8. Typical Applications
243
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
www.tundra.com
It is recommended that the selected ferrite bead have a value of 600
Ω
@ 100 MHz and be
capable of sustaining 200 mA current. It is not recommended that a resistor be used in place of
the ferrite bead as the current drawn by the PLL will cause an unacceptable drop in voltage.
8.1.3
Decoupling Capacitor Recommendations
Alliance recommends that each power pin (+1.2V, +1.8V, and +3.3V) of the Tsi308 have one 0.1
or 0.01
μ
F ceramic capacitor to GND. The use of surface-mount capacitor packs makes it easier
to place these decoupling capacitors near and directly underneath the Tsi308 package.
In addition, several bulk capacitors are recommended. Alliance Tsi308 reference platforms
have eight 10
μ
F X5R dielectric ceramic capacitors for +3.3V, eight of the same capacitors for
+1.8V, and one each for +1.2V L0_VLDT and L1_VLDT. These bulk capacitors are placed
directly adjacent to the Tsi308 package.
8.2
PCB Layout Guidelines
8.2.1
Tsi308 HyperTransport Interface Layout Guidelines
The Tsi308 is a PCI/PCI-X to HyperTransport bridge, that also acts as a HyperTransport tunnel.
This layout guide focuses on the HyperTransport interface only. The AS90L10208 conforms to
draft 1.05 of the HyperTransport specification.
HyperTransport is a parallel, unidirectional protocol with differential, DDR signaling on both
the transmit and receive interfaces. The AS90L10208 supports link widths of 8, 4 and 2 bits and
link frequencies of 800, 600, 500, 400, 300 and 200 MHz. The bus width can be independent
between transmit and receive interfaces, permitting efficient allocation of system board
resources, whereby a bigger bus width can be used for data intensive interfaces and a smaller
bus width used for non-intensive applications.
HyperTransport uses a specialized version of LVDS I/Os, with a V
LDT
of 1.2V. Low-voltage
signaling combined with very high data speeds require strict adherence to good layout practices
and power circuitry design on any board using the AS90L10208. The AS90L10208 supports a
bus width of 2, 4, or 8 bits on both the transmit and receive interfaces on both of the
HyperTransport ports.
These are the signals on the AS90L10208 HyperTransport interface:
•
L_TX_CAD_H/L[7:0]
•
L_TX_CLK_H/L
•
L_TX_CTL_H/L
•
L_RX_CAD_H/L[7:0]
•
L_RX_CLK_H/L
Summary of Contents for TSI308
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