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Printed Circuit Board (PCB) considerations of Xilinx devices
Record #1634
Problem Title:
Printed Circuit Board (PCB) considerations of Xilinx devices
Problem Description:
Intelligent Printed Circuit Board layout may prevent future design problems like reflections, glitch
es, ground bounce/rise, crosstalk, and other system related problems in several high speed applicati
ons.
These are some suggestions for PCB layout that may help prevent these undesirable side-effects from
happening.
Further information on minimizing Ground Bounce may be found in the 1996 Xilinx Data Book on pages 1
3-10 to 13-11 or on the Xilinx WWW site at :
http://www.xilinx.com/xapp/xapp045.pdf
Solution 1:
1. PC-Boards should contain seperate Vcc and ground planes
connected directly to the device's supply pins.
2. Decouple each Vcc pin on the device with a low-inductance
decoupling capacitor of 0.01 to 0.1 uF very close to each
Vcc pin. For more information on decoupling capacitors
please refer to (Xilinx Solution 777).
3. Decouple the Printed Circuit Board power inputs with a
0.1 uF cearmic (high frequency) and 100 uF electrolytic
(low frequency) filter capacitors.
4. Use wide spacing between fast signal lines (particularly
clocks) to minimize crosstalk.
5. All device ground pins must be tied together.
6. Avoid using sockets to attach the device to the board.
Sockets usually provide a higher pin capacitance and
a poorer connection than if the device is soldered
to the board.
7. Connect clocks to input pins that are close to a ground
pin.
8. Locate the device as close as possible to the chip(s) it
drives and/or is driven by. This will minimze transmission
line effects.
End of Record #1634 - Last Modified: 03/04/98 09:11 |
