# VIPER35LD

**STMicroelectronics** · AC-DC Controllers And Regulators · SO-16

VIPER35LD from STMicroelectronics, in a SO-16. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | GND | power_in | Device ground and source of the power MOSFET. |
| 2 | GND | power_in | Device ground and source of the power MOSFET. |
| 3 | N.C. | unconnected | Not internally connected; it can be connected to GND. |
| 4 | N.A. | passive | Not available for user; mechanically connected to the controller die pad and should be connected to GND (pins 1, 2) to improve noise immunity. |
| 5 | VDD | power_in | Supply voltage of the control section; this pin provides the charging current of the external capacitor during power-up. |
| 6 | ZCD | input | Multifunction pin used for zero-current detection for quasi-resonant operation, drain current limit (IDlim) setup, feed-forward compensation (RFF) setup, and output overvoltage protection (ROVP/RLIM) setup. |
| 7 | FB | input | Control input for duty cycle control; a voltage below threshold VFBbm activates burst-mode operation and a level close to VFBlin means the cycle-by-cycle overcurrent setpoint is close. |
| 8 | BR | input | Brown-out protection input with hysteresis; a voltage below VBRth shuts down (not latch) the device, which restarts when the voltage exceeds VBRth + VBRhyst, and it must be connected to ground when not used. |
| 9 | N.C. | unconnected | Not internally connected; must be left floating to get a safe clearance distance. |
| 10 | N.C. | unconnected | Not internally connected; must be left floating to get a safe clearance distance. |
| 11 | N.C. | unconnected | Not internally connected; must be left floating to get a safe clearance distance. |
| 12 | N.C. | unconnected | Not internally connected; must be left floating to get a safe clearance distance. |
| 13 | DRAIN | passive | High voltage drain pin from which the built-in high voltage switched start-up bias current is drawn; pins connected to the metal frame help heat dissipation. |
| 14 | DRAIN | passive | High voltage drain pin from which the built-in high voltage switched start-up bias current is drawn; pins connected to the metal frame help heat dissipation. |
| 15 | DRAIN | passive | High voltage drain pin from which the built-in high voltage switched start-up bias current is drawn; pins connected to the metal frame help heat dissipation. |
| 16 | DRAIN | passive | High voltage drain pin from which the built-in high voltage switched start-up bias current is drawn; pins connected to the metal frame help heat dissipation. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | STMicroelectronics |
| Package | SO-16 |
| Category | Power Management (PMIC) |
| Pins | 16 |

## CAD (KiCad official)

- Symbol: `VIPER35LD`
- Footprint: `Package_SO:SOIC-16_3.9x9.9mm_P1.27mm`
- 3D model: SO-16 (KiCad packages3D, STEP)
- 3D model files: `viper35ld-etched.step` / `viper35ld-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `viper35ld.step` / `viper35ld.glb` are the bare package body.

## Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

- **Datasheet:** [STMicroelectronics datasheet](https://jlcpcb.com/api/file/downloadByFileSystemAccessId/8590456089570811904) (38 pp, sha256 `e4cfc539b430a68d`, retrieved 2026-10-10, tier: lcsc)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-haiku-5-5` (text), consensus `claude-sonnet-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/viper35ld-datasheet.pdf)