Obsolete — last-time-buy sourcing
Littelfuse has marked the 0603SFS400F/32-2 as Obsolete. No pin-compatible replacement is listed; a board spin may be required if a functional equivalent is needed.
Overcurrent protection envelope
Rated 4 A continuous at 32 VDC, the fuse opens within its slow-blow time-current characteristic when the current exceeds the rating. The 50 A breaking capacity at rated voltage means it safely interrupts faults up to that level without rupturing — adequate for secondary-side protection in low-voltage DC rails where the available fault current stays under 50 A. The melting I²t of 2.3 quantifies the energy needed to open the element. A slow-blow response allows brief inrush pulses (from capacitive input filters or motor start) to pass without nuisance opening — the element absorbs the pulse energy as long as the I²t of the pulse stays below the fuse's rated I²t.
Board-fit and environmental range
Housed in the standard 0603 (1608 metric) surface-mount package, the fuse shares the same footprint as a chip resistor or capacitor — no special pad geometry beyond the usual 0603 land pattern. DC cold resistance is 0.017 Ohms, so the voltage drop at 4 A is under 70 mV, negligible for most low-voltage rails. No derating is specified by the datasheet at the high end, but the element's time-current curve shifts with temperature — expect faster opening at elevated ambient.
Approvals and compliance
UL recognized — the fuse is accepted for use in UL-listed equipment without additional component-level testing. The 0603SFS400F/32-2 is supplied in Tape & Reel (TR) and Cut Tape (CT) packaging, suitable for pick-and-place assembly.