UG445 Datasheet, PDF (13/24 Pages) –

R
Thresholds
Reading I/V Curves
Customers who need to understand what threshold their outputs will have can use the I/V
curve (for example, if you are using an I/O standard powered at 3.3V, and need to know
how much current can be sourced from the I/O). The threshold that the CPLD drives out
can be determined by the Vihmin of the downstream device (i.e., if the downstream device
requires a Vihmin of 3.0V, then you must ensure that the CPLD can drive out this voltage
with its current loading). If the Vohmin is 3.0V, then you can extrapolate from the curve in
Figure 1; under typical conditions, the device can source 18 mA of current without
dropping below the required threshold.
Figure 1: I/V Curve Example 1
UG445_01_052207
CPLD I/O User Guide
www.xilinx.com
13
UG445 (v1.2) January 14, 2014