onsemi NCP1117ST33T3G 3V LDO Voltage Regulator: Datasheet, Pinout, and Application Circuits
The onsemi NCP1117ST33T3G is a popular positive low-dropout (LDO) voltage regulator from a renowned semiconductor manufacturer. Designed to deliver a fixed 3.3V output at currents up to 1A, this component is a cornerstone in power management for countless electronic devices. Its combination of performance, robustness, and ease of use makes it an excellent choice for both novice and experienced engineers.
This device belongs to the NCP1117 series, which is known for its low dropout voltage—typically 1V at 800 mA of load current. This means it can continue to regulate its output voltage even when the input voltage is as low as ~4.3V, making it highly efficient and suitable for applications where the input voltage is not much higher than the output. Furthermore, it offers internal current limiting and thermal shutdown protection, safeguarding both the regulator and the load circuit under fault conditions. The NCP1117ST33T3G is offered in the SOT-223 package, which provides an excellent balance between compact size and thermal performance, allowing it to dissipate heat effectively.
Pinout Configuration
Understanding the pinout is crucial for proper circuit design. The NCP1117ST33T3G in the SOT-223 package has three pins and an integrated tab that is also electrically connected.
Pin 1 (Adjust/Ground): For fixed-voltage versions like the 'ST33T3G, this pin is the ground (GND) connection. It must be connected to the system's common ground.
Pin 2 (Output): This is the regulated 3.3V output (Vout). It is essential to use capacitors on this pin for stability.
Pin 3 (Input): This is the unregulated input voltage (Vin) supply pin. The input voltage must be higher than the output voltage plus the dropout voltage.
Tab: The metal tab is internally connected to the Output (Pin 2). It acts as a heatsink to dissipate heat into the PCB or to an external heatsink if necessary.
Key Datasheet Specifications
A thorough review of the datasheet is essential. Here are some of the most critical specifications:
Output Voltage: Fixed at 3.3V (with a typical tolerance of ±2%).
Output Current: Up to 1A.
Dropout Voltage: 1V (max) at 800 mA load current.
Line Regulation: 0.2% (max).
Load Regulation: 0.4% (max).
Operating Junction Temperature: -40°C to +125°C.
Application Circuits
The primary application for the NCP1117ST33T3G is as a simple 3.3V power supply. The basic application circuit is straightforward, requiring only a minimum of two capacitors for stable operation.
1. Basic Fixed Output Regulator Circuit:
This is the most common application. A capacitor (C_IN, typically 10 µF) is placed on the input pin to filter any incoming noise and ensure stability. A larger capacitor (e.g., 22 µF to 100 µF) may be needed if the input supply is noisy or located far from the regulator. A capacitor (C_OUT, typically 22 µF) on the output pin is critical for stability and improves the transient response of the regulator. For best performance, especially for dynamic loads, a small 100 nF ceramic capacitor should be placed in parallel very close to the regulator's output pin.
2. Circuit with Enhanced Filtering:
In sensitive applications, such as for powering analog-to-digital converters (ADCs) or radio frequency (RF) modules, additional filtering is often added. A small-value ferrite bead (e.g., 600Ω @ 100MHz) can be placed in series with the output, followed by an additional capacitor to ground to create a low-pass filter, further reducing output noise.
Design Considerations:
Heatsinking: When operating at high currents or with a small voltage difference between input and output (low dropout), power dissipation (P_DISS = (V_IN - V_OUT) I_LOAD) can be significant. The SOT-223 package relies on a copper pour on the PCB connected to the tab (Pin 2) to act as a heatsink. A sufficiently large copper area is mandatory for full 1A operation.
Capacitor Selection: While the datasheet specifies tantalum capacitors for stability, modern low-ESR (Equivalent Series Resistance) ceramic capacitors can also be used. It is often recommended to include a small series resistor (e.g., 1Ω) with a ceramic output capacitor to add damping and prevent instability.
ICGOODFIND Summary
The onsemi NCP1117ST33T3G is a highly reliable and versatile 3.3V LDO regulator, prized for its 1A output capability, low dropout voltage, and robust protection features. Its simple three-pin design and minimal external component requirement make it a fundamental building block for power subsystems in a vast array of electronic products, from consumer gadgets to industrial equipment. Proper attention to PCB layout for heatsinking and capacitor selection is key to unlocking its full performance potential.
Keywords:
LDO Voltage Regulator
3.3V Output
1A Output Current
Low Dropout Voltage
SOT-223 Package
