The LP2985-N allows for low-noise performance by using a bypass capacitor connected to the internal band-gap reference with the BYPASS pin. This high-impedance band-gap circuitry is biased in the microampere range and, thus, cannot be loaded significantly, otherwise, the output (and, correspondingly, the output of the regulator) changes. Thus, for best output accuracy, minimize the dc leakage current through C_BYPASS as much as possible and never exceed 100nA. The C_BYPASS capacitor also impacts the start-up behavior of the regulator. Inrush current and start-up time increase with larger bypass capacitor values.

Use a 10nF capacitor for C_BYPASS. Ceramic and film capacitors are good choices for this purpose. High-quality ceramic capacitors with either NPO or COG dielectric typically have very low leakage. 10nF polypropylene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current.