Voltage Regulators for Next Generation Microprocessors

420 Pages·2011·12.44 MB·English

by  Toni López

Voltage Regulators for Next Generation
Microprocessors
.
Toni Lo´pez Reinhold Elferich Eduard Alarco´n
l l
Voltage Regulators for Next
Generation Microprocessors
ToniLo´pez ReinholdElferich
PhilipsResearch PhilipsResearch
Weisshausstrasse2 Weisshausstrasse2
D-52066Aachen D-52066Aachen
Germany Germany
[email protected] [email protected]
EduardAlarco´n
TechnicalUniversityofCatalunya
DepartmentofElectronicsEngineering
TelecomEngineeringOffice105
c/GranCapita`s/n
08034Barcelona
Spain
ISBN978-1-4419-7559-1 e-ISBN978-1-4419-7560-7
DOI10.1007/978-1-4419-7560-7
SpringerNewYorkDordrechtHeidelbergLondon
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Preface
With the rapid advances in computer processing speed and consequent increasing
demands in energy consumption of CPUs, soon it became obvious that break-
throughs may need to be realized to enable compliant power units featuring
compact sizeandhighefficiency.Itwas then,aroundyear2000,whenagroupof
scientistsledbyProf.Dr.ThomasDu¨rbaumdecidedtostartitallupatthePhilips
researchlabsfromAachen,Germany.
Inthepowerelectronicscommunity,researcherswerealreadywonderingabout
whatcouldbedonetodrivesuchstringentloads.TheCenterofPowerElectronics
Systems(CPES)fromtheVirginiaTechinstitute,amongothers,hadalreadystarted
exploringnumerousconvertertopologiesasalternativestothemostwidelyadopted
hard-switchingscheme:Thebuckconverter.
The strategy in Aachen was far more conservative and yet not less ambitious.
Thekeyquestiontostartupwithwas:WhatmakestheMOSFETssohot?Atthat
time,manyspecialistsbelievedthattheONstateresistanceandtheMillercapaci-
tancewerethemajorcausesoflossesintheconverter.AsMOSFETtechnologists
effusively exploited the simple and extensively used Q ·R expression as
GD DSon
baseline for their technology developments, soon it was realized that behind the
apparentsimplicityofthebuckconvertertherewerenumerouslyhidden,generally
unwantedelementsthatmadefastswitchingoperationafarmorecomplexcombi-
nationofdynamiceffectsthaninitiallyexpected.Theaddeddifficultywassuchthat
switching phenomena may only be accurately describable with an awfully large
nonlinearimpedancenetwork.“That’sfun!!”OrthatisatleastwhatIthoughtback
thenwhenIfirstglancedatafirstattempttomodeltheconverterwithmorethan30
lumpedelements:“Parasiticelementscomealwaysforfree,”Thomasusedtosay.
“Well...”Iusedtothink,“ifitwasso,MOSFETswouldbealotcheaper.”
The complexity of the equivalent network that accurately described switching
transientshadtobeimplementedinacircuitsimulator.TheAachenteamhadthus
thetasktobuildadedicatedmacroMOSFETmodelforSPICE.Combinedwithan
extensive device characterization for the calibration of the model parameters, the
numerical calculations should enlighten the foundations of switching phenomena,
vii
viii Preface
which will then lead the team to the right answer to the initially formulated
question. This answer would be of great value to Philips Semiconductors (now
NXPSemiconductors),astheycouldalreadyexperiencethattheirfigureofmerits
started to be highly inaccurate and even misleading. Therefore, collaborations
betweenthetwoorganizationsstarted.
Shortly after everything was in place and rolling, I joined the Aachen team,
formed by Reinhold Elferich, Dr. Tobias Tolle, Thomas, and myself. The team
from Philips Semiconductors was led by Dr. Phil Rutter, from Hazel Grove, UK.
Colleagues like Steven T. Peake and Nick Koper were crucial to provide us
with model data from device physics calculations and other relevant information
to investigate the performance benefits of solutions such as power multichip
modules, which were emerging at that time as potential alternatives to overcome
anumberoflimitationsofexistingdiscretesolutions.
Through this intensive communication the so-called virtual design loop con-
cept emerged as a methodology for Hazel Grove to receive direct feedback from
circuit simulations regarding the performance of their novel virtual MOSFET
structures, which they could refine accordingly before their actual technological
implementation.
Unfortunatelyforus,ThomasjoinedtheUniversityofErlangen(Germany)and
later, Tobias moved to Philips Lighting, leaving Reinhold and myself as the only
membersoftheAachenteam.
The disentanglement of Philips Semiconductors that gave birth to NXP Semi-
conductorchangedthecourseofeventsquiteconsiderably.Resultsweretransferred
to NXP so that Phil’s team could carry on with their relentless technology devel-
opments employing the new methods and modeling tools, whereas I continued a
parallelworkincollaborationwithProf.Dr.EduardAlarco´n,fromthePolytechnic
UniversityofCatalunya,Barcelona,Spain,whogavemeallthesupportIhaveever
neededtoturnthisindustriallyorientedprojectintoanacademicthesis.
As the reader will notice, this treatise goes beyond finding the answer to the
initialformulatedquestion.Essentialtomeetingthetargetrequirementshasbeenan
overview of all critical aspects of the converter by means of active simulations.
Thus,Chap.2throughChap.5extensivelyanalyzesanumberofcircuitanddevice
models mainly devoted to MOSFET switching analysis. Each modeling approach
isthoroughlydescribedinseparatechaptersintermsofimplementation,function-
ality,computationrequirements,andperformancepredictions.Thelatterareexten-
sivelysupportedwithexperimentaldata.
The potential use of every model will be highlighted in each corresponding
chapterbymeansofanalyzingparticularaspectsoftheconvertercircuit.Therefore,
in Chap. 2, an in-depth analysis of power MOSFETs’ switching behavior and
related loss mechanisms will be provided based on a MOSFET model for circuit
simulations. In Chap. 3, a piecewise linear model will be developed to study
switching phenomena at a fundamental level. Different case examples will be
presented to illustrate the need to move towards integrating power solutions. In
Chap. 4, a power loss model will be used to breakdown the losses of a multichip
module and quantify important loss mechanisms under fast switching operation.
Preface ix
Chap.5focusesondesignguidelinesforconverteroptimization.Relevantelements
of the converter will be considered, including the passive filter elements and the
gatedrivers.SpecialemphasiswillbegiventothedesignofthepowerMOSFETs
andtheselectionoftheswitchingfrequencyandnumberofphases.
Chap.6exploitsthedevelopedmodelstodeterminetheperformancelimitations
of the converter topology and proposes measures to enhance its performance.
Basedontheguidelines ofChap.5,thepowerdensityandefficiencylimitsofthe
converter based on present and future technologies will be identified. Finally,
roadmap targets and improvement options for next generation power solutions
willbepresentedanddiscussed.
ConclusionsandfutureworkwillbeexposedinChap.7.
Theappendixsectionsoffertechnicaldetailsthat,forthesakeofcompleteness,
allowthereadertodwellonsomeofthecentraldiscussionswithextensiveancillary
information.
Because this dissertation would not have been possible without them, thanks
gotoDr.PhilRutter,Prof.Dr.ThomasDuerbaum,andProf.Dr.EduardAlarco´n.
My thanks go as well with great appreciation to Reinhold Elferich, Dr. Tobias
Tolle, and Nick Koper for their incommensurable guidance. Special thanks go to
Steven T. Peak, Jim Parkin, Steven Hodgskiss, Victor Guijarro, and Mark Gadja
fromNXPSemiconductorsfortheirpricelesssupport.
Aachen,Germany ToniLo´pez
.