# CD431

**Changjing** · Voltage Reference · SOT-23

CD431 from Changjing, in a SOT-23. 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 | CATHODE | passive | Cathode (K). Sinks the regulating current; VKA is regulated to a value set by the external divider between cathode, reference, and anode. Absolute max VKA=36V, IKA continuous range -100 to +150mA, minimum cathode current for regulation 0.45-1.0mA. |
| 2 | REFERENCE | input | Reference input (R). Internal amplifier compares this pin against the internal 2.5V bandgap (Vref typ 2.5V, 2.475-2.525V) and adjusts cathode current to hold VREF equal to Vref. Reference input current typ 1.5µA (max 4µA). |
| 3 | ANODE | passive | Anode (A). Common/ground return for the shunt regulator; the divider that programs VKA references this pin. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | Changjing |
| Package | SOT-23 |
| Category | PMIC |
| Pins | 3 |

## Electrical characteristics

Limits as printed in the datasheet (page.json `metadata.characteristics` carries them as data).

| Parameter | Symbol | Min | Typ | Max | Unit | Conditions | Page |
|---|---|---|---|---|---|---|---|
| Reference input voltage | Vref | 2.475 | 2.5 | 2.525 | V | VKA=VREF, IKA=10mA | 1 |
| Deviation of reference input voltage over temperature | △Vref/△T |  | 4.5 | 17 | mV | VKA=VREF, IKA=10mA; TMIN=-25℃, TMAX=+85℃ (note) | 1 |
| Ratio of change in reference input voltage to change in cathode voltage (VKA = 10V to VREF) | △Vref/△VKA |  | -1 | -2.7 | mV/V | IKA=10mA, △VKA=10V~VREF | 1 |
| Ratio of change in reference input voltage to change in cathode voltage (VKA = 36V to 10V) | △Vref/△VKA |  | -0.5 | -2 | mV/V | IKA=10mA, △VKA=36V~10V | 1 |
| Reference input current | lref |  | 1.5 | 4 | μA | IKA=10mA, R1=10kΩ, R2=∞ | 1 |
| Deviation of reference input current over full temperature range | △lref/△T |  | 0.4 | 1.2 | μA | IKA=10mA, R1=10kΩ, R2=∞ | 1 |
| Minimum cathode current for regulation | IKA(min) |  | 0.45 | 1 | mA | VKA=VREF | 1 |
| Off-state cathode current | IKA(OFF) |  | 0.05 | 0.5 | μA | VKA=36V, VREF=0 | 1 |
| Dynamic impedance | ZKA |  | 0.15 | 0.5 | Ω | VKA=VREF, IKA=1 to 100mA, f≤1.0kHz | 1 |
| Cathode voltage | VKA |  |  | 36 | V |  | 1 |
| Cathode current range (continuous) | IKA | -100 |  | 150 | mA |  | 1 |
| Reference input current range | Iref | 0.05 |  | 10 | mA |  | 1 |
| Power dissipation | PD |  |  | 300 | mW |  | 1 |
| Operating temperature range | Topr | -25 |  | 85 | ℃ |  | 1 |
| Storage temperature range | Tstg | -65 |  | 150 | ℃ |  | 1 |
| Junction temperature | TJ |  |  | 150 | ℃ | TMIN≤Ta≤TMAX, TA=-25 to 85℃ | 1 |
| Thermal resistance from junction to ambient | RθJA |  | 417 |  | ℃/W |  | 1 |

## CAD (KiCad official)

- Symbol: `CD431`
- Footprint: `Package_TO_SOT_SMD:SOT-23`
- 3D model: SOT-23 (KiCad packages3D, STEP)
- 3D model files: `cd431-etched.step` / `cd431-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `cd431.step` / `cd431.glb` are the bare package body.

## 3D model downloads

Two STEP files. Same geometry, different body top:

| File | Size | Use it when |
|---|---|---|
| [`cd431.step`](cd431.step) | 59 KB | You want the bare part, or you mark your own boards. |
| [`cd431-etched.step`](cd431-etched.step) | 1008 KB | You want the part with `CD431` already on it. |

The marking in the etched file is real recessed geometry cut into the solid, not a
texture or a decal: 250 faces against 69 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:** [Changjing datasheet](docs/cd431-datasheet.pdf) (3 pp, sha256 `74c36e847d4914f5`, 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](docs/cd431-datasheet.pdf)