Lantronix Micro Embedded Integration Kit (EIK) - Integration Guide - Page 44

Network Connector, Virtual Ground, Integration Guidelines, Multi-Layer Board Strategy - 100 device server

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Integration Guidelines To maintain the necessary voltage, provide ground to the appropriate connector header with a low inductance and low DC resistance path. The best solution is a solid ground plane. Place a de-coupling capacitor pair as close as possible to the connector headers of the board's power supply. We recommend a ceramic (X7R material or equivalent, value 0.022µF to 0.1µF) and a low DC resistance (electrolytic or tantalum value 10 µF to 100 µF) capacitor. Network Connector If you want to add an RJ45 connector, we recommend that it be at least partially shielded in case it will be used in a noisy environment. (Please refer to the productspecific section.) Take care regarding the trace length and routing for the two differential pairs, TX and RX. Neither of them may cross or run in parallel with any digital signal nor run through a digital ground or power plane. The trace length inside of the unit running from the device server to the RJ45 should be as short as possible. The trace length may have an impact on signal quality (link length), especially if internal ambient noise is a factor. If trace length cannot be shortened, or the internal noise frequencies are hitting the carrier frequency or the multiples of these (depending on the product and operating mode either 10MHz or 100MHz and up to the 11th overtone), we suggest a different strategy. Use a multi-layer board and a separated shield layer on the solder and assembly sides of the board, which are routed in the inner layers. (Refer to the following figure.) These shield layers can either be connected to the RJ45s shield or to a virtual ground signal provided by the device server. (See also next section and product-specific section.) Figure 6-1. Multi-Layer Board Strategy RJ45 shield connection CoBox network connector digital ground and power Plane (inner layer) shield planes inner layer signal traces Virtual Ground The device servers provide a virtual ground at a (plated) mounting hole. It is a ground imitation. It uses the tap of two capacitors (ceramic 0.1 µF) conducted symmetrically to ground and VCC. In the absence of a solid ground (earth), this virtual ground can be used for shielding or balancing metal parts of the case. Embedded Integration Kit Integration Guide 6-5

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Integration Guidelines
Embedded Integration Kit Integration Guide
6-5
To maintain the necessary voltage, provide ground to the appropriate connector
header with a low inductance and low DC resistance path. The best solution is a solid
ground plane.
Place a de-coupling capacitor pair as close as possible to the connector headers of
the board’s power supply. We recommend a ceramic (X7R material or equivalent,
value 0.022
µ
F to 0.1
µ
F) and a low DC resistance (electrolytic or tantalum value
10
µ
F to 100
µ
F) capacitor.
Network Connector
If you want to add an RJ45 connector, we recommend that it be at least partially
shielded in case it will be used in a noisy environment. (Please refer to the product-
specific section.)
Take care regarding the trace length and routing for the two differential pairs, TX and
RX. Neither of them may cross or run in parallel with any digital signal nor run
through a digital ground or power plane. The trace length inside of the unit running
from the device server to the RJ45 should be as short as possible. The trace length
may have an impact on signal quality (link length), especially if internal ambient noise
is a factor.
If trace length cannot be shortened, or the internal noise frequencies are hitting the
carrier frequency or the multiples of these (depending on the product and operating
mode either 10MHz or 100MHz and up to the 11th overtone), we suggest a different
strategy. Use a multi-layer board and a separated shield layer on the solder and
assembly sides of the board, which are routed in the inner layers. (Refer to the
following figure.) These shield layers can either be connected to the RJ45s shield or
to a virtual ground signal provided by the device server. (See also next section and
product-specific section.)
Figure 6-1. Multi-Layer Board Strategy
CoBox network
connector
RJ45 shield
connection
shield planes
inner layer signal traces
digital ground
and power Plane
(inner layer)
Virtual Ground
The device servers provide a virtual ground at a (plated) mounting hole. It is a ground
imitation. It uses the tap of two capacitors (ceramic 0.1
µ
F) conducted symmetrically
to ground and VCC. In the absence of a solid ground (earth), this virtual ground can
be used for shielding or balancing metal parts of the case.