I am designing a board with four AD9915s. I have two questions regarding the EPAD. I plan on routing digital and analog grounds seperately and joining them at the power supply. A seperate chassis ground is also available that is capactively coupled to the AGND and DGND.
1) Is the EPAD required for electrical or is it only a thermal path? If it is only for thermal I would lean towards a chassis ground connection which would provide a better thermal path.
2) Assuming that the EPAD is both an electrical and thermal requirement and given the proposed board topology, is it preferred to connect the AD9915s EPADs to the analog (AGND) or digital ground (DGND)? (My inital assumption is to connect to the analog ground since it should be "quieter" - digital switching noise may be present on the DGND).