we use LTM4646 and 4622 , for layout ,some questions to consult.
In both datasheets, it mentions that " Use a separated SGND ground copper area for components connected to signal pins. Connect the SGND to GND underneath the unit ".
1. For LTM4646, IS this mean SINGLE point connection ONLY under the IC ?
I also checked the DSN file of evaluation-kit (DC2527A-B), the SGND pins and GND pins SEEMS connected together as left part of following snapshot. However, I found they are Independent nets in PCB files (there is a small SGND plane on L5 layer, not connected to GND.)..... then I went back to SCH .dsn file and found this....I move the connection line between SGND pins and GND pins, as right part of followig snapshot, it turned out to be a line without electrical property. I am very confused why designed as so.
2. For LTM4622, there is similar requirement for layout on page 21 " Use a separated SGND ground copper area for components connected to signal pins. Connect the SGND to GND underneath the unit. " But there is no SGND for LTM4622.
I checked with evaluation kit (DC2249A) and found R13 as connection point for SGND and GND. There is a small SGND plane on bottom layer, but it is not UNDERNEATH the IC as reuired.
3. In general, for both twoIC , if we use mutilple layer GND planes and do not seperate so-called SGND and GND, vias are used directly down to internal Ground layer, will it be ok?