PROASIC3E Datasheet, PDF (22/37 Pages) Actel Corporation – I/O Structures in IGLOOe and ProASIC3E Devices

I/O Structures in IGLOOe and ProASIC3E Devices
Solution 3
The board-level design must ensure that the reflected waveform at the pad does not exceed the
voltage overshoot/undershoot limits provided in the datasheet. This is a requirement to ensure
long-term reliability.
This scheme will also work for a 3.3 V PCI/PCI-X configuration, but the internal diode should not be
used for clamping, and the voltage must be limited by the bus switch, as shown in Figure 12.
Relying on the diode clamping would create an excessive pad DC voltage of 3.3 V + 0.7 V = 4 V.
Solution 3
I/O Input
5.5 V
Bus
Switch
IDTQS32X23
3.3 V
5.5 V
Figure 12 • Solution 3
Requires a bus switch on the board,
LVTTL/LVCMOS 3.3 V I/Os.
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