DM385 datasheet(248/281 Pages) TI

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Rtt

Vtt

(A)

CACLMX

CACLMY

DM385, DM388

SPRS821D – MARCH 2013 – REVISED DECEMBER 2013

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It is very likely that the longest CK/ADDR_CTRL Manhattan distance will be for Address Input 8 (A8) on the DDR3

memories. CACLM is based on the longest Manhattan distance due to the device placement. Verify the net class that

satisfies this criteria and use as the baseline for CK/ADDR_CTRL skew matching and length control.

The length of shorter CK/ADDR_CTRL stubs as well as the length of the terminator stub are not included in this

length calculation. Non-included lengths are grayed out in the figure.

Assuming A8 is the longest, CALM = CACLMY + CACLMX + 300 mils.

The extra 300 mils allows for routing down lower than the DDR3 memories and returning up to reach A8.

Figure 8-81. CACLM for Two Address Loads on One Side of PCB

Table 8-70. CK and ADDR_CTRL Routing Specification(1)(2)

NO.

PARAMETER

MIN

TYP

MAX

UNIT

A1+A2 length

2500

mils

A1+A2 skew

mils

A3 length

660

mils

A3 skew(3)

mils

A3 skew(4)

125

mils

A4 length

660

mils

A4 skew

mils

AS length

100

mils

AS skew

100

mils

AS+/AS- length

mils

AS+/AS- skew

mils

AT length(5)

500

mils

AT skew(6)

100

mils

AT skew(7)

mils

CK/ADDR_CTRL nominal trace length(8)

CACLM-50

CACLM

CACLM+50

mils

(1)

The use of vias should be minimized.

(2)

Additional bypass capacitors are required when using the DVDD_DDR[0] plane as the reference plane to allow the return current to

jump between the DVDD_DDR[0] plane and the ground plane when the net class switches layers at a via.

(3)

Non-mirrored configuration (all DDR3 memories on same side of PCB).

(4)

Mirrored configuration (one DDR3 device on top of the board and one DDR3 device on the bottom).

(5)

While this length can be increased for convenience, its length should be minimized.

(6)

ADDR_CTRL net class only (not CK net class). Minimizing this skew is recommended, but not required.

(7)

CK net class only.

(8)

CACLM is the longest Manhattan distance of the CK and ADDR_CTRL net classes + 300 mils. For definition, see Section 8.13.3.16.1,

Figure 8-80, and Figure 8-81.

248

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