LDO Voltage Regulator Selection Guide
Low-dropout (LDO) linear regulators provide clean, stable power supplies for sensitive analog and digital circuits. Selecting the right LDO requires understanding your application's voltage, current, noise, and efficiency requirements.
Key Parameters
Dropout voltage is the minimum input-to-output voltage differential required for regulation. For battery-powered applications, low dropout (100-300mV) extends battery life. Calculate worst-case dropout at maximum load current and minimum battery voltage.
PSRR (Power Supply Rejection Ratio) measures how well the LDO rejects input voltage ripple. For noise-sensitive circuits (RF, audio, precision analog), select LDOs with PSRR >60dB at relevant frequencies. SGM2019 offers 70dB PSRR at 1kHz.
Quiescent current (Iq) is the current consumed by the LDO's internal circuitry. For always-on circuits in battery-powered devices, Iq directly impacts standby battery life. SGM2028 offers ultra-low 35μA Iq.
Output noise is critical for sensitive analog circuits. SGM2019 provides ultra-low 30μVRMS output noise, suitable for RF and precision applications.
Selection Guidelines
For RF/analog circuits: Prioritize high PSRR (>60dB) and low noise (<50μV). SGM2019 is ideal. For battery-powered devices: Minimize Iq (<50μA). SGM2028 offers excellent efficiency. For high-current applications: Consider dropout voltage and thermal management. Ensure adequate PCB copper for heat sinking.
Thermal Considerations
Power dissipation in LDOs is P = (Vin - Vout) × Iout. At 5V input, 3.3V output, and 100mA load, dissipation is 170mW. Ensure adequate PCB copper area or consider switching regulators for high power dissipation.
As an authorized Sindachip distributor, LiTong provides comprehensive LDO selection support and application guidance.
💡 FAE Insights
📋 Customer Cases
IoT Device Manufacturer
IoT / Smart Home
Challenge
Required 5-year battery life from CR2032 coin cell while maintaining low noise for sensor accuracy.
Solution
Implemented SGM2028 LDO with 35μA quiescent current for always-on sensor supply. Used load switches to disconnect RF module between transmissions.
Customer Feedback
"Achieved 6+ year battery life exceeding requirements. Sensor accuracy maintained with clean LDO supply. Product successfully deployed with 100K+ units."
Frequently Asked Questions
1. What is dropout voltage and why does it matter?
Dropout voltage is the minimum input-to-output voltage differential required for the LDO to maintain regulation. It matters because it determines the minimum battery voltage at which your circuit can operate. Lower dropout means longer battery life as the battery discharges. For example, with 3.3V output and 200mV dropout, the LDO maintains regulation down to 3.5V input.
2. What is PSRR and when is it important?
PSRR (Power Supply Rejection Ratio) measures how well an LDO rejects ripple and noise on its input from appearing at the output. It's important when your input supply has significant ripple, such as from a switching converter. High PSRR (>60dB) is critical for noise-sensitive circuits like RF, audio, and precision analog. PSRR varies with frequency, so check specifications at your frequencies of interest.
3. How does quiescent current affect battery life?
Quiescent current is the current the LDO consumes to operate its internal circuitry. In battery-powered devices with light loads or long standby periods, Iq can dominate total power consumption. For example, a device in standby 99% of the time with 100μA Iq consumes more energy in standby than active operation. Selecting low-Iq LDOs (SGM2028: 35μA) significantly extends battery life.
4. What output capacitor should I use with an LDO?
Most modern LDOs are stable with ceramic capacitors from 1μF to 10μF. Use X5R or X7R dielectric for temperature stability. Place the capacitor close to the output pin (within 2-5mm). Larger capacitors improve transient response but increase size and cost. Some LDOs have specific ESR requirements - check the datasheet for stability criteria.
5. When should I use an LDO versus a switching regulator?
Use LDOs for noise-sensitive, low-current applications where simplicity and low noise are priorities. Use switching regulators for high-efficiency, high-current, or large voltage differential applications. LDOs are simpler, cheaper, and produce less EMI but have lower efficiency when input-output voltage difference is large. Switching regulators are more efficient but more complex and produce more noise.