Intel Pentium 4 Processor in the 478-pin Package / Intel 850 Chipset Platform Family Design Guide

Power Distribution Guidelines
R
Intel
®
Pentium
®
4 Processor / Intel
®
850 Chipset Family Platform Design Guide 235
12.5 Intel
®
850 Chipset Power Sequencing Requirements
The Intel
®
850 chipset needs the following power supplies for operation – VCC1_8, VDDQ and
VTT.
To avoid forward-biasing the ESD protection-diodes from the IO to Core power supplies, it is
necessary that the VCC1_8 power supply ramp up ahead (See Figure 178) of the VDDQ and VTT
power supplies. For the same reason, it is necessary to have the VCC1_8 power supply ramp down
later than the VDDQ and VTT power supplies. If this cannot be guaranteed, it is important that the
VCC1_8 power supply lag (see Figure 179) the I/O supplies by no greater than 1.0 V. There are
no dependencies between VDDQ and VTT supplies.
Figure 178. Desired Mode of Power Sequencing
Time
Voltage
VDDQ/VTT
VCC1_8
Figure 179. Optional Mode of Power Sequencing
1.0V 1.0V
Time
Voltage
VDDQ/VTT
VCC1_8