BL7121AH from BL Shanghai Belling, in a SOIC-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	VDD1	power_in	Side 1 power supply, 2.5 V to 5.5 V (recommended). Requires a 0.1 uF bypass capacitor to GND1 close to the pin. Absolute max 6 V.
2	VOA	output	Channel A digital output on side 1 (reverse channel). Referenced to VDD1/GND1. Drives IOH up to -4 mA / IOL up to 4 mA at 5 V supply. Default state is HIGH (AH suffix) when input power or signal is lost.
3	VIB	input	Channel B digital input on side 1 (forward channel). Referenced to VDD1/GND1. VIH >= 0.7VDD1, VIL <= 0.25VDD1. High-Z if left open (output goes to default HIGH state).
4	GND1	power_in	Ground reference for side 1 (VDD1 domain). Isolated from GND2 by the SiO2 capacitive barrier (up to 3750 VRMS working isolation).
5	GND2	power_in	Ground reference for side 2 (VDD2 domain). Isolated from GND1 by the SiO2 capacitive barrier.
6	VOB	output	Channel B digital output on side 2 (forward channel). Referenced to VDD2/GND2. Drives IOH up to -4 mA / IOL up to 4 mA at 5 V supply. Default state is HIGH (AH suffix) when input power or signal is lost.
7	VIA	input	Channel A digital input on side 2 (reverse channel). Referenced to VDD2/GND2. VIH >= 0.7VDD2, VIL <= 0.25VDD2. High-Z if left open (output goes to default HIGH state).
8	VDD2	power_in	Side 2 power supply, 2.5 V to 5.5 V (recommended). Requires a 0.1 uF bypass capacitor to GND2 close to the pin. Absolute max 6 V.

Key specifications

Parameter	Value
Manufacturer	BL Shanghai Belling
Package	SOIC-8
Category	Comm/UART
Pins	8

Ordering variants

Same part, different packaging or reel option.

BL7121AH

CAD (KiCad official)

Symbol: BL7121AH
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`bl7121ah.step`	122 KB	You want the bare part, or you mark your own boards.
`bl7121ah-etched.step`	1.4 MB	You want the part with `BL7121AH` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 366 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: BL Shanghai Belling datasheet (13 pp, sha256 b22900b73aef2795, 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