8. Typical Applications
250
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
www.tundra.com
8.3
Power Distribution
AS90L10208 power distribution is split into V
LDT
(+1.2 V for HT PHY), V
CORE
(+1.8 V for
the core), V
ANALOG
(+1.8 V for the PLL circuitry), and VDDIO (+3.3 V for the I/O).
•
V
ANALOG
should be derived from V
CORE
using a ferrite bead.
•
V
CORE
should be supplied from a dedicated plane or an island in the power plane.
•
V
ANALOG
and VDDIO should be supplied from a dedicated island located close to the pins
supplied by it.
HyperTransport supports a very high data-rate transaction. Careful design practices must be
exercised to ensure a low DC and AC impedance path from the regulator that supplies V
LDT
.
V
LDT
to each HT link must be delivered by an independent interconnect in order to provide
maximum isolation between the individual links. This will minimize the high frequency noise
on the individual HyperTransport supply due to the switching of high data-rate signals on other
HyperTransport links. AS90L10208 has dedicated V
LDT
pins for each of its two,
HyperTransport ports. It is recommended that a separate regulator be used for each port and that
power is supplied from a dedicated island for each V
LDT
in the power plane. Detailed
information on V
LDT
layout is provided in the following sections.
8.3.1
Number of Layers
The number of layers on the board dictates if V
LDT
is routed on the board as a trace or as section
of a plane. A larger number of layers alleviates some of the signal routing constraints allowing
for placing a greater number of discrete decoupling capacitors closer to the AS90L10208
packages or on the back of the board. Ideally, power should be supplied from a dedicated island
for each V
LDT
in the power plane.
8.3.2
VLDT Layout
Regardless of the number of layers in the board, the HyperTransport voltage regulator should be
as close to the AS90L10208 package as possible. The maximum recommended distance is 1.5 to
2.0 inches. If possible, a section of a plane on one of the inner signal layers should be used to
deliver V
LDT
to AS90L10208, as is done with 6- or 8-layer motherboards. This plane should be
large enough to accommodate the placement of all V
LDT
regulator components and to make
connections to every V
LDT
ball on the AS90L10208 package. The plane should be subdivided
into islands, with each island used to supply an individual link.
If a V
LDT
plane is not available, the minimum width of the trace should be 0.2 inches or greater
whenever possible.
Summary of Contents for TSI308
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