XM014034B datasheet(29/83 Pages) XMOS

29 / 83 page

XU6--QF6A Datasheet

General routing and placement guidelines

The following guidelines will help to avoid signal quality and EMI problems on high speed

designs. They relate to a four-layer (Signal, GND, Power, Signal) PCB.

For best results, most of the routing should be done on the top layer (assuming the de-

vices are on the top layer) closest to GND. Reference planes should be below the trans-

mission lines in order to maintain control of the trace impedance.

We recommend that the high-speed clock and high-speed differential pairs are routed

rst before any other routing. When routing high speed signals, the following guidelines

should be followed:

High speed differential pairs should be routed together.

High-speed signal pair traces should be trace-length matched.

Ensure that high speed signals (clocks, differential pairs) are routed as far away from

off-board connectors as possible.

High-speed clock and periodic signal traces that run parallel should be at least a dis-

tance S3 away from D+/D- (see Figure 8 and Figure

Low-speed and non-periodic signal traces that run parallel should be at least S2 away

from D+/D- (see Figure 8 and Figure

Route high speed signals on the top of the PCB wherever possible.

Route high speed traces over continuous power planes, with no breaks. If a trade-off

must be made, changing signal layers is preferable to crossing plane splits.

Follow the 20 × h rule; keep traces 20 × h (the height above the power plane) away

from the edge of the power plane.

Use a minimum of vias in high speed traces.

Avoid corners in the trace. Where necessary, rather than turning through a

degree

angle, use two

degree turns or an arc.

DO NOT route differential pair traces near clock sources, clocked circuits or magnetic

devices.

Avoid stubs on high speed signals.

Land patterns and solder stencils

The package is a 6 pin Quad Flat No lead Package (QFN) on a .mm pitch with four

VDD paddles and an exposed ground paddle.

The land patterns and solder stencils will depend on the PCB manufacturing process. We

recommend you design them with using the IPC specications “Generic Requirements

for Surface Mount Design and Land Pattern Standards”

IPC-B. This standard aims

XM014034B Datasheet(PDF) 29 Page - Xmos Ltd.