TPS65910: Ferrite beads on PMIC LDO outputs

Paddu,

The Ferrite beads are used to filter out unwanted high-frequency noise on a power supply, usually near the point of load.

VMMC, VPLL, VDIG2, VAUX2, are all power supplies for portions of the AM335x processor that are susceptible to noise interference (ADC, PLL, etc) and the ferrite bead is needed to ensure a clean reference is supplied to the processor.

I cannot say exactly why this value was chosen, but if you look at the datasheet for the Ferrite Bead used in this design, it will show you a chart of the impedance vs. frequency and the region where the impedance is highest should be around the region where noise was present before adding the ferrite beads.

You should add these ferrite beads because they are on the reference design and the reference design is a verified solution.
If you are looking to save cost, you can test your design by replacing these ferrite beads with 0-Ohm resistors or different ferrite beads with a similar transfer function (frequency response).

We cannot guarantee the system will perform as expected if you remove the ferrite beads from your design.

paddu,

Based on a similar question that was asked to me offline, I think the high frequency "noise" is actually an overshoot due to the nearly instantaneous rise time of the LDOs:

VAUX2, VDIG1, & VMMC have similar waveforms without the ferrite bead and both use a single FB at the point-of-load (POL, near AM335x).
VPLL is extra sensitive and have slightly different waveform, so it uses 1x FB and 1x 10nF cap for additional filtering at POL.
VDAC has similar overshoot but also has a little undershoot when load is applied, so instead of FB this rail uses 4x 10nF cap to slow down overshoot and a 10uF cap to prevent the undershoot.

This is the most likely explanation for needing these special passive components.