DS705 XILINX [Xilinx, Inc], DS705 Datasheet - Page 29

• Manufacturer Part Number: DS705
• Description: XA Spartan-3A DSP Automotive FPGA Family Data Sheet
• Manufacturer: XILINX [Xilinx, Inc]

model with V
table. A fourth parameter, C
parameters describe all relevant output test conditions. IBIS
models are found in the Xilinx development software as well
as at the following link:
Delays for a given application are simulated according to its
specific load conditions as follows:
1. Simulate the desired signal standard with the output
2. Record the time to V
3. Simulate the same signal standard with the output
4. Record the time to V
5. Compare the results of steps 2 and 4. Add (or subtract)
Simultaneously Switching Output
Guidelines
This section provides guidelines for the recommended
maximum allowable number of Simultaneous Switching
Outputs (SSOs). These guidelines describe the maximum
number of user I/O pins of a given output signal standard
that should simultaneously switch in the same direction,
while maintaining a safe level of switching noise. Meeting
these guidelines for the stated test conditions ensures that
the FPGA operates free from the adverse effects of ground
and power bounce.
Ground or power bounce occurs when a large number of
outputs simultaneously switch in the same direction. The
output drive transistors all conduct current to a common
voltage rail. Low-to-High transitions conduct to the V
rail; High-to-Low transitions conduct to the GND rail. The
resulting cumulative current transient induces a voltage
difference across the inductance that exists between the die
pad and the power supply or ground return. The inductance
is associated with bonding wires, the package lead frame,
and any other signal routing inside the package. Other
variables contribute to SSO noise levels, including stray
inductance on the PCB as well as capacitive loading at
receivers. Any SSO-induced voltage consequently affects
internal switching noise margins and ultimately signal
quality.
Table 28
guidelines. For each device/package combination,
DS705 (v1.1) January 20, 2009
Product Specification
www.xilinx.com/support/download/index.htm
driver connected to the test setup shown in
Use parameter values V
C
driver connected to the PCB trace with load. Use the
appropriate IBIS model (including V
and V
load.
the increase (or decrease) in delay to (or from) the
appropriate Output standard adjustment
yield the worst-case delay of the PCB trace.
REF
and
is zero.
MEAS
R
REF
Table 29
values) or capacitive value to represent the
(the input-switching threshold) from the
provide the essential SSO
M
MEAS
.
REF
T
, R
.
, is always zero. The four
T
, and V
REF
M
from
, R
(Table
REF
Table
Figure
, C
Table 28
26) to
REF
CCO
27.
www.xilinx.com
8.
,
XA Spartan-3A DSP Automotive FPGA Family Data Sheet
provides the number of equivalent V
equivalent number of pairs is based on characterization and
may not match the physical number of pairs. For each
output signal standard and drive strength,
recommends the maximum number of SSOs, switching in
the same direction, allowed per V
I/O bank. The guidelines in
package style, slew rate, and output drive current.
Furthermore, the number of SSOs is specified by I/O bank.
Generally, the left and right I/O banks (Banks 1 and 3)
support higher output drive current.
Multiply the appropriate numbers from
Table 29
allowed within an I/O bank. Exceeding these SSO
guidelines might result in increased power or ground
bounce, degraded signal integrity, or increased system jitter.
The recommended maximum SSO values assumes that the
FPGA is soldered on the printed circuit board and that the
board uses sound design practices. The SSO values do not
apply for FPGAs mounted in sockets, due to the lead
inductance introduced by the socket.
The SSO values assume that the V
3.3V. Setting V
characteristics.
Table 28: Equivalent V
XA3SD1800A
XA3SD3400A
SSO
Device
MAX
to calculate the maximum number of SSOs
/IO Bank =
CCAUX
to 2.5V provides better SSO
Table 28
CCO
CSG484
Table 29
Package Style (Pb-free)
/GND Pairs per Bank
6
6
CCO
x
Table 29
CCAUX
CCO
are categorized by
/GND pair within an
Table 28
/GND pairs. The
is powered at
Table 29
FGG676
and
10
9
29