The **LL431G-AB3-R** is a specific part number for a **Programmable Shunt Regulator**. It is widely used in power management circuits to provide a stable reference voltage. Below is a detailed breakdown of its specifications, pinout, and typical applications. --- ## 1. Component Overview The LL431 series is functionally equivalent to the industry-standard **TL431**, but the suffix "-AB3-R" refers to its specific tolerance, package type, and packing method. | Feature | Specification | | :--- | :--- | | **Device Type** | Adjustable Precision Shunt Regulator | | **Output Voltage Range** | 2.495V to 36V (Adjustable) | | **Reference Voltage Tolerance** | ±0.5% (Grade A) | | **Sink Current Capability** | 1.0mA to 100mA | | **Package Type** | SOT-89 | | **Operating Temperature** | -40°C to +125°C | --- ## 2. Pin Configuration (SOT-89) The SOT-89 package is a surface-mount package designed for better thermal dissipation than the standard SOT-23. | Pin Number | Pin Name | Description | | :--- | :--- | :--- | | **1** | **Reference (REF)** | Used to set the output voltage via a resistor divider. | | **2** | **Anode (A)** | Connected to the system ground. | | **3** | **Cathode (K)** | The regulated output/input pin. | --- ## 3. Key Technical Characteristics ### Precision and Stability The "G" in the part number often signifies a **Halogen-Free** or "Green" component. With a 0.5% voltage tolerance, it is highly reliable for high-precision feedback loops in switching power supplies. ### Adjustable Output The output voltage ($V_{out}$) can be calculated using two external resistors ($R1$ and $R2$): $$V_{out} = V_{ref} \times \left(1 + \frac{R1}{R2}\right) + I_{ref} \times R1$$ *(Note: $V_{ref}$ is typically 2.495V)* --- ## 4. Typical Applications * **Linear Regulators:** Used as a reference for high-current pass transistors. * **Switching Power Supplies (SMPS):** Commonly used on the secondary side of an optocoupler to provide feedback for voltage regulation. * **Voltage Monitoring:** Acting as a comparator to trigger an alarm if a voltage threshold is crossed. * **Constant Current Sources:** By utilizing the stable reference voltage across a fixed resistor. ---