Crystal LAN CS8920, Техническое справочное руководство, Страница: 20 / 67

AN84REV1 20
CS8920 Technical Reference Manual
2.2 Layout considerations for the
CS8920
The CS8920 is a mixed signal device
having digital and analog circuits for an
Ethernet communication. While doing the
PCB layout and signal connections, it is
important to take the following precautions:
(a) Provide a low inductive path to
reduce power and ground
connection noise.
(b) Provide proper impedance
matching especially to the Ethernet
analog signals.
(c) Provide low inductive path, wider
and short traces, for all analog
signals.
It is important that a PCB designer follow
suggestions made in this document for
proper and reliable operation of the
CS8920. These guidelines will also help to
ensure good EMI test results.
2.2.1 General guidelines
Figure 2.2.1 shows component placement
for an ISA COMBO Ethernet adapter card
using a CS8900. For a CS8920 Combo
card, substitute CS8920 in place of
CS8900. The placement of the CS8920
should be such that the routes of the analog
signals and the digital signals are not
intermixing. No signal should route
beneath the CS8920 on any plane.
2.2.2 Power supply connections
The CS8920 has 3 analog and 5 digital
power pin pairs (Vcc and GND).
Additional ground connections are
provided. Each power pin pair should be
connected to a 0.1
µ
F bypass capacitor.
Connect the extra ground pins directly to
the ground plane.