[SI-LIST] Re: Strange resets happening in one of our circuit boards
- From: Doug Smith <doug@xxxxxxxxxx>
- To: steven.salkow@xxxxxxxx
- Date: Thu, 01 Jun 2006 21:02:00 -0700
Hi Steven and the group,
The chair is definitely a possibility. If sparking is occuring within
the chair (about a third of office chairs) you will get radiated
fields of thousands of volts per meter.....dwarfs anthing the EMC guys
normally deal with.
If you have leads attached as in the emulator they could be acting
like antennas.
I have seen this effect take down just about every type of equipment
from gigabit lightwave systems, to electronics in the aviation
industry, and more. The equipment needs have good immunity to ESD
radiated fields to operate with this type of noise.
What's worst is that a chair that does this produces typically a dozen
or two sparks over the first 15 seconds after rising from the chair.
To test your chair, set a small AM radio tuned to an empty frequency
on the floor under the chair. When you get up, popcorn noise in the
radio confirms the chair is radiating very strong EMI.
I have written a few papers on the subject. Try looking at the
following pdf files from my website:
http://emcesd.com/pdf/eos93.pdf
http://emcesd.com/pdf/uesd99-w.pdf
Hope this helps.
Doug
Salkow, Steven wrote:
> It's not magic. Do you power the emulator from the Jtag port?
> A uncharged cap on the emulator side as a sudden load is a short to
> your power supply and maybe is firing off your under voltage reset
> circuit. As far as what you see, question your test set up. Rolling your
> chair does not produce +5/-3V worth of noise - vibration shake
> something? When you have eliminated everything else, what is left,
> however improbable, is usually the answer.
> Good luck
>
> Steven Salkow
> Lockheed IS&S
> 3130 Zanker Rd, San Jose
> Ca. 94588
> (408) 473-4058
> steven.salkow@xxxxxxxx
> salkow@xxxxxxxxxxxx
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Zhangkun
> Sent: Thursday, June 01, 2006 6:20 PM
> To: Shiraz.Bashir@xxxxxx; SI-List
> Subject: [SI-LIST] Re: Strange resets happening in one of our circuit
> boards
>
> Shiraz Bashir
>
> Normally, the power ground noise could not be so strong to reset the
> system.
>
> Best Regards
>
> Zhangkun
> 2006.6.2
>
> ----- Original Message -----
> From: "Bashir, Shiraz (GE Healthcare)" <Shiraz.Bashir@xxxxxx>
> To: "SI-List" <si-list@xxxxxxxxxxxxx>
> Sent: Friday, June 02, 2006 7:42 AM
> Subject: [SI-LIST] Strange resets happening in one of our circuit boards
>
>
>
>>Hi,
>>A unit with microprocessor based system circuit board is resetting
>
> when
>
>>we plug in emulator port in JTAG port.
>>Using scope we see that CPU reset pin is asserted, hence the reset.
>>We see +5/-3V worth of noise on the signal just by rolling my chair
>
> back
>
>>and forth in front of the emulator.
>>
>>This happens in following scenario:
>>1. User is sitting on chair, user gets up (doesn't touches the
>>unit) and unit resets.
>> We demonstrated this on three randomly selected units.
>>Sounds ridiculous but it is true
>>
>>OR
>>
>>2. If we keep solder wires for scoping purposes.
>>
>>It doesn't happen when Unit is enclosed in it's metal housing.
>>
>>Investigated..
>>a. Reviewed schematics and CPU's reset line is pulled to 3.3V using 1K
>>ohm resistor.
>>b. Physically checked that pull up resistor is in place and is
>
> connected
>
>>with BGA ball of reset pin.
>>c. We checked power monitor chip which can drive reset too..but no
>
> issue
>
>>there.
>>D. Reset line is not going anywhere else other than JTAG port and
>
> Power
>
>>Monitor Chip
>>
>>Brainstormed..
>>a. Soldering issue due to BGA ? Ruled out as how can soldering issue
>
> be
>
>>on three randomly selected units.
>>b. ESD- Ruled out as per our understanding ESD (air discharge) cannot
>>"arc over" from 2-3 feet distance.
>>
>>Fix:=20
>>A team member recommended to put a capacitor across resistor. Did that
>>and problem went away.
>>
>>Can anybody explain why it is happening ? Is it noise from Power
>
> Supply
>
>>but how can it defeat a strong pull up ?
>>
>>Thanks,
>>Shiraz Bashir
>>General Electric Healthcare
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--
------------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
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