AMS1117: 1 A Low-Dropout Regulator (UMW / Youtai Semiconductor)

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

This page is the UMW / Youtai Semiconductor part only. Everything here 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.

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 SOT-89.

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
• 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
• Ripple rejection: 60 dB min, 75 dB typ (120 Hz, VIN − VOUT = 3 V)
• Adjust pin current: 60 µA typ, 120 µA max
• Output voltage temperature stability: 0.3 % 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 and 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 temperature: −40 to +125 °C recommended, 150 °C absolute maximum; storage −65 to +150 °C
• Soldering: lead temperature 260 °C, 5 s
• Required output capacitor: 22 µF tantalum covers all cases

Pin configuration

The pinout is the same on all three packages, and on all three 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. All three footprints shipped here carry the tab as pad 2.

Topside marking

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.

The order code is AMS1117 {CD | blank} -{voltage | ADJ} {S}. Where CD = TO-252-2L, blank = SOT-223-3L, and a trailing S selects SOT-89-3L.

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.

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

Applications

1. 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.
2. 1 A Low-Dropout Regulator AMS - AMS1117. The original Advanced Monolithic Systems part.

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; 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 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.

Provenance

• Datasheet: UMW / Youtai Semiconductor AMS1117, 1 A LDO Voltage Regulator. Every electrical number on this page is read from it. 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.
• Symbol: generated with adom-symbol to the datasheet's pin description table (1 = GND/ADJ, 2 = VOUT, 3 = VIN).
• Footprints: KiCad 10 official library land patterns, renamed: SOT-223-3_TabPin2, TO-252-3_TabPin2, 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, 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.