DS50PCI402_14 Datasheet, PDF (28/35 Pages) Texas Instruments – 2.5 Gbps / 5.0 Gbps 4 Lane PCI Express Repeater with Equalization and De-Emphasis

DS50PCI402
SNLS320G – APRIL 2010 – REVISED MAY 2011
EXTERNAL MICROSTRIP
20 mils
INTERNAL STRIPLINE
100 mils
20 mils
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VDD
VDD
VDD
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 ¹
19
54
20
53
21
52
22
51
23
BOTTOM OF PKG
50
GND
24
49
25
48
26
47
27
46
28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
VDD
VDD
Figure 9. Typical Routing Options
The graphic shown above depicts different transmission line topologies which can be used in various
combinations to achieve the optimal system performance. Impedance discontinuities at the differential via can be
minimized or eliminated by increasing the swell around each hole and providing for a low inductance return
current path. When the via structure is associated with thick backplane PCB, further optimization such as back
drilling is often used to reduce the deterimential high frequency effects of stubs on the signal path.
POWER SUPPLY BYPASSING
Two approaches are recommended to ensure that the DS50PCI402 is provided with an adequate power supply.
First, the supply (VDD) and ground (GND) pins should be connected to power planes routed on adjacent layers
of the printed circuit board. The layer thickness of the dielectric should be minimized so that the V_DD and GND
planes create a low inductance supply with distributed capacitance. Second, careful attention to supply
bypassing through the proper use of bypass capacitors is required. A 0.01 μF bypass capacitor should be
connected to each V_DD pin such that the capacitor is placed as close as possible to the DS50PCI402. Smaller
body size capacitors can help facilitate proper component placement. Additionally, three capacitors with
capacitance in the range of 2.2 μF to 10 μF should be incorporated in the power supply bypassing design as
well. These capacitors can be either tantalum or an ultra-low ESR ceramic.
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