FS431M from FOSAN, in a SOT-23. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	REF	input	Reference input. Compared internally against the 2.495 V bandgap reference; typically driven from an external R1/R2 divider between Cathode and Anode to program the regulation voltage. Input current ~1.8 µA typ (4 µA max).
2	K	passive	Cathode. Shunt regulation terminal; sinks 1-100 mA to hold VKA at the programmed voltage (up to 40 V absolute max, 36 V programmable). Dynamic impedance 0.27 Ω typ.
3	A	passive	Anode. Common/ground return for the shunt regulator; the resistor divider low side and Vref return are referenced here.

Key specifications

Parameter	Value
Manufacturer	FOSAN
Package	SOT-23
Category	PMIC
Pins	3

CAD (KiCad official)

Symbol: FS431M
Footprint: Package_TO_SOT_SMD:SOT-23
3D model: SOT-23 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`fs431m.step`	59 KB	You want the bare part, or you mark your own boards.
`fs431m-etched.step`	1.1 MB	You want the part with `FS431M` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 288 faces against 69 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: FOSAN datasheet (4 pp, sha256 44eae1ca9d167d08, retrieved 2026-08-17, tier: lcsc)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF