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

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

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

Contents

February Hardware Design Guidelines HDD Contents 12.1 Figures Tables Control Group Topology Transmission Line Characteristics Date Revision Description Revision History HDD Chapter Name Description Content Overview Title Document # Related Documentation Overview List of Acronyms and AbbreviationsTerm Explanation Smii Intel IXP465 Component Block Diagram Dslam Typical Applications System Memory Map System Architecture Description Intel 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 1 Ddriwen DDR Sdram Interface Pin Description Sheet 2Ddrircveninn Ddrircomp Expansion 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 1 Boot/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 Interface Uart Interface Sram InterfaceDesign Notes Name Input Pull Recommendations Output Down Uart Signal Recommendations Uart Interface Example MII/SMII Interface Signal Interface MII MII NPE a Signal RecommendationsMII NPE B Signal Recommendations Sheet 1 MII NPE C Signal Recommendations MII NPE B Signal Recommendations Sheet 2 MAC Management Signal Recommendations NPE A,B,C Device Connection, MIINPE A,B,C Smii Signal Recommendations NPE A, B, C Signal Interface, Smii Device Connection, Smii Gpio Interface Gpio Signal Recommendations I2C Signal Recommendations I2C InterfaceDevice Connection I2C Eeprom Interface Example USB Interface USB Host/Device Signal Recommendations Host Device USB Device Interface Example Utopia Level 2 Interface Utopia Signal Recommendations Utopia Interface Example HSS Interface HSSTXDATA0 High-Speed, Serial InterfaceHSSTXCLK0 HSSRXDATA0 HSSTXCLK1 HSSTXDATA1HSSRXDATA1 HSSRXCLK1 HSS Interface Example SSP Interface Synchronous Serial Peripheral Port Interface PCI Interface PCI Controller Sheet 1Input Pull Name Outpu Recommendations Down PCI Controller Sheet 2 PCI Interface Block Diagram PCI Interface Supporting 5 V PCI Interface PCI Host/Option Interface Pin Description Sheet 1 PCI Option Interface PCI Host/Option Interface Pin Description Sheet 2 PCI Host/Option Interface Pin Description Sheet 3 Jtag Interface Clock Signals Clock SignalsInput System Clock Clock Oscillator Power Power Interface Sheet 1Name Nominal Description Voltage Reset Timing Power SequenceDe-Coupling Capacitance Recommendations VCC De-Coupling HDD HDD PCB Overview Component PlacementGeneral Recommendations Component Selection Stack-Up Selection Component Placement on a PCB Controlled-impedance traces Low-impedance power distribution Layer Stackup General Layout Guidelines General Layout and Routing Guide General Component Spacing Signal Changing Reference Planes Good Design Practice for VIA Hole Placement Pad-to-Pad Clearance of Passive Components to a PGA or BGA Clock Signal Considerations Smii Signal Considerations MII Signal ConsiderationsUSB Considerations EMI-Design Considerations Cross-Talk Trace Impedance Power and Ground Plane HDD Topology Electrical Interface@33 MHz @66 MHz Clock Distribution PCI Address/Data Routing GuidelinesParameter Routing Guidelines PCI Clock Routing Guidelines Trace Length Limits Routing Guidelines Signal Loading Group Signal Name Description No of Single Ended Signals DDR Signal GroupsIntroduction DDRIDQS40 DDR Sdram HDD Clock Banks Memory Size Supported Memory Configurations VTT VTT Terminating Circuitry Selecting VTT Power Supply DDR 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 Parameters Printed Circuit Board Layer Stackup Printed Circuit Board Layer Stackup Printed Circuit Board Controlled Impedance Printed Circuit Board Controlled Impedance Signal Group Absolute Minimum Absolute Maximum Length Timing RelationshipsTiming Relationships Clock Group Resistive Compensation Register Rcomp Data, Command, and Control Group Routing Guidelines Clock Signal Group Routing GuidelinesParameter Definition DDRIBA10, DDRIRASN, DDRICASN, Ddriwen Simulation Results Clock Group Topology Transmission Line CharacteristicsClock Group Transmission Line Length DDR Clock Topology Two-Bank x16 Devices DDR Clock Simulation Results Two-Bank x16 Devices Data Group Data 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 Characteristics DDR RAS Simulation Results Two-Bank x16 Devices Command Group Topology Transmission Line Characteristics Command Group DDR 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 Rcvenout DDR RCVENIN/RCVENOUT Simulation Results Rseries = 0 Ω DDR RCVENIN/RCVENOUT Simulation Results Rseries = 60 Ω 108