SPRACU1A October   2020  – June 2021 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6441 , AM6442

 

  1.   Trademarks
  2. 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
  3. 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  VPP
    8. 2.8  Net Classes
    9. 2.9  DDR4 Signal Termination
    10. 2.10 VREF Routing
    11. 2.11 VTT
    12. 2.12 POD Interconnect
    13. 2.13 CK and ADDR_CTRL Topologies and Routing Guidance
    14. 2.14 Data Group Topologies and Routing Guidance
    15. 2.15 CK and ADDR_CTRL Routing Specification
      1. 2.15.1 CACLM - Clock Address Control Longest Manhattan Distance
      2. 2.15.2 CK and ADDR_CTRL Routing Limits
    16. 2.16 Data Group Routing Specification
      1. 2.16.1 DQLM - DQ Longest Manhattan Distance
      2. 2.16.2 Data Group Routing Limits
    17. 2.17 Bit Swapping
      1. 2.17.1 Data Bit Swapping
      2. 2.17.2 Address and Control Bit Swapping
  4. 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  Net Classes
    8. 3.8  LPDDR4 Signal Termination
    9. 3.9  LPDDR4 VREF Routing
    10. 3.10 LPDDR4 VTT
    11. 3.11 CK and ADDR_CTRL Topologies
    12. 3.12 Data Group Topologies
    13. 3.13 CK and ADDR_CTRL Routing Specification
    14. 3.14 Data Group Routing Specification
    15. 3.15 Channel, Byte, and Bit Swapping
  5. 4Revision History

3.11 CK and ADDR_CTRL Topologies

The CK and ADDR_CTRL net classes are routed similarly, and are length matched from the DDR controller in the processor to the LPDDR4 SDRAM to minimize skew between the signals and ensure that the ADDR_CTRL signals are properly sampled at the SDRAM. The CK net class requires more care because it runs at a higher transition rate and is differential. The CK and ADDR_CTRL topologies are point-to-point.

Figure 3-4 shows the topology of the CK net class, and Figure 3-5 shows the topology for the corresponding ADDR_CTRL net classes. Length matching requirements for the routing segments are detailed in Table 3-6.

GUID-20200903-CA0I-4B9W-BPL1-LHJHWKJZGWT5-low.gif Figure 3-4 LPDDR4 CK Topology
GUID-20200903-CA0I-XKPV-GWXF-QHPRL3HTRZTC-low.gif Figure 3-5 LPDDR4 ADDR_CTRL Topology

Minimize layer transitions during routing. If a layer transition is necessary, it is preferable to transition to a layer using the same reference plane. If this cannot be accommodated, ensure there are nearby stitching vias to allow the return currents to transition between reference planes when both reference planes are ground or VDDS_DDR. Alternately, ensure there are nearby bypass capacitors to allow the return currents to transition between reference planes when one of the reference planes is ground and the other is VDDS_DDR. This must occur at every reference plane transition. The goal is to minimize the size of the return current path thus minimizing the inductance in this path. Lack of these stitching vias or capacitors results in impedance discontinuities in the signal path that increase crosstalk and signal distortion.

There are no stubs or terminations allowed on the nets of the CK and ADDR_CTRL routing group topologies. All test and probe access points must be in line without any branches or stubs.