## Overview of LM317SL-AA3-R The **LM317SL-AA3-R** is a low-power, adjustable 3-terminal positive voltage regulator. It is a specific variant of the classic LM317 series, designed to provide a stable output voltage that can be set by the user via an external resistor divider. --- ### 1. Key Technical Specifications The "L" in the part number typically signifies the **Low Power** (100mA) version, and the "AA3" suffix usually refers to the **SOT-89** surface-mount package. | Parameter | Specification | | :--- | :--- | | **Output Type** | Adjustable Positive Voltage | | **Output Current** | Up to 100mA | | **Output Voltage Range** | 1.25V to 37V | | **Input-Output Differential** | Max 40V | | **Line Regulation** | 0.01% / V (Typical) | | **Load Regulation** | 0.1% (Typical) | | **Operating Temperature** | -40°C to +125°C | | **Package Type** | SOT-89 (Surface Mount) | --- ### 2. Pin Configuration (SOT-89) The SOT-89 package is a small, three-terminal power package. The pinout is critical for PCB layout: | Pin Number | Function | Description | | :--- | :--- | :--- | | **1** | **ADJ** | Adjustment pin for setting output voltage. | | **2** | **VOUT** | Regulated output voltage (connected to tab). | | **3** | **VIN** | Unregulated input voltage. | --- ### 3. Functional Features * **Internal Protection:** It includes internal current limiting, thermal overload protection, and safe-area compensation. These features make it virtually "blow-out proof." * **Floating Operation:** Since the regulator "floats" and only sees the differential voltage between input and output, it can be used to regulate high voltages as long as the 40V differential limit is not exceeded. * **Simplified Design:** Only two external resistors are required to set the output voltage. --- ### 4. Basic Application Circuit To calculate the output voltage ($V_{OUT}$), the following formula is used: ```text Vout = 1.25V * (1 + R2 / R1) + (Iadj * R2) ``` *(Note: Iadj is usually small enough to be neglected in basic calculations.)* #### Typical Component Selection: * **R1:** Usually 240Ω or 120Ω. * **R2:** Potentiometer or fixed resistor to set the desired voltage. * **C1 (Input):** 0.1µF disc ceramic or 1µF tantalum to bypass high-frequency noise. * **C2 (Output):** 1µF tantalum or 10µF electrolytic to improve transient response. --- ### 5. Common Use Cases 1. **Local On-card Regulation:** For noise-sensitive analog circuits requiring less than 100mA. 2. **Programmable Output Regulators:** Used in digitally controlled power supplies. 3. **Constant Current Source:** By placing a fixed resistor between the VOUT and ADJ pins. 4. **Battery Chargers:** Charging small NiCd or Li-ion cells with current limiting.