R
XC3000 Series Field Programmable Gate Arrays
7-36
November 9, 1998 (Version 3.1)
Power
Power Distribution
Power for the FPGA is distributed through a grid to achieve
high noise immunity and isolation between logic and I/O.
Inside the FPGA, a dedicated VCC and ground ring sur-
rounding the logic array provides power to the I/O drivers.
An independent matrix of VCC and groundlines supplies the
interior logic of the device. This power distribution grid pro-
vides a stable supply and ground for all internal logic, pro-
viding the external package power pins are all connected
and appropriately decoupled. Typically a 0.1-
F capacitor
connected near the VCC and ground pins will provide ade-
quate decoupling.
Output buffers capable of driving the specified 4- or 8-mA
loads under worst-case conditions may be capable of driv-
ing as much as 25 to 30 times that current in a best case.
Noise can be reduced by minimizing external load capaci-
tance and reducing simultaneous output transitions in the
same direction. It may also be beneficial to locate heavily
loaded output buffers near the ground pads. The I/O Block
output buffers have a slew-limited mode which should be
used where output rise and fall times are not speed critical.
Slew-limited outputs maintain their dc drive capability, but
generate less external reflections and internal noise.
1.00
0.80
0.60
0.40
0.20
SPECIFIED WORST-CASE VALUES
MAX
CO
MMERCIAL
(4.75
V)
MAX
MILITARY
(4.5
V)
– 55
MIN MILITARY
(5.5 V)
MIN COMMERCIAL
(4.75 V)
MIN COMMERCIAL
(5.25 V)
TYPICAL COMMERCIAL
(+ 5.0 V, 25
°C)
TYPICAL MILITARY
TEMPERATURE (
°C)
– 40
– 20
0
25
40
70
80
100
125
NORMALIZED
DELAY
X6094
MIN MILITARY
(4.5 V)
Figure 32: Relative Delay as a Function of Temperature, Supply Voltage and Processing Variations
System
Clock
(MHz)
250
200
150
100
50
3 CLBs
(3-12)
4 CLBs
(4-16)
2 CLBs
(2-8)
1 CLB
(1-4)
XC3100A-3
XC3000A--6
CLB Levels:
Gate Levels:
300
Toggle
Rate
0
X7065
Figure 33: Clock Rate as a Function of Logic
Complexity (Number of Combinational Levels between
Flip-Flops)
Product Obsolete or Under Obsolescence