# AMS1117

Advanced Monolithic Systems 1 A LDO · AMS

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

This page is the Advanced Monolithic Systems part only. Everything below 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 instead.
Output 1 A Dropout 1.3 V max VIN 15 V max Versions 6 fixed + ADJ Packages SOT-223 · TO-252 · SO-8 Pins 3 (8 on SO-8)

## At a glance

Output current
1 A
Current limit 1.1 A typ · 900 mA min
Dropout
1.3 V max
1.1 V typ at IOUT = 0.8 A
Fixed outputs
6 versions
1.5 · 1.8 · 2.5 · 2.85 · 3.3 · 5.0 V
Adjustable
1.25 V ref
VOUT = VREF(1 + R2/R1) + IADJR2
Packages
3 options
SOT-223 · TO-252 (DPAK) · 8L SOIC
Junction temp
−40 to +125 °C
Thermal shutdown at 165 °C

## 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, IOUT = 10 mA)
Dropout voltage 1.1 V typ, 1.3 V max at IOUT = 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), 10 mA ≤ IOUT ≤ 0.8 A
Current limit 900 mA min / 1100 mA typ / 1500 mA max at VIN − VOUT = 1.5 V
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 (120 Hz, COUT = 22 µF)
Adjust pin current 55 µA typ, 120 µA max · change 0.2 µA typ, 5 µA max
Thermal regulation 0.008 %/W typ, 0.04 %/W max (30 ms pulse)
RMS output noise 0.003 % of VOUT (10 Hz to 10 kHz)
Temperature stability 0.5 % typ
Long term stability 0.3 % typ, 1 % max (1000 h at 125 °C)
Protection Internal current limit + thermal shutdown at 165 °C junction
Thermal resistance θJA SOT-223 90 °C/W* · TO-252 80 °C/W · SO-8 160 °C/W (*46 °C/W achievable with copper area)
Thermal resistance θJC 15 °C/W max, all packages
Operating junction temp−40 to +125 °C · storage −65 to +150 °C
Soldering Lead temperature 265 °C, 25 s
Required output cap 22 µF solid tantalum. Part of the loop compensation, not optional

## Symbol & footprint

Schematic symbol: hover a pin for its function
PCB footprint: switch package bottom-right (SOT-223 / TO-252 / SO-8)

## Pin map 3 terminals on SOT-223 / TO-252, 8 leads on SOIC

On both SOT-223 and TO-252 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. Both footprints shipped here carry the tab as pad 2.
SOT-223 & TO-2523 + tab

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 SOIC8

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.
AMS1117 CD-3.3
AMS1117
base part: 1 A LDO
CD / CS / blank
`CD` = TO-252 (DPAK) · `CS` = 8-lead SOIC · blank = SOT-223
-3.3
fixed output voltage. Blank means the adjustable version

### SOT-223no letter

6.30 to 6.71 × 3.30 to 3.71 mm, 1.80 mm max height · 2.30 mm lead pitch · tab = VOUT
Fixed: `AMS1117-1.5` `-1.8` `-2.5` `-2.85` `-3.3` `-5.0`
Adjustable: `AMS1117`
θJA 90 °C/W · 1.2 W max dissipation

### TO-252 (DPAK) `CD`

6.48 to 6.73 × 5.97 to 6.22 mm body, 2.21 to 2.39 mm height · tab = VOUT
Fixed: `AMS1117CD-1.5` `-1.8` `-2.5` `-2.85` `-3.3` `-5.0`
Adjustable: `AMS1117CD`
θJA 80 °C/W · 2.2 W max dissipation. The best thermal option

### 8-lead SOIC `CS`

4.80 to 5.00 × 3.81 to 3.99 mm body, 1.27 mm pitch · VOUT on four leads
Fixed: `AMS1117CS-1.5` `-1.8` `-2.5` `-2.85` `-3.3` `-5.0`
Adjustable: `AMS1117CS`
θJA 160 °C/W · 780 mW max dissipation: lowest power

## Output voltage versions

Limits at TJ = 25 °C. The test VIN is the datasheet condition for each part; 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) + PDθJA 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. Note the spreading copper does not have to be electrically connected to the tab to be effective. A plane on the opposite side of the board works.

## Assets

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

KiCad symbols | ams1117.kicad_sym (3-pin) · ams1117-so8.kicad_sym (8-lead)
KiCad footprints | AMS1117_SOT-223 · AMS1117_TO-252 · AMS1117_SO-8
3D models | SOT-223 .step / .glb · TO-252 .step / .glb · SO-8 .step / .glb
Canonical | ams1117.adom-lbr.json
Fusion 360 / EAGLE | Not available yet
Altium | Not available yet

## Implementation

- 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.
- 1 A Low-Dropout Regulator UMW - AMS1117. The second-source part. Different voltage lineup, different third package, different limits.

## 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. Bypassing the adjust pin improves ripple rejection but raises the output-capacitor requirement.
- 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; the internal diode already handles 50 to 100 A microsecond surges.
- Kelvin the divider, not the load. On the adjustable version, connect the top of R1 to the regulator case rather than the load, so parasitic line resistance is not multiplied by (R2+R1)/R1. Fixed versions Kelvin the top of R1 internally, so the ground pin can do negative-side sensing.
- 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). With R1 = 100 Ω that is >13 µF at 120 Hz, but only 0.16 µF at 10 kHz.
- Adjustable output: VOUT = VREF(1 + R2/R1) + IADJR2, with VREF = 1.25 V and IADJ ≈ 55 µA. The IADJ term is small and constant and can usually be ignored.

## Datasheet

Download the full datasheet (PDF) · Advanced Monolithic Systems, AMS1117 1 A Low Dropout Voltage Regulator · advanced-monolithic.com

## Provenance

- Every electrical number on this page is read from the Advanced Monolithic Systems datasheet embedded above. Features and ordering from page 1, limits from the Electrical Characteristics tables on pages 2 to 3, application and thermal guidance from pages 4 to 5, package dimensions from pages 7 to 8. Nothing from any second source is mixed in.
- Symbols: generated with `adom-symbol` to the datasheet pin connections (3-pin fixed/adjustable version, and the 8-lead SOIC pinout).
- Footprints: the KiCad 10 official library land patterns, renamed: `SOT-223-3_TabPin2`, `TO-252-3_TabPin2` and `SOIC-8_3.9x4.9mm_P1.27mm`. The `TabPin2` variants are the correct choice 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`, `SOIC-8_3.9x4.9mm_P1.27mm.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`.
- 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, so nothing is shipped here until it can be checked in the tool itself.