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# 38957

Virtex-4/-5/-6 - Small leakage path might exist between a differential pair when Vin levels exceed data sheet recommended operating conditions

Description

If operating with an input voltage that exceeds the Input Voltage Spec (Vin) for a Virtex-4 or Virtex-5 device, there is a small leakage path from theP to N pin regardless of how the pair is configured.

For example, if a pair of pins is configured as LVCMOS_25 inputs, and the P pin has a 10K pull-up while the N pin is being driven, such that there is significant negative voltage, then the P pin might see the pull-up level drop due to uAs of leakage from P to N.

Solution

The user I/O pins for the Virtex-4, Virtex-5, and Virtex-6device families can be used as differential pin pairs.Between the two pins of every differential pin pair, there is a programmable circuit that behaves like a differential termination resistor. This circuit can be enabled in differential signalingapplications using the DIFF_TERM attribute, but is otherwise disabled.

When one pin of a differential pair interfaces with voltages that fall outside the Vin specification from the recommended operating conditions of the family data sheet, there can be a small amount of leakage between the pair regardless of the configuration of the I/Os.If operating within the data sheet specifications, the Pin Leakage (IL) does not violate the specification.

To avoid excessive leakage:

  1. Ensure all pins stay within the Vin specification.
  2. Use stronger pull-up resistors (more overshoot/undershoot results in a stronger leakage path).
AR# 38957
Date Created 07/29/2011
Last Updated 12/15/2012
Status Active
Type General Article
Devices
  • Virtex-4 FX
  • Virtex-4 LX
  • Virtex-4 QPro/R
  • More
  • Virtex-4 SX
  • Virtex-5 FXT
  • Virtex-5 LX
  • Virtex-5 LXT
  • Virtex-5 SXT
  • Virtex-5 TXT
  • Virtex-5Q
  • Virtex-5QV
  • Virtex-6 CXT
  • Virtex-6 HXT
  • Virtex-6 LX
  • Virtex-6 LXT
  • Virtex-6 SXT
  • Less