## LD1085D2T90-R Electronic Component Overview The **LD1085D2T90-R** is a high-performance, low-dropout (LDO) positive voltage regulator produced by **STMicroelectronics**. It is designed to provide a stable, fixed output voltage while maintaining high efficiency even when the input voltage is only slightly higher than the output voltage. --- ### 1. Key Technical Specifications The following table outlines the core electrical characteristics of the LD1085D2T90-R: | Feature | Specification | | :--- | :--- | | **Output Voltage** | 9.0 V (Fixed) | | **Output Current** | Up to 3.0 A | | **Dropout Voltage** | Typically 1.3 V at 3A | | **Input Voltage (Max)** | 30 V | | **Package Type** | D2PAK (TO-263) | | **Operating Temperature** | -40°C to 125°C | | **Voltage Tolerance** | ±1% at 25°C; ±2% over full temperature range | --- ### 2. Internal Architecture & Components The device integrates several protective and functional circuits within its silicon structure: * **Pass Transistor:** An internal NPN transistor capable of handling high current (up to 3A). * **Thermal Overload Protection:** Automatically shuts down the device if the internal junction temperature exceeds safe limits (typically around 150°C). * **Current Limiting:** Includes internal circuitry to limit output current in case of a short circuit, preventing permanent damage to the regulator. * **Reference Voltage:** A precise internal bandgap reference ensures the 9V output remains stable across varying loads and temperatures. --- ### 3. Pin Configuration (D2PAK) The D2PAK package is a surface-mount device designed for high power dissipation. | Pin Number | Name | Function | | :--- | :--- | :--- | | **1** | **GND** | Ground / Common | | **2 / TAB** | **Vout** | Regulated Output Voltage (9V) | | **3** | **Vin** | Unregulated Input Voltage | --- ### 4. Application Considerations To ensure stable operation of the LD1085D2T90-R, the following external components are typically required: 1. **Input Capacitor ($C_{in}$):** A 10µF tantalum or electrolytic capacitor is recommended if the regulator is located far from the power supply filter. 2. **Output Capacitor ($C_{out}$):** A minimum of **10µF** (tantalum or low-ESR electrolytic) is **required for stability**. This capacitor helps manage the internal control loop. 3. **Heat Sinking:** Since this is a linear regulator, it dissipates power as heat ($P_d = (V_{in} - V_{out}) \times I_{out}$). The D2PAK tab should be soldered to a large copper area on the PCB to act as a heat sink. --- ### 5. Common Use Cases * High-efficiency linear power supplies. * Post-regulation for switching power supplies. * Battery-powered equipment requiring high current delivery. * Logic systems requiring a stable 9V rail.