The 0603SFP400F/32-2: Rated 4 A continuous at 32 VDC with a breaking capacity of 50 A at rated voltage — the fuse safely interrupts a fault current up to 50 A without rupturing the 0603 ceramic body. The DC cold resistance is 0.018 Ohms, so the voltage drop at rated current is under 75 mV, keeping power dissipation low in a tight board layout. Melting I²t is 2.63 — this is the energy needed to clear the fuse element. For a downstream DC-DC converter with input capacitors, the inrush current pulse must stay below this I²t threshold to avoid nuisance opens during power-up. The 0603 package (1.60 mm x 0.81 mm x 0.81 mm) fits dense SMT layouts where board space is at a premium.
Sourcing this obsolete part
Because Littelfuse has discontinued the SFP series, no official successor or pin-compatible cross-reference is maintained. No stock-holding claim; sourced per request.