Xilinx Zynq-7000, Design Manual

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Zynq-7000 PCB Design Guide www.xilinx.com 16
UG933 (v1.8) November 7, 2014
Chapter 3: Power Distribution System
PCB Bulk Capacitors
The purpose of the bulk capacitors is to cover the low-frequency range between where the
voltage regulator stops working and where the on-package ceramic capacitors start
working. As specified in Table 3-1 and Table 3-2 , all AP SoC supplies require bulk capacitors.
The tantalum and niobium oxide capacitors specified in Table 3-3 were selected for their
values and controlled ESR values. They are also ROHS compliant. If another manufacturer's
tantalum, niobium oxide, or ceramic capacitors are used, ensure they meet the
specifications of Table 3-3 and are properly evaluated via simulation, s-parameter
extraction, or bench testing.
PCB High-Frequency Capacitors
Table 3-3 shows the requirements for the 0.47 µF and 4.7 µF capacitors in the 0402 package.
Substitutions can be made for some characteristics, but not others. For details, refer to the
notes in Table 3-3 .
PCB Capacitor Placement and Mounting Techniques
PCB Bulk Capacitors
Bulk capacitors can be large and sometimes are difficult to place very close to the AP SoC.
Fortunately, this is not a problem because the low-frequency energy covered by bulk
capacitors is not sensitive to capacitor location. Bulk capacitors can be placed almost
anywhere on the PCB, but the best placement is as close as possible to the AP SoC.
Capacitor mounting should follow normal PCB layout practices, tending toward short and
wide shapes connecting to power planes with multiple vias.
Mid and High Frequency Capacitors
The 4.7 µF capacitor covers the middle frequency range, while the 0.47 µF capacitor covers
the high frequency range. Placement has some impact on performance. The 4.7 µF
capacitors should be placed as close as possible to the AP SoC. Any placement within two
0.47 µF C > 0.47 µF 0603 2-Terminal
Ceramic X7R
or X5R
0.5 nH 1 m Ω < ESR < 20 m Ω 6.3V GRM188R70J474KA01
Notes:
1. Values can be larger than specified.
2. Body size can be smaller than specified.
3. ESR must be within the specified range.
4. Voltage rating can be higher than specified.
Table 3-3: PCB Capacitor Specifications (Cont’d)
Ideal
Value
Value
Range
(1)
Body
Size
(2)
Type
ESL
Maximum
ESR Range
(3)
Voltage
Rating
(4)
Suggested
Part Number
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