Electronic Design

Microprocessor Power Management</A><BR><FONT CLASS=body11>Sponsored by: <A HREF="http://www.cdtechno-cps.com" TARGET=_blank CLASS=body11>CELESTICA POWER SYSTEMS</A></FONT><A>

Choosing The Right Voltage Regulator

Upgrading microprocessor performance requires packing more transistors into a chip, which necessitates operating at a lower voltage and higher current. To meet these power-oriented requirements, Intel developed voltage-regulator design guidelines for its Pentium microprocessor family.

Present VRM/VRD10.x guidelines describe a voltage-regulator model (VRM) and a voltage-regulator down (VRD) whose voltage-regulator components mount on the motherboard. Both employ a 6-bit "voltage identity" or VID code that controls its output voltage from 0.8375 to 1.6 V dc. Regardless of the approach, the six VID code pins on the VRM/VRD connect to the corresponding pins on the microprocessor. Internal coding within the microprocessor then controls its applied voltage.

VRM/VRD guidelines set the voltage tolerances of the initial dc output voltage set-point error, output ripple and noise, no-load offset centering error, current-sensing, droop errors, and dynamic load limits. Advanced Micro Devices (AMD) developed similar guidelines for its microprocessors, which operate at voltages different from those of Intel. Managing the power supplied to a microprocessor was relatively easy when the required current was 40 to 50 A at about 2 V, so most desktop computer manufacturers used the VRD technique. Now, some microprocessors operate at 1.2 V with 120 A continuously and 150 A on peaks, which could be difficult with a VRD approach.

In the future, microprocessor power management will become even more difficult. Projections in the International Technology Roadmap for Semiconductors (ITRS) published by the Semiconductor Industry Association (SIA) point to lower voltages and higher current by 2010. If these ITRS projections turn out to be true, microprocessors will operate at 0.6 V and 300 A with 15-GHz clock rates.

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