Datasheet

46
47
48
49
50
51
52
53
54
43
4241
40
39
38
37
36
22
27
26
25
24
23
21
20
19
45
44
3
4
5
6
7
89
10
1
2
GND
BOTTOM OF PKG
13
14
15
16
17
18
11
12
33
32
3130
29
28
35
34
VDD
VDD
VDD
VDD
100 mils
20 mils
20 mils
VDD
INTERNAL STRIPLINE
EXTERNAL MICROSTRIP
DS50PCI401
www.ti.com SNLS292J –JUNE 2009–REVISED APRIL 2013
APPLICATION INFORMATION
GENERAL RECOMMENDATIONS
The DS50PCI401 is a high performance circuit capable of delivering excellent performance. Careful attention
must be paid to the details associated with high-speed design as well as providing a clean power supply. Refer
to the information below and the latest version of the LVDS Owner's Manual for more detailed information on
high speed design tips to address signal integrity design issues.
PCB LAYOUT CONSIDERATIONS FOR DIFFERENTIAL PAIRS
The CML inputs and LPDS outputs have been optimized to work with interconnects using a controlled differential
impedance of 100Ω. It is preferable to route differential lines exclusively on one layer of the board, particularly for
the input traces. The use of vias should be avoided if possible. If vias must be used, they should be used
sparingly and must be placed symmetrically for each side of a given differential pair. Whenever differential vias
are used the layout must also provide for a low inductance path for the return currents as well. Route the
differential signals away from other signals and noise sources on the printed circuit board. See AN-1187
(SNOA401) for additional information on WQFN packages.
Figure 8. 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.
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