5V Dual Switch; Vtt; 165; Vddq - Intel 815EG Design Manual

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In addition to the power planes provided by the ATX power supply, an instantly available 815EG
universal platform (using Suspend-to-RAM) requires 6 power planes to be generated on the board.
The requirements for each power plane are documented in this section. In addition to on-board
voltage regulators, the CRB will have a 5V Dual Switch.
13.1.1

5V Dual Switch

This switch will power the 5V Dual plane from the 5 V core ATX supply during full-power
operation. During Suspend-to-RAM, the 5V Dual plane will be powered from the 5 V Standby
power supply. Note: the voltage on the 5V Dual plane is not 5 V! There is a resistive drop through
the 5V Dual Switch that must be considered. Therefore, no components should be connected
directly to the 5V Dual plane. On the CRB, the only devices connected to the 5V Dual plane are
voltage regulators (to regulate to lower voltages).
This switch is not required in an 815EG universal platform that does not support Suspend-to-RAM
(STR).
13.1.2

VTT

This power plane is used to power the AGTL/AGTL+ termination resistors. Refer to the latest
revisions of:
• Pentium III processor (CPUID=068xh) and Celeron processor (CPUID=068xh) datasheets
This regulator is required in ALL designs.
13.1.3 1.85 V
The 1.85 V plane powers the GMCH core and the ICH2 hub interface I/O buffers. This power
plane has a total power requirement of approximately 1.7A. The 1.85 V plane should be decoupled
with a 0.1 µF and a 0.01 µF chip capacitor at each corner of the GMCH, and with a single 1 µF
and 0.1 µF capacitor at the ICH2.
Note: This regulator is required in ALL designs.
13.1.4

VDDQ

The VDDQ plane is used to power the GMCH internal graphics component interface.
NOTE: AGP card functionality has been disabled in the 82815EG GMCH devices. However,
VDDQ voltage must be maintained in 82815EG designs even though the AGP card capability is
removed.
For the designer developing an 82815EG motherboard, there is no distinction between VCC and
VDDQ, as both are tied to the 3.3 V power plane on the motherboard.
For the consideration of component long-term reliability, the following power sequence is strongly
recommended while the internal graphics interface of the GMCH is running at 3.3 V. The power
sequence recommendations are:
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Intel 815EG Chipset Platform Design Guide
Power Delivery

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