AN_6612_007
78M6612 Hardware Design Guidelines
Rev 2
19
Figure 20: Crystal Y1 and Capacitors C7/C9
Figure 21: GND Shield Surrounds Crystal Traces
Figure 21 shows the placement and layout of the crystal oscillator components on the same side of the
PCB with the integrated circuit (a 78M6613 is used in the example). There is a ground guard-ring
surrounding the crystal oscillator. One way to accomplish this is by surrounding the circuit with a wide
grounded trace. For this to work, the grounded trace must have zero current flowing through it. In this
example, there is a “floating ground” with no connections other than the oscillator’s VSS.
v
C1
Y1
U1
V3P3 PLANE / TOP LAYER
MULTIPLE VIAS TO GND PLANE
(BOTTOM LAYER)
MULTIPLE VIAS TO GND PLANE
(BOTTOM LAYER)
Y1 CRYSTAL BOTTOM VIEW
C2
Y1
GNDA
GNDD
Figure 22: Crystal Oscillator Components on the Same Side
GND Shield
V3P3 Plane
