Micropower micro SMD 150 mA Ultra Low-Dropout CMOS Voltage Regulators with sleep MODE# Technical Datasheet: LP3987ITLX285 Ultra-Low Noise, High PSRR LDO Voltage Regulator
## 1. Application Scenarios
### Typical Use Cases
The LP3987ITLX285 is a 285 mA, ultra-low noise, high PSRR (Power Supply Rejection Ratio) low-dropout (LDO) linear voltage regulator designed for precision analog and RF power supply applications. Its primary use cases include:
* RF/IF Circuits : Providing clean, stable voltage to voltage-controlled oscillators (VCOs), phase-locked loops (PLLs), mixers, and low-noise amplifiers (LNAs) in communication systems (cellular base stations, satellite receivers, software-defined radios)
* High-Fidelity Audio Systems : Powering sensitive pre-amplifiers, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and op-amps where power supply noise directly impacts total harmonic distortion (THD)
* Medical Imaging Equipment : Supplying precision analog front-ends in ultrasound machines, MRI systems, and portable medical monitors
* Test and Measurement Instruments : Voltage references for high-resolution data acquisition systems, spectrum analyzers, and precision sensors
* Portable Battery-Powered Devices : Extending battery life in portable medical devices, industrial handhelds, and premium consumer electronics where both noise performance and efficiency are critical
### Industry Applications
* Telecommunications : 5G infrastructure, microwave backhaul, fiber optic networks
* Automotive Infotainment : Premium audio systems, navigation displays, camera modules
* Industrial Automation : Process control instrumentation, sensor interfaces, data loggers
* Aerospace/Defense : Avionics systems, radar receivers, secure communications
* Consumer Electronics : High-end audio/video equipment, digital cameras, gaming consoles
### Practical Advantages and Limitations
Advantages:
* Exceptional Noise Performance : Typically 30 μVRMS output noise (10 Hz to 100 kHz) with optional noise reduction pin
* High PSRR : 75 dB at 1 kHz, maintaining >40 dB up to 1 MHz for effective ripple rejection
* Low Dropout Voltage : 150 mV typical at 150 mA load (enables operation with minimal headroom)
* Excellent Line/Load Regulation : 0.04%/V and 0.04%/mA respectively
* Thermal and Current Protection : Built-in thermal shutdown and current limit protection
* Small Package : SOT-23-5 package (2.9mm × 1.6mm) saves board space
Limitations:
* Limited Output Current : Maximum 285 mA constrains high-power applications
* Linear Regulator Efficiency : Efficiency equals VOUT/VIN × 100%, causing heat dissipation at high input-output differentials
* Fixed Output Voltage : 2.85V fixed output (ITLX285 variant) lacks programmability
* External Components Required : Requires input/output capacitors for stability
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Thermal Management
* Problem : Excessive power dissipation (PD = (VIN - VOUT) × ILOAD) in small SOT-23 package causes thermal shutdown
* Solution : Calculate maximum junction temperature: TJ = TA + (PD × θJA). For continuous 285 mA operation with 5V input, PD = (5-2.85)×0.285 = 0.61W. With θJA ≈ 250°C/W, TJ = 25°C + (0.61×250) = 177.5°C (exceeds 125°C typical limit). Reduce input voltage differential, decrease load current, or improve PCB thermal design.
Pitfall 2
