SPRAD06C March   2022  – March 2025 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM62L

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Overview
    1. 1.1 Board Designs Supported
    2. 1.2 General Board Layout Guidelines
    3. 1.3 PCB Stack-Up
    4. 1.4 Bypass Capacitors
      1. 1.4.1 Bulk Bypass Capacitors
      2. 1.4.2 High-Speed Bypass Capacitors
      3. 1.4.3 Return Current Bypass Capacitors
    5. 1.5 Velocity Compensation
  5. 2DDR4 Board Design and Layout Guidance
    1. 2.1  DDR4 Introduction
    2. 2.2  DDR4 Device Implementations Supported
    3. 2.3  DDR4 Interface Schematics
      1. 2.3.1 DDR4 Implementation Using 16-Bit SDRAM Devices
      2. 2.3.2 DDR4 Implementation Using 8-Bit SDRAM Devices
    4. 2.4  Compatible JEDEC DDR4 Devices
    5. 2.5  Placement
    6. 2.6  DDR4 Keepout Region
    7. 2.7  DBI
    8. 2.8  VPP
    9. 2.9  Net Classes
    10. 2.10 DDR4 Signal Termination
    11. 2.11 VREF Routing
    12. 2.12 VTT
    13. 2.13 POD Interconnect
    14. 2.14 CK and ADDR_CTRL Topologies and Routing Guidance
    15. 2.15 Data Group Topologies and Routing Guidance
    16. 2.16 CK and ADDR_CTRL Routing Specification
      1. 2.16.1 CACLM - Clock Address Control Longest Manhattan Distance
      2. 2.16.2 CK and ADDR_CTRL Routing Limits
    17. 2.17 Data Group Routing Specification
      1. 2.17.1 DQLM - DQ Longest Manhattan Distance
      2. 2.17.2 Data Group Routing Limits
    18. 2.18 Bit Swapping
      1. 2.18.1 Data Bit Swapping
      2. 2.18.2 Address and Control Bit Swapping
  6. 3LPDDR4 Board Design and Layout Guidance
    1. 3.1  LPDDR4 Introduction
    2. 3.2  LPDDR4 Device Implementations Supported
    3. 3.3  LPDDR4 Interface Schematics
    4. 3.4  Compatible JEDEC LPDDR4 Devices
    5. 3.5  Placement
    6. 3.6  LPDDR4 Keepout Region
    7. 3.7  LPDDR4 DBI
    8. 3.8  Net Classes
    9. 3.9  LPDDR4 Signal Termination
    10. 3.10 LPDDR4 VREF Routing
    11. 3.11 LPDDR4 VTT
    12. 3.12 CK0 and ADDR_CTRL Topologies
    13. 3.13 Data Group Topologies
    14. 3.14 CK0 and ADDR_CTRL Routing Specification
    15. 3.15 Data Group Routing Specification
    16. 3.16 Byte and Bit Swapping
  7. 4LPDDR4 Board Design Simulations
    1. 4.1 Board Model Extraction
    2. 4.2 Board-Model Validation
    3. 4.3 S-Parameter Inspection
    4. 4.4 Time Domain Reflectometry (TDR) Analysis
    5. 4.5 System Level Simulation
      1. 4.5.1 Simulation Setup
      2. 4.5.2 Simulation Parameters
      3. 4.5.3 Simulation Targets
        1. 4.5.3.1 Eye Quality
        2. 4.5.3.2 Delay Report
        3. 4.5.3.3 Mask Report
    6. 4.6 Design Example
      1. 4.6.1 Stack-Up
      2. 4.6.2 Routing
      3. 4.6.3 Model Verification
      4. 4.6.4 Simulation Results
  8. 5Additional Information: Package Delays
  9. 6Summary
  10. 7References
  11. 8Revision History

2.3.2 DDR4 Implementation Using 8-Bit SDRAM Devices

Figure 2-2 shows the schematic connections for a dual rank,16-bit interface using two x8 devices.

Use memory devices with two dies in one package to achieve higher density designs. The connection looks similar to Figure 2-2, except the two x8 memories are in one package, so VTT implementation is not necessary. Make sure to connect BG[1:0] when using these devices, as the internal implementation is still using two x8 memories.

16-Bit, Dual-Rank DDR4 Implementation Using x8 SDRAMs
  1. When designing with VTT regulator (LDO), which can source and sink current, decoupling capacitors (minimum of one capacitor (1.0uF value) must be used for every two termination resistors) must be used to minimize the effect of VTT supply noise. Refer to the AM64x GP EVM for reference.
  2. Zo value for resistors is 30-47ohm. Resistor value must closely match trace impedances.
  3. VTT is optional on address and control signals when using single package memory devices, but termination as shown on CK0/CK0_n is always required.
  4. DDR_VREF is supplied by the VTT regulator. When VTT is not used, VREFCA needs to be connected to a voltage divider. Consult the EVM schematic for an example of the voltage divider implementation.
  5. For single-rank designs, CS1_n, ODT1, and CKE1 can be left unconnected
  6. Single package memories with two x8 dies do not require VTT.
  7. An external 240Ω ±1% resistor must be connected between the DDR0_CAL0 pin and VSS. The maximum power dissipation for the resistor is 5.2mW. No external voltage must be applied to the DDR0_CAL0 pin. Tolerance of ±1% required throughout life of component or product.
  8. RESET_n shall have an external 10k pull-down resistor to control RESET low until the DDR controller drives the signal. RESET_n has no length matching requirement.
Figure 2-2 16-Bit, Dual-Rank DDR4 Implementation Using x8 SDRAMs