Intel IXP43X manual Controlled-impedance traces Low-impedance power distribution

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Intel® IXP43X Product Line of Network Processors—Hardware Design Guidelines

•Poor routing density

•Uncontrolled signal trace impedance

•Lack of power/ground planes, resulting in unacceptable crosstalk

•Relatively high-impedance power distribution circuitry, resulting in noise on the power and ground rails

•High-speed circuits require multi-layer printed circuit boards:

—Advantages:

•Controlled-impedance traces

•Low-impedance power distribution

—Disadvantages:

•Higher cost

•More weight

•Manufactured by fewer vendors

•Symmetry is essential to keep the board stack-up symmetric about the center This minimizes warping

•For best impedance control, have:

—No more than two signal layers between every power/ground plane pair

—No more than one embedded micro-strip layer under the top/bottom layers

•For best noise control, route adjacent layers orthogonally. Avoid layer-to-layer parallelism

•Fabrication house must agree on design rules, including:

—Trace width, trace separation

—Drill/via sizes

•The distance between the signal layer and ground (or power) should be minimized to reduce the loop area enclosed by the return current

—Use 0.7:1 ratio as a minimum.

For example: 5-mil traces, 7-mil prepreg thickness to adjacent power/ground.

Figure 17 and Figure 18 provides an example for a six-layer and eight-layer board. For stripline (signals between planes), the stackup should be such that the signal line is closer to one of the planes by a factor of five or more. Then the trace impedance is controlled predominantly by the distance to the nearest plane.

Intel® IXP43X Product Line of Network Processors
HDG	April 2007
58	Document Number: 316844; Revision: 001US

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Contents Intel IXP43X Product Line of Network Processors Hardware Design GuidelinesHDG Intel IXP43X Product Line of Network ProcessorsApril Contents Figures Tables Document Number 316844 Revision 001US Date Revision Description § §001 Initial release HDG Content Overview Chapter Name DescriptionList of Acronyms and Abbreviations Sheet 1 Related DocumentationAcronyms Term ExplanationOverview List of Acronyms and Abbreviations Sheet 2HDG Intel IXP435 Network Processor Block Diagram Typical Applications System Architecture Description System Memory MapIntel IXP43X Product Soft Fusible Features Sheet 1 Soft Fusible FeaturesSignal Type Definitions Symbol DescriptionDDRII/I Sdram Interface Soft Fusible Features Sheet 2USB Host Each USB can be Enable separately EthernetType Signal InterfaceDDRII/I Sdram Interface Pin Description Sheet 1 Name Device-Pin Connection Terminatio Description FieldDDRII/I Sdram Initialization DDRII/I Sdram Interface Pin Description Sheet 2Expansion Bus Expansion Bus Signal Recommendations Sheet 1Type Pull Name Recommendations Field Down Boot/Reset Strapping Configuration Sheet 1 Reset Configuration StrapsExpansion Bus Signal Recommendations Sheet 2 Name Type Pull Recommendations Field DownBoot/Reset Strapping Configuration Sheet 2 Intel XScale Processor Cfg0 Cfg1 Cfgenn Actual Core Speed Setting Intel XScale Processor Operation Speed3 8-Bit Device Interface MHz4 16-Bit Device Interface Flash Interface 16-Bit Device InterfaceUart Interface Flash Interface ExampleUart Signal Recommendations MII Interface Uart Interface ExampleMII NPE a Signal Recommendations Signal Interface MIIMII NPE C Signal Recommendations Sheet 1 MAC Management Signal Recommendations NPE a and NPE C MII NPE C Signal Recommendations Sheet 2Device Connection, MII Gpio Interface MII Interface ExampleUSB Interface Gpio Signal RecommendationsDesign Notes USB Host Signal Recommendations Name Type Pull Description Field DownCommon Mode Choke Host Device Utopia Level 2/MIIA Utopia Level 2 InterfaceType Pull Name Description Field Down UTPOPADDR40 UTPOPDATA4UTPOPDATA75 UtpopfciUtpipsoc ClavUtpipfci ETHARXDATA30 EtharxclkUTPIPDATA7 UTPIPDATA5UTPIPDATA6 UTPIPADDR40HSS Interface Device ConnectionHSSTXCLK0 High-Speed, Serial InterfaceHSSTXDATA0 HSSRXDATA0SSP Interface HSS Interface ExampleSynchronous Serial Peripheral Port Interface PCI Interface Serial Flash and SSP Port SPI Interface ExamplePCI Controller Sheet 1 Pciintan PCI Interface Block DiagramPCI Controller Sheet 2 PciclkinPCI Host/Option Interface Pin Description Sheet 1 Connect signal to same pin between PCI Parity Two devicesPCI Option Interface Type Option Description Name Device-Pin Connection FieldPCI Host/Option Interface Pin Description Sheet 2 On the Option device, these signals are notSignal PCIREQN0 to one PCIREQN30 inputs to the Host Type Option Name Device-Pin Connection Description FieldJtag Interface PCI Host/Option Interface Pin Description Sheet 3Input System Clock Clock SignalsClock Signals Clock OscillatorRecommendations for Crystal Selection Power Supply PowerNominal Name Voltage Description Decoupling Capacitance Recommendations Power SequenceReset Timing VCC Decoupling§ § General Recommendations Component PlacementPCB Overview Component SelectionComponent Placement on a PCB Stack-Up SelectionControlled-impedance traces Low-impedance power distribution Layer Stackup General Layout and Routing Guide General Layout GuidelinesSignal Changing Reference Planes General Component SpacingGood Design Practice for VIA Hole Placement Clock Signal Considerations Pad-to-Pad Clearance of Passive Components to a PGA or BGAUSB V2.0 Considerations MII Signal ConsiderationsCrosstalk EMI Design Considerations Power and Ground PlaneTrace Impedance § § @33 MHz Electrical InterfaceTopology Tcyc = 30 nSec Tval = 11 nSec Tprop = 10 nSecPCI Address/Data Routing Guidelines Clock DistributionParameter Routing Guidelines Trace Length Limits PCI Clock Routing GuidelinesSignal Loading Routing GuidelinesDdrii / Ddri Sdram IntroductionDrasn / Ddrrasn DDRII/I Signal GroupsGroup Signal Name Description Dcasn / DdrcasnDDR Sdram Supported Ddri 16-bit Sdram Configurations Supported Ddri 32-bit Sdram ConfigurationsSupported Ddrii 32-bit Sdram Configurations SizeaAddress Size Leaf Select Total Supported Ddrii 16-bit Sdram ConfigurationsDDRII/DDRI Rcomp and Slew Resistances Pin Requirements Technology Arrangement BanksDdrii OCD Pin Requirements DDR-II Symbol Parameter Units Min MaxDDR Clock Timings DDR Sdram Write Timings DDRII-400 MHz Interface -- Signal Timings Symbol Parameter Minimum Nominal Maximum UnitsTiming Relationships DDR II/I Sdram Interface -- Signal TimingsSymbol Parameter Minimum Nom Maximum Units Printed Circuit Board Layer StackupGroup Signal Name Length mil Signal Package Lengths Sheet 1Timing Relationships Signal Package Lengths Sheet 2 Signal Package Lengths Sheet 3 Clock GroupData and Control Groups Parameter DefinitionDdrii Data and Control Signal Group Routing Guidelines DCB70/DDRCB70, DDQ310 / DDRDQ310Ddrii Command Signal Group Routing Guidelines Signal Group Members§ §