[SI-LIST] Re: Ground plane question
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Mike S." <powersurf@xxxxxxxxx>
- Date: Tue, 02 Aug 2005 17:19:52 -0700
Bruno, from your drawing
Low frequency PWM signal return currents will not flow in SC1
Low frequency power supply return currents will not flow in SC1
If there is any kind of external loop between the input signal common, and
the output signal common as might happen with external chassis connections,
then you will have aggravated and not improved your situation.
Steve.
At 11:29 PM 8/2/2005 +0100, Mike S. wrote:
>Thanks for the reply Steve and Curt.
>In the output connectors, the signal and power lines share the same
>ground return path (typical servo connection). The same happens in the
>ground plane 1, where the power return current goes back to the power
>connector and the signal return currents goes back to the stack
>connector 2.
>I send the diagram of the board in the attachment.
>
>Thanks in advance
>Best Regards
>Bruno
>
>On 8/2/05, steve weir <weirsi@xxxxxxxxxx> wrote:
> > Curt, a good deal of caution is called for here. The most common mistake
> > that people make when attempting to moat or island commons is the creation
> > of a big loop that is far more dangerous and destructive than one big
> > contiguous common.
> >
> > Bruno needs to consider how the current will flow in his servo drivers all
> > the way from the power supply through the drivers and out to the
> > motor(s). Then he can figure out whether his logic can share a common with
> > the servo drivers, and then how to implement it contiguous or moated, or
> > whether he needs to galvanically isolate his logic with optos or magnetics.
> >
> > Regards,
> >
> >
> > Steve.
> > At 11:31 AM 8/2/2005 -0500, Curt McNamara wrote:
> > >Given that you have high current on one end of your daughter=20
> > >board I would keep this ground separate -- you will need bulk=20
> > >up there and I would view this end of your daughter card as
> > >a power card sitting in a backplane. You want to contain all=20
> > >energy in that area. If the design is well done the signaling=20
> > >to the output end only comes through that connector and not the=20
> > >input connector so this should work fine.
> > >
> > >I sometimes leave sites between grounds where I can later
> > >add a resistor (zero ohm or larger) or ferrite.
> > >
> > >The general recommendation to keep grounds the same is always a=20
> > >good one, however the presence of high current and separate=20
> > >signaling appears to make this a better path.
> > >
> > >If there is any communications between the ends of the card then
> > >you will need to trade this off vs. keeping power separate.
> > >
> > > Curt
> > >
> > >Curt McNamara. P.E.=20
> > >Senior Electrical Engineer=20
> > >Logic Product Development=20
> > >411 Washington Ave. N Suite 101=20
> > >Minneapolis, MN 55401=20
> > >Tel 612-436-5178=20
> > >Fax 612-672-0443=20
> > >curtm@xxxxxxxxxxx=20
> > >www.logicpd.com=20
> > >This message (including any attachments) contains confidential
> > >information intended for a specific individual and purpose, and is
> > >protected by law. If you are not the intended recipient, you should
> > >delete this message and are hereby notified that any disclosure,
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> > >based on it, is strictly prohibited.
> > >
> > >
> > >
> > >-----Original Message-----
> > >From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > >On Behalf Of Mike S.
> > >Sent: Tuesday, August 02, 2005 5:46 AM
> > >To: si-list@xxxxxxxxxxxxx
> > >Subject: [SI-LIST] Ground plane question
> > >
> > >
> > >Hello to all
> > >I'm designing a daughter card (more like a connector expansion card) for
> > >digital low frequency PWM input/output. This daughter card connects to
> > >the motherboard with 2 stack connectors (similar to PC104 but a lot
> > >smaller) separated by 1 inch. Both these connectors have ground pins.
> > >One is only for input, and the other only for output. The daughter card
> > >is a dual layer board. Since the trace routing is very simple I will use
> > >the bottom layer as a ground plane. My question is: Should the ground
> > >plane be connected to both connectors, or, to avoid ground loops (with
> > >the motherboard) should I do two ground planes (both in the bottom
> > >layer) one for each stack connector? One ground plane would be under the
> > >input stack connector and the digital input connectors. The other would
> > >be under the output stack connectors, the digital output connectors
> > >(these are 3 way connectors to drive servos) and an alternate power
> > >supply to drive the Vcc pin of each output connector to the servos
> > >(possibly high currents). Any pointers, suggestions, design examples?
> > >Thanks in advance Best Regards Bruno
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