Design Guide
175
Platform Power Delivery Guidelines
12.2.9.2
Bulk Decoupling
lists the recommended bulk capacitance parameters for Intel Xeon processors. The
following recommendations indicate the decoupling suggested for each processor in the system.
Place some bulk decoupling on the baseboard as close to the processor socket as possible
(maximum of 0.5 inch away). The location of bulk capacitance is not as critical as the high-
frequency decoupling because more inductance is already expected for these components.
However, good placement of these components will affect the transient response of the system for
the better, as shown in simulation. Place the remaining bulk capacitors next to the voltage converter
module.
12.2.10
GTLREF[3:0]
GTLREF[3:0] are low current inputs (less than 15 µA each) to the differential receivers within each
of the components on the AGTL+ bus. Use a voltage divider to generate a GTLREF[3:0] of 2/3
VCC_CPU ± 2%.
R1 and R2 should be small enough values that the current drawn by the GTLREF inputs (IREF) is
negligible versus the current through R2 and R1.
shows GTLREF, where “n” is the
number of IREF inputs supplied by the divider.
The worst case GTLREF should be analyzed with IREF at the maximum and minimum values
determined for the number of loads being supplied. If the number of loads can change from model
to model because of upgrades, this should be taken into account as well. Analyze
with R1 and R2 at the extremes of their tolerance specifications.
Table 12-6. Processor Bulk Capacitance Recommendations
Design Type
Bulk Capacitance
Quantity
ESR
ESL
RMS Current
Rating
On-board Design
OS-CON, 560 µF
9
12 m
Ω
3.1 nH Max
5.04 Arms
Figure 12-13. GTLREF Divider
s
Vcc_CPU
R
2
R
1
GTLREF
I
S
I
REF
Equation 12-1. GTLREF
1
2
REF
2
CC
1
1
R
R
I
n
R
V
GTLREF
+
×
−
=
Содержание Xeon
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