STM811LW16F from STMicroelectronics, in a SOT-143-4. 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	VSS	power_in	Ground reference (0 V). Connect to system ground close to the device.
2	RST	output	Active-low push-pull reset output. Asserted (driven low) whenever VCC falls below the reset threshold (VRST) or when MR is pulled low; remains asserted for at least trec (140 ms min) after VCC returns above threshold. Guaranteed valid down to VCC = 1.0 V; both sources and sinks current. Open circuit for VCC < 1 V - add a 100 kOhm pull-down if a valid low is required down to 0 V.
3	MR	input	Active-low manual (push-button) reset input. A logic low on MR asserts RST; RST remains asserted while MR is low and for trec after MR returns high. MR has an internal 20 kOhm pull-up to VCC, so it can be left open when unused. Compatible with TTL/CMOS logic levels or open-drain/open-collector drivers; add an optional 0.1 uF cap to GND for extra noise immunity in noisy environments.
4	VCC	power_in	Supply voltage input, monitored by the internal reset comparator against VRST. Typical supply current ~6 uA. Bypass with a 0.1 uF ceramic capacitor mounted as close as possible to the pin for transient immunity.

Key specifications

Parameter	Value
Manufacturer	STMicroelectronics
Package	SOT-143-4
Category	Power Supply Chip
Pins	4

Ordering variants

Same part, different packaging or reel option.

STM811LW16F
STM811MW16F
STM811TW16F
STM811SW16F
STM811RW16F
STM812LW16F
STM812MW16F
STM812TW16F
STM812SW16F
STM812RW16F
STM809LWX6F
STM809MWX6F
STM809TWX6F
STM809SWX6F
STM809RWX6F
STM810LWX6F
STM810MWX6F
STM810TWX6F
STM810SWX6F
STM810RWX6F

CAD (KiCad official)

Symbol: STM811LW16F
Footprint: Package_TO_SOT_SMD:SOT-143
3D model: SOT-143-4 (KiCad packages3D, STEP)

Provenance

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

Datasheet: STMicroelectronics datasheet (21 pp, sha256 24f3f88facdeb210, 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