AP1117E33G-13

The AP1117E33G-13 is a 1-A low-dropout positive linear regulator from Diodes Incorporated, configured for a fixed 3.3-V output. It belongs to the AP1117 family, which also offers fixed 1.5-V, 1.8-V, 2.5-V, and 5.0-V variants plus an adjustable version with a 1.25-V reference.

The device delivers up to 1 A of output current with a maximum dropout of 1.4 V at full load. The input voltage range extends to 18 V, making it suitable for stepping down from 5-V or higher rails to 3.3-V logic supplies. The output voltage accuracy is ±1% at 25°C.

Internal protection includes current limiting and thermal shutdown (activated at approximately 150°C junction), which protects the device under fault conditions without requiring external components. The 60 dB PSRR at 180 Hz provides adequate supply noise rejection for most digital logic loads.

The SOT-223-3 package features a tab connected to VOUT that serves as both an electrical contact and a thermal path. With a thermal resistance of 107°C/W junction-to-ambient (typical), the package can dissipate approximately 1.1 W at 25°C ambient without a heatsink, corresponding to about 780 mA at a 1.4-V dropout.

The E33G suffix denotes: E = SOT-223 package, 33 = 3.3-V fixed output, G = Green molding compound (no Br/Sb), -13 = tape and reel packaging. Note that this part is obsolete as of 2015; Diodes recommends the AZ1117CH-3.3TRG1 as a direct substitute with improved dropout voltage (1.1 V at 1 A) and wider temperature range (-40°C to +125°C).

**Series Pass Element:** The AP1117 uses a PNP pass transistor in a series regulator topology. Unlike NPN-based LDOs, the PNP structure allows dropout voltage to approach the VCE(sat) of the transistor, achieving 1.4 V at 1 A. The base drive current is the primary contributor to the 10-mA quiescent current, which flows from input to ground regardless of load.

**Error Amplifier and Reference:** A bandgap voltage reference sets the output at 3.3 V (fixed version). The error amplifier compares a divided sample of the output with the internal reference and drives the PNP pass transistor base to maintain regulation. The feedback loop is internally compensated, requiring only a 10-µF output capacitor with ESR between 0.15 Ω and 20 Ω for stability.

**Thermal and Current Protection:** The current limit circuit senses the pass transistor current and clamps the base drive when it exceeds approximately 1.5 A. The thermal shutdown sensor monitors junction temperature and disables the pass transistor when Tj exceeds approximately 150°C, re-enabling the output once the junction cools by the hysteresis margin.