANO²® 451 series surface-mount fuse rated 1.6 A at 125 V AC or DC. The fast-blow characteristic means it clears quickly on moderate overcurrents — the 1.06 melting I²t figure tells you the energy needed to open it, which matters when coordinating with downstream silicon that may fail short before the fuse blows. Breaking capacity is 50 A at rated voltage, so it safely interrupts faults up to that level without rupturing the package. The 0.058 ohm cold resistance adds a voltage drop of under 100 mV at rated current — negligible for most 125 V rails but worth checking if the load is marginal on headroom.
Obsolete — sourcing reality for this SMD fuse
Littelfuse lists the 045101.6MR as obsolete. No pin-compatible drop-in replacement is documented by Littelfuse; a parametric search for 1.6 A fast-blow SMD fuses in the 2-SMD square end block footprint is the practical path for a BOM update. The approvals — CSA, PSE, UL — mean this fuse was accepted in North American, Japanese, and Canadian regulatory jurisdictions when it was in production. For a repair bench, a UL-recognized replacement from another manufacturer is the safe swap; the scorch mark on the board tells you the original failed as designed.
Temperature range and board-fit note
The Tape & Reel packaging is the original production format; surplus lots may arrive in cut tape or loose tubes.