Answers Database

XC9500: The high level output voltage of an 9500 CPLD is ~4 volts


Record #2150

Product Family:  Hardware

Product Line:  9500

Problem Title:
XC9500:	The high level output voltage of an 9500 CPLD is ~4 volts


Problem Description:
Keywords: 9500 output, VOH, VIH

Urgency: Standard

General Description:
The 9500 uses two N-type transistors in the totem-pole of
an output driver.  This allows the driver to be much faster and
smaller than if a P-type transistor were used for the pull up.

One drawback of this approach is that the Ntype transistor will
drop 1.0-1.2V and the high level output voltage will be
aproximately 4 volts.

This is not a problem with standard TTL and CMOS logic as the
requireddVIH for these families is 2.0V and 3.0V respectively.
However, some CMOS devices families require VIH to be 4.0 Volts
or greater.

Is there anything that can be done to increase the 9500 high
output voltage level?


Solution 1:

There are no switches that can be set to change the
configuration of the 9500 output drivers to CMOS but there are
a few things that can be done external to the chip.

1) Set Vccint to 5.5v which is the absolute max.
     - Check the IIH (leakage current) of the Cmos devices
       being driven.
     - Multilpy it with the number of the Cmos i/o to be
       driven.
     - As long as the total leakage current does not exceed
       4mA, and Vccint is at 5.5V, the outputs should give a
       VOH of about 4.5v.

2) Use buffers between pins that need extra drive.




End of Record #2150