VS1010 Developer Board Grounding Question

Designing hardware and software for systems that use the VS1010 MP3 Audio DSP Microcontroller.
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MikeG
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VS1010 Developer Board Grounding Question

Post by MikeG » Tue 2018-09-18 16:49

Hi,
The VS1010 Developer Board schematic (rev 1.42 4.7.2018 14.17) shows an analog and a digital ground. However, I don't see where these two grounds are tied together anywhere? Since Eagle PCB files have not been released on the web site for this board I can't tell if you are actually using separate grounds on the board or not? Am I missing something?
Thanks,
Mike

MikeG
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Re: VS1010 Developer Board Grounding Question

Post by MikeG » Tue 2018-09-18 16:58

There are also bypass caps on CVDD and IOVDD_H1 that go to both analog and digital ground?

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Panu
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Re: VS1010 Developer Board Grounding Question

Post by Panu » Wed 2018-09-19 15:20

Please see this thread about PCB design and grounding: viewtopic.php?f=2&t=1101

Best analog performance and best digital performace is achieved when the ground is the same for both analog and digital, e.g. single ground plane, and strict routing rules are used for both the analog and the digital signals: never cross the analog signal region with any digital signals. Never route digital signals in the PCB region that has analog signals, in any layer. But do keep the grounds same. This is essential.

I know it is difficult to route the PCB with these rules. But it does give the best performance.

-Panu
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MikeG
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Re: VS1010 Developer Board Grounding Question

Post by MikeG » Wed 2018-09-19 18:33

HI Panu,
Thanks. I'm up to speed on that stuff, been doing pcb layouts for 25 years. Just curious why I didn't see the analog and digital grounds attached in the schematic and I didn't have the layout to look at. I was going to say that separate grounds like that are a big no no. But if it's one ground on the Developer Board, that is the best way.
Thanks,
Mike

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Panu
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Re: VS1010 Developer Board Grounding Question

Post by Panu » Wed 2018-09-19 20:08

Glad that we agree! :mrgreen:

I think the PCB engineer's style of drawing was to use separate AGND and DGND when drawing, so he could keep the grounds separate during the layout and routing phase, and more easily keep track that no signals were crossing, and then in the end pour copper over the gap to unite the grounds. I'm not sure, I didn't oversee it as I was on holiday at the time. I'll check it when I get to work tomorrow.

Anyway, not all designers, even at VLSI, are so strick about the no gap rule. The only thing that we insist 100% is that below the chip, the grounds are united over the whole IC area. Otherwise substrate currents flowing through the IC from one ground pin to another could cause latch-up and cause a total disaster.

-Panu
Info: Line In and Line Out, VS1000 User interface, Overlay howto, Latest VSIDE, MCU Howto, Youtube
Panu-Kristian Poiksalo, VLSI Solution Oy

Hannu
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Re: VS1010 Developer Board Grounding Question

Post by Hannu » Thu 2018-09-20 7:52

To confirm, I'd like to say that the AGND and GND are connected in VS1010 GNDPAD and in ground layer just right under the VS1010.

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