UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 17089

Virtex-II Pro RocketIO - How can I derive the 1.6-1.8 volts necessary for the VTX supply in an AC coupled link without a separate regulator?

Description

How can I derive 1.6 - 1.8 volts for the VTRX supply without a separate regulator?

Solution

Because of the very small current draw of the VTRX pins, you can use the following circuit to derive 1.78 V from the 2.5 V analog supply for the VTRX pins on the Virtex-II Pro device. This configuration has been verified on the ML321 RocketIO Characterization Board. Using a separate voltage divider for each VTRX pin, a ferrite bead is not necessary for acceptable filtering, as a result of sufficient inductance available from the resistor package.

Voltage Divider
Voltage Divider

Voltage dividers can be shared across multiple transceivers. In this case, the values of the divider should be scaled down accordingly. For two VTRX pins, scale the divider resistors 201 ohm and 500 ohm; for eight VTRX pins, make the divider resistors 50 ohm and 125 ohm. In this setup, each transceiver's VTRX pin must have its own bypass network, which always includes a ferrite bead and, depending on package, a bypass capacitor. (For more information on the bypass capacitor, see (Xilinx Answer 18872)).

AR# 17089
Date Created 09/03/2007
Last Updated 12/15/2012
Status Active
Type General Article