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Nora
Joined: 31 Mar 2006
Posts: 49
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 14 Aug 2008 16:40 Multiple grounds on PCB- why? |
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Hi-
These are two separate questions about grounds on a PCB.
1. There are at least 3 DC grounds on a PCB board that I am evaluating that have a small potential between them (0.3-0.7).
Each ground seems to go with its own area on the PCB.
2. One of the ICs, a quad channel isolator recommends 2 separate grounds for each "side" of the IC.
Can someone explain to me why? I have looked for reading material online but have come up short.
Thanks very much,
N_N
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FvM
Joined: 22 Jan 2008
Posts: 2635
Helped: 431
Location: Bochum, Germany
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| 14 Aug 2008 20:05 Multiple grounds on PCB- why? |
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| Isolation is a requirement of the outer world, e. g. electrical safety, not the PCB itself. Without knowing about the application enviroment, I just can guess, that it serves a purpose.
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seadolphine2000
Joined: 12 Apr 2005
Posts: 563
Helped: 31
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| 14 Aug 2008 20:55 Re: Multiple grounds on PCB- why? |
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2. One of the ICs, a quad channel isolator recommends 2 separate grounds for each "side" of the IC.
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Two separaet grounds are for complete isolation between the two sides. If they are connected to the same ground node, then any problem on the ground node can easily transfered to the other side.
I hope that this helps you.
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insrusingh
Joined: 08 Jul 2008
Posts: 16
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| 19 Aug 2008 14:13 Multiple grounds on PCB- why? |
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HI
reasons are given below
1) Every ic is allocated a separate power planes to restrict the noise tothe specific area.
2) When we talk about he ground we mean AC signal because we donot consider DC return path.
3) First remeber that every signal which originae from an IC has to come back to the source if retun path is not provided it will come through the enviroment which has impedence typically 400ohms ehich leads to EMI/EMC problems.
4) So all power planes are connectd through ferrite beads and capacitor(lowa pass LC filter) just to remove high frequency noise.
5) On board we can use multiple grounds like digital and analog grounds but it should be connected at single point using ferrite beads note otherwise it can create loop area and lad to EMI problem.
I think it helps
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