FM4057S42 from Shenzhen Fuman, 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	CHRG	output	Charge-in-progress status output. Open-drain LED driver: sinks current (LED on) while charging is active, high-Z (LED off) when charging completes. Connect an external LED with series resistor to VIN.
2	GND	power_in	Device ground reference.
3	BAT	power_out	Battery output terminal. Connects to the positive terminal of the single-cell Li-ion battery. Regulated to 4.2V for the '42' variant. Absolute max 6V; recommended 10 µF bulk cap to GND.
4	VIN	power_in	Charger input supply. Recommended 4.2 V-6.5 V (typ 5V from AC adapter or USB); absolute maximum 32V. Input OVP trips at 6.5V for the standard FM4057; 1 µF decoupling to GND recommended.
5	DONE	output	Charge-complete status output. Open-drain LED driver: high-Z (LED off) while charging, sinks current (LED on) once the battery is fully charged. Connect an external LED with series resistor to VIN.
6	ISET	input	Charge-current programming pin. Connect a resistor from ISET to GND to set the constant-current charge level (up to 1A). Also participates in thermal regulation feedback.

Key specifications

Parameter	Value
Manufacturer	Shenzhen Fuman
Package	SOT-23-6
Category	PMIC
Pins	6

Ordering variants

Same part, different packaging or reel option.

FM4057S42
FM4057S43
FM4057S44
FM4057S52
FM4057BS52
FM4057S53
FM4057S54
FM4057E42
FM4057BE42
FM4057E43
FM4057E44
FM4057D42
FM4057D43
FM4057D44

CAD (KiCad official)

Symbol: FM4057S42
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
`fm4057s42.step`	97 KB	You want the bare part, or you mark your own boards.
`fm4057s42-etched.step`	1.7 MB	You want the part with `FM4057S42` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 435 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: Shenzhen Fuman datasheet (14 pp, sha256 bfc23830eabbc3b5, 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