**LT1117CST-3#PBF: A Comprehensive Datasheet and Application Guide for the 800mA LDO Voltage Regulator**

The **LT1117CST-3#PBF** is a popular and robust **low-dropout (LDO) voltage regulator** from Analog Devices, designed to deliver a fixed **3.3V output** at a current of up to **800mA**. Housed in a surface-mount SOT-223 package, this regulator is a cornerstone component in countless electronic designs, prized for its balance of performance, size, and cost-effectiveness. This article provides a detailed overview of its key specifications, features, and practical application considerations.

**Key Features and Electrical Characteristics**

The LT1117 series is renowned for its low dropout voltage, which is a critical parameter for battery-powered and energy-sensitive applications. The **dropout voltage** is typically **1.1V at 800mA**, meaning the input voltage only needs to be approximately 4.4V to maintain a regulated 3.3V output at full load. This allows for efficient operation and longer battery life.

Other notable features include:

* **High Output Current:** Capable of sourcing up to **800mA** of continuous output current.

* **Output Voltage Tolerance:** The fixed 3.3V version offers a tight **±1.5%** output voltage tolerance over line, load, and temperature variations.

* **Internal Current Limiting and Thermal Shutdown:** These built-in protection mechanisms safeguard the regulator and the load from damage under fault conditions, such as a short circuit or excessive power dissipation.

**Critical Application Guidelines**

Successful implementation of the LT1117CST-3#PBF requires attention to several key areas:

1. **Input and Output Capacitors:** Unlike many older regulators, the LT1117 is designed for stability with low-ESR (Equivalent Series Resistance) capacitors. A **10µF tantalum or aluminum electrolytic capacitor** on the output is typically sufficient for stability. While an input capacitor is not strictly required for stability, a **10µF** capacitor is recommended on the input to improve transient response and filter incoming noise, especially if the regulator is located far from the primary power source.

2. **Thermal Management:** The **SOT-223 package** offers a good balance between size and power handling due to its exposed thermal pad. However, at high input-output differentials and high load currents, power dissipation (P_DISS = (V_IN - V_OUT) * I_LOAD) can become significant. **Proper PCB layout is crucial**; the exposed pad must be soldered to a sufficiently large copper pour on the PCB to act as a heat sink. Failure to manage heat will activate the **thermal shutdown** feature, causing the regulator to temporarily turn off until it cools down.

3. **Load and Line Regulation:** The LT1117 exhibits excellent performance in maintaining a stable output voltage despite changes in the input voltage (line regulation) or the output current (load regulation). These parameters are detailed in the datasheet and are key for powering sensitive circuitry like analog-to-digital converters and microcontrollers.

**Typical Applications**

The LT1117CST-3#PBF is incredibly versatile, finding use in:

* **Post-regulation** for switching power supplies to reduce noise and ripple.

* Powering **3.3V microcontrollers, FPGAs, and ASICs** from a 5V or higher voltage bus.

* **Battery-powered devices** where minimizing dropout voltage extends usable life.

* **General-purpose 3.3V power rails** in industrial, automotive, and consumer electronics.

**ICGOODFIND:** The **LT1117CST-3#PBF** remains a highly reliable and efficient solution for providing a stable **3.3V power rail**. Its robust feature set, including **low dropout voltage** and integrated protections, combined with simple application requirements, makes it an excellent choice for designers seeking a proven **800mA LDO regulator** for a wide array of modern electronic systems. Careful attention to capacitor selection and thermal management is the key to unlocking its full performance.

**Keywords:** LDO Voltage Regulator, 800mA, 3.3V Output, Low Dropout Voltage, Thermal Shutdown