Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
631
UG586 November 30, 2016
Chapter 4:
LPDDR2 SDRAM Memory Interface Solution
Design Guidelines
Guidelines for LPDDR2 SDRAM designs are covered in this section.
For general PCB routing guidelines, see
Appendix A, General Memory Routing Guidelines
.
LPDDR2 SDRAM
This section describes guidelines for LPDDR2 SDRAM designs, including bank selection, pin
allocation, pin assignments, termination, I/O standards, and trace lengths.
Design Rules
Memory types, memory parts, and data widths are restricted based on the selected FPGA,
FPGA speed grade, and the design frequency. The final frequency ranges are subject to
characterization results.
Pin Assignments
The MIG tool generates pin assignments for a memory interface based on physical layer
rules.
Bank and Pin Selection Guides for LPDDR2 Designs
Xilinx 7 series FPGAs are designed for very high-performance memory interfaces, and
certain rules must be followed to use the LPDDR2 SDRAM physical layer. Xilinx 7 series
FPGAs have dedicated logic for each
DQS
byte group. Four
DQS
byte groups are available in
each 50-pin bank. Each byte group consists of a clock-capable I/O pair for the
DQS
and 10
associated I/Os.
In a typical LPDDR2 configuration, 8 of these 10 I/Os are used for the
DQS
: one is used for
the data mask (DM), and the remaining one is used for
DQS
sampling. However, there would
not be any physical connect on this pin because it would be internally used to capture the
DQS
for the phase detector.
Xilinx 7 series FPGAs have dedicated clock routing for high-speed synchronization that is
routed vertically within the I/O banks. Thus, LPDDR2 memory interfaces must be arranged
in the banks vertically and not horizontally. In addition, the maximum height is three banks.