FS4054A from FOSAN, in a SOT-23-5L. 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	Open-drain charge status indicator. Pulls low (sinks current, typically driving an LED to VCC through a series resistor such as 330 Ω) while charging is in progress; goes to high impedance when charging terminates (C/10) or the part is in shutdown/standby. Absolute max voltage 7 V.
2	GND	power_in	Device ground reference for all internal circuitry and the external PROG resistor return.
3	BAT	power_out	Charge current output to the single-cell Li-ion battery. Regulates to the 4.2 V float voltage in CV mode and delivers up to 500 mA in CC mode. Sources <=2 uA leakage from the battery when VCC is removed. Absolute max 7 V; continuous short-circuit safe. Typically decoupled with ~10 uF to GND.
4	VCC	power_in	Input supply, 4.5-5.5 V nominal (absolute max 7 V), commonly driven from a USB port or 5 V DC adapter. Undervoltage lockout threshold ~3.4 V; supply current is typically 170 uA during charge and <=25 uA in standby. Decouple with ~1 uF to GND.
5	PROG	input	Charge current programming pin. Connect a resistor R_PROG from PROG to GND to set the constant-current charge level per I_BAT (mA) = 1000 / R_PROG (kΩ); e.g. 2 kΩ → 500 mA, 10 kΩ → 100 mA. Servos to ~1.03 V in CC mode; can also be used to monitor the actual charge current. Absolute max VCC+0.3 V, 800 uA.

Key specifications

Parameter	Value
Manufacturer	FOSAN
Package	SOT-23-5L
Category	PMIC
Pins	5

Ordering variants

Same part, different packaging or reel option.

FS4054A
FS4054B

CAD (KiCad official)

Symbol: FS4054A
Footprint: Package_TO_SOT_SMD:SOT-23-5
3D model: SOT-23-5L (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`fs4054a.step`	85 KB	You want the bare part, or you mark your own boards.
`fs4054a-etched.step`	1.4 MB	You want the part with `FS4054A` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 361 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: FOSAN datasheet (5 pp, sha256 42d795be437a7d9c, retrieved 2026-08-17, tier: lcsc)
Datasheet language: Chinese. Pin names, descriptions, and specs on this page were extracted and translated to English by ds2sf; the linked PDF is the manufacturer original.
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