If you have ever picked up an ESP8266 module, an Arduino Nano clone, or a cheap DC-DC power board, you have likely seen a small, three-legged chip labeled 1117.
The AMS1117 is arguably the most popular Low Dropout (LDO) voltage regulator in the maker and embedded electronics world. It is the go-to solution for stepping down 5V USB power to the 3.3V required by modern microcontrollers.
Despite its ubiquity, the AMS1117 is often misunderstood, leading to oscillating circuits or burned fingers. This guide covers the essential specs, the notorious capacitor requirements, and how to design it correctly.
Table of Contents
- 1. AMS1117 Datasheet & Key Specs
- 2. Circuit Design: The Capacitor Trap
- 3. AMS1117-ADJ: Adjustable Voltage Configuration
- 4. Thermal Management: Why Your LDO Gets Hot
- 5. Conclusion
1. AMS1117 Datasheet & Key Specs
The AMS1117 is a series of low dropout voltage regulators capable of providing up to 1A of output current. It comes in fixed voltage versions (1.2V, 1.8V, 2.5V, 3.3V, 5.0V) and an Adjustable (ADJ) version.
Key Specifications Matrix
| Feature | Specification | Notes |
|---|---|---|
| Max Output Current | 1A | Requires adequate heat sinking. |
| Max Input Voltage | 15V | Absolute maximum rating. |
| Dropout Voltage | 1.1V (Typ) | At 1A load. Input must be > (Vout + 1.1V). |
| Line Regulation | 0.2% | Max deviation. |
| Load Regulation | 0.4% | Max deviation. |
| Package | SOT-223 | Most common. Also available in TO-252. |
Important Note on "Low Dropout": While "1.1V" is lower than the 2.0V dropout of the ancient 7805 regulator, it is not "Ultra-Low" by modern standards. You typically need at least 4.5V input to get a stable 3.3V output.
Pinout Guide (SOT-223)
The standard SOT-223 package has 3 pins and a large Tab:
- GND / ADJ: Ground for fixed versions; Adjust pin for ADJ version.
- VOUT: Output Voltage (The large Tab is also connected to VOUT).
- VIN: Input Voltage.
Price Analysis & Stock Availability
The AMS1117 is incredibly cost-effective, costing cents per unit.
Procurement Tip: Due to its popularity, the market is flooded with clones. [Check Stock for Genuine AMS1117 at Aichiplink] to ensure you get chips that actually meet the 1A spec.
2. Circuit Design: The Capacitor Trap
This is where 90% of designs fail.
Tantalum vs. Ceramic (MLCC) Issues
The original AMS1117 datasheet specifies that the output stability requires a 22µF Tantalum capacitor.
- The Physics: The regulator relies on the capacitor having a specific ESR (Equivalent Series Resistance) to maintain the stability of its internal feedback loop.
- The Problem: Modern Ceramic capacitors (MLCC) have extremely low ESR. If you use a 22µF ceramic cap on the output, the AMS1117 may oscillate, causing ripples on your power line.
- The Fix: If you must use Ceramic capacitors, place a small resistor (e.g., 0.5Ω to 1Ω) in series with the capacitor to simulate the ESR of a Tantalum cap. Or, simply use a Tantalum capacitor on the output.
5V to 3.3V Step-Down Schematic
The most common application is powering a 3.3V microcontroller from 5V USB.
- Vin: Connect 5V. Place a 10µF capacitor near Pin 3.
- GND: Connect Pin 1 to Ground.
- Vout: Output 3.3V. Place a 22µF Tantalum capacitor near Pin 2.
3. AMS1117-ADJ: Adjustable Voltage Configuration
The adjustable version allows you to set the output voltage ($V_{OUT}$) using two resistors, $R1$ and $R2$.
Formula: $$V_{OUT} = V_{REF} \times (1 + \frac{R2}{R1}) + I_{ADJ} \times R2$$
- $V_{REF}$ is typically 1.25V.
- $R1$ is usually connected between VOUT and ADJ (Recommend 100Ω - 200Ω).
- $R2$ is connected between ADJ and Ground.
- $I_{ADJ}$ (Adjust Pin Current) is small (typically 50µA) and can often be ignored for rough calculations.
4. Thermal Management: Why Your LDO Gets Hot
The AMS1117 is a Linear Regulator. It works by "burning off" the excess voltage as heat.
The Math: $$Power Dissipated (P_D) = (V_{IN} - V_{OUT}) \times I_{LOAD}$$
Example: If you feed 12V into an AMS1117-3.3 to power a 500mA load:
- Voltage Drop = $12V - 3.3V = 8.7V$
- Power = $8.7V \times 0.5A = \mathbf{4.35 Watts}$
The Result: The SOT-223 package can only dissipate about 0.8W to 1.0W without a massive copper plane or heatsink. At 4.35W, the chip will enter thermal shutdown instantly.
- Guideline: Only use AMS1117 when the voltage difference is small (e.g., 5V to 3.3V) or the current is low. For 12V inputs, use a Buck Converter instead.
5. Conclusion
The AMS1117 is the workhorse of the 3.3V logic world. It is cheap, easy to use, and reliable—provided you respect its thermal limits and use the correct output capacitors.
Sourcing Voltage Regulators Ensure your power rail is stable. Visit Aichiplink.com to search for AMS1117-3.3, AMS1117-ADJ, and compatible Tantalum capacitors.
Written by Jack Elliott from AIChipLink.
AIChipLink, one of the fastest-growing global independent electronic components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.
We mainly source and distribute integrated circuit (IC) products of brands such as Broadcom, Microchip, Texas Instruments, Infineon, NXP, Analog Devices, Qualcomm, Intel, etc., which are widely used in communication & network, telecom, industrial control, new energy and automotive electronics.
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Frequently Asked Questions
Is the AMS1117 the same as LM1117?
Functionally, yes. They are pin-compatible and have nearly identical specs. The AMS1117 is often cheaper, while the LM1117 (from TI) is considered a premium version.
Can I use a 10uF capacitor instead of 22uF?
Many datasheets suggest 10uF is the *minimum*. However, 22uF provides better transient response (stability when the load current changes suddenly).
What happens if I connect Pin 1 of AMS1117-ADJ to Ground?
It will act as a 1.25V regulator (since $V_{REF}$ is 1.25V).
Does it have short-circuit protection?
Yes, the AMS1117 has internal current limiting and thermal shutdown protection.
