AR# 11182: Virtex-II/-II Pro - What is the purpose of the VCCAUX power supply pins?
Virtex-II/-II Pro - What is the purpose of the VCCAUX power supply pins?
Keywords: input, JTAG, configuration, I/O, IOU, volt
What is the purpose of VCCAUX power supply pins on Virtex-II or Virtex-II Pro devices?
VCCAUX is used to power the JTAG and dedicated configuration pins, thus making them independent of VCCO. (This resolves the issue encountered in Virtex-E, where banks 2 and 3 were required to be powered by 3.3V for JTAG configuration.)
Additionally, VCCAUX powers IOB pre-drivers, differential input amplifiers/comparators, LVDS bias generators, DCM delay lines, and other internal reference supplies.
VCCAUX must ALWAYS be connected and bypassed properly in order for the Virtex-II and Virtex-II Pro device to function correctly.
The VCCAUX value does not need to be the same as the VCCO or VREF value in the same bank.
When VCCAUX is applied, VBATT does not draw any current; thus, the battery can be removed or exchanged.
If VCCAUX and VCCO are both 3.3V on the same bank, they can be powered by the same supply. VCCAUX is required regardless of the I/O standard used. This configuration simplifies PCB power management, provided the power plane is properly decoupled/ bypassed.
In a design where DCM is used, it might be beneficial to separate VCCAUX and VCCO power planes to prevent VCCO droop (that might be caused by SSO) from disturbing VCCAUX. For more information about this guideline, see (Xilinx Answer 13756).
NOTE: For more information about VCCAUX and specific voltage requirements for each family, see the Virtex-II and Virtex-II Pro data sheet and user guide.
The Hardware User Guides -> Virtex-II/Pro Platform FPGA User Guide -> Configuration -> Introduction -> Mixed Voltage Environment contains brief information of circuitry powered by VCCINT, VCCAUX, and VCCO powers.
The Virtex-II/Virtex-II Pro DC and Switching Characteristic (Module 3) contains specifications of VCCAUX.