TMS320C6748_1 Datasheet, PDF (111/254 Pages) Texas Instruments – Fixed/Floating-Point DSP

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TMS320C6748 Fixed/Floating-Point DSP
SPRS590A – JUNE 2009 – REVISED AUGUST 2009
6.11.3.6 Bulk Bypass Capacitors
Bulk bypass capacitors are required for moderate speed bypassing of the DDR2/mDDR and other
circuitry. Table 6-28 contains the minimum numbers and capacitance required for the bulk bypass
capacitors. Note that this table only covers the bypass needs of the DSP and DDR2/mDDR interfaces.
Additional bulk bypass capacitance may be needed for other circuitry.
Table 6-28. Bulk Bypass Capacitors
No. Parameter
1 DDR_DVDD18 Supply Bulk Bypass Capacitor Count
2 DDR_DVDD18 Supply Bulk Bypass Total Capacitance
3 DDR#1 Bulk Bypass Capacitor Count
4 DDR#1 Bulk Bypass Total Capacitance
5 DDR#2 Bulk Bypass Capacitor Count
6 DDR#2 Bulk Bypass Total Capacitance
Min Max Unit
Notes
3
Devices See Note ⁽¹⁾
30
µF
1
Devices See Note ⁽¹⁾
22
µF
1
Devices See Notes ⁽¹⁾, ⁽²⁾
22
µF
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 to minimize the parasitic series inductance of the HS bypass cap, DSP/DDR2/mDDR
power, and DSP/DDR2/mDDR ground connections. Table 6-29 contains the specification for the HS
bypass capacitors as well as for the power connections on the PCB.
Table 6-29. High-Speed Bypass Capacitors
No. Parameter
1 HS Bypass Capacitor Package Size
Min
Max
Unit
Notes
0402
10 Mils See Note ⁽¹⁾
2 Distance from HS bypass capacitor to device being bypassed
3 Number of connection vias for each HS bypass capacitor
250
Mils
2
Vias See Note ⁽²⁾
4 Trace length from bypass capacitor contact to connection via
1
30
Mils
5 Number of connection vias for each DDR2/mDDR device power or
ground balls
1
Vias
6 Trace length from DDR2/mDDR device power ball to connection via
7 DDR_DVDD18 Supply HS Bypass Capacitor Count
35
Mils
10
Devices See Note ⁽³⁾
8 DDR_DVDD18 Supply HS Bypass Capacitor Total Capacitance
0.6
9 DDR#1 HS Bypass Capacitor Count
8
µF
Devices See Note ⁽³⁾
10 DDR#1 HS Bypass Capacitor Total Capacitance
11 DDR#2 HS Bypass Capacitor Count
12 DDR#2 HS Bypass Capacitor Total Capacitance
0.4
µF
8
Devices See Notes ⁽³⁾, ⁽⁴⁾
0.4
µF
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
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