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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, glitches, ground bounce/rise, crosstalk, and other system related
problems in several high speed applications.

These are some suggestions for PCB layout that may help prevent these undesirabl
e side-effects from happening.

Further information on minimizing Ground Bounce may be found in the 1996 Xilinx
Data Book on pages 13-10 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