LJ3405 from GUOXIN JIAPIN SEMICONDUCTOR, 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	E1OUT	output	Output of the internal first-stage op-amp. Connect the gain-setting feedback network (R3/C3 in the typical circuit) between this pin and E1IN.
2	E1IN	input	Inverting input of the internal first-stage op-amp. Non-inverting input is internally biased at 0.3 VDD; drive the PIR AC output into this pin through an AC-coupling capacitor.
3	VC	input	Trigger inhibit input. When VC < 0.2 VDD triggering is inhibited and OUT is forced low; when VC > 0.2 VDD triggering is enabled and OUT follows the input signal. VDD=5V: VIH ≥ 1.1 V, VIL ≤ 0.5 V; VDD=3V: VIH ≥ 0.7 V, VIL ≤ 0.4 V.
4	A	input	Retrigger-mode select. A=1 enables retriggerable operation (Tx timer restarts on new triggers); A=0 selects non-retriggerable mode. VDD=5V: VIH ≥ 3.5 V, VIL ≤ 0.7 V; VDD=3V: VIH ≥ 2 V, VIL ≤ 0.5 V.
5	GND	power_in	Chip ground reference (0 V). All bypass caps and the CT timing capacitor return here.
6	OUT	output	Active-high control signal output. Drives ~10 mA at VDD=5V (VOH ≥ 4.3 V, VOL ≤ 0.6 V) and ~3 mA at VDD=3V. Goes high for the Tx delay after a valid trigger, then low during the Ti blocking period.
7	CT	passive	Oscillator timing pin. Requires an external timing capacitor CT to GND and a pull-up resistor RT (>80 kΩ) to VDD. Frequency set by Tosc ≈ 0.4·CT·RT·(RT/(RT−27)) (RT in kΩ, CT in nF, Tosc in μs). Tx = 100000·Tosc; K=Tx/Ti default 14.
8	VIN	power_in	Positive supply input (also referred to internally as VDD). Operating range 3 V to 6 V; absolute max 7 V. ICC typ 30 uA @ 3 V, 60 uA @ 5 V.

Key specifications

Parameter	Value
Manufacturer	GUOXIN JIAPIN SEMICONDUCTOR
Package	SOP-8
Category	Sensor
Pins	8

Ordering variants

Same part, different packaging or reel option.

LJ3405SR-G
LJ3405CPR-G

CAD (KiCad official)

Symbol: LJ3405
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
`lj3405.step`	122 KB	You want the bare part, or you mark your own boards.
`lj3405-etched.step`	1.5 MB	You want the part with `LJ3405` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 372 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: GUOXIN JIAPIN SEMICONDUCTOR datasheet (9 pp, sha256 819c87b69c45624a, 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