# LM3549SQX

**Texas Instruments** · LED Drivers · WQFN-24-EP(4x4)

LM3549SQX from Texas Instruments, in a WQFN-24-EP(4x4). 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 | NC | unconnected | No internal connection on this pin. |
| 2 | L1 | passive | SMPS inductor positive terminal 1, connected to the 2.2 µH buck-boost inductor in the typical application circuit. |
| 3 | L1 | passive | SMPS inductor positive terminal 2, on the same L1 node as pin 2. |
| 4 | GND_SW | power_in | SMPS (buck-boost converter) ground. |
| 5 | L2 | passive | SMPS inductor negative terminal 1, on the L2 node of the buck-boost converter. |
| 6 | L2 | passive | SMPS inductor negative terminal 2, on the same L2 node as pin 5. |
| 7 | VOUT | power_out | Buck-boost converter output terminal 1. |
| 8 | NC | unconnected | No internal connection on this pin. |
| 9 | VOUT | power_out | Buck-boost converter output terminal 2, on the same VOUT node as pin 7. |
| 10 | R_EN | input | Red output enable input. |
| 11 | VDDS | power_in | Supply voltage pin; the datasheet's input voltage range is 2.7 V to 5.5 V. |
| 12 | G_EN | input | Green output enable input. |
| 13 | B_EN | input | Blue output enable input. |
| 14 | PWM | input | Master fader input; scales the total brightness of the LED outputs. |
| 15 | GND | power_in | Ground reference; all device voltages are referenced to the GND pin. |
| 16 | R_OUT | output | Red LED constant-current driver output. |
| 17 | G_OUT | output | Green LED constant-current driver output. |
| 18 | B_OUT | output | Blue LED constant-current driver output. |
| 19 | FAULT | output | Fault detection interrupt output; active LOW open-drain. |
| 20 | SDA | bidirectional | I2C data line. |
| 21 | SCL | input | I2C clock line. |
| 22 | EN | input | Enable input and I/O reference level. |
| 23 | VDDP | power_in | SMPS supply voltage pin. |
| 24 | NC | unconnected | No internal connection on this pin. |
| 25 | EP | passive | Exposed pad (from the footprint; not named in the datasheet pin table). |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | Texas Instruments |
| Package | WQFN-24-EP(4x4) |
| Category | Nixie Tube Driver/LED Driver |
| Pins | 25 |

## CAD (KiCad official)

- Symbol: `LM3549SQX`
- Footprint: `Package_DFN_QFN:QFN-24-1EP_4x4mm_P0.5mm_EP2.7x2.7mm`
- 3D model: WQFN-24-EP(4x4) (KiCad packages3D, STEP)
- 3D model files: `lm3549sqx-etched.step` / `lm3549sqx-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `lm3549sqx.step` / `lm3549sqx.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [Texas Instruments datasheet](https://www.ti.com/cn/lit/gpn/lm3549) (28 pp, sha256 `912c4e49951a58aa`, retrieved 2026-10-08, 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/lm3549sqx-datasheet.pdf)