Micropower micro SMD 150 mA Ultra Low-Dropout CMOS Voltage Regulators with sleep MODE# Technical Documentation: LP3987ITLX28 Low-Dropout Voltage Regulator
Manufacturer : National Semiconductor (NS) / Texas Instruments (acquired NS)
Component Type : Ultra-Low Noise, High PSRR, 300mA CMOS Low-Dropout (LDO) Voltage Regulator
Package : 5-Pin Thin SOT-23 (ITLX)
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## 1. Application Scenarios
### Typical Use Cases
The LP3987ITLX28 is a precision, ultra-low-noise linear voltage regulator designed for powering noise-sensitive analog and RF circuits. Its primary use cases include:
* RF/Analog Power Supplies : Providing clean, stable voltage to Voltage-Controlled Oscillators (VCOs), Phase-Locked Loops (PLLs), Low-Noise Amplifiers (LNAs), and Analog-to-Digital Converters (ADCs) where power supply noise directly impacts phase noise, signal integrity, and signal-to-noise ratio (SNR).
* Portable/Battery-Powered Devices : Efficiently regulating voltage from a Li-Ion battery (typically 3.7V nominal) down to 2.8V (for the ITLX28 variant) for system-on-chips (SoCs), microprocessors, and memory in smartphones, tablets, and wearables, leveraging its low dropout voltage to extend battery life.
* Post-Regulation : Following a switching DC-DC converter. The LP3987's high Power Supply Rejection Ratio (PSRR) attenuates the residual switching noise, creating a "quiet" analog supply rail from a noisy but efficient switching rail.
* Sensor and Precision Measurement Systems : Powering sensitive sensors (e.g., image sensors, biometric sensors, precision amplifiers) where supply ripple can introduce measurement errors.
### Industry Applications
* Wireless Communications : Cellular handsets (4G/LTE, 5G RF sections), WiFi/Bluetooth modules, GPS receivers, and IoT transceivers.
* Consumer Audio/Video : Portable media players, digital cameras, and audio codecs where low noise is critical for high-fidelity output.
* Medical Electronics : Portable monitoring devices (e.g., ECG, pulse oximeters) and imaging equipment requiring stable, noise-free analog supplies.
* Industrial Instrumentation : Test and measurement equipment, data acquisition systems, and control systems.
### Practical Advantages and Limitations
Advantages:
* Exceptional Noise Performance : Very low output noise voltage (typically 30µVrms, 10Hz to 100kHz) minimizes interference with sensitive circuits.
* High PSRR : Typically 70dB at 1kHz, effectively rejecting input ripple and noise from upstream power stages.
* Low Dropout Voltage : ~120mV at 300mA load (typical), enabling operation with small headroom, crucial for battery-powered applications.
* Low Quiescent Current : ~75µA (typical), enhancing efficiency in standby and light-load conditions.
* Stable with Small Ceramic Capacitors : Designed for stability with low-ESR ceramic output capacitors as low as 2.2µF, saving board space and cost.
* Integrated Protection : Includes current limit and thermal shutdown.
Limitations:
* Fixed Output Voltage : The "28" in ITLX28 denotes a fixed 2.8V output. A different variant is required for other voltages.
* Limited Output Current : Maximum 300mA continuous output current. Not suitable for high-power loads like display drivers or motor controllers.
* Power Dissipation Constraint : In the small SOT-23 package, the maximum power dissipation is limited (approx. 400mW). Careful thermal management is required for high input-output differentials at full load.
* Linear
