Overview

The NCP1117ST33T3G (NCP1117-3.3) is an automotive- and industrial-grade fixed +3.3V low dropout (LDO) positive linear voltage regulator manufactured by ON Semiconductor (onsemi). Serving as a high-reliability, pin-compatible alternative to the ubiquitous AMS1117-3.3 and LM1117-3.3, it delivers continuous output currents exceeding $1.0\text{ A}$ with a low dropout voltage of $1.07\text{ V}$ at $800\text{ mA}$ ($1.2\text{ V}$ maximum at $1.0\text{ A}$).

Capable of accepting input voltages up to $20.0\text{ V}$, the NCP1117 incorporates internal short-circuit current limiting, safe operating area (SOA) protection, and thermal shutdown circuitry. Packaged in an industry-standard SOT-223 surface-mount footprint, it is widely utilized across microcontroller development boards (STM32, ESP32, Arduino), networking routers, industrial PLC interfaces, and point-of-load 3.3V sub-regulation.

Quick reference

Pinout (SOT-223 Package)

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

          ┌─────────────┐
          │  TAB (VOUT) │  (Metal Tab connected internally to Pin 2 VOUT)
          ├─────────────┤
          │  NCP1117-33 │  (Top Face)
          └──┬───┬───┬──┘
             1   2   3
           GND VOUT VIN

Standard Circuit & Capacitors

       +V_IN Input (4.75V - 12V DC)
          │
       [Pin 3: VIN]
        NCP1117ST33T3G
       [Pin 2: VOUT] ──────────────┬─────────────── +3.3V Regulated Output (1.0A max)
          │                       │
       [Pin 1: GND]          [ C_OUT = 10µF Tantalum/Ceramic ]
          │                       │
   [ C_IN = 10µF Tantalum ]      GND
          │
         GND

• Input Capacitor ($C_{IN} = 10\ \mu\text{F}$): Required to filter inductive transients on power supply input traces.
• Output Capacitor ($C_{OUT} = 10\ \mu\text{F}$): Tantalum or low-ESR electrolytic capacitor required for control loop stability ($0.3\ \Omega \le \text{ESR} \le 22\ \Omega$).

Specifications

Common mistakes

• Using ultra-low ESR ($< 0.1\ \Omega$) ceramic output capacitors without damping: The internal NPN Darlington pass-transistor architecture requires a small amount of ESR ($0.3\ \Omega \dots 2.2\ \Omega$) in the output capacitor for loop phase margin. Connecting a modern ceramic capacitor with $< 0.05\ \Omega$ ESR can cause high-frequency oscillations unless a small $0.5\ \Omega$ resistor is placed in series with the ceramic cap (or a standard tantalum capacitor is used).
• Overheating on 12V-to-3.3V conversion: Stepping down $12\text{V}$ to $3.3\text{V}$ at $500\text{mA}$ dissipates $(12 - 3.3) \times 0.5 = 4.35\text{ Watts}$. An SOT-223 package with typical PCB thermal resistance ($\approx 65^\circ\text{C/W}$) can only dissipate $\approx 1.5\text{ Watts}$ before exceeding $150^\circ\text{C}$ junction temperature. Keep input voltages below $6.0\text{V}$ for continuous loads $> 500\text{ mA}$.

Notes

• Pin-to-Pin Compatibility: The NCP1117 is an exact pin-for-pin drop-in replacement for the AMS1117, LM1117, and AZ1117 series, offering higher maximum input voltage ($20\text{V}$ vs $15\text{V}$) and tighter output voltage tolerance ($\pm 1\%$).