4 A slow-blow in a 1206 footprint
The 1206SFS400F/32-2: The slow-blow characteristic means it tolerates brief inrush current spikes without nuisance opening — a fit for circuits with capacitive or inductive loads that draw a short surge at power-up.
Breaking capacity and I²t for the BOM
Rated breaking capacity is 50 A at the rated 32 V DC — the fuse safely interrupts a fault current up to that level without rupturing the package. The melting I²t of 2.2 A²s gives the energy needed to open the element; this number is what you compare against the I²t of the upstream protection and the let-through energy the downstream components can survive. DC cold resistance is 0.024 Ω, which at 4 A continuous dissipates about 0.38 W — negligible in most designs but worth checking against the trace thermal budget on a dense board.
Obsolete — sourcing through independent channels
Littelfuse lists the 1206SFS400F/32-2 as obsolete. If you are stocking for a long-production-run BOM, consider qualifying a current-production 1206 slow-blow fuse with matching I²t and breaking capacity to avoid a last-time-buy scramble.
UL recognition and storage note
The fuse carries UL recognition, which simplifies acceptance in UL-listed end equipment. Supplied on Tape & Reel (TR) or Cut Tape (CT) — store the reels in a dry, temperature-stable environment; the 1206 ceramic body is not moisture-sensitive, but the plating on the terminations can tarnish in high-humidity storage.