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LMK03318: VDDO's connectivity to power domain

Omer Kvitel
Prodigy 140 points
Part Number: LMK03318

Hi

I would like to consult on the following issue with respect to the board design/layout:

In my design, I have an LMK03318: VDDO's are fed by an LDO (TPS7A8500).

Do I need to put a ferrite bead on each VDDO power domain? 

In the current design, they are all shared with the same output voltage of the LDO and routed via a power plane.

Regards

Omer

 

  • 0
    TI__Mastermind 28960 points

    Hello Omer,

    If any of the output supplies drive outputs with a common frequency, they can share a ferrite bead. For example, if OUT4, OUT5, and OUT6 are 100MHz, and OUT7 is 125MHz, VDDO4/VDDO5/VDDO6 could share a supply line and a ferrite bead, but VDDO7 would need a separate ferrite bead. The reasoning for ferrite bead placement on output supplies is to prevent crosstalk spurs coupling through the supply pins, so if the output frequencies for the power domains are shared, they can share a ferrite bead since they cannot crosstalk at the same frequency, and one ferrite bead is sufficient to isolate those VDDO supplies from other PLL supplies.

    Additionally, if any output groups are completely powered down, they do not need a ferrite bead. If both OUT2/OUT3 are powered down, VDDO23 can be directly connected to the power plane without issues.

    Regards,