Dual Micropower 150 mA Ultra Low-Dropout CMOS Voltage Regulators in micro SMD Package# Technical Datasheet: LP3986BL285285 Low-Dropout (LDO) Voltage Regulator
Manufacturer : National Semiconductor (NS)
Component Type : 300 mA, Ultra-Low-Noise, High-PSRR CMOS LDO Regulator
Fixed Output Voltage: 2.85V
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## 1. Application Scenarios
The LP3986BL285285 is a precision, ultra-low-noise linear voltage regulator designed for power-sensitive analog and RF circuitry. Its primary function is to provide a clean, stable 2.85V supply from a higher input voltage, making it indispensable in modern portable and noise-sensitive electronic systems.
### Typical Use Cases
* RF and Analog Front-Ends: Provides a quiet bias voltage for Low-Noise Amplifiers (LNAs), Voltage-Controlled Oscillators (VCOs), mixers, and phase-locked loops (PLLs) in communication systems (Wi-Fi, Bluetooth, cellular modules). Its low noise prevents phase noise degradation and receiver desensitization.
* Portable Medical Devices: Powers sensitive sensor interfaces, analog-to-digital converters (ADCs), and precision amplifiers in hearing aids, portable monitors, and diagnostic equipment where supply noise directly impacts signal fidelity and accuracy.
* Audio Codecs and DACs/ADCs: Serves as the analog supply rail for high-fidelity audio components, minimizing audible noise and harmonic distortion. Essential in digital audio players, mixers, and premium motherboards.
* Microcontroller & FPGA I/O Banks: Isolates and cleans the power supply for digital I/O sections, reducing ground bounce and switching noise that can couple into analog sections or affect signal integrity.
* Battery-Powered Equipment: Efficiently regulates a decaying Li-Ion/Polymer battery voltage (e.g., 3.7V nominal down to ~3.0V) down to a stable 2.85V, extending usable battery life for the core circuitry.
### Industry Applications
* Consumer Electronics: Smartphones, tablets, digital cameras, GPS units.
* Telecommunications: RF transceivers, baseband processors, network infrastructure cards.
* Industrial & IoT: Industrial sensors, data acquisition systems, gateway modules.
* Automotive Infotainment: Audio subsystems, display logic, and connectivity modules (where specified for extended temperature ranges).
### Practical Advantages and Limitations
| Advantages | Limitations |
| :--- | :--- |
| Ultra-Low Output Noise: Typically ~30 µVrms (10 Hz to 100 kHz), critical for noise-sensitive analog loads. | Fixed Output Voltage: The `285285` variant is fixed at 2.85V. A different output requires a different part number. |
| High Power Supply Rejection Ratio (PSRR): >70 dB at 1 kHz, effectively attenuating ripple from preceding switching regulators or noisy supplies. | Linear Regulator Efficiency: Efficiency ≈ (Vout / Vin) * 100%. Significant voltage drops (e.g., 5V to 2.85V) result in power dissipation as heat (Pd = (Vin - Vout) * Iload). |
| Low Dropout Voltage: ~120 mV at 300 mA, allowing operation with input voltages very close to 2.85V, maximizing battery life. | Current Limit: Maximum continuous output current is 300 mA. Not suitable for high-power loads like motors or high-performance processors. |
| Excellent Line/Load Transient Response: Maintains stable voltage during rapid changes in input or load current. | Requires External Capacitors: Stability and performance are dependent on proper selection and placement of input/output ceramic capacitors. |
| Integrated Protection: Includes thermal shutdown, current limit, and under-voltage lockout (UVLO). | Heat Dissipation
