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2.2.5.2 Single Socket-370 Processor Capacitive Decoupling
A suggested decoupling capacitor placement for the Socket-370 CPU is shown in Figure 2-11. The high frequency decoupling
capacitors (0.1uF and 1uF) should be located as close to the power and ground pins of the Socket-370 as possible. One hundred
and twelve 56 ohm termination resistors are required for the GTL+ bus (HD[63:0], HA[31:3] and 19 host control signals) on the
motherboard. There are at least 28 R-packs (4 resistors for a discrete R-pack) for the VTT termination. It is recommended to
place one 1uF decoupling capacitor for each two R-packs. There are also four 1000uF capacitors for GTL+ termination voltage
(VTT) located at the four corners of the Socket-370 in Figure 2-11. Most of the high frequency decoupling capacitors are located
in Socket-370 cavity. The recommended distribution of these high frequency and bulk decoupling capacitors for various voltage
power pins is listed in Table 2-3.
Figure 2-11. Decoupling Capacitor Placement for Single Socket-370 Processor
Table 2-3. High Frequency and Bulk Decoupling Capacitor Distribution around Socket-370
Power Pin Name
VCORE x 59
(CPU Core Voltage)
VREF x 8
(GTL+ Reference Voltage)
VCC15 x 1
(GTL+ Termination Voltage)
VCCCMOS x 1
(CMOS Interface Voltage)
VCC25 x 1
Preliminary Revision 0.5, November 19, 1999
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Voltage Level
Decoupling & Bulk Capacitor
2.0V or
4.7uF x 10, 1uF x 23, 0.1uF x 21
1.55V (future)
1000uF x 6 (4 for switching regular) 3 at upper middle and 3 at lower middle
1.0V
0.1uF x 6
(2/3 VCC15)
1uF x 1, 0.1uF x 1
1.5V
1uF x 1
1000uF x 4
2.5V or
1uF x 1
1.5V(future)
2.5V
1uF x 1
19
Location
Socket-370 inner block
Socket-370 inner block
Around Socket-370
Around Socket-370
Four corners of the Socket-370
Around Socket-370
Around Socket-370
Motherboard Design Guidelines
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