AMS1117 Voltage Regulator: Specs, Circuits & Selection Guide

Key Takeaways:

• The AMS1117 is a low-dropout (LDO) linear voltage regulator.
• Output up to 800 mA with 1.1–1.3 V dropout from a PNP pass transistor
• Fixed options from 1.2 V to 5.0 V; adjustable output with two external resistors
• Requires output capacitor ESR of 0.3–22 Ω for stable operation
• Thermal management is critical at full load — use copper pour on SOT-223
• Broad second-source availability makes dual-sourcing straightforward
• Not ideal for battery designs; quiescent current of 5–10 mA is high for light-load use

What Is the AMS1117 Voltage Regulator?

The AMS1117 is a low-dropout linear voltage regulator IC. It delivers a stable DC output from a higher DC input voltage. Engineers widely deploy it in embedded systems, consumer electronics, and industrial boards.

It supports fixed outputs of 1.2 V, 1.5 V, 1.8 V, 2.5 V, 2.85 V, 3.0 V, 3.3 V, and 5.0 V. An adjustable variant also exists for custom output voltages. Therefore, it covers most digital, analogue, and RF supply rails.

How the AMS1117 LDO Regulates Output

The AMS1117 uses three terminals: input (VIN), output (VOUT), and ground (GND). The adjustable variant replaces GND with an adjust pin (ADJ). An internal bandgap reference and error amplifier compare the output to a 1.25 V reference. As a result, the device maintains a stable output despite load or input fluctuations.

Key AMS1117 Voltage Regulator Specifications

The table below summarises the main electrical and thermal parameters. Values come from the AMS datasheet (Revision B) at typical conditions. Always verify worst-case limits in the full datasheet.

AMS1117 Thermal Management Calculation

Thermal design is critical at full load. For example, at 800 mA with VIN = 5 V and VOUT = 3.3 V, power dissipation equals (5 − 3.3) × 0.8 = 1.36 W.

In a SOT-223 package with θJA = 60 °C/W and 40 °C ambient, junction temperature reaches ~122 °C. That is dangerously close to the 125 °C maximum. However, adding a 1 cm² copper pour beneath the thermal pad reduces θJA to 35–40 °C/W, providing comfortable thermal margin.

AMS1117 Key Features and Advantages

The AMS1117 delivers several practical engineering advantages:

• Low Dropout Voltage: A 1.1–1.3 V dropout enables 3.3 V regulation from a 5 V USB rail, where higher-dropout devices like the LM7805 would fail.
• Wide Output Range: Fixed options from 1.2 V to 5.0 V plus an adjustable version cover most embedded supply rails.
• Integrated Protection: Built-in current limiting and thermal shutdown simplify designs compared to discrete pass-transistor solutions.
• Strong Regulation: Line regulation of 0.2%/V and load regulation of 0.4% keep rails stable across varying loads.
• Multiple Packages: SOT-223, SOT-89, TO-252, and TO-220 support dense SMD boards and hand-soldered prototypes.

AMS1117 Circuit Configuration Options

Fixed-Voltage AMS1117 Circuit

Fixed-voltage variants arrive pre-trimmed to ±1% output accuracy. First, add a 10 µF ceramic or tantalum input capacitor. Next, add a 10 µF output capacitor with ESR between 0.3 Ω and 22 Ω for stable compensation. That is all the external circuitry required.

Adjustable AMS1117 Output Voltage Formula

The adjustable variant uses an external resistor divider between VOUT, ADJ, and GND:

VOUT = 1.25 × (1 + R2/R1)

Use R1 = 120–240 Ω to minimise adjust-pin current errors. For instance, to set 2.5 V with R1 = 120 Ω: R2 = 120 × ((2.5/1.25) − 1) = 120 Ω. Use 1% tolerance resistors for best accuracy.

AMS1117 Package Selection Guide

Common AMS1117 Application Scenarios

MCU Power Rails: 3.3 V from 5 V USB

The most common use places an AMS1117-3.3 between a USB connector and a 3.3 V MCU. The 1.7 V headroom exceeds the worst-case 1.3 V dropout. Therefore, regulation holds across the full USB tolerance range of 4.75–5.25 V. Add 10 µF tantalum in parallel with 100 nF ceramic at input and output.

FPGA and CPLD Auxiliary Supplies

FPGAs often need multiple rails at 1.2 V, 1.8 V, and 3.3 V. The AMS1117 efficiently handles lower-current auxiliary and I/O bank rails under 500 mA. In addition, a switching pre-regulator can supply the high-current core rail. This two-stage approach combines efficiency with low-noise LDO regulation.

Wi-Fi and Bluetooth Module Regulation

RF modules such as the ESP-12, CC2530, and nRF52840 are sensitive to supply noise. Ripple degrades receiver sensitivity and increases transmission errors. However, the AMS1117’s switching-free architecture and ~65 dB PSRR at 120 Hz make it ideal as a post-regulator after a switching converter.

ADC Reference Voltage Generation

The adjustable AMS1117 with precision resistors generates stable reference-like voltages. Its 1% accuracy and low noise floor suit 10-bit to 12-bit ADC VREF and DAC supply applications. For instance, this approach avoids the cost and complexity of a dedicated shunt reference in mid-resolution systems.

AMS1117 vs Alternatives: Voltage Regulator Comparison

For most 3.3 V rails from 5 V USB, the AMS1117 is the pragmatic choice. It costs under $0.10 in volume and needs no external inductor or controller. However, battery-operated designs should evaluate the MCP1700 or a buck converter instead. Quiescent current savings of 10× or more can dramatically extend battery life.

AMS1117 Procurement Guide

The AMS1117 benefits from one of the broadest second-source ecosystems among LDO regulators. Manufacturers include Advanced Monolithic Systems, Diodes Incorporated, HTC Korea, and UTC. As a result, dual-sourcing strategies are straightforward to implement.

Where to Buy AMS1117 Components

Distributors such as Mouser, DigiKey, and LCSC stock millions of units across all voltage variants. Typical lead times run 1–2 weeks for standard orders. Minimum order quantities start at one unit in cut-tape, making the device accessible for prototyping and volume production alike.

AMS1117 Quality and Compliance

End-of-line testing follows JEDEC standards, covering output accuracy, dropout, quiescent current, and thermal shutdown. All mainstream suppliers offer halogen-free, Pb-free variants. Furthermore, AEC-Q100 Grade B qualification is available from select suppliers such as Diodes Inc. (AP1117) for automotive-adjacent industrial applications.

Frequently Asked Questions

How do I calculate resistors for the adjustable AMS1117?

Use VOUT = 1.25 × (1 + R2/R1). For 2.5 V with R1 = 120 Ω, R2 = 120 Ω. The adjust pin draws ~50 µA. Therefore, compensate by recalculating R2 = (VOUT/1.25 − 1) × R1 − IADJ × R2. Always use 1% resistors.

What ESR does the AMS1117 output capacitor require?

The AMS1117 needs an output capacitor ESR between 0.3 Ω and 22 Ω. Very low-ESR ceramics (below ~50 mΩ) can cause oscillation. As a result, add a 1–3 Ω series resistor when using ceramics. Tantalum capacitors in the 10–100 µF range fall within the stable ESR window naturally.

Is the AMS1117 suitable for automotive use?

Standard commercial-grade parts are rated to 85 °C ambient — insufficient for under-hood automotive environments. However, AEC-Q100-qualified variants from Diodes Inc. are rated for extended temperature ranges. Always verify the manufacturer’s qualification status before specifying in automotive designs.

How does AMS1117 quiescent current affect battery life?

The AMS1117 draws 5–10 mA quiescent current. In a design drawing 10 mA average load, quiescent current represents 33–50% of total consumption. Therefore, switching to an LDO with sub-10 µA quiescent current — such as the MCP1700 at 1.6 µA — can extend battery life by 10× or more.

What is the maximum power dissipation in SOT-223?

At 25 °C ambient with θJA = 60 °C/W, the SOT-223 package dissipates a maximum of (125 − 25)/60 = 1.67 W. At 40 °C this drops to 1.42 W. However, a 1 cm² copper pour reduces θJA to ~35 °C/W, raising capability to ~2.43 W at 40 °C — adequate for full 800 mA operation.

Conclusion

The AMS1117 voltage regulator remains the go-to LDO for general-purpose embedded design. Its balance of dropout performance, availability, protection features, and low cost is hard to match. In summary, use it for 3.3 V MCU rails, FPGA auxiliaries, RF modules, and mid-resolution ADC references. For battery-critical or high-efficiency applications, however, consider the MCP1700 or a switching regulator instead.

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