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 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

8-lead SOIC

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.

Output voltage versions

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

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:

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

Applications

1. 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.
2. 1 A Low-Dropout Regulator 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. 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.