Dual Linear Regulator with 300mA and 150mA Outputs and Power-On-Reset # Technical Documentation: LP3996SD3333 Ultra-Low Noise LDO Voltage Regulator
Manufacturer : National Semiconductor (NS/Texas Instruments)
Document Version : 1.0
Last Updated : October 2023
---
## 1. Application Scenarios
### 1.1 Typical Use Cases
The LP3996SD3333 is a 150mA, ultra-low-noise, high-PSRR (Power Supply Rejection Ratio) low-dropout (LDO) linear voltage regulator designed for noise-sensitive analog and RF circuits. Its primary use cases include:
* Precision Analog Front-Ends : Providing clean 3.3V (±2%) rails for operational amplifiers, instrumentation amplifiers, and data converters (ADCs/DACs) in measurement systems, medical devices, and audio equipment. Its 30µVrms typical output noise (10Hz–100kHz) preserves signal integrity.
* RF and Communication Modules : Powering voltage-controlled oscillators (VCOs), phase-locked loops (PLLs), LNAs (Low-Noise Amplifiers), and mixers in wireless transceivers, base stations, and satellite receivers. High PSRR (70dB at 1kHz) isolates sensitive RF blocks from noisy digital supply lines.
* Portable/Battery-Powered Instruments : Extending battery life in handheld test gear, portable medical monitors, and industrial sensors due to its low quiescent current (75µA typical) and low dropout voltage (120mV typical at 150mA load).
* Sensitive Sensor Interfaces : Supplying stable, low-noise bias to MEMS sensors, photodiodes, and bridge sensors in IoT nodes, automotive sensing modules, and environmental monitors.
### 1.2 Industry Applications
* Medical Electronics : Patient monitors, portable ultrasound, hearing aids, and diagnostic equipment where supply noise can interfere with low-level biopotential signals (ECG, EEG).
* Automotive Infotainment & ADAS : GPS modules, radar sensors, and audio head units requiring immunity to automotive electrical noise (load dump, transients).
* Industrial Automation : Process control transmitters, data acquisition systems, and precision instrumentation where line/load transients are common.
* Consumer Audio/Video : High-fidelity audio DACs, preamplifiers, and professional video switching equipment.
### 1.3 Practical Advantages and Limitations
Advantages:
* Exceptional Noise Performance : Integrated noise-filtering capacitor (NR pin) reduces external component count.
* High PSRR : >60dB up to 10kHz, effectively attenuating switching regulator ripple.
* Stable with Ceramic Capacitors : Requires only 2.2µF (min) ceramic output capacitor for stability, saving board space and cost.
* Protection Features : Includes current limit, thermal shutdown, and reverse-battery protection.
* Small Package : 6-pin WSON (3mm × 3mm) suitable for space-constrained designs.
Limitations:
* Limited Output Current : 150mA maximum; not suitable for powering processors or high-current peripherals.
* Dropout Voltage : While low (120mV typical at 150mA), it may still limit operation in very low-input-voltage scenarios (e.g., single-cell Li-ion nearing discharge).
* Thermal Dissipation : In high-ambient-temperature environments, the small package’s θJA (~45°C/W) may restrict usable output current without heatsinking.
* Fixed Output Voltage : The “3333” variant provides only 3.3V; adjustable versions require a different part number.
---
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Insufficient Input/Output Decoupling
* Issue : Poor transient
