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Intel
®
820E Chipset
R
Design Guide 187
Figure 102. 1.8 V and 2.5 V Power Sequencing (Schottky Diode)
1.8 V
2.5 V
diode_1.8V&2.5V
V
DDQ
The V
DDQ
plane is used to power the MCH AGP interface and the graphics component AGP interface.
Refer to the
AGP Interface Specification, Revision 2.0 (http://www.agpforum.org).
For long-term component reliability, the following power sequence is strongly recommended while the
AGP interface of the MCH is running at 3.3 V. If the AGP interface is running at 1.5 V, the following
power sequence recommendations no longer apply. The power sequence recommendations are as
follows:
1. During the power-up sequence, the 1.8 V must ramp up to 1.0 V
before the 3.3 V ramps up to
2.2 V.
2. During the power-down sequence, the 1.8 V
cannot ramp below 1.0 V before the 3.3 V ramps
below 2.2 V.
3. The same power sequence recommendation applies when entering and exiting the S3 state, because
MCH power is completely off during the S3 state.
System designers must keep this requirement in mind while designing the voltage regulators and
selecting the power supply. For further details regarding the voltage sequencing requirements, refer to the
latest revision of the
Intel
®
820 Chipset: Intel
®
82820 Memory Controller Hub (MCH) Datasheet
(http://developer.intel.com/design/chipsets/datashts/290630.htm?iid=PCG+820blue&).
Note: This regulator is required in all designs (unless the design does not support 1.5 V AGP, and therefore
does not support 4× AGP).
3.3VSB
The 3.3 V
SB
plane powers the I/O buffers in the resume well of the ICH2 and the PCI 3.3 V
AUX
suspend
power pins. The 3.3 V
AUX
requirement states that during suspend, the system must deliver 375 mA to
each
wake-enabled card and 20 mA to each non-wake-enabled card. During full-power operation, the
system must be able to supply 375 mA to
each card. Therefore, the total current requirement is as
follows:
• Full-power operation: 375 mA × number of PCI slots
• Suspend operation: (375 + 20) × (number of PCI slots – 1)
In addition to the PCI 3.3 V
AUX
, the ICH2 suspend well power requirements must be considered, as
shown in
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Note: This regulator is required in all designs.