SLLS983J June 2009 – September 2019 ISO1050
A minimum of four layers is required to accomplish a low EMI PCB design (see Figure 32). Layer stacking should be in the following order (top-to-bottom): high-speed signal layer, ground plane, power plane and low-frequency signal layer.
If an additional supply voltage plane or signal layer is needed, add a second power / ground plane system to the stack to keep it symmetrical. This makes the stack mechanically stable and prevents it from warping. Also the power and ground plane of each power system can be placed closer together, thus increasing the high-frequency bypass capacitance significantly.
For detailed layout recommendations, see Application Note SLLA284, Digital Isolator Design Guide.