8. Typical Applications
249
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8.2.4.2
L_POWER_OK, L_RST_N and LDTSTOP_N
Open-drain signals require a pull-up resistor to VDDIO, +2.5V or +3.3 V, depending on the
other devices in the HT chain.
8.2.4.3
HyperTransport Trace Referencing to VSS/VDD
•
HyperTransport is a ground-referenced differential bus. Differential pairs are weakly
coupled and reference V
SS
more than each other.
•
Ideally, all HyperTransport signals reference V
SS
/V
DD
.
•
If traces cross two reference planes, the plane separation should be 15 mils or less and
should use one 0.01 uF 0603 or 0402 ceramic capacitor to bridge the boundary between the
planes for every four diff-pairs.
•
All signal groups must match the length requirement.
8.2.4.4
HyperTransport Trace Layer Changes
•
In general, layer changes are discouraged for bus speeds > 400 Mb/s with the exception of
vias for breakout under the package.
•
If a clock/data group must change layers, place a pair’s vias as close as possible in order to
prevent a major Z
OD
discontinuity. It is all right for the via anti-pad plane clearances to
overlap in this instance.
•
If a clock/data group is split between top and bottom routing layers, trace length must be
inserted on the top layer nets to approximately match the extra delay due to the vias for the
bottom layer routing.
•
One 0.01 uF 0603 or 0402 ceramic decoupling capacitor is in the vicinity of layer
transitions for every four differential pairs to minimize plane bounce.
•
All signal groups must match the length requirement.
800 MT/s
20/5/5/5/20
20/5/5/5/20
1000 MT/s
20/5/5/5/20
20/5/5/5/20
1200 MT/s
20/5/5/5/20
20/5/5/5/20
1600 MT/s
20/5/5/5/20
20/5/5/5/20
7
CAD/CTL/CLK impedance
control and stack up
Recommended dielectric thickness from signal
layer to plane layer
Microstrip
Stripline
4.7
6.0
Table 43: System Board Design Rules
Description
Definition/Parameter
Rules
Содержание TSI308
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