[SI-LIST] Re: Sacrificial ground: Is it useful?

Darn, sorry guys, but I lost over half of my comments to John on the last 
E-mail. I didn't save it, so here's a brief summary of what "disappeared."
The result is minimal disturbance (under the circumstances) because of the 
use of the low inductance current path and the lowest current density entry 
point to the internal circuits of the PCB.

RE: Capacitors around the periphery

I recommended PROVISIONS for "spoiler" capacitors be spaced around the ring 
at varying intervals.  Because the ring forms a loop antenna that is resonant 
at a low to intermediate frequency, a susceptibility coul be encountered, 
depending on the using environment. If so, addition of either capacitors or low 
value damping resistors could be used to "spoil" or significantly reduce the 
susceptibility. These mounting provisions are not recommended to be populated 
unless a problem is encountered.

The guard ring approach solved many ESD problems, particularly on portable 
designs. I presented the concept in lectures across the US and Europe, as well 
as incorporating custom variations in many designs over the years. Perhaps many 
designers now use the concept without understanding whether they have need 
for it in their particular design.

I had considerably more to comment, but don't have any more time now.

Have fun,


Mike

Michael L. Conn
Owner/Principal Consultant
Mikon Consulting
Cell: 408-821-9843

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