AR# 41511

MIG 7 Series DDR3 SDRAM - Vccaux_io usage and requirements


VCCAUX_IO is the auxiliary supply voltage relative to ground (pre-driver voltage). For memory interfaces, this can be set to either 1.8V or 2.0V. The selection of the Vccaux_io voltage is dependent on the target memory interface frequency, the selected 7 Series FPGA/Package, as well as the bank selection (High Range versus High Performance). This answer record details the usage and requirements of Vccaux_io.

NOTE: This Answer Record is part of the Xilinx MIG Solution Center (Xilinx Answer 34243). The Xilinx MIG Solution Center is available to address all questions related to MIG. Whether you are starting a new design with MIG or troubleshooting a problem, use the MIG Solution Center to guide you to the right information.


7 series FPGAs include an improved I/O driver structure allowing a higher pre-driver voltage (Vccaux_io) to achieve higher data rates. Vccaux_io is a separate rail providing power to the I/O circuitry in the High Performance banks. Vccaux_io must be set to 2.0V to achieve higher data rates and can be set to 1.8V for lower data rate. Setting Vccaux_io=2.0v does not affect other IO standards and unless it is being used for high performance memory applications Vccaux_io should be set to 1.8v.

The MIG tool includes a Vccaux_io setting. For higher data rates that require Vccaux_io=2.0v, the option cannot be changed. When the frequency is lower and 1.8V is feasible, users can select either 1.8V or 2.0V. Selecting 2.0V is not needed at lower frequencies. The MIG output sets the Vccaux_io voltage on each I/O within the generated UCF file. When Vccaux_io is 2.0V, the VCCAUX_IO is set to HIGH. When it is 1.8V, the value is NORMAL. Here is an example:

NET "ddr3_dq[0]" LOC = "L9" | IOSTANDARD = SSTL15_T_DCI | VCCAUX_IO = HIGH ; # Bank: 39 - Byte: T3

Virtex-7 devices all have Vccaux_io available in the High Performance banks. Not all Kintex devices have Vccaux_io available in High Performance banks (only the FFG package). If you are using MIG and do not see the Vccaux_io option, you have selected a 7 series FPGA that does not have Vccaux_io.

More Information

Refer to the 7 Series FPGAs SelectIO Resources User Guide for more information on Vccaux_io.

Refer to the Virtex-7 FPGAs DC and Switching Characteristics Data Sheet and the Kintex-7 FPGAs DC and Switching Characteristics Data Sheet for performance information and availability of Vccaux_io.

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
51475 MIG 7 Series Design Assistant - MIG 7 Series DDR2/DDR3, Board Layout and Design Guidelines N/A N/A
AR# 41511
Date 08/24/2012
Status Active
Type Solution Center