WM8804 and WM8524 supply confusion - diyAudio
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Old 25th November 2011, 04:09 PM   #1
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Location: Denmark
Default WM8804 and WM8524 supply confusion

I made the attached design.

From reading the datasheets I was sure that WM8804 DVDD=digital supply and PVDD=analog supply as well as WM8524 AVDD=analog supply and LINEVDD=digital supply.

Therefore I connected the 2 digital supplies to 1 regulator and the 2 analog supplies to another regulator.

However, after reading the datasheets more carefully and the application notes to these 2 IC's I'm not so sure that I have done it correctly.

The only thing I'm sure of is that WM8804 DVDD=digital supply and WM8524 AVDD=analog supply.

WM8804 PVDD and WM8524 LINEVDD I'm not so sure of.
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Last edited by Neutrality; 25th November 2011 at 04:16 PM.
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Old 25th November 2011, 04:38 PM   #2
JensH is offline JensH  Denmark
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The LINEVDD of the WM8524 seems to be the supply for the on-chip charge pump. It is probably not terribly sensitive to noise, but it will generate some noise on your VCC line, so connecting it to the digital supply of the WM8804 will probably be OK.

The PVDD of the WM8804 is the supply for the internal PLL, so I would expect this supply to be fairly sensitive to noise, just as the AVDD of the WM8524.

You could perhaps connect a 0 ohm resistor in series with the supplies, before the decoupling capacitors C11 and C18. Then you have a chance to add a little bit of filtering and separation if needed. The PVDD only consumes around 1.7mA, so e.g. a 10ohm resistor will not cause much voltage drop.
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Old 25th November 2011, 05:01 PM   #3
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The PLL needing a low noise supply, why didn't I think of that, should be obvious.

Also, the LINEVDD is also used for the digital interface(MCLK, BCLK, LRCLK, DACDAT) so connecting it together with the DVDD digital supply of the WM8804 should be ok.

Would be nice if the datasheets were a little more clear on these things.

However, it looks like my proposed desing is good enough as is.

But it is always good to get a second opinion from someone else, some things you just need some more experience to get right.

Your suggesting of adding a 0 ohm resistor in series with the supplies, with option of changing it to eg. a 10 ohm resistor is a good one. Though about that myself, albeit with ferrite beads instead. It should give some added separation and filtering.

However, I ws a little too fast and sent the gerbers away for manufacturing 2 days ago.

It would be well-advised to remember these small optional features on future designs.
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