SPRACN9E september   2022  – may 2023 AM67 , AM67A , AM68 , AM68A , AM69 , AM69A , DRA829J , DRA829J-Q1 , DRA829V , DRA829V-Q1 , TDA4AEN-Q1 , TDA4VEN-Q1 , TDA4VM , TDA4VM-Q1

 

  1.   1
  2.   Jacinto 7 LPDDR4 Board Design and Layout Guidelines
  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
    5. 1.5 Velocity Compensation
  5. 2LPDDR4 Board Design and Layout Guidance
    1. 2.1  LPDDR4 Introduction
    2. 2.2  LPDDR4 Device Implementations Supported
    3. 2.3  LPDDR4 Interface Schematics
    4. 2.4  Compatible JEDEC LPDDR4 Devices
    5. 2.5  Placement
    6. 2.6  LPDDR4 Keepout Region
    7. 2.7  Net Classes
    8. 2.8  LPDDR4 Signal Termination
    9. 2.9  LPDDR4 VREF Routing
    10. 2.10 LPDDR4 VTT
    11. 2.11 CK and ADDR_CTRL Topologies
    12. 2.12 Data Group Topologies
    13. 2.13 CK and ADDR_CTRL Routing Specification
    14. 2.14 Data Group Routing Specification
    15. 2.15 Channel, Byte, and Bit Swapping
  6. 3LPDDR4 Board Design Simulations
    1. 3.1 Board Model Extraction
    2. 3.2 Board-Model Validation
    3. 3.3 S-Parameter Inspection
    4. 3.4 Time Domain Reflectometry (TDR) Analysis
    5. 3.5 Simulation Integrity Analysis
      1. 3.5.1 Simulation Setup
      2. 3.5.2 Simulation Parameters
      3. 3.5.3 Simulation Targets
        1. 3.5.3.1 Waveform Quality
        2. 3.5.3.2 Eye Quality
        3. 3.5.3.3 Delay Report
        4. 3.5.3.4 Mask Report
    6. 3.6 Design Example
      1. 3.6.1 Stack-Up
      2. 3.6.2 Routing
      3. 3.6.3 Model Verification
      4. 3.6.4 Simulation Results
  7. 4Revision History

3.6.3 Model Verification

Before simulating, it is recommended to verify the models. One verification method described is the impedance plot (or impedance scan). The Impedance scans for a 10 layer design are provided.

GUID-418C3B84-40B3-491F-9E84-2BA08EC33FB0-low.pngFigure 3-10 Example LPDDR4 Trace Impedance Scan
Table 3-8 Example LPDDR4 Trace Impedance Summary for Data
LayerDDR BusDQ SE Impedance (Ω)DQS/CLK Difference Impedance (Ω)
L2B1 and B340.977.7
L2CA51.7101.4
L4B0 and B241.177.7
L7CA41.177.7

For CK and CA signals, the goal is to have the branch segment equal to two times the impedance of the feed trace. Note its common for the PCB to limit the achievable impedances. Simulations will show you if the compromises are acceptable.

Table 3-9 Example LPDDR4 Trace Impedance Summary for CA
BoardCA Feed Impedance (Ω)CA Branch Impedance (Ω)CA Branch Target (Ω)Impedance Mismatch (Ω)
Initial Design49.159.698 (49x2)38.6
Final Design41.151.782 (41x2)30.5

The simulation results show the improvement made by closer matching the impedances to their targets.

Table 3-10 Example LPDDR4 Simulation Results From Improved Trace Impedance
BoardTotal Eye Width Margin (ps)Total Eye Height Margin (ps)Min Ringback Margin H (mV)Min Ringback Margin L (mV)
Initial Design58.0014.0069.5918.18
Final Design124.6848.0889.4325.49