Answers Database
CPLD: XC9500: The high level output voltage of an 9500 CPLD is ~4 volts
Record #2150
Product Family: Hardware
Product Line: 9500
Product Part: 9500
Problem Title:
CPLD: XC9500: The high level output voltage of an 9500 CPLD is ~4 volts
Problem Description:
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 N-type transistor will
drop 1.0-1.2V and the high level output voltage will be
approximately 4 volts.
This is not a problem with standard TTL and CMOS logic as the
required VIH 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.
- Multiply it with the number of the CMOS I/O to be
driven.
- As long as the total leakage current does not exceed
4 mA, 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 - Last Modified: 12/17/99 14:23 |
