
Spartan-3 FPGA Family: DC and Switching Characteristics
DS099-3 (v1.5) December 17, 2004
Advance Product Specification
39
www.xilinx.com
23
R
The capacitive load (C
L
) is connected between the output
and GND.
The Output timing for all standards, as published
in the speed files and the data sheet, is always based on a
C
L
value of zero.
High-impedance probes (less than 1 pF)
are used for all measurements. Any delay that the test fix-
ture might contribute to test measurements is subtracted
from those measurements to produce the final timing num-
bers as published in the speed files and data sheet.
Using IBIS Models to Simulate Load
Conditions in Application
IBIS Models permit the most accurate prediction of timing
delays for a given application. The parameters found in the
IBIS model (V
REF
, R
REF
, and V
MEAS
) correspond directly
with the parameters used in
Table 21
, V
T
, R
T
, and V
M
. Do
not confuse V
REF
(the termination voltage) from the IBIS
model with V
REF
(the input-switching threshold) from the
table. A fourth parameter, C
REF
, is always zero. The four
parameters describe all relevant output test conditions.
IBIS models are found in the Xilinx development software as
well as at the following link:
http://www.xilinx.com/support/sw_ibis.htm
Simulate delays for a given application according to its spe-
cific load conditions as follows:
1.
Simulate the desired signal standard with the output
driver connected to the test setup shown in
Figure 4
.
Use parameter values V
T
, R
T
, and V
M
from
Table 21
.
C
REF
is zero.
2.
Record the time to V
M
.
3.
Simulate the same signal standard with the output
driver connected to the PCB trace with load. Use the
appropriate IBIS model (including V
REF
, R
REF
, C
REF
,
and V
MEAS
values) or capacitive value to represent the
load.
4.
Record the time to V
MEAS
.
5.
Compare the results of steps 2 and 4. The increase (or
decrease) in delay should be added to (or subtracted
from) the appropriate Output standard adjustment
(
Table 20
) to yield the worst-case delay of the PCB
trace.
Simultaneously Switching Output Guidelines
Table 22:
Equivalent V
CCO
/GND Pairs per Bank
Device
VQ100
TQ144
(1)
PQ208
FT256
FG320
FG456
FG676
FG900
FG1156
XC3S50
1
1.5
2
-
-
-
-
-
-
XC3S200
1
1.5
2
3
-
-
-
-
-
XC3S400
-
1.5
2
3
3
5
-
-
-
XC3S1000
-
-
-
3
3
5
5
-
-
XC3S1500
-
-
-
-
3
5
6
-
-
XC3S2000
-
-
-
-
-
-
6
9
-
XC3S4000
-
-
-
-
-
-
-
10
12
XC3S5000
-
-
-
-
-
-
-
10
12
Notes:
1.
The V
CCO
lines for the pair of banks on each side of the TQ package are internally tied together. Each pair of interconnected banks
has three V
CCO
/GND pairs.
The information in this table also applies to Pb-free packages.
2.