This application note describes performance verification of low noise, low dropout linear regulators (LDOs), including LDO dropout, input voltage range, maximum output current, noise, stability, surge current, load regulation, output voltage regulation, and thermal characteristics.
The document introduces a family of low noise, low dropout linear regulators (LDO) designed for telecommunications, networking, audio, and instrumentation applications. It highlights specific devices in this family that offer 20 mVRMS noise with low dropout voltages and small quiescent currents.
A significant portion of the text is dedicated to the methodology for verifying LDO performance, specifically regarding noise. The authors discuss the complexities of noise testing, emphasizing the need for a defined bandwidth (10Hz to 100kHz) and proper operating conditions. Detailed descriptions are provided for a custom test setup involving shielded enclosures, specific filter circuits using LTC amplifiers, and thermally responding RMS voltmeters to ensure accurate measurements free from ground loops.
| Noise (Typical) | 20 mVRMS |
|---|---|
| Dropout Voltage | 300mV at 100mA |
| Quiescent Current | 20 mA |
| Noise Bandwidth | 10Hz to 100kHz |
The recommended measurement bandpass is from 10Hz to 100kHz with steep slopes at the limits.
The reference bypass capacitor filters internal voltage reference noise, which is a major contributor to device output noise.