UM823SS from Union Semiconductor, in a SOT-23-5. 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	RESET	output	Active-low reset output. Pulses low for 200ms (tRP) when triggered and remains low whenever VCC is below the 2.93V reset threshold or when MR is a logic low. Guaranteed valid down to VCC=1V. VOL<=0.3V @ 4mA sink; VOH>=0.8*VCC @ 1mA source.
2	GND	power_in	Ground reference for all signals.
3	MR	input	Manual-Reset Input (active low). Triggers a reset pulse when pulled below 0.3*VCC. Has an internal ~52kΩ pull-up resistor; can be driven from TTL/CMOS logic or shorted to GND with a switch. Leave open or tie to VCC if unused.
4	WDI	input	Watchdog Input. If WDI stays high or low for longer than the watchdog timeout period (1.6s typical), the internal watchdog timer expires and a reset is triggered. The timer clears whenever RESET is asserted or WDI sees a rising or falling edge (min pulse width 50ns). Leaving WDI unconnected or three-stated disables the watchdog.
5	VCC	power_in	Supply voltage input. Operating range 1V to 7V; L-version electrical characteristics apply at VCC=4.75V to 5.5V for the family, but this S-variant is monitored at a 2.93V reset threshold.

Key specifications

Parameter	Value
Manufacturer	Union Semiconductor
Package	SOT-23-5
Category	PMIC
Pins	5

Ordering variants

Same part, different packaging or reel option.

UM823SS
UM823SSSP

CAD (KiCad official)

Symbol: UM823SS
Footprint: Package_TO_SOT_SMD:SOT-23-5
3D model: SOT-23-5 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`um823ss.step`	85 KB	You want the bare part, or you mark your own boards.
`um823ss-etched.step`	1.9 MB	You want the part with `UM823SS` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 448 faces against 102 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 (11 pp, sha256 9413e8dcc1f62525, 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