what is ADM3053's reference power layer in 4-layer PCB design?

Question

hello, I have a question about ADM3053 recently. I am designing a 4-layer PCB board (TOP、GND、VCC、BOT) with ADM3053, when it comes to the reference power layer of ADM3053, which should I choose: pin12&pin19 or float?

ericb · Accepted Answer

Hi Caroline, 
 I'd encourage you to follow the PCB layout and layer assignments as used in the ADM3053's evaluation board EVAL-ADM3053EBZ , at least in the area surrounding the ADM3053. The different layers are shown in the eval board's user guide . This board was tested and passed EN55022 Class B for radiated emissions. 
 In terms of your question about the connection between pins 12 & 19, these pins should be connected through a ferrite bead and using a wide trace (not plane) between the ferrite and Pin 19. See the PCB Layout Recommendations section on page 4 of the user guide. 
 Eric 
 ps Some resources which discuss the considerations behind the design choices in the evaluation board are AN-0971 Recommendations for Control of Radiated Emissions with isoPower Devices or AN-1349 PCB Implementation Guidelines to Minimize Radiated Emissions on the ADM2582E/ADM2587E RS-485/RS-422 Transceivers . Note that AN-1349 is specifically for a different part, but the concepts and guidelines are similar.)