LM1117 3.3V Regulator (TO-220)

• Pin order is GND, OUT, IN from left to right on the front, not the IN, GND, OUT of a 7805, and the metal tab is the output (TI datasheet, p. 3). Keep the tab away from other metal or insulate it on a heatsink.
• Fit at least 10 µF from OUT to GND, close to the pins. TI asks for a tantalum with an ESR of 0.3 Ω to 22 Ω; more capacitance only improves stability (p. 15). A 10 µF capacitor on IN is recommended too (p. 14).
• Feed IN from 4.75 V up to 15 V for a fully specified 3.3 V output (pp. 4, 5): a 5 V rail, an Arduino's 5V or VIN pin, a 9 V battery or a 12 V adapter. From a 3.3 V or 3.7 V source the output follows the input minus the dropout and sags.
• Heat is (VIN minus 3.3 V) times the load current, plus VIN times the 5 mA ground current (p. 18). From 5 V at 500 mA it dissipates about 0.9 W; from 12 V at the same current, about 4.4 W, which needs a heatsink. The junction must stay under 125 °C, and thermal shutdown cuts the output if it does not.
• Share the regulator's GND with the microcontroller that talks to the 3.3 V part, and feed only 3.3 V parts from OUT.

Output voltage

3.3 V (3.267 V to 3.333 V at 10 mA, 25 °C)TI LM1117 datasheet (SNOS412Q), p. 5

Output current

800 mATI LM1117 datasheet, p. 1

Dropout voltage

1.1 V at 100 mA, 1.15 V at 500 mA, 1.2 V at 800 mA (typical)TI LM1117 datasheet, p. 6

Input voltage

15 V max recommended; 20 V absolute maximumTI LM1117 datasheet, p. 4

Current limit

800 mA min, 1200 mA typical, 1500 mA maxTI LM1117 datasheet, p. 6

Quiescent current

5 mA typical, 10 mA maxTI LM1117 datasheet, p. 6

Output capacitor

10 µF minimum (tantalum), ESR 0.3 Ω to 22 ΩTI LM1117 datasheet, p. 15

TO-220 pinout

1 ADJ/GND, 2 VOUT (and tab), 3 VINTI LM1117 datasheet, p. 3

Junction temperature

0 °C to 125 °C (LM1117); thermal shutdown built inTI LM1117 datasheet, pp. 4, 18

Dimensions

10.16 × 4.57 × 28.7 mm

Weight

2 g

From the Texas Instruments's datasheet, published by Texas Instruments.

1. Wiring it like a 7805

   The 7805 is IN, GND, OUT; the LM1117 is GND, OUT, IN (TI datasheet, p. 3). Swapping them feeds the supply into the output or ground and the part regulates nothing.

2. Leaving out the output capacitor

   The LM1117 needs at least 10 µF on its output, with an ESR between 0.3 Ω and 22 Ω, to stay stable (p. 15). Without it the output can oscillate and devices on the 3.3 V rail reset at random.

3. Using only a tiny ceramic on the output

   A small multilayer ceramic alone can have an ESR below the 0.3 Ω TI asks for (p. 15). Use a 10 µF tantalum, or an electrolytic of 10 µF or more, as the output capacitor.

4. Feeding it from 3.3 V or a single Li-ion cell

   With about 1.2 V of dropout at 800 mA (p. 6), the output cannot reach 3.3 V from a 3.3 V or 3.7 V source. Use 4.75 V or more in, or a lower-dropout regulator.

5. Pulling high current from 12 V without a heatsink

   All of the 8.7 V dropped from 12 V to 3.3 V turns into heat. At a few hundred milliamps that is several watts, enough to trip the thermal shutdown (p. 18). Add a heatsink or use a buck converter.

• Electrolytic Capacitor (470µF)wired with it in its circuit
• Red LEDwired with it in its circuit
• 220Ω Resistorwired with it in its circuit
• MB102 Breadboard Power Modulesame job: regulates a supply
• AMS1117 3.3V Regulator Modulesame job: regulates a supply
• LM2596 Buck Converter Modulesame job: regulates a supply

• 3.3 V rail from a 5 V Arduino

  Power an nRF24L01, RC522 RFID reader or a 3.3 V sensor from the Uno's 5V pin with more current than its 3V3 pin gives.

• ESP8266 or ESP-01 power supply

  Give an ESP module a steady 3.3 V from USB 5 V, with a bulk capacitor for its Wi-Fi bursts.

• Breadboard power rail

  Build a 3.3 V rail on a breadboard from a 9 V battery or 12 V adapter, with input and output capacitors.

• Learning linear regulation

  Measure dropout and heat at different loads to see why LDOs need headroom and a heatsink.