# AMS1117: 1 A Low-Dropout Regulator (UMW / Youtai Semiconductor)

UMW's **second-source** AMS1117: a positive **1 A low-dropout linear voltage regulator** with a typical dropout of 1.2 V at the full 1 A, available in fixed 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V versions or as an adjustable regulator set by two resistors around a 1.25 V reference. Output tolerance is 1.5 % on every fixed version except 1.2 V, which is 2 %. Includes thermal shutdown and current limiting, and takes up to 18 V in. Comes in SOT-223-3L, TO-252-2L and SOT-89-3L.

> **This page is the UMW / Youtai Semiconductor part only.** Everything here comes from the UMW datasheet and applies to UMW-branded silicon. The part number originated at Advanced Monolithic Systems, whose version has a different voltage lineup, a different third package and materially different limits. If your BOM says AMS, use [1 A Low-Dropout Regulator AMS - AMS1117](https://wiki.adom.inc/adom/ams-ams1117) instead.

The interactive **symbol** and **footprint** viewers above are rendered by the wiki from the CAD shipped with this page. Use the toggle at the **bottom-right of the footprint viewer** to switch between **SOT-223**, **TO-252** and **SOT-89**.

## Specifications

- **Output current**: 1 A
- **Fixed output voltages**: 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V; also available adjustable
- **Output accuracy**: 1.5 % on 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V and the adjustable version; **2 % on the 1.2 V version**
- **Reference voltage**: 1.250 V typ; 1.231 to 1.268 V at 25 °C, 1.225 to 1.275 V over the full range
- **Dropout voltage**: 1.00 typ / 1.20 max at 100 mA; 1.05 / 1.25 at 500 mA; **1.20 / 1.30 at 1 A**
- **Input voltage**: 18 V absolute maximum; 12 V recommended operating maximum
- **Line regulation**: 9 mV typ, 18 mV max
- **Load regulation**: 10 mV typ, 18 mV max (10 mA ≤ IOUT ≤ 1 A)
- **Current limit**: **2.1 A min, 2.5 A max**
- **Quiescent current**: 5 mA typ, 10 mA max
- **Ripple rejection**: 60 dB min, 75 dB typ (120 Hz, VIN − VOUT = 3 V)
- **Adjust pin current**: 60 µA typ, 120 µA max
- **Output voltage temperature stability**: 0.3 % typ
- **Long term stability**: 0.3 % typ (1000 h at 125 °C)
- **RMS output noise**: 0.003 % of VOUT (10 Hz to 10 kHz)
- **Protection**: current limiting and thermal shutdown at **150 °C** typ
- **Thermal resistance RθJA**: SOT-223-3L 88 °C/W, TO-252-2L 86 °C/W, SOT-89-3L 102 °C/W
- **ESD tolerance**: 2000 V minimum
- **Operating junction temperature**: −40 to +125 °C recommended, 150 °C absolute maximum; storage −65 to +150 °C
- **Soldering**: lead temperature 260 °C, 5 s
- **Required output capacitor**: 22 µF tantalum covers all cases

## Pin configuration

The pinout is the same on all three packages, and **on all three the metal tab is VOUT**, internally bonded to pin 2. It is the heat path, so solder it to a copper pour on the output net: never to ground. All three footprints shipped here carry the tab as pad 2.

| Pin | Name | I/O | Function |
|---|---|---|---|
| 1 | GND/ADJ |: /O | Ground on fixed versions; adjust (feedback) node on the adjustable version |
| 2 | VOUT | O | Regulated output. Also the metal tab |
| 3 | VIN | I | Input supply voltage, 18 V max |
| n/a | TAB | n/a | Thermal pad, bonded to pin 2 (VOUT) |

### Topside marking

| Package | Marking |
|---|---|
| SOT-223-3L | `AMS1117` / `3.3` + lot code |
| TO-252-2L | `1117 CD` / `3.3` + lot code |
| SOT-89-3L | `STK17` / `3.3` + lot code. Note the different prefix |

## Internal structure

The pass element is a **single NPN transistor driven by a PNP**, so dropout is set by VDROP = VBE + VSAT. Which is why this family cannot get below about 1 V and why dropout rises with load. Fixed and adjustable versions are the **same die**: an on-chip link selection (F1 and F2 connected with A open for fixed, A connected with F1 and F2 open for adjustable) either wires the internal divider to the output or brings the feedback node out on pin 1.

## Component variants

All variants are the same silicon. The order code carries the **package** and the **output voltage** independently. Unlike the AMS original, UMW spells the adjustable version out as `-ADJ` rather than leaving the suffix blank.

The order code is `AMS1117` `{CD | blank}` `-{voltage | ADJ}` `{S}`. Where `CD` = TO-252-2L, blank = SOT-223-3L, and a trailing `S` selects SOT-89-3L.

| Package | Code | Body | RθJA | Fixed order codes |
|---|---|---|---|---|
| SOT-223-3L | *(none)* | 5.90 to 6.70 × 3.90 ±0.30 mm, 1.60 ±0.15 mm high, 2.30 mm TYP pitch | 88 °C/W | `AMS1117-1.2` … `AMS1117-5.0` |
| TO-252-2L | `CD` | 6.40 to 6.70 × 6.00 to 6.30 mm, 2.20 to 2.30 mm high | 86 °C/W | `AMS1117CD-1.2` … `AMS1117CD-5.0` |
| SOT-89-3L | `S` | 4.50 ±0.30 × 2.45 ±0.30 mm, 1.50 ±0.20 mm thick, 3.00 mm BSC pitch | 102 °C/W | `AMS1117-1.2S` … `AMS1117-5.0S` |

The AMS original offers an **8-lead SOIC** in place of SOT-89, and a **2.85 V** version that UMW does not carry. See the [AMS page](https://wiki.adom.inc/adom/ams-ams1117).

### Output voltage versions

Two limit sets per version: the tighter one at TJ = 25 °C with IOUT = 10 mA, and the wider one over the full load and line range.

| Version | VOUT typ | Min to max at 25 °C | Min to max, full range | Test VIN | Accuracy |
|---|---|---|---|---|---|
| AMS1117-1.2 | 1.200 V | 1.176 to 1.224 V | 1.152 to 1.248 V | 3.2 V | **2 %** |
| AMS1117-1.5 | 1.500 V | 1.477 to 1.522 V | 1.470 to 1.530 V | 3.5 V | 1.5 % |
| AMS1117-1.8 | 1.800 V | 1.773 to 1.827 V | 1.746 to 1.854 V | 3.8 V | 1.5 % |
| AMS1117-2.5 | 2.500 V | 2.462 to 2.538 V | 2.450 to 2.550 V | 4.5 V | 1.5 % |
| AMS1117-3.3 | 3.300 V | 3.250 to 3.349 V | 3.235 to 3.365 V | 5.0 V | 1.5 % |
| AMS1117-5.0 | 5.000 V | 4.925 to 5.075 V | 4.900 to 5.100 V | 7.0 V | 1.5 % |
| AMS1117-ADJ | 1.250 V ref | 1.231 to 1.268 V | 1.225 to 1.275 V | VOUT + 2 V | 1.5 % |

**Datasheet inconsistency worth knowing.** The Features bullet on page 1 claims "1.5 % output accuracy" for a list that *includes* 1.2 V, but the General Description on the same page says 1.2 V is 2 %, and the Electrical Characteristics table settles it: 1.176 to 1.224 V at 25 °C is ±2.0 %, where every other version works out to ±1.5 %. Design to **2 %** on the 1.2 V part.

## Assets

| Tool | Files |
|---|---|
| **KiCad symbol** | [`ams1117.kicad_sym`](ams1117.kicad_sym) (3-pin, all three packages) |
| **KiCad footprints** | [`ams1117-sot223.kicad_mod`](ams1117-sot223.kicad_mod), [`ams1117-to252.kicad_mod`](ams1117-to252.kicad_mod), [`ams1117-sot89.kicad_mod`](ams1117-sot89.kicad_mod) |
| **3D models** | [`ams1117-sot223.step`](ams1117-sot223.step) / [`.glb`](ams1117-sot223.glb), [`ams1117-to252.step`](ams1117-to252.step) / [`.glb`](ams1117-to252.glb), [`ams1117-sot89.step`](ams1117-sot89.step) / [`.glb`](ams1117-sot89.glb) |
| **Canonical** | [`ams1117.adom-lbr.json`](ams1117.adom-lbr.json) |
| **Fusion 360 / EAGLE** | *Not available yet* |
| **Altium** | *Not available yet* |

## Applications

1. [**Large Automotive Eth Switch Molecule**](https://wiki.adom.inc/adom/large-automotive-eth-switch-molecule). An AMS1117-1.2 supplies the KSZ9131 gigabit PHY 1.2 V core rail (U902) from the board's 3.3 V rail. 1.2 V is a UMW-only version, so this is a UMW part.
2. [**1 A Low-Dropout Regulator AMS - AMS1117**](https://wiki.adom.inc/adom/ams-ams1117). The original Advanced Monolithic Systems part.

## Application notes

- **Typical circuit is 10 µF in, 22 µF out.** The output capacitor is part of the device's stability, not just decoupling. 22 µF tantalum covers every case including a bypassed adjust pin; the datasheet is explicit that stability degrades as output current rises.
- **Dropout is load-dependent and specified all the way to 1 A**: 1.20 V max at 100 mA rising to 1.30 V max at the full amp. Size the input rail from the 1 A figure unless the load is genuinely light.
- **Current limit is high.** At 2.1 to 2.5 A this part will push well past its 1 A rating into a fault before folding back, so the thermal path, not the current limit, is what protects the board. Thermal shutdown is at 150 °C.
- **Copper is the heat sink.** PD(max) = (TJ(max) − Tamb) / RθJA, and the datasheet is clear that RθJA depends on mounting technique. The 88 / 86 / 102 °C/W figures are a starting point, not a guarantee.
- **Adjustable output:** VOUT = VREF × (1 + R2/R1) + IADJ × R2, with VREF = 1.25 V and IADJ ≈ 60 µA.

## Provenance

- **Datasheet:** [UMW / Youtai Semiconductor AMS1117, *1 A LDO Voltage Regulator*](docs/ams1117-datasheet-umw.pdf). Every electrical number on this page is read from it. Nothing from the Advanced Monolithic Systems datasheet is mixed in.
- **The 2 % accuracy call on the 1.2 V version** resolves a contradiction inside the datasheet itself, in favour of the Electrical Characteristics table over the Features bullet.
- **Symbol:** generated with `adom-symbol` to the datasheet's pin description table (1 = GND/ADJ, 2 = VOUT, 3 = VIN).
- **Footprints:** KiCad 10 official library land patterns, renamed: `SOT-223-3_TabPin2`, `TO-252-3_TabPin2`, `SOT-89-3`. The `TabPin2` variants are correct here because the AMS1117 tab is VOUT, which is pin 2.
- **3D models:** the matching KiCad 10 official STEP models, converted to GLB with `step2glb`.
- **Canonical JSON:** imported from the KiCad symbol + SOT-223 footprint with `adom-lbr import-kicad`.
- **Fusion and Altium libraries are deliberately absent**. They are generated rather than hand-verified, and the generated Altium symbol encoding has produced wrong geometry before.