5-4
Intel
®
Pentium
®
III Processor with 512KB L2 Cache Dual Processor Platform Design Guide
5.3.2
Multiple Voltages
The VRM 8.5 module or embedded voltage regulator, which provides the Vcc
CORE
supply to the Intel
®
Pentium
®
III Processor with 512KB L2 Cache, has the capability of supplying voltages from +1.05V to
+1.825V. The voltage regulator solutions designed to the VRM 8.5 DC-DC Converter Design Guidelines
can provide adequate power for all speed versions of Intel
®
Pentium
®
III Processors with 512KB L2
Cache.
Multiple voltages required for an Intel
®
Pentium
®
III Processor with 512KB L2 Cache dual processor
system are Vcc
CORE
, V
REF
, V
TT
, Vcc
CMOS1.5
, Vcc
CMOS1.8
, Vcc
CMOS2.0
, and V
SS
. Refer to the Intel
®
Pentium
®
III Processor with 512KB L2 Cache Datasheet for the pin location of these voltages.
5.3.3
Voltage Sequencing
When designing a system with multiple voltages, there is always the issue of ensuring that no damage
occurs to the system during voltage sequencing. Voltage sequencing is the timing relationship between
two or more voltages. Sequencing applies to the power voltage levels and the levels of certain other
crucial signals when the user turns on or off the power supply, or the system enters a failure condition.
Systems should be designed such that neither supply stays on for extended time while the other is off.
Excessive exposure to these conditions can compromise long-term component reliability. Please refer to
the Intel
®
Pentium
®
III Processor with 512KB L2 Cache Datasheet for the voltage sequencing
requirements.
5.4
Meeting Power Requirements
Intel recommends using VRM 8.5 compliant modules or embedded regulator designs for Intel
®
Pentium
®
III Processor with 512KB L2 Cache dual processor system board designs. The system board designer
should properly place high frequency and bulk decoupling capacitors as needed between the voltage
regulator and processor to ensure voltage fluctuations remain in specification.
Intel
®
Pentium
®
III Processor with 512KB L2 Cache dual processor power distribution designs require
trade-offs between power supply, distribution and decoupling technologies. This section discusses how
to do a step by step design of a system using the more accurate power distribution model shown in
Figure 5-3
.
5.4.1
Supplying Voltage
Local (point of load) regulation is recommended for the Intel
®
Pentium
®
III Processors with 512KB L2
Cache to satisfy their higher current requirements and to maintain power converter output voltage
tolerance. For example, a DC-to-DC converter, placed close to the load, converts a higher DC voltage to
a lower level using either a linear or switching regulator. Distributing lower current at a higher voltage to
the converter minimizes unwanted losses (I x R) and localizes losses to the planes between the
converter and the processor sockets.
It is recommended that voltage regulator solutions (VRD or VRM) employ differential remote sense (as
illustrated in
Figure 5-4
) to compensate for voltage drops between the regulators and the socket pins.
The sense lines should be terminated as close to the center of the socket as possible and should not
have an impedance greater than 1
Ω
.
