R
Spartan-IIE FPGA Family: DC and Switching Characteristics
Calculation of T
Capacitance
as a Function of
Constants for Calculating T
IOOP
IOOP
(1)
CSL
FL
TIOOP is the propagation delay from the O Input of the IOB
to the pad. The values for TIOOP are based on the standard
capacitive load (CSL) for each I/O standard as listed in the
table Constants for Calculating TIOOP, below.
Standard
(pF)
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
10
10
0
(ns/pF)
LVTTL Fast Slew Rate, 2 mA drive
LVTTL Fast Slew Rate, 4 mA drive
LVTTL Fast Slew Rate, 6 mA drive
LVTTL Fast Slew Rate, 8 mA drive
0.41
0.20
For other capacitive loads, use the formulas below to calcu-
0.13
late an adjusted propagation delay, TIOOP1
.
0.079
0.044
0.043
0.033
0.41
TIOOP1 = TIOOP + Adj + (CLOAD – CSL) * FL
LVTTL Fast Slew Rate, 12 mA drive
LVTTL Fast Slew Rate, 16 mA drive
LVTTL Fast Slew Rate, 24 mA drive
LVTTL Slow Slew Rate, 2 mA drive
LVTTL Slow Slew Rate, 4 mA drive
LVTTL Slow Slew Rate, 6 mA drive
LVTTL Slow Slew Rate, 8 mA drive
LVTTL Slow Slew Rate, 12 mA drive
LVTTL Slow Slew Rate, 16 mA drive
LVTTL Slow Slew Rate, 24 mA drive
LVCMOS2
Where:
Adj
is selected from IOB Output Delay Adjustments
for Different Standards(1), page 40, according
to the I/O standard used
CLOAD is the capacitive load for the design
FL is the capacitance scaling factor
0.20
0.100
0.086
0.058
0.050
0.048
0.041
0.050
0.050
0.033
0.014
0.017
0.022
0.016
0.014
0.028
0.016
0.029
0.016
0.035
0.037
Delay Measurement Methodology
VREF
Point Typ(2)
Meas.
(1)
(1)
Standard
LVTTL
VL
VH
0
3
1.4
-
LVCMOS2
PCI33_3
PCI66_3
GTL
0
2.5
1.125
-
LVCMOS18
Per PCI Spec
Per PCI Spec
-
PCI 33 MHz 3.3V
-
PCI 66 MHz 3.3V
VREF – 0.2 VREF + 0.2 VREF
VREF – 0.2 VREF + 0.2 VREF
0.80
1.0
0.75
0.90
0.90
1.5
1.25
1.5
GTL
GTL+
GTL+
0
HSTL Class I VREF – 0.5 VREF + 0.5 VREF
HSTL Class III VREF – 0.5 VREF + 0.5 VREF
HSTL Class IV VREF – 0.5 VREF + 0.5 VREF
SSTL3 I and II VREF – 1.0 VREF + 1.0 VREF
SSTL2 I and II VREF – 0.75 VREF + 0.75 VREF
HSTL Class I
20
20
20
30
30
30
30
20
10
HSTL Class III
HSTL Class IV
SSTL2 Class I
SSTL2 Class II
CTT
AGP
VREF – 0.2 VREF + 0.2 VREF
VREF VREF VREF
(0.2xVCCO) (0.2xVCCO
1.2 – 0.125 1.2 + 0.125 1.2
1.6 – 0.3 1.6 + 0.3 1.6
SSTL3 Class I
–
+
Per AGP
Spec
SSTL3 Class II
)
CTT
LVDS
AGP
LVPECL
Notes:
Notes:
1. I/O parameter measurements are made with the capacitance
values shown above. Refer to Application Note XAPP179 for
appropriate terminations.
1. Input waveform switches between VL and VH.
2. Measurements are made at VREF Typ, Maximum, and
Minimum. Worst-case values are reported.
2. I/O standard measurements are reflected in the IBIS model
3. I/O parameter measurements are made with the capacitance
values shown in the following table, Constants for Calculating
TIOOP. Refer to Application Note XAPP179 for appropriate
terminations.
information except where the IBIS format precludes it.
4. I/O standard measurements are reflected in the IBIS model
information except where the IBIS format precludes it.
DS077-3 (v2.3) June 18, 2008
www.xilinx.com
41
Product Specification
XILINX [ XILINX, INC ]
