Re: SD module

["C. Cuevas" <cuevas@jlab.org>]

Hall D Electronics:

Hi Gerard,

These are the LTM4604 high efficiency switchers and I understand your 
concerns.  These parts are on the top side of the board, and this B 
switch module will be adjacent to whatever board is placed in physical 
slot 12(PayloadPort2).  There is some room to move these regulators 
toward the backplane, and we will consider doing that before the board 
is sent for manufacturing.  We have no plans to enclose these devices in 
a metal shield, but the regulators are very low profile and it may be a 
good idea and the 'shield' could be used for heat sinking, even though 
we do not anticipate any cooling problems with these devices. 

There have been plenty of updates to the functional description and 
specification document for the SD and CTP and the schematics will be 
appended to the document.  I plan to post these by Friday.

I could not agree more about your comments regarding a full crate test.  
As you know we only have 8 FADC250 and we will not  assemble any more at 
the present prototype revision.  There are scores of tests that will be 
performed in a few months once we have the SD and CTP prototypes 
assembled and installed in our present test stand, and if these 
prototypes do not meet or exceed specifications or cause unwanted 
interference, we will make corrections for the final production modules.

Regards,
Chris
~~~~~~~~~~~~~~~~`



Gerard Visser wrote:
> Hi Fernando,
>     By the way I tried to dial in to the meeting but there was no-one 
> on the EVO at least for me (who dialed in on the plain telephone). I 
> tried at 10:45, 11:00, 11:10.
>     I am writing now because I am just looking over Dave Doughty's 
> talk and see the layout plot of the SD module.
>     I am very concerned by the placement of what I take to be 
> switching regulators near the front of the board (at bottom edge). 
> Unless this all is very carefully handled, I suspect we are going to 
> have EMI issues between this board and the ADC (125 or 250) or TDC in 
> adjacent slots. I am going to great lengths to keep all switching 
> power supplies as far back on the ADC125 board as possible. I am sure 
> that if there is a few hundred fF coupling from a 5V or higher 
> switching node to my analog line receiver circuitry, there will be 
> visible effects in the ADC signals.
>     Perhaps the plan is to fully enclose the SD module at least in the 
> area of the switching supplies in grounded metal shields. Although I 
> believe it would be difficult to do so on the bottom side. As you know 
> the channel density and airflow/cooling requirements of the ADC125 
> will preclude adding any additional shields beyond the pcb's 
> themselves. You probably would say similarly re the ADC250 and the 
> TDC. Anyway, a full crate test is clearly needed as soon as practical 
> (next summer), preceeded with a statement that if the TI or SD module 
> is generating interference to either of the ADC's or to the TDC's, the 
> TI or SD will be respun to fix it.
>     Thanks,
>
>         Gerard
>
> p.s. Also, is that an aluminum electrolytic in the bottom center? 
> Might want to avoid that...