Linear / LDO
AMS1117-3.3
Fixed 3.3V LDO, SOT-223 — 1A max, but budget 1.1-1.3V of dropout headroom above 3.3V.
AMS1117-3.3 · Advanced Monolithic Systems (widely second-sourced)
Overview
The AMS1117-3.3 is the linear regulator soldered onto more 3.3V breakout boards than any other single part — cheap, three pins, no inductor. Feed it anywhere from about 4.6V up to 15V and it holds a steady 3.3V out, up to 1A. The number that catches people out is dropout: 1.1V typical, 1.3V max at a full 1A load, which means the input needs to sit at least that far above 3.3V — call it 4.4-4.6V minimum — before the chip can regulate at all. Below that it just tracks Vin-dropout instead of holding 3.3V. That makes it a bad choice for running a 3.3V rail straight off a single-cell LiPo: a 'nominal 3.7V' cell is only above ~4.4V for a sliver of its charge curve near full, and sags under load well before that — so a LiPo-fed AMS1117-3.3 either loses regulation almost immediately or delivers a rail that isn't really 3.3V, depending on load and charge state. For a LiPo-powered 3.3V rail, reach for a buck or buck-boost converter instead, not this LDO. It is, however, an excellent fit for 5V-in-3.3V-out: USB power, a 5V Arduino rail, a 9-12V wall adapter through a earlier-stage 5V regulator.
Wiring tip: VIN → 5V+ rail, GND → GND, VOUT → 3.3V rail — needs ≥22µF on the output for stability
Pins & wiring
AMS1117-3.3
SOT-223
Physical pin order shown left to right.
All pins
Hover · click to selectSelected pin
GND
- Direction
- Passive
Full pin table
| Pin | Name | Role | Direction | Note |
|---|---|---|---|---|
| 1 | Ground | Passive | — | |
| 2 | Power | Out | The package tab (pin 4, if present on your footprint) is internally tied to VOUT, not GND — it's there for heatsinking, not as a fourth net. | |
| 3 | Power | Power | — |
Wiring examples
Dedicated 3.3V rail for a 3.3V-only sensor on a 5V board
Any 5V hostTaps the host's 5V rail to create a clean, separately-regulated 3.3V supply — useful when a board's own 3V3 pin is current-limited or absent.
| AMS1117-3.3 pin | Connects to | Note |
|---|---|---|
| VIN | 5V | — |
| GND | GND | — |
| VOUT | BME280 · vcc | Feeds a 3.3V-only sensor without relying on the host's onboard 3V3 pin, which on some boards has a low current budget. |
You also need
- Required10 µF capacitor between VIN and GND — Input bulk capacitor — improves transient response if the 5V source is more than a few cm away.
- Required22 µF capacitor between VOUT and GND — The datasheet requires at least 22µF (low-ESR — tantalum or a modern low-ESR ceramic) on the output for loop stability. Skimping on this is a common cause of a 'noisy' or oscillating 3.3V rail.
- Do not feed VIN from a single-cell LiPo expecting a clean 3.3V out. Dropout is 1.1-1.3V at 1A, so VIN needs to stay above about 4.4-4.6V — a LiPo (nominal 3.7V, sagging under load) can't guarantee that. Use a buck/boost converter for a LiPo-powered 3.3V rail instead.
- 1A is the package/thermal ceiling on a small SOT-223 with modest PCB copper, not a number to run continuously against — expect real-world sustainable current to be lower without a copper pour under the tab.
Specifications
Electrical
Performance
- Switching Frequency
- N/A
Physical
- Package
- SOT-223
- Mounting
- smd
Thermal
- Max Operating Temp
- 125 °Csrc
Footprint
No independently verified physical footprint is on file for this part yet.
Alternatives
Upgrades
Strictly better on the headline spec, but expect to touch firmware or wiring to actually use the difference.
A more efficient step-down option when the input always remains safely above 3.3V. It is not a fix for a single-cell LiPo rail that can fall near or below 3.3V; that case needs buck-boost.
Compare with AMS1117-3.3- Topology: linear (LDO) → switching (buck) — Needs input headroom above Vout and adds switching noise. Use buck-boost, not LM2596, for a 1S LiPo-to-3.3V rail.
Similar parts
Does the same job with a different part. Expect wiring and library changes — a starting point, not a guarantee.
Same linear-regulator family and the same dropout-headroom caveat, but fixed 5V in a bigger TO-220 package with a real tab for a heatsink — reach for it when the downstream load wants 5V instead of 3.3V.
Compare with AMS1117-3.3- Output voltage: 3.3V → 5V — Not interchangeable without also changing whatever the output feeds.
- Package: SOT-223 → TO-220 — Different footprint entirely.
Documents
Datasheets
- AMS1117 1A Low Dropout Voltage RegulatorAdvanced Monolithic Systems
Frequently asked questions
What voltage does the AMS1117-3.3 run at?
The AMS1117-3.3 runs at 3.3V, per the spec sheet below. Always double-check against the specific board you have — some breakouts add an onboard regulator that changes the usable input range.
How many pins does the AMS1117-3.3 have?
The AMS1117-3.3 has 3 pins. See the full pinout table in Pins & wiring for each pin's role.
Can I simulate the AMS1117-3.3 before ordering hardware?
Not yet — the AMS1117-3.3 does not have a live simulation model in Banana Board today, so validate the wiring here and test on real hardware.
Where is the AMS1117-3.3 datasheet?
Linked in the Documents section on this page, and cited on every spec that came from it.
Related references
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