LM1117-3.3Fixed 3.3 V LDO regulator
A 3.3 V rail, with stability designed in.
LM1117-3.3 is a three-terminal low-dropout linear regulator with a fixed 3.3 V output. This reference follows Texas Instruments LM1117 devices in TO-220 and D²PAK packages, using pin 1 GND, pin 2 OUTPUT and pin 3 INPUT. An internal reference and feedback divider control the pass stage. The metal tab is connected to OUTPUT, and the external output capacitor must satisfy both capacitance and ESR requirements. A 5 V source is convenient for a 3.3 V rail, but the voltage difference becomes heat. Check input headroom, load current and cooling together; the 800 mA rating is conditional on the operating limits.
Ground referenceOutput & tabInput supply
LM1117T-3.3/NOPBTO-220Front view · marking toward you · leads down
LM1117SX-3.3/NOPBD²PAKTop view · thermal tab is pin 2 (OUTPUT)
Click a lead or use the arrow keys. Front view · marking toward you · leads down
PIN 1 · Ground reference
Ground referenceGND
Function
Return for the internal reference, feedback divider and bias current in the fixed 3.3 V version.
How to connect
Connect to the input-supply return, load return and both capacitor returns.
Electrical note
This is GND on the fixed-output part. The adjustable LM1117 uses this lead as ADJ and is a different circuit.
PIN 2 · Output & tab
Regulated outputOUTPUT
Function
Supplies the nominal 3.3 V rail. The metal tab is electrically connected to this output.
How to connect
Connect the load and a suitable output capacitor close to the regulator.
Electrical note
The output capacitor is part of the stability requirements: TI specifies at least 10 µF tantalum with ESR from 0.3 Ω to 22 Ω. The tab is not ground.
PIN 3 · Input supply
DC inputINPUT
Function
Feeds the pass stage and bias circuit from a supply above the output by sufficient headroom.
How to connect
Use a regulated 5 V source for the example and a local 10 µF input bypass.
Electrical note
Check input tolerance, ripple and dropout at the intended load and temperature. The 20 V absolute maximum is not the 15 V recommended maximum.
At a glance
Fixed 3.3 V LDO regulator
The fixed-output feedback divider is inside the package. External capacitors and a good thermal path complete the supply.
3.3 V nominalFixed output
800 mA · thermal limits applyRated output current
0–125 °C · selected LM1117 gradeOperating junction
≥ 10 µF tantalum · check ESROutput capacitor
Operating profile
LM1117T-3.3/NOPB
Operating characteristics
Key parameters and their test conditions
- Nominal output
- 3.3 VConditions / notes: Fixed 3.3 V option
- Output at 25°C
- 3.267 / 3.3 / 3.333 VConditions / notes: Minimum / typical / maximum; VIN = 5 V, IOUT = 10 mA
- Output across specified conditions
- 3.235–3.365 VConditions / notes: 0–800 mA; VIN = 4.75–10 V; TJ = 0–125°C
- Output current
- Up to 800 mAConditions / notes: Requires headroom and adequate thermal design
- Junction operating range
- 0–125°CConditions / notes: Selected LM1117 grade
- Recommended input maximum
- 15 VConditions / notes: Must also satisfy thermal and dropout constraints
Package details
Follows the selected physical package
- Manufacturer
- Texas Instruments
- Part number
- LM1117T-3.3/NOPB
- Package
- TO-220
- Connections
- 3 pins
- Mounting
- Through-hole
- Lead pitch
- 2.54 mm
- Package code
- NDE
- Thermal reference
- Board and heatsink dependent; see TI SNOS412Q
Connections by function
Select a pin to open its function, electrical notes and wiring guidance.
Ground reference1 pins
Output & tab1 pins
Input supply1 pins
Ground reference1 pins
Output & tab1 pins
Input supply1 pins
Compare and regulate
A reference and internal feedback network set the fixed 3.3 V output. The amplifier adjusts the pass stage as input or load changes.
Stabilize the feedback loop
The output capacitor is required, not merely decorative bypassing. Select its capacitance and ESR for the manufacturer’s operating conditions.
Account for power loss
The voltage dropped across the pass stage produces heat. Ground current adds another loss term, and the package needs a suitable thermal path.
For 5 V input, 3.3 V output and a 100 mA load, pass-stage loss is 0.17 W. Adding 5 mA typical ground current gives approximately 0.195 W total regulator dissipation.
Pin reference
Select a pin to explore its function and connection.
3 pins
| Pin | Signal | Type | Function |
|---|---|---|---|
| GND | Ground reference | Return for the internal reference, feedback divider and bias current in the fixed 3.3 V version. | |
| OUTPUT | Regulated output | Supplies the nominal 3.3 V rail. The metal tab is electrically connected to this output. | |
| INPUT | DC input | Feeds the pass stage and bias circuit from a supply above the output by sufficient headroom. |
No pins match. Try a signal name or choose All pins.
Operating characteristics
TI LM1117-3.3 · fixed-output grade
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Nominal output | 3.3 V | Fixed 3.3 V option |
| Output at 25°C | 3.267 / 3.3 / 3.333 V | Minimum / typical / maximum; VIN = 5 V, IOUT = 10 mA |
| Output across specified conditions | 3.235–3.365 V | 0–800 mA; VIN = 4.75–10 V; TJ = 0–125°C |
| Output current | Up to 800 mA | Requires headroom and adequate thermal design |
| Junction operating range | 0–125°C | Selected LM1117 grade |
| Recommended input maximum | 15 V | Must also satisfy thermal and dropout constraints |
No specifications match. Try a parameter name or a unit.
The LM1117I grade has a different temperature range. This reference follows the selected non-I devices.
Regulation and supply current
Retain the measurement conditions
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Line regulation | 1 mV typical; 6 mV maximum | IOUT = 0 mA, VIN = 4.75–15 V; typical at 25°C, maximum over 0–125°C |
| Load regulation | 1 mV typical; 10 mV maximum | VIN = 4.75 V, IOUT = 0–800 mA; typical at 25°C, maximum over 0–125°C |
| Ground current | 5 mA typical; 10 mA maximum | VIN ≤ 15 V; typical at 25°C, maximum over 0–125°C |
| Dropout criterion | Output falls by 100 mV | Referenced to VOUT measured with VIN = VOUT + 1.5 V |
| Current limiting | Built in | An overload protection feature, not an extra operating-current allowance |
No specifications match. Try a parameter name or a unit.
Dropout changes with output current and junction temperature; use TI’s table and curves when choosing the supply margin.
Capacitors and stability
Capacitance and ESR both matter
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input bypass | 10 µF tantalum | TI’s suitable input capacitor for most applications |
| Output capacitor | At least 10 µF tantalum | Required for the selected fixed-output circuit |
| Output capacitor ESR | 0.3–22 Ω | Manufacturer stability guidance |
| Low-ESR substitution | Check before changing technology | A ceramic capacitor is not automatically a valid drop-in replacement |
| Placement | Short input, output and ground paths | Keep the load return and regulator ground well connected |
No specifications match. Try a parameter name or a unit.
Check capacitance, ESR, voltage rating and temperature behavior for the actual capacitor part.
5 V to 3.3 V example
100 mA nominal resistive load
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply | Regulated 5 V DC | Feed pin 3 INPUT |
| Return | Pin 1 GND | Common with input supply, capacitors and load |
| Output | Pin 2 OUTPUT | Nominal 3.3 V; tab is the same net |
| Example load | 33 Ω · at least 1 W | 3.3 / 33 = 0.10 A; resistor power = 0.33 W |
| Pass-stage loss | 0.17 W | (5 − 3.3) × 0.10 |
| Including typical ground current | Approximately 0.195 W | 0.17 + 5 × 0.005 |
No specifications match. Try a parameter name or a unit.
These are nominal calculations, not measured results. Output tolerance and actual ground current change the values.
Thermal and stress limits
Package ratings require a thermal context
Manufacturer specifications 7 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Power estimate | PD ≈ (VIN − VOUT) × ILOAD + VIN × IGND | Include both loss terms |
| Junction estimate | TJ ≈ TA + PD × RθJA | Only for the board and airflow represented by the thermal resistance |
| TO-220 RθJA / RθJC(bottom) | 23.8 / 1.5°C/W | TI thermal characterization conditions |
| D²PAK RθJA / RθJC(bottom) | 41.3 / 1.3°C/W | TI thermal characterization conditions |
| Input absolute maximum | 20 V | Stress rating, not the recommended operating maximum |
| Junction absolute maximum | 150°C | Recommended operation ends at 125°C |
| Storage range | −65 to +150°C | Unpowered |
No specifications match. Try a parameter name or a unit.
The output-connected tab must not be shorted to a grounded heatsink. Thermal shutdown does not replace cooling design.
Local logic rails
Supply a modest 3.3 V digital load from a regulated 5 V rail after checking load transients and heating.
Manufacturer application guidePost-regulation
Regulate a sufficiently higher DC rail near a load using the specified capacitor network.
Manufacturer application guidePower-supply learning
Explore dropout, capacitor ESR and the relationship between voltage drop and heat.
Manufacturer application guideTake it into ProTech
Find LM1117-3.3 in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech