AM1808AZCED3 datasheet(114/264 Pages) TI

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AM1808

SPRS653A – FEBRUARY 2010 – REVISED APRIL 2010

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6.11.3.6 Bulk Bypass Capacitors

Bulk bypass capacitors are required for moderate speed bypassing of the DDR2/mDDR and other

circuitry. Table 6-29 contains the minimum numbers and capacitance required for the bulk bypass

capacitors. Note that this table only covers the bypass needs of the device and DDR2/mDDR interfaces.

Additional bulk bypass capacitance may be needed for other circuitry.

Table 6-29. Bulk Bypass Capacitors

No.

Parameter

Min

Max

Unit

Notes

DDR_DVDD18 Supply Bulk Bypass Capacitor Count

Devices

See Note (1)

DDR_DVDD18 Supply Bulk Bypass Total Capacitance

DDR#1 Bulk Bypass Capacitor Count

Devices

See Note (1)

DDR#1 Bulk Bypass Total Capacitance

DDR#2 Bulk Bypass Capacitor Count

Devices

See Notes (1), (2)

DDR#2 Bulk Bypass Total Capacitance

See Note (2)

(1)

These devices should be placed near the device they are bypassing, but preference should be given to the placement of the high-speed

(HS) bypass caps.

(2)

Only used on dual-memory systems

6.11.3.7 High-Speed Bypass Capacitors

High-speed (HS) bypass capacitors are critical for proper DDR2/mDDR interface operation. It is

particularly

important

minimize

the

parasitic

series

inductance

the

bypass

cap,

device/DDR2/mDDR power, and device/DDR2/mDDR ground connections. Table 6-30 contains the

specification for the HS bypass capacitors as well as for the power connections on the PCB.

Table 6-30. High-Speed Bypass Capacitors

No.

Parameter

Min

Max

Unit

Notes

HS Bypass Capacitor Package Size

0402

10 Mils

See Note (1)

Distance from HS bypass capacitor to device being bypassed

250

Mils

Number of connection vias for each HS bypass capacitor

Vias

See Note (2)

Trace length from bypass capacitor contact to connection via

Mils

Number of connection vias for each DDR2/mDDR device power or

Vias

ground balls

Trace length from DDR2/mDDR device power ball to connection via

Mils

DDR_DVDD18 Supply HS Bypass Capacitor Count

Devices

See Note (3)

DDR_DVDD18 Supply HS Bypass Capacitor Total Capacitance

0.6

DDR#1 HS Bypass Capacitor Count

Devices

See Note (3)

DDR#1 HS Bypass Capacitor Total Capacitance

0.4

DDR#2 HS Bypass Capacitor Count

Devices

See Notes (3), (4)

DDR#2 HS Bypass Capacitor Total Capacitance

0.4

See Note (4)

(1)

LxW, 10 mil units, i.e., a 0402 is a 40x20 mil surface mount capacitor

(2)

An additional HS bypass capacitor can share the connection vias only if it is mounted on the opposite side of the board.

(3)

These devices should be placed as close as possible to the device being bypassed.

(4)

Only used on dual-memory systems

114

Peripheral Information and Electrical Specifications

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