Micropower, 150mA Low-Noise Ultra Low-Dropout CMOS Voltage Regulator# Technical Documentation: LP3985IBP26 Ultra-Low Noise, 150 mA CMOS Voltage Regulator
Manufacturer : National Semiconductor (NS)
Document Version : 1.0
Last Updated : October 2023
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The LP3985IBP26 is a high-performance, ultra-low dropout (ULDO) CMOS voltage regulator designed for noise-sensitive applications requiring precise power conditioning. Its primary use cases include:
* Portable/Battery-Powered Devices : Operates with input voltages as low as 2.5V, making it ideal for single-cell Li-ion (3.0V-4.2V) or dual-cell alkaline/NiMH battery systems where extending battery life is critical.
* RF/Analog Circuit Power Supplies : Provides clean, stable voltage to sensitive components such as VCOs (Voltage-Controlled Oscillators), PLLs (Phase-Locked Loops), ADCs (Analog-to-Digital Converters), and DACs (Digital-to-Analog Converters), where power supply noise directly impacts signal integrity.
* Post-Regulation for Switching Supplies : Used as a secondary filter/regulator following a noisy DC-DC switching regulator to achieve low-noise, low-ripple output required by precision analog circuits.
* Always-On Power Domains : Powers real-time clocks (RTCs), microcontroller keep-alive memory, and sensor interfaces in low-power sleep modes, benefiting from its low quiescent current (typically 75 µA).
### 1.2 Industry Applications
* Wireless Communications : Cellular handsets, Wi-Fi/Bluetooth modules, GPS receivers, and IoT transceivers where clean power for RFICs and baseband processors is mandatory to minimize phase noise and bit-error rates.
* Medical Electronics : Portable monitoring devices (e.g., pulse oximeters, glucose meters), hearing aids, and diagnostic equipment where signal accuracy and device longevity are paramount.
* Consumer Audio/Video : Portable media players, digital cameras, and audio codecs, suppressing power supply-induced hum and noise in audio paths and image sensors.
* Industrial Instrumentation : Data acquisition systems, sensor signal conditioning modules, and test/measurement equipment requiring stable references and low-noise amplification.
### 1.3 Practical Advantages and Limitations
Advantages:
* Ultra-Low Noise : Typically 30 µV RMS (10 Hz to 100 kHz), eliminating the need for additional LC filtering in many noise-critical paths.
* High PSRR : 70 dB at 1 kHz, effectively attenuating ripple from preceding power stages.
* Low Dropout Voltage : 120 mV typical at 150 mA load (for the 2.6V output variant), maximizing efficiency and usable battery capacity.
* Low Quiescent Current : 75 µA typical, minimally impacting battery life in always-on applications.
* Thermal and Overcurrent Protection : Integrated safeguards enhance system reliability.
* Stable with Ceramic Capacitors : Designed for use with small, low-ESR ceramic capacitors (≥1 µF), reducing solution size and cost.
Limitations:
* Fixed Output Voltage : The LP3985IBP26 provides a fixed 2.6V output (other variants in the family offer different voltages). An adjustable version is not available in this specific part number.
* Limited Output Current : Maximum 150 mA output current restricts use to low-to-moderate power loads.
* Input Voltage Range : Maximum input voltage is 6.0V, not suitable for applications directly powered from 9V or 12V rails without prior regulation.
* Power Dissipation : In SOT-23-5 package, power dissipation is limited by junction temperature; continuous high-current operation near dropout may require thermal analysis.
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