Zynq-7000 PCB Design Guide www.xilinx.com 17
UG933 (v1.8) November 7, 2014
Chapter 3: Power Distribution System
inches of the device’s outer edge is acceptable. The 0.47 µF capacitors should be placed as
close to the AP SoC as possible, within 0.5 inches of the outer edge.
The capacitor mounting (solder lands, traces, and vias) should be optimized for low
inductance. Vias should be butted directly against the pads. Vias can be located at the ends
of the pads (see Figure 3-1B), but are more optimally located at the sides of the pads (see
Figure 3-1C). Via placement at the sides of the pads decreases the mounting’s overall
parasitic inductance by increasing the mutual inductive coupling of one via to the other.
Dual vias can be placed on both sides of the pads (see Figure 3-1D) for even lower parasitic
inductance, but with diminishing returns.
Basic PDS Principles
The purpose of the PDS and the properties of its components are discussed in this section.
The important aspects of capacitor placement, capacitor mounting, PCB geometry, and PCB
stackup recommendations are also described.
Noise Limits
In the same way that devices in a system have a requirement for the amount of current
consumed by the power system, there is also a requirement for the cleanliness of the power.
This cleanliness requirement specifies a maximum amount of noise present on the power
X-Ref Target - Figure 3-1
Figure 3-1: Example Capacitor Land and Mounting Geometries
Land Pattern
End Vias
Long Traces
(A)
UG933_c3_01_102413
(B)
Land Pattern
End Vias
Not Recommended.
Connecting Trace is Too Long
(C)
Land Pattern
Side Vias
(D)
Land Pattern
Double Side Vias
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