The rules for the ground planes are very important and should be carefully implemented. Pulsed current are very noisy and they should not interfere with small signal sensing information (e.g FB). Therefore, it is advised to have the noisy ground as much isolated from the clean analog signal ground as possible to avoid interference and cross talk that could deteriorate the regulation, load step performance and internal compensation. Similarly, the placement of bypass capacitors should be followed as per in the datasheet recommendations.