afs600 Actel Corporation, afs600 Datasheet - Page 147

• Manufacturer Part Number: afs600
• Description: Actel Fusion Programmable System Chips Mixed-signal Family With Optional Arm Support
• Manufacturer: Actel Corporation

Simultaneously Switching Outputs and PCB Layout
Simultaneously switching outputs (SSOs) can produce
signal integrity problems on adjacent signals that are not
part of the SSO bus. Both inductive and capacitive
coupling parasitics of bond wires inside packages and of
traces on PCBs will transfer noise from SSO busses onto
signals adjacent to those busses. Additionally, SSOs can
produce ground bounce noise and V
two noise types are caused by rapidly changing currents
through GND and V
switching activities:
Any group of four or more input pins switching on the
same clock edge is considered an SSO bus. The shielding
should be done both on the board and inside the
package unless otherwise described.
• Ground bounce noise voltage = L(GND) * di/dt
• V
CCI
dip noise voltage = L(V
CCI
package pin inductances during
CCI
) * di/dt
CCI
dip noise. These
A d v an c ed v1 . 4
In-package shielding can be achieved in several ways; the
required shielding will vary depending on whether pins
next to SSO bus are LVTTL/LVCMOS inputs, LVTTL/
LVCMOS outputs, or GTL/SSTL/HSTL/LVDS/LVPECL inputs
and outputs. Board traces in the vicinity of the SSO bus
have to be adequately shielded from mutual coupling
and inductive noise that can be generated by the SSO
bus. Also, noise generated by the SSO bus needs to be
reduced inside the package.
PCBs perform an important function in feeding stable
supply voltages to the IC and, at the same time,
maintaining signal integrity between devices.
Key issues that need to considered are as follows:
• Power and ground plane design and decoupling
• Transmission line reflections and terminations
network design
Actel Fusion Programmable System Chips
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