Platform Power Delivery Guidelines
168
Design Guide
Single or Dual Processor Operation
Many OEMs require that a dual-processor VRD supplying an Intel processor’s common voltage
plane operate with either one or two processors installed on the board (i.e., the design must meet
the static and transient voltage characteristics of both the dual- and single-processor load lines). A
solution is to adjust the load line for the number of installed processors. OEMs that want jumper-
free systems can do this with logic that detects the presence of processors in each of the sockets,
and selects resistor combinations to produce the right slopes. For example: no processors (00) =
disable VRD; one processor (01 or 10) = single-processor load line; both processors (11) = dual
processor load line.
The theory of operation of the dual processor load line selection circuit is straightforward. If a
second processor (Processor 1) is not present, then the base of Q3 will be pulled high. This will
cause Q3’s collector to go to ground, turning off Q1 and Q2. The VCC_CPU voltage will then go
through R2 (droop resistor) to pin 7 (FB) of the HIP6311A controller. The offset voltage comes
from the +5 V source through R1 into pin 7 of the controller. R3 and R4 will have no effect.
If a second processor is present, then the base of Q3 will be pulled low and Q3’s collector will be
high, turning on Q1 and Q2. The droop resistor, R2, will now be paralleled by R4, providing the
droop required for a two-processor system. The offset resistor, R1, will be paralleled by R3
providing the offset for a two-processor system.
Figure 12-5. Example Load Line Selection Circuit
Processor 1
S KTOCC#
HIP6311A
7
R1
R3
R2
R4
R6
R5
392 K
Ω
340 K
Ω
2.61 K
Ω
1.96 K
Ω
10 K
Ω
10 K
Ω
Q 3
2N3904
BSS138
Q 2
VCC_3.3
+5V
+5V
VCC_CO RE
No CPU = HIG H
CPU = LOW
Summary of Contents for Xeon
Page 24: ...Introduction 24 Design Guide This page is intentionally left blank ...
Page 30: ...Component Quadrant Layout 30 Design Guide This page is intentionally left blank ...
Page 52: ...Platform Clock Routing Guidelines 52 Design Guide This page is intentionally left blank ...
Page 66: ...System Bus Routing Guidelines 66 Design Guide This page is intentionally left blank ...
Page 118: ...Intel 82870P2 P64H2 118 Design Guide This page is intentionally left blank ...
Page 146: ...I O Controller Hub 146 Design Guide This page is intentionally left blank ...
Page 148: ...Debug Port 148 Design Guide This page is intentionally left blank ...
Page 210: ...Schematic Checklist 210 Design Guide This page is intentionally left blank ...
Page 220: ...Layout Checklist 220 Design Guide This page is intentionally left blank ...
Page 222: ...Schematics 222 Design Guide This page is intentionally left blank ...