Advantech EVA-X4300, User Manual

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15 EVA-X4300 System Design Guide
Chapter 2
Layout
Guide
b. 6 layers
2.6 Crystal / External Oscillator
The EVA-X4300 requires a 14.318 MHz clock to generate all the internal and external
clocks. Connect an external 14.318 MHz crystal (Parallel-resonant) between Xtal_I
and Xtal_o pins to operate as a Pierce oscillator. The EVA-X4300 specification
requires a frequency tolerance of ±30 parts pre million (PPM).
The other way is to use an external 14.318MHz oscillator, and directly route the oscil-
lator is output into XTALi pin of EVA-X4300. A serial damping resistor and a bypass
capacitor are recommended for EMI reduction. The XTALo pin should leave uncon-
nected. The requirement of the clock is duty cycle should be between 40% ~60%.
Recommended Layout:
! Route the signal traces of the crystal to EVA-X4300 as SHORT as possible.
! When use external crystal with EVA-X4300 internal oscillation circuitry to work
as clock oscillator, be sure to put all the related components close to EVA-
X4300 chip. The ground area under the crystal circuitry should be physically
insolated from system ground plane with only a small bridge between them for
signals crossing. This isolation prevents noise located elsewhere on the PCB
from corrupting the oscillator circuitry.
! The power plane under the crystal/ oscillator area should be void, when no use,
or insolated with exactly the same pattern of ground plane.
! Do NOT run any signals under this area, for EMI and interference enhance-
ment.
Layer Type Description Material/ Thickness
1 Signal Top Routing Copper/ 0.5~1oz
FR4/ 5mil
2 Plane Ground Copper/ 1oz
FR4/ 5mil
3 Plane Power Copper/ 1oz
FR4/ 40mil
4 Signal Internal Routing Copper/ 1oz
FR4/ 5mil
5 Plane Ground Copper/ 1oz
FR4/ 5mil
6 Signal Bottom Routing Copper/ 0.5~1oz