Intel IXP45X, IXP46X manual Trace Impedance, Power and Ground Plane

Page 69

General Layout and Routing Guide—Intel®IXP45X and Intel® IXP46X Product Line of Network Processors

5.2.8Trace Impedance

All signal layers require controlled impedance of 50 Ω ±10 % microstrip or stripline (unless otherwise specified) where appropriate. Selecting the appropriate board stack- up to minimize impedance variations is very important.

When calculating flight times, it is important to consider the minimum and maximum trace impedance based on the switching neighboring traces.

5.2.9Power and Ground Plane

Power and ground planes should have sufficient de-coupling capacitors to ensure sustainable current needed for high-speed switching devices. (See Section 3.15.1, “De- Coupling Capacitance Recommendations” on page 56.)

•It is highly recommended to use sufficient internal power and ground planes.

•Due to the complexity of the IXP45X/IXP46X network processors, there are a number of power supplies required. It is appropriate to use power islands in the power plane under the processor, as it would be too expensive to have a power plane for each power source.

•Power islands must be large enough to include the required power supply decoupling capacitance, and the necessary connection to the voltage source and destination.

•Islands can be separated by a minimum of 20-mil air gap.

•Use at least one via per power or ground pin, wherever possible use more vias, depending on current drawn.

•Use at least one de-coupling capacitor per power pin and place it as close as possible to the pin.

•Minimize the number of traces routed across the air gaps between power islands.

—Each crossing introduces signal degradation due to the impedance discontinuity.

—For traces that must cross air gaps, route them on the side of the board next to a ground plane to reduce or eliminate signal degradation caused by crossing the gap.

—When this is not possible, then route the trace to cross the gap at a right angle (90°).

	Intel® IXP45X and Intel® IXP46X Product Line of Network Processors
February 2007	HDD
Document Number: 305261; Revision: 004	69

Image 69

Contents February Hardware Design GuidelinesHDD Contents 12.1 Figures Tables Control Group Topology Transmission Line CharacteristicsDate Revision Description Revision HistoryHDD Chapter Name Description Content OverviewTitle Document # Related DocumentationOverview List of Acronyms and AbbreviationsTerm Explanation Smii Intel IXP465 Component Block Diagram Dslam Typical ApplicationsSystem Memory Map System Architecture DescriptionIntel IXP465 Example System Block Diagram Soft Fusible Features Signal Type DefinitionsSymbol Description Soft Fusible Features Signal InterfaceDDR-266 Sdram Interface DDR Sdram Interface Pin Description Sheet 1Ddriwen DDR Sdram Interface Pin Description Sheet 2Ddrircveninn DdrircompExpansion Bus DDR Sdram Memory InterfaceDDR Sdram Initialization Reset Configuration Straps Expansion Bus Signal RecommendationsInput Pull Name Recommendations Output Down Name Function Description Boot/Reset Strapping Configuration Sheet 1Boot/Reset Strapping Configuration Sheet 2 3 8-Bit Device Interface4 16-Bit Device Interface 5 32-Bit Device Interface Bit Device 16/32-Bit Device Interface Byte Enable Flash Interface Example Flash InterfaceUart Interface Sram InterfaceDesign Notes Name Input Pull Recommendations Output Down Uart Signal RecommendationsUart Interface Example MII/SMII InterfaceSignal Interface MII MII NPE a Signal RecommendationsMII NPE B Signal Recommendations Sheet 1 MII NPE C Signal Recommendations MII NPE B Signal Recommendations Sheet 2MAC Management Signal Recommendations NPE A,B,C Device Connection, MIINPE A,B,C Smii Signal Recommendations NPE A, B, C Signal Interface, SmiiDevice Connection, Smii Gpio InterfaceGpio Signal Recommendations I2C Signal Recommendations I2C InterfaceDevice Connection I2C Eeprom Interface Example USB InterfaceUSB Host/Device Signal Recommendations Host Device USB Device Interface Example Utopia Level 2 InterfaceUtopia Signal Recommendations Utopia Interface Example HSS InterfaceHSSTXDATA0 High-Speed, Serial InterfaceHSSTXCLK0 HSSRXDATA0HSSTXCLK1 HSSTXDATA1HSSRXDATA1 HSSRXCLK1HSS Interface Example SSP InterfaceSynchronous Serial Peripheral Port Interface PCI Interface PCI Controller Sheet 1Input Pull Name Outpu Recommendations Down PCI Controller Sheet 2 PCI Interface Block DiagramPCI Interface Supporting 5 V PCI InterfacePCI Host/Option Interface Pin Description Sheet 1 PCI Option InterfacePCI Host/Option Interface Pin Description Sheet 2 PCI Host/Option Interface Pin Description Sheet 3 Jtag InterfaceClock Signals Clock SignalsInput System Clock Clock OscillatorPower Power Interface Sheet 1Name Nominal Description Voltage Reset Timing Power SequenceDe-Coupling Capacitance Recommendations VCC De-CouplingHDD HDD PCB Overview Component PlacementGeneral Recommendations Component SelectionStack-Up Selection Component Placement on a PCBControlled-impedance traces Low-impedance power distribution Layer Stackup General Layout Guidelines General Layout and Routing GuideGeneral Component Spacing Signal Changing Reference PlanesGood Design Practice for VIA Hole Placement Pad-to-Pad Clearance of Passive Components to a PGA or BGA Clock Signal ConsiderationsSmii Signal Considerations MII Signal ConsiderationsUSB Considerations EMI-Design Considerations Cross-TalkTrace Impedance Power and Ground PlaneHDD Topology Electrical Interface@33 MHz @66 MHzClock Distribution PCI Address/Data Routing GuidelinesParameter Routing Guidelines PCI Clock Routing Guidelines Trace Length LimitsRouting Guidelines Signal LoadingGroup Signal Name Description No of Single Ended Signals DDR Signal GroupsIntroduction DDRIDQS40DDR Sdram HDD Clock Banks Memory Size Supported Memory ConfigurationsVTT VTT Terminating Circuitry Selecting VTT Power SupplyDDR Command and Control Setup and Hold Values Symbol Parameter Min Max UnitsDdrmclk 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 Layer Stackup Printed Circuit Board Controlled ImpedancePrinted Circuit Board Controlled Impedance Signal Group Absolute Minimum Absolute Maximum Length Timing RelationshipsTiming Relationships Clock Group Resistive Compensation Register RcompData, Command, and Control Group Routing Guidelines Clock Signal Group Routing GuidelinesParameter Definition DDRIBA10, DDRIRASN, DDRICASN, DdriwenSimulation Results Clock Group Topology Transmission Line CharacteristicsClock Group Transmission Line LengthDDR Clock Topology Two-Bank x16 Devices DDR Clock Simulation Results Two-Bank x16 Devices Data GroupData 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 Control Group Topology Transmission Line CharacteristicsDDR RAS Simulation Results Two-Bank x16 Devices Command Group Topology Transmission Line Characteristics Command GroupDDR Command MA3 Topology Two-Bank x16 Devices DDR Address Simulation Results Two-Bank x16 Devices DDR Command RAS Topology Two-Bank x16 Devices 104 DDR RCVENIN/RCVENOUT Topology Rcvenin and RcvenoutDDR RCVENIN/RCVENOUT Simulation Results Rseries = 0 Ω DDR RCVENIN/RCVENOUT Simulation Results Rseries = 60 Ω 108