Improve the ultra-low noise floor and PSRR of the device by carefully selecting:

• C_NR/SS for the low-frequency range
• C_FF in the mid-band frequency range
• C_OUT for the high-frequency range
• V_IN – V_OUT for all frequencies
• V_BIAS at lower input voltages

A larger noise-reduction capacitor improves low-frequency PSRR by filtering any noise coupling from the input into the reference. To improve mid-band PSRR, use the feed-forward capacitor to place a zero-pole pair near the edge of the loop bandwidth and push out the loop bandwidth. Use larger output capacitors to improve high-frequency PSRR.

A higher input voltage improves PSRR by giving the device more headroom to respond to noise on the input. A bias rail also improves PSRR at lower input voltages because greater headroom is provided for the internal circuits.

The noise-reduction capacitor filters out low-frequency noise from the reference, and the feed-forward capacitor reduces output voltage noise by filtering out mid-band frequency noise. However, a large feed-forward capacitor can create new issues that are discussed in the Pros and Cons of Using a Feed-Forward Capacitor with a Low Dropout Regulator application note.

Use a large output capacitor to reduce high-frequency output voltage noise. Additionally, a bias rail or higher input voltage improves noise because greater headroom is provided for the internal circuits.

Table 7-1 lists the output voltage noise for the 10Hz to 100kHz band at a 5.0V output for a variety of conditions with an input voltage of 5.5V, an R₁ of 12.1kΩ, and a load current of 3.0A. The 5.0V output is used because this output is the worst-case condition for output voltage noise.