Conclusion
Figure 10–22. Output Drive Characteristics of a 5.0-V Device
I
150
135
OL
V
V
= 5.0 V
= 5.0 V
120
CCINT
CCIO
90
60
Typical I
o
I
OH
3
30
0
Output
Current (mA)
1
2
4
5
V
Output Voltage (V)
o
As shown above, R1 = 5.0-V/135 mA.
1
The values shown in data sheets usually reflect typical operating
conditions. Subtract 20% from the data sheet value for guard
band. This subtraction when applied in the example in
Figure 10–22 gives R1 a value of 30 Ω.
R2 should be selected so that it does not violate the driving device’s IOH
specification. For example, if the device has a maximum IOH of 8 mA,
given that the PCI clamping diode, VIN = VCCIO + 0.7-V = 3.7-V, and the
maximum supply load of a 5.0-V device (VCC) is 5.25-V, the value of R2 can
be calculated as follows:
R2 = (5.25 V – 3.7 V) – (8 mA × 30 Ω) = 164 Ω
8 mA
This analysis assumes worst case conditions. If your system does not have
a wide variation in voltage-supply levels, you can adjust these
calculations accordingly.
1
Because 5.0-V device tolerance in Cyclone II devices requires use
of the PCI clamp, and this clamp is activated during
configuration, 5.0-V signals may not be driven into the device
until it is configured.
Cyclone II device I/O capabilities enable you to keep pace with
increasing design complexity utilizing a low-cost FPGA device family.
Support for I/O standards including SSTL and LVDS compatibility allow
Cyclone II devices to fit into a wide variety of applications. The Quartus II
Conclusion
10–36
Altera Corporation
Cyclone II Device Handbook, Volume 1
February 2008
ALTERA [ ALTERA CORPORATION ]
