FM2542S from Shenzhen Fuman, in a SOP-8. 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	VCC	power_in	Chip power supply. Start-up threshold 15-18 V (typ 16.5 V), UVLO at 8-10 V (typ 9 V), OVP at 29-33 V (typ 31 V), internal Zener clamp ~34.5 V. Start-up current ~1.5 uA, operating current ~530 uA. Decouple with a bulk cap plus the auxiliary-winding rectifier network.
2	GND	power_in	Chip ground / reference return for VCC decoupling, CS sense resistor and FB divider. Also the source return of the integrated power MOSFET.
3	FB	input	Feedback sense input from the auxiliary winding via a resistor divider. Internal reference is 2 V (1.97-2.03 V) for output-voltage regulation; output V0 = 2(RFBH+RFBL)/RFBL Ns/Naux. Also used for short-circuit detection (threshold 0.7 V) and for cable-drop compensation (offset current up to ~45 uA). Absolute range -40 V to +8.5 V.
4	CS	input	Primary current-sense input. Tie to the source-side sense resistor Rcs; peak current is limited when Vcs reaches 500 mV (Ipk = 500 mV / Rcs). Includes 500 ns leading-edge blanking and 100 ns overcurrent turn-off delay. Absolute range -0.3 V to +7 V.
5	D	output	Drain of the internal 650 V Cool-MOSFET power switch (Rds_on max 1.5 Ω, ID 3 A). Multiple drain pins (5-8) are bonded together to share current and improve thermal dissipation; connect all four to the transformer primary switching node.
6	D	output	Drain of the internal 650 V Cool-MOSFET power switch. Tied internally to pins 5/7/8; all four should be connected together to the transformer primary switching node.
7	D	output	Drain of the internal 650 V Cool-MOSFET power switch. Tied internally to pins 5/6/8; connect together to the transformer primary switching node for current sharing and heat spreading.
8	D	output	Drain of the internal 650 V Cool-MOSFET power switch. Tied internally to pins 5/6/7; connect together to the transformer primary switching node.

Key specifications

Parameter	Value
Manufacturer	Shenzhen Fuman
Package	SOP-8
Category	PMIC
Pins	8

Ordering variants

Same part, different packaging or reel option.

FM2542SS
FM2542SD

CAD (KiCad official)

Symbol: FM2542S
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOP-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`fm2542s.step`	122 KB	You want the bare part, or you mark your own boards.
`fm2542s-etched.step`	1.6 MB	You want the part with `FM2542S` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 411 faces against 147 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 (9 pp, sha256 5dd312446c8299e1, 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