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Assuming the power load is low enough for a linear to supply, what are the repercussions of using a linear supply to derive our VCC (0.9V) supply?
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There is no problem using linear supplies for all power rails.
The main reason you see switchers suggested is that the core current requirements often exceed what is possible with a linear regulator, eg., currents higher than 1 to 2A.
The main design constraint with a linear regulator is the power dissipation. Even if you have a linear regulator that is rated for a maximum output current of 5A or 6A, the input-to-output voltage drop and power dissipation usually limits you to much less.
The nice thing about the PCGs telling you which supplies can use switching regulators, is that it helps tell you that those supplies are tolerant to switching noise.
Why are you interested in minimizing noise? Do you have analog circuits on the same PCB? If your board is fully digital, then using switchers for the design is fine. To reduce the switching noise on some power rails, you can use ferrite beads or linear regulators on the switcher outputs.
Cheers,
Dave
Honored Contributor
