## Overview of the LM317K-TQ2-R The **LM317K-TQ2-R** is a high-performance, 3-terminal adjustable positive voltage regulator. It is designed to supply more than 1.5A of load current with an output voltage adjustable over a range of 1.2V to 37V. The suffix **TQ2-R** typically refers to the package type (TO-263 / D2PAK) and the packing method (Tape & Reel). --- ### 1. Key Technical Specifications | Parameter | Value | | :--- | :--- | | **Output Voltage Range** | 1.2V to 37V | | **Output Current** | > 1.5A | | **Input-Output Differential** | 40V (Maximum) | | **Line Regulation** | 0.01% / V (Typical) | | **Load Regulation** | 0.1% (Typical) | | **Operating Temperature** | 0°C to +125°C | | **Reference Voltage** | 1.25V | --- ### 2. Pin Configuration (TO-263 Package) The TO-263 (D2PAK) is a surface-mount package. The pinout is usually as follows: 1. **ADJ (Adjust):** Used to set the output voltage via a resistive divider. 2. **Vout (Output):** The regulated output voltage (also connected to the large metal tab). 3. **Vin (Input):** The unregulated input voltage. --- ### 3. Core Features & Protections * **Internal Short-Circuit Current Limiting:** Protects the device during a fault or overload. * **Thermal Overload Protection:** The device shuts down if the internal junction temperature exceeds safe limits. * **Output Safe-Area Compensation:** Limits power dissipation based on the voltage across the chip. * **Floating Operation:** Since the adjustment terminal is "floating," the regulator can be used for high-voltage applications as long as the input-to-output differential limit is not exceeded. --- ### 4. Typical Application Circuit To set the output voltage, two external resistors are required. The formula for the output voltage ($V_{out}$) is: $$V_{out} = 1.25V \times (1 + \frac{R_2}{R_1}) + (I_{adj} \times R_2)$$ ```text Vin ---- [ LM317 ] ---- Vout | | |---[ R1 ]---| | | ADJ ---------(+) | | [ R2 ] [C_out] | | GND ---------(+) ``` --- ### 5. Design Considerations 1. **Heat Sinking:** In the TO-263 package, the tab is connected to $V_{out}$. Proper PCB copper pour area is required to dissipate heat, especially when the voltage drop ($V_{in} - V_{out}$) or current is high. 2. **Capacitors:** * A **0.1μF** disc or **1μF** tantalum capacitor is recommended on the input if the device is far from the power supply filter. * An optional **1μF** tantalum or **10μF** aluminum electrolytic capacitor on the output improves transient response. 3. **Minimum Load:** The LM317 requires a minimum load current (typically 3.5mA to 10mA) to maintain regulation.