MT3540 from Aerosemi, 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	SW	output	Power switch output - drain of the internal 0.5Ω, 1.5A N-channel power MOSFET. Connect the boost inductor and Schottky rectifier here. Node swings between GND and up to 28V; absolute max 30V. Keep the SW copper area small to minimize EMI.
2	GND	power_in	Ground return for the IC and the internal power MOSFET source. Tie to a solid ground plane for heat sinking and low-noise operation.
3	FB	input	Feedback input to the internal error amplifier. Regulates to VREF = 1.20V (MT3540), 1.23V (-F23) or 1.25V (-F25). Set VOUT with a resistor divider: VOUT = VREF × (1 + R1/R2). Bias current ≈ −10nA (max −50nA). Absolute max −0.3V to 6V.
4	EN	input	Enable / on-off control. VIH ≥ 1.5V turns the converter on; VIL ≤ 0.4V shuts it down (IQ ≈ 0.1µA). Tie to VIN for automatic startup when unused. Absolute max −0.3V to 6V.
5	VIN	power_in	Input supply pin, 2.5V to 5.5V (absolute max 6V). UVLO ≈ 2.2V with 100mV hysteresis. Must be locally bypassed with a low-ESR ceramic capacitor (1µF or larger, X5R/X7R) close to the pin.

Key specifications

Parameter	Value
Manufacturer	Aerosemi
Package	SOT-23-5
Category	PMIC
Pins	5

Ordering variants

Same part, different packaging or reel option.

MT3540
MT3540-F23
MT3540-F25

CAD (KiCad official)

Symbol: MT3540
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
`mt3540.step`	85 KB	You want the bare part, or you mark your own boards.
`mt3540-etched.step`	1.3 MB	You want the part with `MT3540` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 329 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: Aerosemi datasheet (8 pp, sha256 e4331b29563556e7, 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