USL1801
300mA low-noise LDO with 1.8-5.5V input, ultra-low dropout, and 20µVRMS noise for RF and precision analog applications.
Product Overview
Description
The USL1801 is a high-performance low-dropout (LDO) linear regulator optimized for noise-sensitive applications.
With ultra-low output noise of 20µVRMS and high power supply rejection ratio (PSRR) of 70dB at 1kHz, it provides clean power for RF circuits, ADCs, and precision analog systems.
The device features low dropout voltage of 150mV at 300mA and is stable with small ceramic capacitors.
Product Series
USL
Primary Application
RF power supply
Key Features
- Ultra-low output noise 20µVRMS
- High PSRR 70dB at 1kHz
- Low dropout voltage 150mV
- Stable with 1µF ceramic cap
- Current limit and thermal protection
- Enable/shutdown control
Specifications
| Input Voltage | 1.8V - 5.5V |
|---|---|
| Output Voltage | 1.2V - 3.3V (Fixed) / Adjustable |
| Output Current | 300mA |
| Dropout Voltage | 150mV @ 300mA |
| Output Noise | 20µVRMS (10Hz-100kHz) |
| PSRR | 70dB @ 1kHz |
Applications
RF power supply
Power conversion and supply
ADC/DAC reference
Data acquisition and conversion
Precision analog circuits
Electronic system design
Camera modules
Electronic system design
Audio circuits
Electronic system design
FAE Expert Insights
"The USL1801 is my go-to LDO for noise-sensitive applications. I've used it in RF transceivers, precision measurement systems, and high-end audio products. The noise performance is excellent - 20µVRMS is comparable to much more expensive LDOs from ADI and TI. PSRR is also very good, effectively filtering switching noise from upstream DC-DC converters. Dropout voltage is reasonable at 150mV. The small SOT-23-5 package is convenient for space-constrained designs. For RF and precision analog applications where noise matters, this LDO delivers premium performance at a competitive price."
Low-noise LDO with excellent PSRR for RF/analog
— Li Hua, BeiLuo
Frequently Asked Questions
What makes USL1801 suitable for RF applications?
USL1801 RF-suitable features: Ultra-low noise: 20µVRMS doesn't add phase noise to VCOs. High PSRR: 70dB at 1kHz filters switching noise. Clean output: No switching artifacts. Fast transient: Responds quickly to PA current steps. Low dropout: Can work with minimal headroom. These characteristics make it ideal for powering VCOs, PLLs, mixers, and LNAs in RF systems.
Use for VCO, PLL, mixer, LNA power. Cascade after DC-DC for efficiency.
How do I minimize output noise further?
Techniques to reduce USL1801 output noise: Bypass capacitor: Add 0.01-0.1µF ceramic close to load. Filter: Add LC or RC filter for specific frequencies. Reference: Use external reference voltage if adjustable version. Layout: Keep traces short, minimize loop area. Input: Clean input supply with adequate bypassing. Load: Minimize load transients. These techniques can reduce effective noise below 10µVRMS at the load.
Use bypass caps at load. Consider output filter for critical applications.
Can I use USL1801 for ADC reference voltage?
USL1801 is excellent for ADC reference applications: Low noise: 20µVRMS preserves ADC SNR. Stable: No switching artifacts affecting conversion. Accurate: 1% initial accuracy, good for 12-bit+ ADCs. Clean: No ripple-induced code errors. Considerations: Use fixed voltage version for best accuracy. Add bypass cap at ADC reference pin. Ensure load regulation doesn't affect reference. For highest precision, consider dedicated voltage reference IC.
Excellent for most ADC applications. Use dedicated reference for >16-bit precision.
What is the dropout behavior of USL1801?
USL1801 dropout characteristics: Dropout voltage: 150mV at 300mA load. Scales with load current: ~50mV at 100mA, ~150mV at 300mA. Behavior in dropout: Output follows input minus dropout. Pass transistor fully on. No damage but regulation lost. Recovery: Returns to regulation when Vin > Vout + Vdropout. Thermal: May increase in dropout due to higher Vdrop × Iload. Design for Vin > Vout + 300mV to avoid dropout operation.
Maintain Vin > Vout + 300mV for proper regulation. Account for input ripple.
How does USL1801 handle load transients?
USL1801 transient response: Response time: ~10µs for 10-90% of load step. Undershoot/overshoot: <5% for 50% load step. Output capacitor: Larger cap improves transient but slows response. Ceramic caps: Use low-ESR ceramic for best transient. Load step: Minimize di/dt if possible. For large load steps: Consider adding bulk capacitance at load. Or use DC-DC for high-current switching loads.
Add output capacitance for large load steps. Consider DC-DC for switching loads.
What is the power dissipation in USL1801?
USL1801 power dissipation: Pd = (Vin - Vout) × Iout. Example: 3.3V to 1.8V at 200mA = (3.3-1.8) × 0.2 = 300mW. Thermal considerations: SOT-23-5 thermal resistance: ~200°C/W. Temperature rise: 300mW × 200°C/W = 60°C. Max ambient: 85°C - 60°C = 25°C max. For higher power: Use larger package if available. Add copper area for heatsinking. Reduce Vin-Vout differential. Consider DC-DC for high current or large differentials.
Calculate dissipation and temperature rise. Use DC-DC for high power.