Micropower, 150mA Low-Noise Ultra Low-Dropout CMOS Voltage Regulator# Technical Datasheet: LP3985IBLX26 Low-Dropout (LDO) Voltage Regulator
Manufacturer : National Semiconductor (NS)
Component : LP3985IBLX26
Description : 150mA, Ultra-Low-Noise, Ultra-Fast RF LDO Voltage Regulator with Enable
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## 1. Application Scenarios
### Typical Use Cases
The LP3985IBLX26 is a precision, low-dropout voltage regulator engineered for noise-sensitive, power-critical applications. Its primary use cases include:
* RF and Analog Circuitry Power Supply : 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 : Powering microcontroller cores, sensors, and memory in handheld instruments, medical devices, and IoT endpoints. Its low quiescent current (~75 µA typical) and low dropout voltage extend battery life.
* Post-Regulation for Switching Supplies : Acting as a "clean-up" regulator downstream from a switching DC-DC converter to attenuate switching noise, providing a low-noise rail for sensitive circuits.
* Noise-Sensitive Audio Circuits : Supplying power to pre-amplifiers, audio codecs, and high-fidelity DACs where power supply induced hum and noise must be minimized.
### Industry Applications
* Telecommunications : Cellular base stations, RF transceivers, satellite communication modules, and network infrastructure equipment.
* Test & Measurement : High-precision oscilloscopes, spectrum analyzers, and signal generators.
* Medical Electronics : Portable imaging devices, patient monitoring systems, and diagnostic equipment requiring stable, noise-free power.
* Consumer Electronics : Smartphones (for RF and audio sections), tablets, digital cameras, and GPS receivers.
* Industrial Automation : Sensor interfaces, data acquisition systems, and control modules in electrically noisy environments.
### Practical Advantages and Limitations
Advantages:
* Ultra-Low Output Noise : Typically 30 µVrms (10 Hz to 100 kHz), crucial for high-performance RF and analog circuits.
* Excellent Power Supply Rejection Ratio (PSRR) : High PSRR (>60 dB at 1 kHz) effectively filters input ripple and noise.
* Fast Transient Response : Quickly responds to sudden load changes, minimizing output deviation.
* Low Dropout Voltage : ~120 mV at 150 mA load, enabling operation with input voltages very close to the output set point, conserving power.
* Integrated Enable (EN) Pin : Allows for logic-controlled shutdown, reducing current consumption to <1 µA in disable mode.
* Stable with Small, Low-ESR Ceramic Capacitors : Reduces solution size and cost.
Limitations:
* Fixed Output Voltage : The `26` suffix denotes a fixed 2.6V output. For adjustable voltages, a different variant of the LP3985 family must be selected.
* Limited Output Current : Maximum 150 mA. Not suitable for powering high-current loads like motors or high-power amplifiers.
* Power Dissipation : As a linear regulator, efficiency is (Vout/Vin). High input-output differentials at high load currents can lead to significant heat dissipation, requiring thermal management.
* Input Voltage Range : Absolute maximum is 6.5V. It is not suitable for applications directly powered from sources like 12V rails without prior step-down regulation.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall:
