# AMS1117: 1 A Low-Dropout Regulator (Advanced Monolithic Systems)

The **original** AMS1117: a three-terminal **1 A low-dropout linear voltage regulator** from Advanced Monolithic Systems, available in fixed 1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V versions or as an adjustable regulator set by two resistors around a 1.25 V reference. It operates down to 1 V input-to-output differential (1.3 V max dropout at 0.8 A), is trimmed on-chip to 1.5 %, and includes internal current limiting and thermal shutdown. It is pin-compatible with older three-terminal SCSI regulators, and comes in SOT-223, TO-252 (DPAK) and 8-lead SOIC.

> **This page is the Advanced Monolithic Systems part only.** Everything here comes from the AMS datasheet and applies to AMS-branded silicon. The same part number is second-sourced by UMW with a different voltage lineup, different packages and materially different limits. If your BOM says UMW, use [1 A Low-Dropout Regulator UMW - AMS1117](https://wiki.adom.inc/adom/umw-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 **SO-8**.

## Specifications

- **Output current**: 1 A
- **Fixed output voltages**: 1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V; also available adjustable
- **Reference voltage**: 1.250 V typ (1.232 to 1.268 V at 25 °C)
- **Dropout voltage**: 1.1 V typ, 1.3 V max at 0.8 A; higher above 0.8 A
- **Input voltage**: 15 V absolute maximum
- **Line regulation**: 0.2 % max (0.015 % typ)
- **Load regulation**: 0.4 % max (0.1 % typ)
- **Current limit**: 900 mA min / 1100 mA typ / 1500 mA max
- **Quiescent current**: 5 mA typ, 11 mA max
- **Minimum load current**: 5 mA typ, 10 mA max (adjustable version)
- **Ripple rejection**: 60 dB min; 75 dB typ adjustable, 72 dB fixed, 68 dB on the 5.0 V version
- **Adjust pin current**: 55 µA typ, 120 µA max
- **Thermal regulation**: 0.008 %/W typ, 0.04 %/W max
- **RMS output noise**: 0.003 % of VOUT (10 Hz to 10 kHz)
- **Long term stability**: 0.3 % typ, 1 % max (1000 h at 125 °C)
- **Protection**. Internal current limit and thermal shutdown at 165 °C junction
- **Thermal resistance θJA**: SOT-223 90 °C/W, TO-252 80 °C/W, SO-8 160 °C/W (θJC 15 °C/W max)
- **Operating junction temperature**: −40 to +125 °C; storage −65 to +150 °C
- **Required output capacitor**: 22 µF solid tantalum (part of the loop compensation)

## Pin configuration

On **both SOT-223 and TO-252 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. Both footprints shipped here carry the tab as pad 2.

### SOT-223 and TO-252: 3 terminals plus tab

| Pin | Name | Function |
|---|---|---|
| 1 | GND/ADJ | Ground on fixed versions; feedback (adjust) node on the adjustable version |
| 2 | VOUT | Regulated output. Also the metal tab |
| 3 | VIN | Unregulated input, 15 V max |
| n/a | TAB | Thermal pad, bonded to pin 2 (VOUT) |

### 8-lead SOIC

| Pin | Name | Function |
|---|---|---|
| 1 | GND/ADJ | Ground on fixed versions; adjust node on the adjustable version |
| 2 | VOUT | Regulated output |
| 3 | VOUT | Regulated output. Tie all VOUT leads together |
| 4 | VIN | Unregulated input, 15 V max |
| 5 | N/C | No internal connection |
| 6 | VOUT | Regulated output |
| 7 | VOUT | Regulated output |
| 8 | N/C | No internal connection |

## Component variants

All variants are the **same AMS1117 silicon**. The order code carries two independent choices: the **package** (a letter pair after the base part) and the **output voltage** (a suffix). A blank voltage suffix means the **adjustable** version. Every version is available in all three packages.

The order code is `AMS1117` `{CD | CS | blank}` `-{voltage}`. Where `CD` = TO-252 (DPAK), `CS` = 8-lead SOIC, blank = SOT-223.

| Package | Code | Body | θJA | Max dissipation | Fixed order codes |
|---|---|---|---|---|---|
| SOT-223 | *(none)* | 6.30 to 6.71 × 3.30 to 3.71 mm, 1.80 mm max | 90 °C/W | 1.2 W | `AMS1117-1.5` … `AMS1117-5.0` |
| TO-252 (DPAK) | `CD` | 6.48 to 6.73 × 5.97 to 6.22 mm, 2.21 to 2.39 mm | 80 °C/W | 2.2 W | `AMS1117CD-1.5` … `AMS1117CD-5.0` |
| 8-lead SOIC | `CS` | 4.80 to 5.00 × 3.81 to 3.99 mm, 1.27 mm pitch | 160 °C/W | 780 mW | `AMS1117CS-1.5` … `AMS1117CS-5.0` |

### Output voltage versions

Limits at TJ = 25 °C. Load regulation is measured at 0 ≤ IOUT ≤ 0.8 A.

| Version | VOUT typ | Min to max | Test VIN | Line reg. typ / max | Load reg. typ / max | Ripple rej. typ |
|---|---|---|---|---|---|---|
| AMS1117-1.5 | 1.500 V | 1.478 to 1.522 V | 3.0 V | 0.3 / 5 mV | 3 / 10 mV | 72 dB |
| AMS1117-1.8 | 1.800 V | 1.773 to 1.827 V | 3.3 V | 0.3 / 5 mV | 3 / 10 mV | 72 dB |
| AMS1117-2.5 | 2.500 V | 2.463 to 2.537 V | 4.0 V | 0.3 / 6 mV | 3 / 12 mV | 72 dB |
| AMS1117-2.85 | 2.850 V | 2.808 to 2.892 V | 4.35 V | 0.3 / 6 mV | 3 / 12 mV | 72 dB |
| AMS1117-3.3 | 3.300 V | 3.251 to 3.349 V | 4.8 V | 0.5 / 10 mV | 3 / 15 mV | 72 dB |
| AMS1117-5.0 | 5.000 V | 4.925 to 5.075 V | 6.5 V | 0.5 / 10 mV | 5 / 20 mV | 68 dB |
| AMS1117 (ADJ) | 1.250 V ref | 1.232 to 1.268 V | n/a | 0.015 / 0.2 % | 0.1 / 0.3 % | 75 dB |

**2.85 V is here for SCSI.** It is the SCSI-2 active-termination voltage. The datasheet lists "Active SCSI Terminators" as an application, and 2.85 V regulators exist almost entirely to hold a SCSI bus at spec through 110 Ω series resistors. It is the one version the UMW second source does not carry.

## Thermal design

PD = (VIN − VOUT) × IOUT, and TJ = TA(max) + PD·θJA must stay under 125 °C. The datasheet's measured SOT-223 θJA against copper area, on 1/16" FR-4 with 1 oz foil:

| Top-side copper | Back-side copper | Board area | θJA |
|---|---|---|---|
| 2500 mm² | 2500 mm² | 2500 mm² | 55 °C/W |
| 1000 mm² | 2500 mm² | 2500 mm² | 55 °C/W |
| 225 mm² | 2500 mm² | 2500 mm² | 65 °C/W |
| 100 mm² | 2500 mm² | 2500 mm² | 80 °C/W |
| 1000 mm² | 1000 mm² | 1000 mm² | 60 °C/W |
| 1000 mm² | 0 | 1000 mm² | 65 °C/W |

The tab is attached to the top-side copper in every row. The spreading copper does **not** have to be electrically connected to the tab to be effective.

## Assets

| Tool | Files |
|---|---|
| **KiCad symbols** | [`ams1117.kicad_sym`](ams1117.kicad_sym) (3-pin), [`ams1117-so8.kicad_sym`](ams1117-so8.kicad_sym) (8-lead) |
| **KiCad footprints** | [`ams1117-sot223.kicad_mod`](ams1117-sot223.kicad_mod), [`ams1117-to252.kicad_mod`](ams1117-to252.kicad_mod), [`ams1117-so8.kicad_mod`](ams1117-so8.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-so8.step`](ams1117-so8.step) / [`.glb`](ams1117-so8.glb) |
| **Canonical** | [`ams1117.adom-lbr.json`](ams1117.adom-lbr.json) |
| **Fusion 360 / EAGLE** | *Not available yet* |
| **Altium** | *Not available yet* |

## Applications

1. [**AMS1117-3.3 Molecule**](https://wiki.adom.inc/adom/ams1117-3v3-molecule). A 5 V → 3.3 V regulator brick: AMS1117-3.3 in SOT-223 with 10 µF input and 22 µF output decoupling on a machine-pin carrier.
2. [**1 A Low-Dropout Regulator UMW - AMS1117**](https://wiki.adom.inc/adom/umw-ams1117). The second-source part.

## Application notes

- **The 22 µF output capacitor is compensation, not decoupling.** The AMS1117 loop depends on it; a solid tantalum 22 µF guarantees stability across all operating conditions.
- **No protection diodes needed.** Internal resistors limit the adjust-pin current paths. A diode from output to input is only recommended when COUT is large (1000 to 5000 µF) and the input can be shorted.
- **Kelvin the divider, not the load.** On the adjustable version, connect the top of R1 to the regulator case rather than the load. Fixed versions Kelvin the top of R1 internally.
- **Adjust-pin bypassing.** For proper ripple rejection the adjust-pin capacitor's impedance at the ripple frequency must be below R1 (typically 100 to 200 Ω): >13 µF at 120 Hz with R1 = 100 Ω, but only 0.16 µF at 10 kHz.
- **Adjustable output:** VOUT = VREF(1 + R2/R1) + IADJ·R2, with VREF = 1.25 V and IADJ ≈ 55 µA.

## Provenance

- **Datasheet:** [Advanced Monolithic Systems AMS1117, *1 A Low Dropout Voltage Regulator*](docs/ams1117-datasheet-ams.pdf). Every electrical number on this page is read from it. Nothing from any second source is mixed in.
- **Symbols:** generated with `adom-symbol` to the datasheet pin connections.
- **Footprints:** KiCad 10 official library land patterns, renamed: `SOT-223-3_TabPin2`, `TO-252-3_TabPin2`, `SOIC-8_3.9x4.9mm_P1.27mm`. 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`.
- **The SCSI note** draws on the datasheet's own applications list plus the SCSI-2 active-termination literature (Linear Technology Design Note 34, which uses an LT1117-2.85 for exactly this).
- **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.