AMS1117-3.3 regulator: specs and pinout
A fixed 3.3 V low-dropout linear regulator. The maker's sheet describes the AMS1117 family as 1 A devices and specifies dropout at 0.8 A. The facts below are the chip's; the module board is not covered by an official document.
Specs
| Spec | Value | Source |
|---|---|---|
| Output voltage (AMS1117-3.3) | 3.3 V typical; 3.251 V to 3.349 V at 25 C with VIN 4.8 V | source Electrical Characteristics, p.2 of the sheet |
| Output current | Up to 1 A (load regulation and dropout are specified up to 0.8 A) | source Features and General Description, p.1; Notes 2 and 4 |
| Dropout voltage | 1.1 V typical, 1.3 V maximum at 0.8 A; higher above 0.8 A | source Electrical Characteristics and Note 4 |
| Current limit | 900 mA minimum, 1100 mA typical, 1500 mA maximum at VIN-VOUT 1.5 V | source Electrical Characteristics |
| Maximum input voltage | 15 V (absolute maximum) | source Absolute Maximum Ratings |
| Quiescent current | 5 mA typical, 11 mA maximum | source Electrical Characteristics |
| Output capacitor | 22 uF solid tantalum on the output ensures stability for all conditions | source Application Hints, Stability, p.4 |
| Thermal resistance, junction to ambient | SOT-223: 90 C/W (46 C/W to over 90 C/W depending on copper area); TO-252: 80 C/W; SO-8: 160 C/W | source Absolute Maximum Ratings |
| Guaranteed power dissipation for regulation specs | 1.2 W (SOT-223), 2.2 W (TO-252), 780 mW (SO-8) | source Note 2 |
| Operating junction temperature | -40 C to 125 C; thermal shutdown above 165 C | source Ordering Information; Application Hints |
Power
| Value | Source | |
|---|---|---|
| Supply | Input must be at least about 1.3 V above the 3.3 V output at 0.8 A (about 4.6 V); absolute maximum 15 V | source Electrical Characteristics |
| Current | 5 mA quiescent (typical) | source Electrical Characteristics |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.
The rows are the AMS1117 chip's 3-pin package pins. The module board's header order, capacitors, and rated current are not covered by an official document; follow the markings on the board.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | Ground/Adjust (GND on the fixed 3.3 V version) | SOT-223 and TO-252 3-pin view. | source Pin Connections, p.1 | |
| 2 | VOUT | 3.3 V | In SOT-223 and TO-252 the tab is also the output. | source Pin Connections, p.1 |
| 3 | VIN | up to 15 V (absolute maximum) | source Pin Connections, p.1 |
Build with it
Project ideas for the AMS1117-3.3 regulator. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- ESP-01S Wi-Fi status page on a breadboard: Ai-Thinker's ESP-01S spec gives a 3.0 V to 3.6 V supply and recommends a supply that can give at least 500 mA peak. The AMS1117 is current-limited at 900 mA minimum, so a 5 V input is enough; at 0.5 A the dissipation is (5 - 3.3) x 0.5 = 0.85 W (derived), under 1.2 W. Check the UART board's logic level (3.3 V) before connecting; that board is not documented on this page.
- Contact-switch event logger on an ESP-01S: The regulator supplies the 3.3 V the module needs. Wire the switch to a 3.3 V input of the module, not to 5 V. Learning project, not a security product.
- Dropout test bench: The sheet says the 3.3 V output needs about 1.3 V of headroom at 0.8 A, and less at light load. Measure the output with a 10 kohm load at 3 and 4 AA cells to see where regulation is lost. Learning project.
Common mistakes
- Powering it from three AA cells (about 4.5 V): the sheet specifies dropout up to 1.3 V at 0.8 A, so the 3.3 V output needs an input of about 4.6 V or more at full load (source: link, Electrical Characteristics).
- Ignoring heat: from a 5 V input at 0.8 A the regulator dissipates (5 - 3.3) x 0.8 = 1.36 W (derived), above the 1.2 W the sheet guarantees for the SOT-223 package, which has 90 C/W junction-to-ambient (source: link, Notes 2 and absolute maximum ratings). Keep the current lower, drop less voltage, or give it copper area.
- Leaving out the output capacitor: the design needs an output capacitor for frequency compensation and the sheet recommends 22 uF solid tantalum (source: link, Application Hints). A bare chip without it can be unstable; check what your board already carries.
Not covered by the official source
- The maker's sheet describes the chip as a 1 A regulator with dropout specified at 0.8 A. The module board's own current rating is not documented.
- The module board's header order, capacitors and package are not covered by an official document.