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 • Placement• PCB Layer Stack• System Block Diagram• Power Topology

• RF matching network• DDR2• PCI-e• Ethernet• RGMII• Others

Placement Comment

? Switching regulator and PMU circuit should be on lower right side

 of MT7620A.

? Ethernet port should be on lower left side of MT7620A.

? DDR2 should be on left side of MT7620A.

? 3.3V to 1.8V LDO should be close to DDR2.

? RF circuit should be on the top of MT7620A.

? Xtal should be close to MT7620, and clock trace should have ground

 plane around to avoid interference, but far away from RF circuit as

 possible.

Power Consumption

MT7620A Main Power Pin and current

? RF part:

PA2_V33N each pin 190mA

PA1_V33A each pin 20mA

VX_LDO each pin 25mA

? DDR2 part: DDRIO_V12D total 30mA

DDRIO_V18D total 100mA

? EPHY part: EPHY_V12 total 58mA

EPHY_V33 total 116mA

Power layout Comment

Bypass cap placement priority

? Of course, we hope every power pin has its own bypass cap and

 put cap close with.

? If can’t, priority is as followed

RF Block:

a. Soc_1.5VD for RF LDO.

b. PA2_3.3V

c. PA1_3.3V

a. SOC_V1.2VD

b. 3.3VD

a. 1.8VD

b. SOC_V1.2VD

Ethernet Block:

DDR2 Block:

DDR2 layout Comment(Conti…)

Suggest routing

? Routing order: 1) Data, VREF, 2) Address/Command, 3) Control,

 4) Clocks, and 5) Power

? Referenced to the solid ground plane.

? Place the series at the line for group signals with a 0~33

? Layer transition should accompany GND via.

DQ trace should be shorter than 1600mil.

Reserve damping resistors and place these close to MT7620A

DDR trace length control : DQ<->DQS: +/-100mil

CLK<-> DQS: +/-500mil

CMD<-> CLK: +/-800mil

DDR2 layout Comment(Conti…)

? VREF should be wider and as short as possible, is isolated from

 noisy aggressor.

? Keep at least a 20–25 mil clearance from VREF and CLK to other

 traces. If possible, isolate VREF with adjacent ground traces.

? By using resistor divider network as VREF generator, make sure

 both resistors the same value and 1% tolerance.