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Separate power supply to PLL and Digital core. How to?

MCH

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Hello,

I have a very specific question, a yes/no answer will do, but if someone care to explain, i will be happy to read and learn.

I am doing a dyi i2s to spdif board using Wofson's wm8804 interface/transceiver chip.

the IC has two separate sets of 3.3V power/ground pairs:
PVDD: PLL core supply
PGND: PLL ground
and
DVDD: Digital core supply
DGND: Digital ground

Both must be the same voltage, i use 3.3V:

1687695462226.png


The recommended schematic is this:

1687695136647.png

This is what i understand (noob alert: i have no idea about electronics):
C1 and C2 are decoupling capacitors, the ground is common, and DVDD and AVDD may come from different sources at roughly the same voltage as explained above.

I am going to power my board (that consists basically on the wm8804 reference circuit and a couple of toslink transmitters) from one single USB input.
I will use a 1117 voltage regulator to do 5V -> 3.3V (the ones i have are AZ1117CH-3.3TRG1 from Diodes Incorporated) wired like this:
1687696803471.png


And my doubt is:
If all the power comes from the same USB socket, does it really make sense to worry about having two different power supplies for PLL and digital?
If the answer is yes, it still does matter: would then using two different 1117 voltage regulators (both taking 5V from the same USB socket), one powering the PLL and the second powering the Digital core make sense or is it complete nonsense?

I know that the device is going to work anyways, it is not the first project i do with this chip and i have even joined DVDD and PVDD directly and it works perfectly, but this time i wanted to do it correctly if possible and if it does not imply too many extra parts.

Again, yes/no answers to the above questions would suffice and be appreciated. Thanks a lot!
 

fpitas

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Were it me, I'd put a ferrite bead in each power leg to isolate the circuits at high frequencies.
 
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MCH

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Were it me, I'd put a ferrite bead in each power leg to isolate the circuits at high frequencies.
thanks fpitas,
you mean a ferrite bead in each power leg of the chip and 3.3V from one single power supply?
 

fpitas

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thanks fpitas,
you mean a ferrite bead in each power leg of the chip and 3.3V from one single power supply?
Yes, I doubt you need separate supplies. Even a bead with a small RF impedance (10 - 100 ohms @ 100MHz) offers good isolation and helps prevent digital hash going back to the supply rail.
 
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