UM1663S from Union Semiconductor, in a SOT-23-6. 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	SW	power_out	Switch pin. Connect the boost inductor and Schottky diode to this pin. Internal NMOS power switch rated to 40V max (Vsw), 1A current limit (typical), Rds(on) ~550 mOhm.
2	GND	power_in	Ground / power ground. Datasheet symbol listed as GND/PGND; single ground return for the device and internal power switch.
3	FB	input	Feedback voltage pin. Regulated to 200mV internal reference (Vref 190-210mV) via an external sense resistor to set LED current. Duty-cycle on SHDN modulates the effective feedback reference for dimming.
4	SHDN	input	Active-low chip enable and single-wire PWM/Pulse-mode dimming input. VIH >=1.5V (Vcc=3.7V) / >=1.8V (Vcc=5V); VIL <=0.6V/0.8V. Initial pulse >=2ms selects PWM dimming (500Hz-50kHz); initial pulse <=1.5ms selects 64-step Pulse dimming. Logic low >20ms shuts the device down.
5	OVP	input	Overvoltage protection sense pin. Connect to the boost output capacitor; the chip clamps output when the pin exceeds the internal threshold. Default OVP threshold is 38V (spec typ 36V).
6	VIN	power_in	Supply voltage pin. Operating range 2.8V to 5.5V; absolute max -0.3V to +6V. Bypass with a local ceramic capacitor (typ 10uF).

Key specifications

Parameter	Value
Manufacturer	Union Semiconductor
Package	SOT-23-6
Category	PMIC
Pins	6

CAD (KiCad official)

Symbol: UM1663S
Footprint: Package_TO_SOT_SMD:SOT-23-6
3D model: SOT-23-6 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`um1663s.step`	97 KB	You want the bare part, or you mark your own boards.
`um1663s-etched.step`	1.8 MB	You want the part with `UM1663S` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 421 faces against 117 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 (16 pp, sha256 da01582bb6963f3e, 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