DM505LRBABF datasheet(263/295 Pages) TI2

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SPRS91v_PCB_DDR3_04

DDR3

Controller

Three Devices

263

DM505

www.ti.com

SPRS976E – NOVEMBER 2016 – REVISED MAY 2018

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Applications, Implementation, and Layout

Table 7-38. PCB Stackup Specifications

NO.

PARAMETER

MIN

TYP

MAX

UNIT

PS1

PCB routing/plane layers

PS2

Signal routing layers

PS3

Full ground reference layers under DDR3 routing region(1)

PS4

Full 1.5-V power reference layers under the DDR3 routing region(1)

PS5

Number of reference plane cuts allowed within DDR routing region(2)

PS6

Number of layers between DDR3 routing layer and reference plane(3)

PS7

PCB routing feature size

Mils

PS8

PCB trace width, w

Mils

PS9

Single-ended impedance, Zo

Ω

PS10

Impedance control(5)

Z-5

Z+5

Ω

(1) Ground reference layers are preferred over power reference layers. Be sure to include bypass caps to accommodate reference layer

return current as the trace routes switch routing layers.

(2) No traces should cross reference plane cuts within the DDR routing region. High-speed signal traces crossing reference plane cuts

create large return current paths which can lead to excessive crosstalk and EMI radiation.

(3) Reference planes are to be directly adjacent to the signal plane to minimize the size of the return current loop.

(4) An 18-mil pad assumes Via Channel is the most economical BGA escape. A 20-mil pad may be used if additional layers are available

for power routing. An 18-mil pad is required for minimum layer count escape.

(5) Z is the nominal singled-ended impedance selected for the PCB specified by PS9.

7.9.2.6

Placement

Figure 7-47 shows the required placement for the processor as well as the DDR3 devices. The

dimensions for this figure are defined in Table 7-39. The placement does not restrict the side of the PCB

on which the devices are mounted. The ultimate purpose of the placement is to limit the maximum trace

lengths and allow for proper routing space. For a 16-bit DDR memory system, the high-word DDR3

devices are omitted from the placement.

Figure 7-47. Placement Specifications

DM505LRBABF Datasheet(PDF) 263 Page - Texas Instruments

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