Intel IXP46X, IXP45X manual General Component Spacing, Signal Changing Reference Planes

Page 64

Intel® IXP45X and Intel® IXP46X Product Line of Network Processors—Category

•Do not place high-frequency oscillators and switching network devices close to sensitive analog circuits.

•Arrange the board so that return currents for high-speed traces never must jump between planes. Restrict traces to remain on either side of whichever ground plane they start out nearest. This allows the use of naturally grouped horizontal and vertical routing layers.

If signals change between layers, the reference voltage changes, as shown in Figure 22. This creates discontinuity in the path of the signal.

Figure 22. Signal Changing Reference Planes

Driver Signal

VIAs

Signal Receiver

GND

Return Current

PWR

ByPass Caps

Trace

Signal

B2269-01

The design in Figure 22, routes a signal on the top layer, close to GND plane, and provides a very good return current path. The signal then is routed to the bottom layer, close to the PWR plane, such that the return currents flows to the ground plane through bypass caps. Hence the path for the return currents is less inductive than in the previous case when the signal is routed on the top layer.

5.2.1General Component Spacing

•Do not place components within 125 mils to the edge of the printed circuit board. For exact dimensions consult your manufacturing vendor.

•Keep a minimum spacing between via and the solder pad edges > 25mil.

•Position devices that interface with each other close to one another to minimize trace lengths.

Intel® IXP45X and Intel® IXP46X Product Line of Network Processors
HDD	February 2007
64	Document Number: 305261; Revision: 004

Image 64

Contents Hardware Design Guidelines FebruaryHDD Contents 12.1 Figures Control Group Topology Transmission Line Characteristics TablesRevision History Date Revision DescriptionHDD Content Overview Chapter Name DescriptionRelated Documentation Title Document #List of Acronyms and Abbreviations OverviewTerm Explanation Smii Intel IXP465 Component Block Diagram Typical Applications DslamSystem Architecture Description System Memory MapIntel IXP465 Example System Block Diagram Signal Type Definitions Soft Fusible FeaturesSymbol Description Signal Interface Soft Fusible FeaturesDDR-266 Sdram Interface DDR Sdram Interface Pin Description Sheet 1DDR Sdram Interface Pin Description Sheet 2 DdriwenDdrircveninn DdrircompDDR Sdram Memory Interface Expansion BusDDR Sdram Initialization Expansion Bus Signal Recommendations Reset Configuration StrapsInput Pull Name Recommendations Output Down Boot/Reset Strapping Configuration Sheet 1 Name Function Description3 8-Bit Device Interface Boot/Reset Strapping Configuration Sheet 24 16-Bit Device Interface 5 32-Bit Device Interface Bit Device 16/32-Bit Device Interface Byte Enable Flash Interface Flash Interface ExampleSram Interface Uart InterfaceDesign Notes Uart Signal Recommendations Name Input Pull Recommendations Output DownMII/SMII Interface Uart Interface ExampleMII NPE a Signal Recommendations Signal Interface MIIMII NPE B Signal Recommendations Sheet 1 MII NPE B Signal Recommendations Sheet 2 MII NPE C Signal RecommendationsDevice Connection, MII MAC Management Signal Recommendations NPE A,B,CNPE A,B,C Signal Interface, Smii Smii Signal Recommendations NPE A, B, CGpio Interface Device Connection, SmiiGpio Signal Recommendations I2C Interface I2C Signal RecommendationsDevice Connection USB Interface I2C Eeprom Interface ExampleUSB Host/Device Signal Recommendations Host Device Utopia Level 2 Interface USB Device Interface ExampleUtopia Signal Recommendations HSS Interface Utopia Interface ExampleHigh-Speed, Serial Interface HSSTXDATA0HSSTXCLK0 HSSRXDATA0HSSTXDATA1 HSSTXCLK1HSSRXDATA1 HSSRXCLK1SSP Interface HSS Interface ExampleSynchronous Serial Peripheral Port Interface PCI Controller Sheet 1 PCI InterfaceInput Pull Name Outpu Recommendations Down PCI Interface Block Diagram PCI Controller Sheet 2Supporting 5 V PCI Interface PCI InterfacePCI Option Interface PCI Host/Option Interface Pin Description Sheet 1PCI Host/Option Interface Pin Description Sheet 2 Jtag Interface PCI Host/Option Interface Pin Description Sheet 3Clock Signals Clock SignalsInput System Clock Clock OscillatorPower Interface Sheet 1 PowerName Nominal Description Voltage Power Sequence Reset TimingDe-Coupling Capacitance Recommendations VCC De-CouplingHDD HDD Component Placement PCB OverviewGeneral Recommendations 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 BGAMII Signal Considerations Smii Signal ConsiderationsUSB Considerations Cross-Talk EMI-Design ConsiderationsPower and Ground Plane Trace ImpedanceHDD Electrical Interface Topology@33 MHz @66 MHzPCI Address/Data Routing Guidelines Clock DistributionParameter Routing Guidelines Trace Length Limits PCI Clock Routing GuidelinesSignal Loading Routing GuidelinesDDR Signal Groups Group Signal Name Description No of Single Ended SignalsIntroduction DDRIDQS40DDR Sdram HDD Supported Memory Configurations Clock Banks Memory SizeVTT Selecting VTT Power Supply VTT Terminating CircuitrySymbol Parameter Min Max Units DDR Command and Control Setup and Hold ValuesDdrmclk DDR Data to DQS Read Timing Parameters DDR-Data-to-DQS-Write Timing Parameters DDR Data to DQS Write Timing ParametersPrinted Circuit Board Layer Stackup Printed Circuit Board Controlled Impedance Printed Circuit Board Layer StackupPrinted Circuit Board Controlled Impedance Timing Relationships Signal Group Absolute Minimum Absolute Maximum LengthTiming Relationships Resistive Compensation Register Rcomp Clock GroupClock Signal Group Routing Guidelines Data, Command, and Control Group Routing GuidelinesParameter Definition DDRIBA10, DDRIRASN, DDRICASN, DdriwenClock Group Topology Transmission Line Characteristics Simulation ResultsClock Group Transmission Line LengthDDR Clock Topology Two-Bank x16 Devices Data Group DDR Clock Simulation Results Two-Bank x16 DevicesData Group Topology Transmission Line Characteristics DDR Data Topology Two-Bank x16 Devices DDR Data Write Simulation Results Two-Bank x16 Devices HDD HDD Control Group Topology Transmission Line Characteristics Control GroupDDR RAS Simulation Results Two-Bank x16 Devices Command Group Command Group Topology Transmission Line CharacteristicsDDR Command MA3 Topology Two-Bank x16 Devices DDR Address Simulation Results Two-Bank x16 Devices DDR Command RAS Topology Two-Bank x16 Devices 104 Rcvenin and Rcvenout DDR RCVENIN/RCVENOUT TopologyDDR RCVENIN/RCVENOUT Simulation Results Rseries = 0 Ω DDR RCVENIN/RCVENOUT Simulation Results Rseries = 60 Ω 108