Platform Power Delivery Guidelines
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Intel
®
855PM Chipset Platform Design Guide
265
11.7. Decoupling
Recommendations
Intel recommends proper design and layout of the system board bulk and high frequency decoupling
capacitor solution to meet the transient tolerances for each component. To meet the component transient
load steps, it is necessary to properly place bulk and high frequency capacitors close to the component
power and ground pins.
11.7.1.
Processor Decoupling Guidelines
See Section 5.9.2 for details on recommended V
CC-CORE
decoupling solutions.
11.7.2.
Intel 855PM MCH Decoupling Guidelines
Table 82. Decoupling Requirements for the Intel 855PM MCH
Pin Decoupling
Requirements
Decoupling Type (Pin type)
Decoupling Placement
VCC_MCH
See Section 5.9.5
Decoupling Cap: See Table 22
Place near balls: See Figure 69
VCC1_5
See Section 7.3.4
Decoupling Cap: See Section
7.3.4
Place near balls: See Section
7.3.4
VCC1_8
(2) 0.1 µF
Decoupling Cap: See Section 8.5
Place near balls: See Section 8.5
VCCGA,
VCCHA
(2) 10 µF (2)
10 nF
Decoupling Cap: See Section 5.2
Place near balls: T13, T17; See
Section 5.2
VCCSM
See Section
11.5.1.1
Decoupling Cap: See Section
11.5.1.1
Place near balls: See Section
11.5.1
V
CCP
See Section 5.9.4
Decoupling Cap: See Table 21
Place near balls: See Figure 64 &
Figure 66
11.7.3.
Intel 82801DBM ICH4-M Decoupling Guidelines
The Intel 82801DBM ICH4-M is capable of generating large current swings when switching between
logic high and logic low. This condition could cause the component voltage rails to drop below
specified limits. To avoid this type of situation, ensure that the appropriate amount of bulk capacitance
is added in parallel to the voltage input pins. Intel recommends that the developer use the amount of
decoupling capacitors specified in
Table 83 to ensure the component maintains stable supply voltages. The capacitors should be placed as
close to the package as possible (100 mils nominal). Rotate caps that set over power planes so that the
loop inductance is minimized (see Figure 146). The basic theory for minimizing loop inductance is to
consider which voltage is on Layer 2 (power or ground) and spin the decoupling cap with the opposite
voltage towards the BGA (Ball Grid Array). This greatly minimizes the total loop inductance. Intel
recommends that for prototype board designs, the designer should include pads for extra power plane
decoupling caps.
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