hardware
[DEPRECATED] 1 A Low-Dropout Regulator - AMS1117 → ams-ams1117 / umw-ams1117
Public Made by Adomby adom
DEPRECATED - split by manufacturer. Use adom/ams-ams1117 (Advanced Monolithic Systems: 1.5-5.0 V incl. 2.85 V, SOT-223/TO-252/SO-8) or adom/umw-ams1117 (UMW/Youtai: 1.2-5.0 V, SOT-223/TO-252/SOT-89). The two vendors ship different voltage lineups, different packages and materially different limits.
DEPRECATED: split by manufacturer
AMS1117 is second-sourced, and the two manufacturers ship different voltage lineups, different packages and materially different limits. Merging them onto one page meant every number needed a vendor caveat. This page has been split in two:
- 1 A Low-Dropout Regulator AMS - AMS1117: Advanced Monolithic Systems, the original. 1.5 to 5.0 V including 2.85 V; SOT-223 / TO-252 / SO-8.
- 1 A Low-Dropout Regulator UMW - AMS1117: UMW / Youtai Semiconductor, the second source. 1.2 V to 5.0 V; SOT-223 / TO-252 / SOT-89.
Check your BOM before picking one. If it does not name a manufacturer, design to the tighter of the two sets of limits. The content below is kept for reference and is no longer maintained.
AMS1117: 1 A Low-Dropout Voltage Regulator
The AMS1117 is a three-terminal 1 A low-dropout linear voltage regulator, available in seven fixed voltages (1.2 / 1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V) across its two manufacturers, 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.
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 (AMS) · 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V (UMW); 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
- Input voltage: 15 V absolute maximum (AMS) · 18 V absolute maximum, 12 V recommended (UMW)
- Line regulation: 0.2 % max
- Load regulation: 0.4 % max
- Current limit: 900 mA min / 1100 typ / 1500 max (AMS) · 2.1 A min / 2.5 A max (UMW)
- Quiescent current: 5 mA typ, 11 mA max
- Ripple rejection: 60 dB min; 75 dB typ adjustable, 72 dB fixed, 68 dB on the 5.0 V version
- Protection. Internal current limit and thermal shutdown at 165 °C (AMS) / 150 °C (UMW)
- Thermal resistance θJA: SOT-223 90 °C/W, TO-252 80 °C/W, SO-8 160 °C/W
- Operating junction temperature: −40 to +125 °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.
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 | Available from |
|---|---|---|---|---|---|
| SOT-223 | (none) | 6.30 to 6.71 × 3.30 to 3.71 mm, 1.80 mm max | 90 °C/W (AMS) · 88 (UMW) | 1.2 W | AMS · UMW |
| TO-252 (DPAK) | CD |
6.48 to 6.73 × 5.97 to 6.22 mm, 2.21 to 2.39 mm | 80 °C/W (AMS) · 86 (UMW) | 2.2 W | AMS · UMW |
| 8-lead SOIC | CS |
4.80 to 5.00 × 3.81 to 3.99 mm, 1.27 mm pitch | 160 °C/W | 780 mW | AMS only |
| SOT-89-3L | S |
4.50 × 2.45 mm | 102 °C/W | n/a | UMW only (no CAD here yet) |
Output voltage versions
Seven fixed voltages exist across the two manufacturers, but no single vendor sells all seven: AMS carries 2.85 V and not 1.2 V, UMW carries 1.2 V and not 2.85 V. Limits are from whichever datasheet defines that version.
| Version | VOUT typ | Min to max at 25 °C | Accuracy | Ripple rej. typ | Available from |
|---|---|---|---|---|---|
| AMS1117-1.2 | 1.200 V | 1.176 to 1.224 V | 2 % | 75 dB | UMW only |
| AMS1117-1.5 | 1.500 V | 1.478 to 1.522 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-1.8 | 1.800 V | 1.773 to 1.827 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-2.5 | 2.500 V | 2.463 to 2.537 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-2.85 | 2.850 V | 2.808 to 2.892 V | 1.5 % | 72 dB | AMS only |
| AMS1117-3.3 | 3.300 V | 3.251 to 3.349 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-5.0 | 5.000 V | 4.925 to 5.075 V | 1.5 % | 68 dB | AMS · UMW |
| AMS1117-ADJ | 1.250 V ref | 1.232 to 1.268 V | 1.5 % | 75 dB | AMS · UMW |
The adjustable version is ordered as plain AMS1117 by AMS and as AMS1117-ADJ by UMW.
The two datasheets
AMS1117 is not one company's part. It began at Advanced Monolithic Systems, became a de-facto industry-standard pinout, and is now second-sourced by several vendors who each build their own die and publish their own datasheet. Both datasheets on this page are genuine and neither is a revision of the other. They describe different silicon from different companies that happen to share a part number, a pinout and a package set.
| Advanced Monolithic Systems (primary) | UMW / Youtai Semiconductor (alternate) | |
|---|---|---|
| Fixed voltages | 1.5 · 1.8 · 2.5 · 2.85 · 3.3 · 5.0 V | 1.2 · 1.5 · 1.8 · 2.5 · 3.3 · 5.0 V |
| Packages | SOT-223 · TO-252 · SO-8 | SOT-223-3L · TO-252-2L · SOT-89-3L |
| VIN absolute max | 15 V | 18 V (12 V recommended) |
| Current limit | 0.9 A min / 1.1 typ / 1.5 max | 2.1 A min / 2.5 A max |
| Thermal shutdown | 165 °C | 150 °C |
| Dropout spec point | 1.3 V max at 0.8 A | 1.30 V max at 1.0 A (1.20 V at 100 mA) |
| Line / load regulation | 0.2 % / 0.4 % max | 18 mV / 18 mV max |
| Quiescent current | 5 mA typ, 11 max | 5 mA typ, 10 max |
| Adjust pin current | 55 µA typ, 120 max | 60 µA typ, 120 max |
| θJA | SOT-223 90 · TO-252 80 · SO-8 160 °C/W | SOT-223 88 · TO-252 86 · SOT-89 102 °C/W |
| ESD rating | not specified | 2000 V min |
Why they differ
- Different companies, different silicon. AMS1117 is Advanced Monolithic Systems' original part number, not a JEDEC standard. UMW (Youtai Semiconductor) builds its own die to the same three-terminal pinout and publishes its own tested limits. The gaps are real device differences, not documentation errors, and they are why a board qualified on one vendor's part is not automatically qualified on the other's.
- The voltage lineups follow each vendor's market. 2.85 V is the SCSI-2 active-termination voltage. The AMS 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. UMW's applications are laptops, cellular phones and SMPS post-regulation, so it drops 2.85 V and carries 1.2 V instead, which is the modern SoC / FPGA / gigabit-PHY core rail.
- Some differences are units and test conditions, not silicon. AMS quotes line and load regulation as a percentage and specifies dropout at 0.8 A; UMW quotes millivolts and specifies dropout at 100 mA, 500 mA and 1 A. The current limit and thermal-shutdown differences, by contrast, are genuine.
- The 1.2 V part is the loosest of the family. UMW rates it to 2 % where every other version is 1.5 %, because 1.2 V sits closest to the 1.25 V bandgap reference and leaves the least headroom for trimming.
- Practical consequence: if a design needs 2.85 V you must buy AMS or another vendor that carries it; if it needs 1.2 V you must buy UMW or another second source. For the five shared voltages, either works, but design to the tighter of the two sets of limits if the BOM does not pin a manufacturer.
Assets
| Tool | Files |
|---|---|
| KiCad symbols | ams1117.kicad_sym (3-pin), ams1117-so8.kicad_sym (8-lead) |
| KiCad footprints | ams1117-sot223.kicad_mod, ams1117-to252.kicad_mod, ams1117-so8.kicad_mod |
| 3D models | ams1117-sot223.step / .glb, ams1117-to252.step / .glb, ams1117-so8.step / .glb |
| Canonical | ams1117.adom-lbr.json |
| Fusion 360 / EAGLE | Not available yet |
| Altium | Not available yet |
Applications
Boards on the Adom wiki that use the AMS1117:
- AMS1117-3.3 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.
- 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.
Per-voltage pages: adom/ams1117-3-3 · adom/ams1117-1-2 (the 1.2 V version, documented by the UMW datasheet on this page).
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, so no diode from ADJ to output or input is required. 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.
- Copper is the heat sink. θJA falls from 90 to about 55 °C/W with 2500 mm² of copper on both sides, and the spreading copper does not have to be electrically connected to the tab.
- Adjustable output: VOUT = VREF(1 + R2/R1) + IADJ·R2, with VREF = 1.25 V and IADJ ≈ 55 µA.
Provenance
- Primary datasheet: Advanced Monolithic Systems AMS1117, 1 A Low Dropout Voltage Regulator. Every unattributed number on this page is read from it.
- Alternate datasheet: UMW / Youtai Semiconductor AMS1117, 1 A LDO Voltage Regulator. The source for the 1.2 V version, the SOT-89 package, the 18 V input rating, the 2.1 to 2.5 A current limit and the 150 °C thermal shutdown.
- Symbols: generated with
adom-symbolto 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. TheTabPin2variants 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.
> # DEPRECATED: split by manufacturer
>
> AMS1117 is second-sourced, and the two manufacturers ship **different voltage lineups, different packages and materially different limits**. Merging them onto one page meant every number needed a vendor caveat. This page has been split in two:
>
> - **[1 A Low-Dropout Regulator AMS - AMS1117](https://wiki.adom.inc/adom/ams-ams1117)**: Advanced Monolithic Systems, the original. 1.5 to 5.0 V including **2.85 V**; SOT-223 / TO-252 / **SO-8**.
> - **[1 A Low-Dropout Regulator UMW - AMS1117](https://wiki.adom.inc/adom/umw-ams1117)**: UMW / Youtai Semiconductor, the second source. **1.2 V** to 5.0 V; SOT-223 / TO-252 / **SOT-89**.
>
> Check your BOM before picking one. If it does not name a manufacturer, design to the tighter of the two sets of limits. The content below is kept for reference and is no longer maintained.
# AMS1117: 1 A Low-Dropout Voltage Regulator
The **AMS1117** is a three-terminal **1 A low-dropout linear voltage regulator**, available in seven fixed voltages (1.2 / 1.5 / 1.8 / 2.5 / 2.85 / 3.3 / 5.0 V) across its two manufacturers, 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.
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 (AMS) · 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V (UMW); 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
- **Input voltage**: 15 V absolute maximum (AMS) · 18 V absolute maximum, 12 V recommended (UMW)
- **Line regulation**: 0.2 % max
- **Load regulation**: 0.4 % max
- **Current limit**: 900 mA min / 1100 typ / 1500 max (AMS) · 2.1 A min / 2.5 A max (UMW)
- **Quiescent current**: 5 mA typ, 11 mA max
- **Ripple rejection**: 60 dB min; 75 dB typ adjustable, 72 dB fixed, 68 dB on the 5.0 V version
- **Protection**. Internal current limit and thermal shutdown at 165 °C (AMS) / 150 °C (UMW)
- **Thermal resistance θJA**: SOT-223 90 °C/W, TO-252 80 °C/W, SO-8 160 °C/W
- **Operating junction temperature**: −40 to +125 °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.
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 | Available from |
|---|---|---|---|---|---|
| SOT-223 | *(none)* | 6.30 to 6.71 × 3.30 to 3.71 mm, 1.80 mm max | 90 °C/W (AMS) · 88 (UMW) | 1.2 W | AMS · UMW |
| TO-252 (DPAK) | `CD` | 6.48 to 6.73 × 5.97 to 6.22 mm, 2.21 to 2.39 mm | 80 °C/W (AMS) · 86 (UMW) | 2.2 W | AMS · UMW |
| 8-lead SOIC | `CS` | 4.80 to 5.00 × 3.81 to 3.99 mm, 1.27 mm pitch | 160 °C/W | 780 mW | AMS only |
| SOT-89-3L | `S` | 4.50 × 2.45 mm | 102 °C/W | n/a | UMW only *(no CAD here yet)* |
### Output voltage versions
Seven fixed voltages exist across the two manufacturers, but **no single vendor sells all seven**: AMS carries 2.85 V and not 1.2 V, UMW carries 1.2 V and not 2.85 V. Limits are from whichever datasheet defines that version.
| Version | VOUT typ | Min to max at 25 °C | Accuracy | Ripple rej. typ | Available from |
|---|---|---|---|---|---|
| AMS1117-1.2 | 1.200 V | 1.176 to 1.224 V | 2 % | 75 dB | **UMW only** |
| AMS1117-1.5 | 1.500 V | 1.478 to 1.522 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-1.8 | 1.800 V | 1.773 to 1.827 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-2.5 | 2.500 V | 2.463 to 2.537 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-2.85 | 2.850 V | 2.808 to 2.892 V | 1.5 % | 72 dB | **AMS only** |
| AMS1117-3.3 | 3.300 V | 3.251 to 3.349 V | 1.5 % | 72 dB | AMS · UMW |
| AMS1117-5.0 | 5.000 V | 4.925 to 5.075 V | 1.5 % | 68 dB | AMS · UMW |
| AMS1117-ADJ | 1.250 V ref | 1.232 to 1.268 V | 1.5 % | 75 dB | AMS · UMW |
The adjustable version is ordered as plain `AMS1117` by AMS and as `AMS1117-ADJ` by UMW.
## The two datasheets
**AMS1117 is not one company's part.** It began at Advanced Monolithic Systems, became a de-facto industry-standard pinout, and is now second-sourced by several vendors who each build their own die and publish their own datasheet. Both datasheets on this page are genuine and neither is a revision of the other. They describe **different silicon from different companies** that happen to share a part number, a pinout and a package set.
| | Advanced Monolithic Systems (primary) | UMW / Youtai Semiconductor (alternate) |
|---|---|---|
| Fixed voltages | 1.5 · 1.8 · 2.5 · **2.85** · 3.3 · 5.0 V | **1.2** · 1.5 · 1.8 · 2.5 · 3.3 · 5.0 V |
| Packages | SOT-223 · TO-252 · **SO-8** | SOT-223-3L · TO-252-2L · **SOT-89-3L** |
| VIN absolute max | 15 V | 18 V (12 V recommended) |
| Current limit | 0.9 A min / 1.1 typ / 1.5 max | **2.1 A min / 2.5 A max** |
| Thermal shutdown | 165 °C | 150 °C |
| Dropout spec point | 1.3 V max at **0.8 A** | 1.30 V max at **1.0 A** (1.20 V at 100 mA) |
| Line / load regulation | 0.2 % / 0.4 % max | 18 mV / 18 mV max |
| Quiescent current | 5 mA typ, 11 max | 5 mA typ, 10 max |
| Adjust pin current | 55 µA typ, 120 max | 60 µA typ, 120 max |
| θJA | SOT-223 90 · TO-252 80 · SO-8 160 °C/W | SOT-223 88 · TO-252 86 · SOT-89 102 °C/W |
| ESD rating | not specified | 2000 V min |
### Why they differ
- **Different companies, different silicon.** AMS1117 is Advanced Monolithic Systems' original part number, not a JEDEC standard. UMW (Youtai Semiconductor) builds its own die to the same three-terminal pinout and publishes its own tested limits. The gaps are real device differences, not documentation errors, and they are why a board qualified on one vendor's part is not automatically qualified on the other's.
- **The voltage lineups follow each vendor's market.** 2.85 V is the SCSI-2 active-termination voltage. The AMS 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. UMW's applications are laptops, cellular phones and SMPS post-regulation, so it drops 2.85 V and carries 1.2 V instead, which is the modern SoC / FPGA / gigabit-PHY core rail.
- **Some differences are units and test conditions, not silicon.** AMS quotes line and load regulation as a percentage and specifies dropout at 0.8 A; UMW quotes millivolts and specifies dropout at 100 mA, 500 mA and 1 A. The current limit and thermal-shutdown differences, by contrast, are genuine.
- **The 1.2 V part is the loosest of the family.** UMW rates it to 2 % where every other version is 1.5 %, because 1.2 V sits closest to the 1.25 V bandgap reference and leaves the least headroom for trimming.
- **Practical consequence:** if a design needs 2.85 V you must buy AMS or another vendor that carries it; if it needs 1.2 V you must buy UMW or another second source. For the five shared voltages, either works, but design to the tighter of the two sets of limits if the BOM does not pin a manufacturer.
## 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
Boards on the Adom wiki that use the AMS1117:
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. [**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.
Per-voltage pages: [adom/ams1117-3-3](https://wiki.adom.inc/adom/ams1117-3-3) · [adom/ams1117-1-2](https://wiki.adom.inc/adom/ams1117-1-2) (the 1.2 V version, documented by the UMW datasheet on this page).
## 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, so no diode from ADJ to output or input is required. 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.
- **Copper is the heat sink.** θJA falls from 90 to about 55 °C/W with 2500 mm² of copper on both sides, and the spreading copper does not have to be electrically connected to the tab.
- **Adjustable output:** VOUT = VREF(1 + R2/R1) + IADJ·R2, with VREF = 1.25 V and IADJ ≈ 55 µA.
## Provenance
- **Primary datasheet:** [Advanced Monolithic Systems AMS1117, *1 A Low Dropout Voltage Regulator*](docs/ams1117-datasheet.pdf). Every unattributed number on this page is read from it.
- **Alternate datasheet:** [UMW / Youtai Semiconductor AMS1117, *1 A LDO Voltage Regulator*](docs/ams1117-datasheet-umw.pdf). The source for the 1.2 V version, the SOT-89 package, the 18 V input rating, the 2.1 to 2.5 A current limit and the 150 °C thermal shutdown.
- **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`.
- **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.