Voltage Regulators & LDOsActive

AMS1117-3.3

Manufacturer: Advanced Monolithic Systems, Various

1A low-dropout positive linear voltage regulator with fixed 3.3V output in SOT-223 package.

PackagesSOT-223

Supply voltage4.75 – — V

Technical Overview

The AMS1117-3.3 is a fixed 3.3 V low-dropout linear regulator from Advanced Monolithic Systems, common on development boards such as NodeMCU and the STM32 Blue Pill. It delivers up to 1 A, with dropout of 1.1 V typical and 1.3 V maximum at 0.8 A (higher above 0.8 A), an on-chip trimmed reference, and protection against short circuit and thermal overload. The facts on this page come from the AMS datasheet; boards often carry compatible 1117 parts from other vendors whose limits and capacitor requirements can differ.

Package Pinout & Alternate Functions

Interactive package pinout and pin mapping for SOT-223-4.

Package illustration, not a dimensioned mechanical drawing.

4 / 4 pins

Pin name	Type	5V Tolerant	Alternate functions / details
GND/ADJ	ground	—	Ground for fixed version, or adjust feedback node
VOUT	power out	—	Regulated 3.3V output (electrically connected to tab)
VIN	power in	—	Unregulated input voltage (15 V absolute maximum; at least 4.75 V for regulation)
VOUT (TAB)	power out	—	Large thermal tab, connected to VOUT

Key Specifications

Parametric attributes

Parameter	Typical	Unit	Test condition
Output Voltage(V_out)	3.3	V	—
Dropout Voltage(V_drop)	1.1	V	IOUT = 0.8 A; higher above 0.8 A
Max Output Current(I_out)	1000	mA	—
Quiescent Current(I_q)	5	mA	—
Minimum Load Current(I_load_min)	5	mA	(VIN − VOUT) = 1.5 V; regulation guaranteed above 10 mA
Regulation Guaranteed Up To(P_reg)	1.2	W	SOT-223; absolute maximum dissipation is internally limited
Input Voltage (VIN − VOUT ≤ 12 V for specified regulation)(V_in_max)	4.75 (test condition)	V	15 V is the absolute maximum

Absolute Maximum Ratings

Max output / pin current	1000 mA
Operating junction temperature	-40 – 125 °C
Storage temperature	-65 – 150 °C

Hardware Engineering Gotchas

Real-world hardware caveats, PCB layout constraints and silicon errata to know before manufacturing.

CRITICAL

Output Capacitor Is Required for Stability

The regulator relies on its output capacitor for frequency compensation. AMS documents 22 µF solid tantalum on the output as stable for all operating conditions; without a bypass capacitor on ADJ, smaller capacitors also work. Some 1117 parts from other vendors specify a capacitor ESR window, so very low-ESR ceramics alone can oscillate on those.

Mitigation: Use 22 µF solid tantalum on VOUT (and 10 µF on VIN), or follow the capacitor requirements of the exact vendor part on your board.

WARNING

Thermal Tab Is VOUT, Not GND

The SOT-223 tab is connected to the output (pin 2). Tying the tab to a ground copper pour shorts the 3.3 V rail.

Mitigation: Assign the copper under the tab to the 3.3 V net, not to the ground plane.

WARNING

Minimum Load of 10 mA

Regulation is guaranteed only when the output current exceeds 10 mA. With no load the output can rise above 3.3 V.

Mitigation: Make sure the circuit draws at least 10 mA, or add a bleeder resistor (about 330 Ω at 3.3 V) when the load can be absent.

Cross-Reference & Equivalents

Part number (MPN)	Manufacturer	Compatibility	Electrical differences / BOM considerations
LM1117-3.3	Texas Instruments	pin to pin drop in	Same SOT-223 pin order (ADJ/GND, VOUT, VIN). Check the LM1117 datasheet for its regulation figures and output-capacitor requirements.

Found on These Boards

This component is physically fitted to the following reference development boards in CircuitBase:

NodeMCU V2

3.3V Wi-Fi Power Regulator

STM32 Blue Pill

3.3V Core Regulator

Official Documentation & Cited Datasheets

Primary semiconductor vendor datasheets, errata, and application notes.

DATASHEETAdvanced Monolithic Systems

AMS1117 1A Low Dropout Voltage Regulator Datasheet

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