I have a question on the layer structure (stack up) for TIDA-00281 (TIDUAY9). In page 85, Section 8.3.2, it said "This design uses a 6-layer board." But the Figure 126 only shows 4 layers, which are Top layer, Internal Plane (Ground), Signal Layer 3, and Bottom Layer. Could you please point me out the other two layers? or it was a typo and should be "This design uses a 4-layer board."