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Old 18th January 2011, 08:46 AM   #1
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Default Eccentric Power Distribution

Hi all,

I’m half way through designing a DAC using a CS8416 and two PCM1794s – at the minute I am doing a bit of research on power supplies/supply decoupling etc – and have come across the suggestion of powering each device from its own linear voltage regulator as a way to decouple the devices from each other. Doing so would mean a single +/- 6V supply could be used for the entire circuit (although I would prefer +/- 15V for the I/V and beyond).

I have had a look around and something like a TPS78833, which comes in a small SOT-23 package, would be ample to supply each chip with 3.3V – there are similar devices for the +/- 5V analogue supply.

I personally would be interest in hearing the results of this.

What do you recon, interesting pursuit or waste of effort?

All the best
Mat
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Old 18th January 2011, 05:47 PM   #2
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Experience with a six ADC video system suggests that your idea may be worthwhile but more important is the earthing arrangment. You should try and isolate the earth plane between each DAC and make sure that all decoupling caps are connected only to the earth and supply for the relevant DAC. Ferrite beads in the individual supply lines can also be usefull. There is no hard and fast "right" way(beyond normal good practice) since you may not have full control over input and output earthing arrangements.
Good Luck

Barry
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Old 19th January 2011, 12:35 PM   #3
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Hi Barry,

How would you suggest implementing the isolated ground planes? I was thinking having a separate ground plane per device and having a star arrangement from each of these terminating close to the ground pin of the corresponding regulator and the board’s ground terminal?

What were you referring to when you said “the individual supply lines”, between each regulator and supply pin or before each regulator?

Mat
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Old 20th January 2011, 08:45 AM   #4
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Your star grounding arrangement sounds O.K. The important thing is to get all earth connections associated with a particular device on the same groundplane. If your routing to the star point is too long it may be worth hard wiring with a length of 16swg copper wire.
I was meaning ferrites on the output side of rhe reg, near the device being powered but if your individual regs are very close this probably woudn`t be required. I wouldn`t expect a ferrite on the input to the reg to be usefull unless your raw supply is very noisy.

Barry
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Old 20th January 2011, 09:53 AM   #5
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That’s great. I will put schematic and board layout together and either post it here else ware in the forum. It might take a while as I’m currently busy with other things but it will be done at some point.

At the minute I think I’ll keep the ferrites in – they won’t cause any harm even if they are not useful.

Thanks for you help.
Mat
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