UM803RS from Union Semiconductor, 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	GND	power_in	Ground reference (0 V).
2	RESET	output	Active-low, open-drain reset output. Remains low while VCC is below the reset threshold (typ 2.63 V for the R version) and for at least 140 ms after VCC rises above the threshold. Requires an external pull-up resistor; the pull-up may be tied to a rail higher than VCC. VOL ≤ 0.3 V at ISINK = 50 µA with VCC ≥ 1.0 V.
3	VCC	power_in	Positive supply and monitored voltage. Absolute max −0.3 V to +6.0 V; operating range 1.0 V to 5.5 V. The R version monitors a nominal +3.0 V rail (reset threshold 2.63 V typ).

Key specifications

Parameter	Value
Manufacturer	Union Semiconductor
Package	SOT-23-3
Category	PMIC
Pins	3

Ordering variants

Same part, different packaging or reel option.

UM803RS
UM803RSRP

CAD (KiCad official)

Symbol: UM803RS
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
`um803rs.step`	59 KB	You want the bare part, or you mark your own boards.
`um803rs-etched.step`	1.8 MB	You want the part with `UM803RS` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 420 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: Union Semiconductor datasheet (12 pp, sha256 064b0eaa669a8ef8, 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