Datasheet
AM3517, AM3505
SPRS550E –OCTOBER 2009–REVISED MARCH 2013
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6.4.2.1.3 PCB Stackup
The minimum stackup required for routing the microprocessor is a six layer stack as shown in Table 6-14.
Additional layers may be added to the PCB stack up to accommodate other circuity or to reduce the size
of the PCB footprint.
Table 6-14. Minimum PCB Stack Up
LAYER TYPE DESCRIPTION
1 Signal Top Routing Mostly Horizontal
2 Plane Ground
3 Plane Power
4 Signal Internal Routing
5 Plane Ground
6 Signal Bottom Routing Mostly Vertical
Table 6-15. PCB Stack Up Specifications
NO. PARAMETER MIN TYP MAX UNIT NOTES
1 PCB Routing/Plane Layers 6
2 Signal Routing Layers 3
3 Full ground layers under LPDDR routing region 2
4 Number of ground plane cuts allowed within LPDDR routing region 0
Number of ground reference planes required for each LPDDR routing 1
5 1
layer
Number of layers between LPDDR routing layer and reference ground 0
6 0
plane
7 PCB Routing Feature Size 4 Mils
8 PCB Trace Width w 4 Mils
9 PCB BGA escape via pad size 18 Mils
10 PCB BGA escape via hole size 8 Mils
11 Device BGA Pad Size See Note
(1)
12 LPDDR Device BGA Pad Size See Note
(2)
13 Single Ended Impedance, ZO 50 75 Ω
14 Impedance Control Z-5 Z Z + 5 Ω See Note
(3)
(1) Please see the Flip Chip Ball Grid Array Package Reference Guide (literature number SPRU811) for device BGA pad size.
(2) Please see the LPDDR device manufacturer documentation for the LPDDR device BGA pad size.
(3) Z is the nominal singled ended impedance selected for the PCB specified by item 12.
6.4.2.1.4 Placement
Figure 6-19 shows the required placement for the microprocessor as well as the LPDDR devices. The
dimensions for Figure 6-19 are defined in Table 6-16. The placement does not restrict the side of the PCB
that the devices are mounted on. The ultimate purpose of the placement is to limit the maximum trace
lengths and allow for proper routing space. For 1x16 and 1x32 LPDDR memory systems, the second
LPDDR device is omitted from the placement.
132 Timing Requirements and Switching Characteristics Copyright © 2009–2013, Texas Instruments Incorporated
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