Micropower 150 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and micro SMD Packages# Technical Documentation: LP2985IM520 Low-Dropout (LDO) Voltage Regulator
Manufacturer : National Semiconductor (NS)
Document Version : 1.0
Date : October 26, 2023
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## 1. Application Scenarios
The LP2985IM520 is a high-accuracy, low-dropout voltage regulator designed for applications requiring a stable, low-noise power supply from a higher input voltage. Its combination of low quiescent current, low dropout voltage, and integrated protection features makes it suitable for a wide range of modern electronic systems.
### Typical Use Cases
* Battery-Powered Portable Devices : The LP2985's low quiescent current (typically 75 µA) is critical for extending battery life in devices like wireless sensors, Bluetooth headsets, handheld meters, and medical monitors. It efficiently regulates the decaying voltage of a Li-Ion or alkaline battery down to a stable 5.2V for microcontrollers, sensors, or analog circuits.
* Post-Regulation for Switching Supplies : In systems with a noisy 5.5V or 6V switching regulator output, the LP2985 provides a second stage of regulation. It significantly attenuates high-frequency switching noise, creating a clean 5.2V rail essential for noise-sensitive analog components, RF circuits, or high-resolution ADCs/DACs.
* Microcontroller and Memory Power : Provides a dedicated, stable voltage rail for a microprocessor core, SRAM, or Flash memory, isolating them from noise on the main system bus. The fast transient response helps maintain stability during the MCU's active/sleep mode transitions.
* Always-On (Keep-Alive) Circuits : In automotive or industrial control modules, the regulator can power real-time clocks (RTCs), non-volatile memory, and microcontroller wake-up circuits directly from the vehicle battery or a backup battery, thanks to its low ground current and shutdown capability.
### Industry Applications
* Consumer Electronics : Smart home IoT nodes, set-top boxes, and portable audio players.
* Automotive Electronics : Infotainment systems, telematics control units (TCUs), and body control modules (BCMs) for non-critical, low-power subsystems.
* Industrial Control : PLC I/O modules, sensor transmitters, and data acquisition systems.
* Medical Devices : Portable diagnostic equipment and patient monitoring sensors where stable, reliable power is paramount.
* Communications : As a local regulator for PLLs, VCOs, or low-power RF front-end modules.
### Practical Advantages and Limitations
Advantages:
* Very Low Dropout Voltage : Typically 280 mV at 150 mA load. This allows it to maintain regulation with an input voltage as low as ~5.48V for a 5.2V output, maximizing utilization of the input power source.
* Low Noise & High PSRR : Excellent power supply ripple rejection (PSRR), especially at lower frequencies, minimizes noise on the output.
* Integrated Protection : Includes current limiting, thermal shutdown, and reverse-battery protection (with an external Schottky diode), enhancing system robustness.
* Stable with Low-ESR Ceramic Capacitors : Designed for stability with small, low-cost ceramic output capacitors (≥ 2.2 µF), saving board space and cost.
Limitations:
* Fixed Output Voltage (5.2V) : The 'IM520' variant provides a fixed 5.2V output. A different output voltage requires a different part number (e.g., LP2985IM5-3.3 for 3.3V).
* Limited Output Current : Maximum continuous output current is 150 mA. It is not suitable for powering high-current loads like motors or high-power LEDs.
* Power
