Overview

The AMS1117-3.3 is a popular 800 mA Low Dropout (LDO) positive linear voltage regulator manufactured by Advanced Monolithic Systems (and generic semiconductor foundries). Populated on nearly every Arduino Mega/Uno, ESP8266 NodeMCU, ESP32, and Raspberry Pi accessory PCB, it regulates 5.0V5.0\text{V} USB or 12V12\text{V} DC input power down to a stable +3.3V+3.3\text{V} DC power rail for microcontrollers and sensors.

Housed in a compact 3-pin SOT-223 package, the AMS1117 features a low dropout voltage of 1.1V1.1\text{V} at maximum 800 mA800\text{ mA} load current, built-in short circuit protection, and thermal overload protection.

Quick reference

Regulator TypeLow Dropout (LDO) Positive Linear Regulator
PackageSOT-223 (Tab connected to Pin 2 VOUT) / TO-252
Pinout (SOT-223 Front)Pin 1: Ground (GND), Pin 2: Output (VOUT), Pin 3: Input (VIN)
Fixed Output Voltage+3.3 V+3.3\text{ V} DC (±1.5%\pm 1.5\% initial accuracy)
Input Voltage Range (VINV_{IN})4.5 V4.5\text{ V} to 15.0 V15.0\text{ V} DC
Dropout Voltage1.1 V1.1\text{ V} max at IOUT=800 mAI_{OUT} = 800\text{ mA} (1.0V1.0\text{V} at 100mA100\text{mA})
Continuous Output Current (IOUTI_{OUT})800 mA800\text{ mA} max (temperature dependent)
Ripple Rejection Ratio60 dB…75 dB60\text{ dB} \dots 75\text{ dB} at f=120 Hzf = 120\text{ Hz}

Pinout (SOT-223 Package)

Looking at the top face of the SOT-223 package with large metal tab at top and 3 leads pointing down:

text
        ┌───────────────┐
        │ [AMS1117 Tab] │  (Metal Tab connected internally to Pin 2 VOUT)
        ├───────────────┤
        │  AMS1117-3.3  │  (Top Package Face)
        └─┬────┬────┬───┘
          1    2    3
         GND  VOUT IN
PinNameDescription
1GND / ADJGround reference (0 V) for fixed versions
2VOUT / TABRegulated +3.3V DC output pin (connected to large heatsink tab)
3VINUnregulated DC input voltage pin (+4.5V to +15V DC)

Specifications

ParameterSymbolMinTypMaxUnitConditions
Regulated Output VoltageVOUTV_{OUT}3.2503.3003.350V4.75V≤VIN≤10V,0≤IO≤800mA4.75\text{V} \le V_{IN} \le 10\text{V}, 0 \le I_O \le 800\text{mA}
Dropout VoltageVDV_D—1.11.3VIOUT=800mA,TJ=25∘CI_{OUT} = 800\text{mA}, T_J = 25^\circ\text{C}
Current LimitILIMITI_{LIMIT}90011001500mAShort circuit peak limit
Quiescent CurrentIQI_Q—5.010.0mAVIN=5.0VV_{IN} = 5.0\text{V}
Line RegulationReglineReg_{line}—0.20.5%VIN=4.8V…12VV_{IN} = 4.8\text{V} \dots 12\text{V}
Load RegulationRegloadReg_{load}—0.21.0%IOUT=10mA…800mAI_{OUT} = 10\text{mA} \dots 800\text{mA}

Decoupling Capacitor & Stability Requirements

text
       +5V USB / Input Power
          │
       [Pin 3: VIN]
        AMS1117-3.3
       [Pin 2: VOUT] ─────────────┬─────────────── +3.3V Regulated Rail
          │                       │
       [Pin 1: GND]         [ C2 = 22µF Tantalum/Electrolytic ]
          │                       │
   [ C1 = 10µF Tantalum ]        GND
          │
         GND
Important

Minimum ESR & Capacitor Requirements:

  • The AMS1117 requires a minimum 22 μF22\ \mu\text{F} output capacitor (10 μF10\ \mu\text{F} minimum tantalum or electrolytic) to maintain loop stability and prevent high-frequency oscillation.
  • Avoid using ceramic output capacitors with ultra-low ESR (<0.1 Ω<0.1\ \Omega) directly on older AMS1117 chips without adding a small series resistor (0.5 Ω0.5\ \Omega), or add a parallel 10 μF10\ \mu\text{F} electrolytic capacitor.

Common mistakes

  • Thermal overload from 12V inputs: Dropping 12V to 3.3V at 500mA creates PD=(12V−3.3V)×0.5A=4.35 WattsP_D = (12\text{V} - 3.3\text{V}) \times 0.5\text{A} = 4.35\text{ Watts}. The tiny SOT-223 package PCB copper trace area can only dissipate ∼1.0 Watt\sim 1.0\text{ Watt}, causing thermal shutdown. Limit VINV_{IN} to 5V when drawing high current (>300mA>300\text{mA}).
  • Shorting VOUT tab to grounded metal enclosures: On SOT-223 AMS1117 packages, the large metal tab is connected to Pin 2 (VOUT), NOT Ground. Grounding the tab short-circuits the 3.3V output.

Notes

  • AMS1117 Output Variants: AMS1117-1.8 (1.8V), AMS1117-2.5 (2.5V), AMS1117-3.3 (3.3V), AMS1117-5.0 (5.0V), AMS1117-ADJ (Adjustable).

Assets & downloads