Gnd Plane Splits, Voids, And Cut-Outs (Anti-Etch); Usb Power Line Layout Topology; Emi Considerations - Intel 855GME Design Manual

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Intel 855GME Chipset and Intel
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Intel 6300ESB Design Guidelines
When crossing a plane split is completely unavoidable, proper placement of stitching caps may
minimize the adverse effects on EMI and signal quality performance caused by crossing the split.
Stitching capacitors are small-valued capacitors (1 µF or lower in value) that bridge voltage plane
splits close to where High-speed signals or clocks cross the plane split. The capacitor ends should
tie to each plane separated by the split. They are also used to bridge, or bypass, power and ground
planes close to where a high-speed signal changes layers. As an example of bridging plane splits, a
plane split that separates V
high-speed signal crossing. One side of the cap should tie to V
V 3.3. Stitching caps provide a high frequency current return path across plane splits. They
CC
minimize the impedance discontinuity and current loop area that crossing a plane split creates.
9.6.2.2

GND Plane Splits, Voids, and Cut-Outs (Anti-Etch)

Avoid anti-etch on the GND plane.
9.6.3

USB Power Line Layout Topology

The following is a suggested topology for power distribution of V
type provide two types of protection during dynamic attach and detach situations on the bus: inrush
current limiting (droop) and dynamic detach fly back protection. These two different situations
require both bulk capacitance (droop) and filtering capacitance (for dynamic detach fly back
voltage filtering). It is important to minimize the inductance and resistance between the coupling
capacitors and the USB ports. That is, capacitors should be placed as close as possible to the port
and the power-carrying traces should be as wide as possible, preferably, a plane. Make the
power-carrying traces wide enough that the system fuse will blow on an over current event. When
the system fuse is rated at 1 amps, the power-carrying traces should be wide enough to carry at
least 1.5 amps.
Figure 110. Good Downstream Power Connection
5 V Sus
9.6.4

EMI Considerations

The following guidelines apply to the selection and placement of common mode chokes and ESD
protection devices.
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6300ESB ICH Embedded Platform Design Guide
5 and V
CC
Thermister
5 V
5 V
Switch
3.3 planes should have a stitching cap placed near any
CC
CC
220µF 470pF
470pF
5 and the other side should tie to
to USB ports. Circuits of this
BUS
V
CC
1
Port 1
4
GND
V
CC
1
Port 2
4
GND
B1162-01