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SPRS717F –OCTOBER 2011–REVISED APRIL 2013
5.6.2.2.2.10 DDR_VREF Routing
DDR_VREF is used as a reference by the input buffers of the DDR2 memories as well as the AM335x
device. DDR_VREF is intended to be half the DDR2 power supply voltage and should be created using a
resistive divider as shown in Figure 5-39 and Figure 5-40. Other methods of creating DDR_VREF are not
recommended. Figure 5-43 shows the layout guidelines for DDR_VREF.
DDR_VREF Bypass Capacitor
DDR2 Device
A1
DDR_VREF Nominal Minimum
Trace Width is 20 Mils
AM335x
A1
Neck down to minimum in BGA escape
regions is acceptable. Narrowing to
accommodate via congestion for short
distances is also acceptable. Best
performance is obtained if the width
of DDR_VREF is maximized.
Figure 5-43. DDR_VREF Routing and Topology
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