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3-Phase Synchronous PWM Controller IC Provides an

Integrated Solution for Intel VRM 9.0 Design Guidelines

Odile Ronat

International Rectifier

The fundamental reason for the rapid change and

growth

in

information

technology

power

requirements is the increase in volume of data

processed, stored, transmitted, and displayed. As

a result, power requirements have grown very

rapidly. To control the increase in power

dissipation,

operating

voltages

have

been

reduced. Power scales as the square of the

voltage: cut the voltage in half, and the power

dissipation is reduced to one fourth. As circuit

output voltages approach the one-volt mark,

operating currents are increasing exponentially.

Today, feeding this much “ultraclean” current at

these low voltages with tremendous transient

response capability is the key technology driver

of power management for IT.

CPUs

used

in

servers,

advance

desktop

computers and motherboards such as the Intel

Pentium™ 4 or Xeon™ or AMD K7™ typically

require currents up to 60A at output voltages

around 1V, with transient response in the order

of 50A/us. Designers prefer a multiphase DC-

DC converter topology to address the higher

current

requirements

and

faster

transient

response problem,

This

article

will

discuss

the

specific

requirements for DC-DC converters required to

power today’s GHz class CPUs, the benefits of

the multiphase topology, and an example of

implementation of Intel VRM 9.0 using an

integrated 3-phase synchronous PWM controller

IC.

An Overview of Intel VRM 9.0 Design

Guidelines

With today’s microprocessor voltage below 2V,

they cannot be powered directly out of the

conventional silver box that typically provides

5V and 12V. Located in proximity to the CPU,

the voltage regulator module (VRM) delivers

regulated, stepped down voltage to the CPU.

The Intel VRM 9.0 definition is specifically

intended to meet the needs of systems based on

the Intel ® Xeon™ and Pentium ® 4 processors.

Table 1 provides a summary of the output

requirements for VRM 9.0.

Table 1 - Summary of the VRM 9.0 output requirements (Source: Intel VRM9.0 DC-DC converter design guidelines.

Other

requirements

include

VID

voltage

identification and Power Good feedback. The

VRM must accept five lines to set the nominal

maximum voltage. Five processor package pins

will have a high-low pattern corresponding to

the voltage required by the individual processor.

The VRM should provide an open collector