Xilinx Spartan-6 FPGA Series Design And Pin Planning Manual

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Xilinx Spartan-6 FPGA Series Design And Pin Planning Manual Manual pdf 16 page image

16 www.xilinx.com Spartan-6 FPGA PCB Design and Pin PlanningUG393 (v1.1) April 29, 2010Chapter 2: Power Distribution SystemCapacitor SpecificationsThe electrical characteristics of the capacitors in Table 2-1 are described in this section.Characteristics of the PCB bulk and high-frequency capacitors are specified in Table 2-2,followed by guidelines on acceptable substitutions. The equivalent series resistance (ESR)ranges specified for these capacitors can be over-ridden. However, this requires analysis ofthe resulting power distribution system impedance to ensure that no resonant impedancespikes result.PCB Bulk CapacitorsThe purpose of the bulk capacitors is to cover the low-frequency range between where thevoltage regulator stops working (~100 KHz) and where the high-frequency capacitors startworking (~2 MHz). As specified in Table 2-1, all FPGA supplies require bulk capacitors.The bulk capacitors in Table 2-1 and Table 2-2 are not necessarily in addition to the voltageregulator output capacitors required by the regulator manufacturer, provided there is noinductor, ferrite bead, choke, or other filter between the FPGA and the bulk capacitors.However, if the FPGA bulk and regulator output requirements are merged, the totalcapacitance of this network must not be less than the total bulk specified in Table 2-1 andTable 2-2, and must comply with the regulator manufacturer’s output capacitorrequirements.The bulk PCB capacitors specified in Table 2-1 are ceramic capacitors from Murata, acapacitor manufacturer. This capacitor was selected for its value, size, and low-cost. It isalso RoHS compliant. If another manufacturer’s capacitors or another type of capacitor(e.g., tantalum or high-performance electrolytic) meet the specifications listed in Table 2-2,substitution is acceptable.PCB High-Frequency CapacitorsThere are two high-frequency capacitor values in Table 2-2: the 4.7 μF capacitor in an 0805package and the 0.47 μF capacitor in an 0402 or 0204 package. Substitutions can be madefor some characteristics, but not others; see the notes attached to Table 2-2 for details.Table 2-2: PCB Capacitor SpecificationsIdealValueValueRange (1)BodySize(2) Type ESLMaximum ESR Range(3) VoltageRating (4)SuggestedPart Number100 μF C > 100 μF 12102-TerminalCeramicX7R or X5R5 nH 10 mΩ < ESR < 60 mΩ 6.3V GRM32ER60J107ME20L4.7 μF C > 4.7 μF 08052-TerminalCeramicX7R or X5R2 nH 10 mΩ < ESR < 60 mΩ 6.3V0.47 μF C > 0.47 μF 0204 or04022-TerminalCeramicX7R or X5R1.5 nH 10 mΩ < ESR < 60 mΩ 6.3VPCB Capacitor Substitution Rules: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.