Mch Power Sequencing Requirement; Filter Topology For Vccahi_1.2 (System Bus); Power Sequencing Requirement For Mch - Intel Xeon Design Manual

Platform Power Delivery Guidelines
Figure 12-18. Filter Topology for VCCAHI_1.2 (System Bus)
12.3.6

MCH Power Sequencing Requirement

The MCH has only one power sequencing requirement. The MCH requires that 1.2 V rises with or
before 2.5 V to avoid electrical overstress of oxide layers and possible component damage. This
means that at any point during system power up, the 2.5 V power plane voltage must not be higher
than the 1.2 V power plane voltage until the 1.2 V voltage is within 1.2 V regulation. This is
depicted in
exceed the 1.2 V plane's value.
Figure 12-19. Power Sequencing Requirement for MCH
NOTE: This graph does not represent specific values or requirements on data/time frames.
A possible solution to safeguard against 2.5 V coming up before 1.2 V, is to tie the power good
signal of the 1.2 V regulator to the output enable pin of the 2.5 V voltage regulator.
If the same voltage regulator is used to derive both 1.2 V and 2.5 V, then other logic must be used.
A solution is to use a comparator to 1.2 V, and connect the output of the comparator to the output
enable signal of the 2.5 V regulator.
180
VCC_CPU
1 Ω
100 nH
100 µF
Figure 12-19. Notice that at no point before 1.2 V is ramped does the 2.5 V plane
2.5
2.0
1.5
1.0
0.5
RLC Network
Within 1"
0.1 µF
Time (t)
Figure 12-20 shows this implementation.
Within 1"
of Ball
VCCACPU
MCH
Route to
ball U15
2.5V
1.2V
Design Guide