# AMS1117

UMW · Youtai Semiconductor 1 A LDO · UMW

UMW's second-source AMS1117: a positive 1 A low-dropout linear voltage regulator with a typical dropout of 1.2 V at 1 A, in fixed 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V versions or an adjustable version 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. Offered in SOT-223-3L, TO-252-2L and SOT-89-3L.

This page is the UMW / Youtai Semiconductor part only. Everything below 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 instead.
Output 1 A Dropout 1.30 V max @ 1 A VIN 18 V max Versions 6 fixed + ADJ Packages SOT-223 · TO-252 · SOT-89 Pins 3

## At a glance

Output current
1 A
Current limit 2.1 A min · 2.5 A max
Dropout
1.30 V max
1.20 V typ at the full 1 A
Fixed outputs
6 versions
1.2 · 1.5 · 1.8 · 2.5 · 3.3 · 5.0 V
Adjustable
1.25 V ref
VOUT = VREF(1 + R2/R1) + IADJR2
Packages
3 options
SOT-223-3L · TO-252-2L · SOT-89-3L
Input voltage
18 V max
12 V recommended operating maximum

## 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 (VIN(min) ≤ VIN ≤ 12 V, IOUT = 10 mA)
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 (4.25 V ≤ VIN ≤ 6.5 V)
Ripple rejection 60 dB min, 75 dB typ (120 Hz, VIN − VOUT = 3 V, 1 VPP ripple)
Adjust pin current 60 µA typ, 120 µA max · change 0.2 µA typ, 5 µA max
Output temperature stability 0.3 % typ
Temperature stability 0.5 % 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 + 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 temp−40 to +125 °C recommended · 150 °C absolute maximum
Storage temperature−65 to +150 °C
Soldering Lead temperature 260 °C, 5 s
Required output cap 22 µF tantalum covers all cases; smaller values work without adjust-pin bypassing

## Symbol & footprint

Schematic symbol: hover a pin for its function
PCB footprint: switch package bottom-right (SOT-223 / TO-252 / SOT-89)

## Pin map 3 terminals, identical across all three packages

The pinout is the same on SOT-223-3L, TO-252-2L and SOT-89-3L, and on all three the metal tab is VOUT, internally bonded to pin 2. It is the heat path, so it must be soldered to a copper pour on the output net, never to ground. All three footprints shipped here carry the tab as pad 2.
All packages3 + tab

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

Topside marking3

| 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.
AMS1117 CD-3.3 S
AMS1117
base part: 1 A LDO
CD / blank
`CD` = TO-252-2L · blank = SOT-223-3L
-3.3 / -ADJ
fixed output voltage, or `-ADJ` for the adjustable version
S
trailing `S` selects SOT-89-3L

### SOT-223-3Lno letter

5.90 to 6.70 × 3.90 ±0.30 mm body, 1.60 ±0.15 mm height · 2.30 mm TYP lead pitch · 4.60 ±0.15 mm lead span · tab = VOUT
Fixed: `AMS1117-1.2` `-1.5` `-1.8` `-2.5` `-3.3` `-5.0`
Adjustable: `AMS1117-ADJ`
RθJA 88 °C/W

### TO-252-2L `CD`

6.40 to 6.70 × 6.00 to 6.30 mm body, 2.20 to 2.30 mm height · 2.20 to 2.40 mm lead pitch · tab = VOUT
Fixed: `AMS1117CD-1.2` `-1.5` `-1.8` `-2.5` `-3.3` `-5.0`
Adjustable: `AMS1117CD-ADJ`
RθJA 86 °C/W. The best thermal option

### SOT-89-3L `S`

4.50 ±0.30 × 2.45 ±0.30 mm body, 1.50 ±0.20 mm thick · 3.00 mm BSC lead pitch · tab = VOUT
Fixed: `AMS1117-1.2S` `-1.5S` `-1.8S` `-2.5S` `-3.3S` `-5.0S`
Adjustable: `AMS1117-ADJS`
RθJA 102 °C/W · smallest footprint, marked `STK17`

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.

## 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 (0 or 10 mA ≤ IOUT ≤ 1 A).

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

KiCad symbol, all three footprints and matching 3D models, plus the canonical adom-lbr JSON the rest is generated from.

KiCad symbol | ams1117.kicad_sym (3-pin, all three packages)
KiCad footprints | AMS1117_SOT-223 · AMS1117_TO-252 · AMS1117_SOT-89
3D models | SOT-223 .step / .glb · TO-252 .step / .glb · SOT-89 .step / .glb
Canonical | ams1117.adom-lbr.json
Fusion 360 / EAGLE | Not available yet
Altium | Not available yet

## Implementation

- 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.
- 1 A Low-Dropout Regulator AMS - AMS1117. The original Advanced Monolithic Systems part. Adds 2.85 V and an 8-lead SOIC; drops 1.2 V and SOT-89.

## 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; without adjust-pin bypassing, smaller values work, but 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 happily 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.

## Datasheet

Download the full datasheet (PDF) · UMW (Youtai Semiconductor), AMS1117 1 A LDO Voltage Regulator · umw-ic.com

## Provenance

- Every electrical number on this page is read from the UMW / Youtai Semiconductor datasheet embedded above: description, features and nomenclature from page 1, absolute maximums and recommended operating conditions from page 2, the Electrical Characteristics table from page 3, pin configuration and function description from page 4, application circuits from page 5, and package outlines from pages 7 to 8. 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. See the note under the version table.
- Symbol: generated with `adom-symbol` to the datasheet's pin description table (1 = GND/ADJ, 2 = VOUT, 3 = VIN).
- Footprints: the KiCad 10 official library land patterns, renamed: `SOT-223-3_TabPin2`, `TO-252-3_TabPin2` and `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 (`SOT-223.step`, `TO-252-3_TabPin2.step`, `SOT-89-3.step`), converted to GLB with `step2glb`.
- Canonical JSON: `ams1117.adom-lbr.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, so nothing is shipped here until it can be checked in the tool itself.