## Overview of the LP2987 The **LP2987** is a fixed-output, low-dropout (LDO) voltage regulator designed for high-precision applications. It is part of a family of regulators known for delivering high output accuracy and very low quiescent current, making it ideal for battery-powered devices. --- ### 1. Key Technical Specifications | Parameter | Value | Notes | | :--- | :--- | :--- | | **Input Voltage Range** | 2.1V to 16V | Supports wide battery ranges. | | **Output Current** | Up to 200 mA | Continuous load capacity. | | **Dropout Voltage** | ~160 mV @ 200 mA | Very low overhead required. | | **Output Tolerance** | 0.5% (A Grade) | High precision for sensitive logic. | | **Quiescent Current** | 120 µA (Typical) | At 200 mA load. | | **Shutdown Current** | < 2 µA | When the ON/OFF pin is pulled low. | --- ### 2. Pin Configuration and Functions The LP2987 is typically available in an 8-pin SOIC or VSSOP package. 1. **Vout:** The regulated output voltage. 2. **SENSE:** Connected to Vout to monitor the voltage (allows for Kelvin sensing). 3. **GND:** System ground. 4. **ON/OFF:** Active-high enable pin. Pull low to enter sleep mode. 5. **ERROR:** Open-collector output that goes low if the output falls more than 5% below nominal. 6. **TAP:** Internal voltage divider access (often unused/left open). 7. **BYPASS:** Connecting a capacitor here reduces output noise. 8. **Vin:** Unregulated input voltage. --- ### 3. Critical Component Selection To ensure stability and performance, specific external components are required: #### Output Capacitor ($C_{OUT}$) * **Requirement:** At least $4.7 \mu F$ is required for stability. * **ESR Matters:** The Equivalent Series Resistance (ESR) must be within a specific range (typically $0.5\Omega$ to $8\Omega$). * **Type:** Tantalum capacitors are preferred over ceramic because ceramic capacitors often have an ESR that is too low, which can cause the regulator to oscillate unless a small resistor is added in series. #### Bypass Capacitor ($C_{BYP}$) * A $10 nF$ capacitor connected to the BYPASS pin significantly reduces noise on the output voltage, which is essential for RF or high-fidelity audio circuits. --- ### 4. Features and Protection * **Low Noise:** High Power Supply Rejection Ratio (PSRR) makes it suitable for sensitive analog circuits. * **Error Flag:** The `ERROR` pin acts as a "Power Good" signal, notifying a microcontroller if the voltage drops due to low input or overloading. * **Protection:** Includes internal thermal shutdown and short-circuit current limiting. ---