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Anonymous
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Jun 25, 2013
03:12 AM
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Jun 25, 2013
03:12 AM
Hi, I have separated power domains for analog and digital with a common ground on a isolated copper area where the battery plugs. I'd like to check if in this case would be a good idea to connect a voltage divider to Vdda using an open-drain pin to ground (as seen on attached pic), since this would make the return current flow through the noisier and possibly shifted digital and battery grounds. Is it worth connecting the bottom node to Vssa using the analog globals for the sake of signal integrity? Even though this would add around 1k resistance to ground. Am I worrying too much? Does it make a noticeable difference? Thanks!
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PSoC 5LP
6 Replies
Anonymous
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Jun 25, 2013
03:41 AM
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Jun 25, 2013
03:41 AM
Anonymous
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Jun 25, 2013
04:01 AM
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Jun 25, 2013
04:01 AM
Hi PSoC73, thanks for the reply, I forgot about that, let's say that I will probably use the ADC in differential mode which will attenuate these effects I describe like the ground shift. But my concern is being able to connect and disconnect the voltage divider dynamically to avoid wasting power and I'm still not sure if mixing analog power with digital GPIOs is a good idea. Thanks again for the advice.
Anonymous
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Jun 25, 2013
04:14 AM
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Jun 25, 2013
04:14 AM
This method is just adapt with rail-to-rail range. AI_Pos and AI_Neg must stay within Vdd to Vss. If you want more spacious range, I recommend you to proper analog isolator.
Anonymous
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Jun 25, 2013
04:22 AM
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Jun 25, 2013
04:22 AM
But, More stable way is Isolate after ADC stage. Use a digital isolator, that is accurate. Do not use photo-couppular, It's my experience.
Jun 25, 2013
05:25 AM
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Jun 25, 2013
05:25 AM
Your question is also a f() of the resolution and accuracy you are
looking for. Clearly digital ground will have noise on it, and ohmic
drop. Noise you can take out of A/D result by filter/averaging. However
it has to be uncorrelated noise to be effective. And digital noise has
strong correlated components in it typically. Ohmic drop by cal routine.
And all of this a f() of resolution you are seeking.
Possible references that may be of use -
www.google.com/url AN60263
www.cypress.com/ AN66444
Regards, Dana.
Anonymous
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Jun 28, 2013
05:50 AM
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Jun 28, 2013
05:50 AM
I'll try your suggestions to see how they work for me. Thanks a lot for your replies.