[SI-LIST] Re: Heat Sink Hook Grounding
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sun, 30 Mar 2014 12:40:29 -0700
Todd, I agree that I need to know where the earth return is, and what
its characteristics are. I do not want anyone to confuse that return
for something that has the same potential as the actual earth under
arbitrary conditions. Ditto, I need to know what constitutes the
chassis in which I wish to contain offending radiation.
Steve.
On 3/30/2014 8:58 AM, Todd Hubing wrote:
> If you are the person responsible for EMC or product safety, ground is a very
> important concept. A person doesn't need to solve Maxwell's equations to
> ground a system properly. Whether your ground is the earth, a vehicle chassis
> or a metallic enclosure, the rules are basically the same. A ground structure
> doesn't always have to be electrically small (e.g. the earth is not
> electrically small at 60 Hz and monopole antenna ground structures are never
> electrically small); however ground structures must provide a reliable, local
> potential reference. There are well-established procedures for ensuring that
> grounding is done properly in various situations.
>
> The concept of "ground" was corrupted when someone suggested that ground was
> "a path for returning currents to their source". Returning currents to their
> source is a very important aspect of EMC and signal integrity, but it has
> nothing to do with ground. In fact, returning currents on a ground structure
> often destroys the ability of the structure to serve as an effective ground.
>
> If your design has 4 or 5 grounds (e.g. D_GND, A_GND, P_GND, CH_GND,...),
> then clearly current returns are being confused with grounds and you should
> focus on the current-return aspect of these nets. Nevertheless, if you are
> responsible for EMC or product safety, you will still need to identify the
> true ground structure and ensure that everything relatively large and
> metallic is properly grounded.
>
> Todd
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of steve weir
> Sent: Saturday, March 29, 2014 2:18 AM
> To: Sanjay G; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Heat Sink Hook Grounding
>
> The path to recovery for ground-aholics is to put their faith in Maxwell's
> equations and let go of the term "ground". There is a green wire safety
> connection to earth. Designs have Vss planes, chassis and other metallic
> structures that may have a DC path to the green safety wire. At any
> appreciable frequency these structures are not iso-potentials.
> You know that you have done an adequate job when the EMFs in your design all
> fall within acceptable limits.
>
> Partial inductance is an artificial but very useful concept. Some people
> don't like it like some people don't like GO TO statements in code, even
> though they have no problem with Switch / Case statements which simply hide
> GO TO statements. Use what is practical and works.
> Appreciate and respect the limitations of partial inductance and it can be
> very practical and useful. EMI no different than any other E/M except that
> we want to limit how much of it gets out of our products.
>
> Steve.
> On 3/28/2014 7:20 PM, Sanjay G wrote:
>> Hi Steve,
>> 'When you say there is no place like ground'. it is all differential
>> potential which should be considered for any design consideration.
>> How do I know whether my Ground plane design is good or bad. Power
>> plane design is good or bad.
>>
>> In some of the SI-list post regarding partial inductance vs loop
>> inductance, some people never believe in partial inductance model,
>> they only believe in overall loop inductance. they claim even if two
>> inductance matrix with different partial inductance but similar loop
>> inductance should give similar results. does this assumption valid
>> for EMI radiation also?
>>
>> Thanks,
>>
>>
>>
>> On Friday, March 28, 2014 1:40 AM, steve weir <weirsi@xxxxxxxxxx> wrote:
>> Indeed.
>>
>> In the famous story and movie: "The (Wonderful) Wizard of Oz" Dorothy
>> must repeat: "There is no place like home." Dr. Bruce Archambeault
>> teaches us that we must repeat: "There is no place called ground."
>> Difference potential along the structure will radiate. The more
>> inductance, the lower the frequencies and the stronger the radiation
>> as well as the greater the susceptibility that you point out. A
>> clever person like Doug Smith might point out that there is an optimum
>> resistance to place between the heat sink and the board to minimize
>> resonant peaking.
>>
>> This could make a good EMC demonstration.
>>
>> Steve.
>> On 3/27/2014 12:52 PM, Antonis Orphanou wrote:
>>> A floating heat-sink is coupled to the rest of the PKG/PCB
>> arrangement by surface capacitance. It will radiate based on half
>> wavelength modes.
>>> Providing now a conductive path of the heat-sink to the rest of the
>> circuit arrangement you have eased the current flow to the antenna
>> (heat-sink). The same antenna is now driven by a stronger source and
>> depending on the dimension of the grounding path (at some point in
>> frequency it will be an open inductive path) you will see an increase
>> in the total power radiated by your heat-sink, as well as radiated
>> power accepted by the same topology.
>>>
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx
>> <mailto:si-list-bounce@xxxxxxxxxxxxx>
>> [mailto:si-list-bounce@xxxxxxxxxxxxx
>> <mailto:si-list-bounce@xxxxxxxxxxxxx>] On Behalf Of Ranjith
>> Raviprakash
>>> Sent: Thursday, March 27, 2014 9:57 AM
>>> To: si-list
>>> Subject: [SI-LIST] Heat Sink Hook Grounding
>>>
>>> Hi Experts,
>>> What is the impact of grounding Heat sink anchors?
>>>
>>> I want to use them as probe ground points for measurement during
>>> proto bring-up (by removing the anchors and using a male header)
>>>
>>> During final shipment, I will place the anchors back and of course
>>> they will remain grounded.
>>>
>>> Ranjith
>>>
>>>
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>>
>> --
>> Steve Weir
>> IPBLOX, LLC
>> 1580 Grand Point Way
>> MS 34689
>> Reno, NV 89523-9998
>> www.ipblox.com
>>
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>>
>
> --
> Steve Weir
> IPBLOX, LLC
> 1580 Grand Point Way
> MS 34689
> Reno, NV 89523-9998
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
> All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved.
> This e-mail may contain confidential material.
> If you are not the intended recipient, please destroy all records and notify
> the sender.
>
>
>
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--
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV 89523-9998
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved.
This e-mail may contain confidential material.
If you are not the intended recipient, please destroy all records
and notify the sender.
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