### Technical Overview of LD2979M38TR The **LD2979M38TR** is a high-accuracy, low-dropout (LDO) linear voltage regulator manufactured by STMicroelectronics. It is specifically designed to provide a stable, fixed output voltage while maintaining a very low quiescent current, making it ideal for battery-powered applications. --- ### 1. Key Technical Specifications Below are the primary electrical characteristics for the LD2979M38TR: | Parameter | Specification | | :--- | :--- | | **Output Voltage ($V_{out}$)** | 3.8 V (Fixed) | | **Input Voltage ($V_{in}$)** | Up to 16 V | | **Output Current ($I_{out}$)** | 50 mA | | **Dropout Voltage ($V_d$)** | Typ. 250 mV @ 50 mA | | **Quiescent Current ($I_q$)** | Typ. 500 $\mu$A (at max load); < 1 $\mu$A in Off mode | | **Package Type** | SOT-23-5L (Small Outline Transistor) | | **Operating Temperature** | -40°C to 125°C | --- ### 2. Functional Pins (SOT-23-5L) The device features five pins, each serving a specific role in voltage regulation and power management: 1. **VIN (Input):** The unregulated supply voltage. 2. **GND (Ground):** Common reference point for all voltages. 3. **EN (Enable):** Logic controlled input. High = ON, Low = Shutdown/OFF. 4. **BYP (Bypass):** Connect an external capacitor here to reduce noise and improve PSRR (Power Supply Rejection Ratio). 5. **VOUT (Output):** The regulated 3.8V output voltage. --- ### 3. Core Features * **Low Dropout Voltage:** The "dropout" is the minimum difference between input and output voltage required for the device to regulate. At only ~250mV, it allows the device to function even as a battery discharges close to the target 3.8V. * **Logic-Controlled Shutdown:** The Enable (EN) pin allows the system to put the regulator into a sleep state, consuming almost zero power, which is critical for extending battery life. * **Internal Protections:** * **Current Limiting:** Protects the device during short circuits or overloads. * **Thermal Shutdown:** Automatically turns off the device if it exceeds safe operating temperatures. * **Very Low Noise:** The inclusion of the Bypass pin allows for a cleaner output signal, which is essential for sensitive analog components or RF circuits. --- ### 4. Typical Application Circuit To ensure stability, the LD2979 series requires specific external capacitors. ```c // Recommended Circuit Configuration: [Input Source] ---> (VIN Pin) --- [1uF Ceramic Cap] --- GND (EN Pin) ---> [Microcontroller Logic Signal] (BYP Pin) ---> [0.01uF (10nF) Capacitor] --- GND (VOUT Pin) ---> [2.2uF Tantalum/Ceramic Cap] --- [Load] ``` --- ### 5. Common Applications * **Cellular Phones:** Providing 3.8V logic power. * **Battery-Powered Handhelds:** Due to the low quiescent current. * **Voltage Reference:** Used in circuits requiring a stable 3.8V reference for sensors. * **Post-Regulator:** Used after a switching regulator to clean up high-frequency noise.