# TL431

**Texas Instruments** · Adjustable shunt voltage reference · SOT-23 (DBZ)

Three-terminal adjustable precision shunt regulator, a programmable Zener, in a SOT-23 package. A resistor divider from the cathode to REF sets the shunt voltage anywhere from the 2.5 V internal reference up to 36 V. It sinks 1-100 mA with ~0.2 ohm output impedance. The default feedback reference for switching supplies and adjustable linear regulators, and a precise Zener replacement. Wire REF to the divider tap, cathode to the node being regulated, anode to ground.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | K | passive | Shunt cathode (K). Current-sink terminal referenced to ANODE; V(KA) may range from Vref (~2.5 V) up to the absolute-max 37 V. Continuous cathode current I(KA) = 1 mA to 100 mA in normal operation (abs-max −100 to 150 mA). Sinks current when V(REF-ANODE) exceeds Vref, regulating V(KA) at the value set by the external divider. |
| 2 | REF | input | Reference (feedback) input, threshold relative to ANODE. Internal error amp regulates V(REF) to Vref (~2.5 V nominal, 0.5%/1%/2% grades). Reference input current I(ref) is very small (abs-max −0.05 to 10 mA); typically driven from a resistor divider between CATHODE and ANODE to program V(KA) = Vref × (1 + R1/R2) + I(ref)·R1. |
| 3 | A | passive | Common return terminal (A), normally connected to circuit ground. All device voltages (V(KA), V(REF)) are referenced to ANODE. Carries the sum of cathode sink current and reference-input current. |

## Key specifications

| Parameter | Value |
|---|---|
| Type | Adjustable shunt voltage reference |
| Reference voltage (Vref) | 2.5 V (typ 2.495 V) |
| Output range | Vref to 36 V (external divider) |
| Cathode current | 1 mA to 100 mA |
| Output impedance | 0.2 Ω typ |
| Package | SOT-23 (DBZ) |
| Body (L×W×H) | 2.9 × 1.3 × 1.1 mm |

## Ordering variants

Same part, different packaging or reel option.

- `TL431AIDBZR (SOT-23, ±0.5%)`
- `TL431BIDBZR (SOT-23, ±0.5%, tighter tempco)`

## CAD (KiCad official)

- Symbol: `Reference_Voltage:TL431DBZ`
- Footprint: `Package_TO_SOT_SMD:SOT-23`
- 3D model: SOT-23 (KiCad packages3D)
- 3D model files: `tl431-etched.step` / `tl431-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `tl431.step` / `tl431.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/lit/ds/symlink/tl431.pdf) (85 pp, sha256 `49d4bc6e1bdcfab7`, retrieved 2026-08-17, tier: manufacturer)
- **Extractor:** `ds2sf` (Claude) — every pin and dimension is cited to a datasheet page; refuses to fabricate.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/tl431-datasheet.pdf)