431S from Shenzhen Fuman, in a SOT-23-3. 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 to the internal 2.5 V bandgap comparator. Tie to the resistive divider between cathode and anode to program VKA = Vref(1+R1/R2)+IrefR1. Reference input current typ 0.2 µA (max 4 µA); IREF absolute range -0.05 to +10 mA.
2	A	power_in	Anode. Common ground/return terminal of the shunt regulator; the low side of the R1/R2 programming divider and the low side of the load.
3	K	power_in	Cathode. High-side terminal; sinks current from the supply through a series resistor. VKA continuous rating 40 V max, cathode current -100 to +150 mA, regulation from IK(min) ~0.05 mA up to 100 mA.

Key specifications

Parameter	Value
Manufacturer	Shenzhen Fuman
Package	SOT-23-3
Category	PMIC
Pins	3

CAD (KiCad official)

Symbol: 431S
Footprint: Package_TO_SOT_SMD:SOT-23-3
3D model: SOT-23-3 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`431s.step`	59 KB	You want the bare part, or you mark your own boards.
`431s-etched.step`	983 KB	You want the part with `431S` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 238 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: Shenzhen Fuman datasheet (4 pp, sha256 89e58cf6f78a06cf, 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