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Pentium® Processor Power Distribution Guidelines
Order Number: 245085-001
Information this document provided connection with Intel products. license, express implied, estoppel otherwise, intellectual property rights granted this document. Except provided Intel's Terms Conditions Sale such products, Intel assumes liability whatsoever, Intel disclaims express implied warranty, relating sale and/or Intel products including liability warranties relating fitness particular purpose, merchantability, infringement patent, copyright other intellectual property right. Intel products intended medical, life saving, life sustaining applications. Intel make changes specifications product descriptions time, without notice. Designers must rely absence characteristics features instructions marked "reserved" "undefined." Intel reserves these future definition shall have responsibility whatsoever conflicts incompatibilities arising from future changes them. Pentium® processor contain design defects errors known errata which cause product deviate from published specifications. Current characterized errata available request. Contact your local Intel sales office your distributor obtain latest specifications before placing your product rder. Copies documents which have ordering number referenced this document, other Intel literature obtained calling 1-800548-4725 visiting Intel's website http://www.intel.com.
Copyright Intel Corporation, 1999 *Third-party brands names property their respective owners.
Pentium® Processor Power Distribution Guidelines
Contents
Introduction
Terminology. References
Typical Power Distribution Pentium® Processor Power Requirements
Voltage Tolerance Multiple Voltages Voltage Sequencing 3.3.1 Non-AGTL+ Signals 3.3.2 AGTL+ Signals 3.3.3 Memory Side Signals 3.3.4 Side Signals 3.3.5 Clock Input Meeting Pentium® Processor Power Requirements Voltage Budgeting Supplying Power 4.2.1 Local DC-to-DC Converters Centralized Power Supply 4.2.2 Input Voltage 4.2.3 Linear Regulators Switching Regulators.17 Decoupling Technologies Transient Response.18 4.3.1 Bulk Capacitance 4.3.2 High Frequency Decoupling Power Planes Islands.24 4.4.1 Location High Frequency Decoupling 4.4.2 Location Bulk Decoupling.27 4.4.3 Impedance Emission Effects Power Islands Tolerance Reference Voltage.28 Generating Distributing Generating Distributing VREF 6.3.1 Distributing VREF VCC_L2.32 VCC_CORE 7.2.1 Main Power Supply 7.3.1 Termination Resistors VREF
AGTL+ Power Requirements.27
Meeting AGTL+ Power Requirements
Recommendations
Pentium® Processor Power Distribution Guidelines
Component Models
Measuring Transients. Existing Technology Pentium® Processor System Design
Solutions VCC_CORE Linear Regulators Termination Resistors Pentium® Processor Power Distribution Network Modeling.
10.0 11.0
Right Angle Connector Power Delivery Considerations
Figures
Ideal Pentium® Processor Power Supply Scheme. Physical Power Distribution Pentium® System Detailed Power Distribution Model Pentium® Processor Substrate SC242 Connector Power Pins, View (Through SC242 Connector) Voltage Sequencing Example Non-AGTL+ Diodes AGTL+ Diodes System Design Model Remote Sense Location Capacitance Power Model with DC-to-DC Converter Effect Transients Power Supply Cylindrical Capacitor. Capacitor Model Required Various Current Demands Capacitance Required 8.5A, Baseboard Layer Definition. Pentium® Processor VCC_CORE Voltage Island Pentium® Processor VCC_L2 Voltage Island Capacitor Layouts. Pentium Processor VTT/VREF Voltage Island Simple Circuit Generating VREF. Local Regulation VCC_CORE Power Delivery Model Transient Response Systems VCC_CORE Power Delivery Model Transient Response Systems VCC_L2 Power Delivery Model Transient Response Power Delivery Model Transient Response
Pentium® Processor Power Distribution Guidelines
Tables
Pentium® Processor Power Delivery Models Sample Frequency Budget Efficiency Linear Regulator Estimating Current.28 Voltage Identification Code Various Component Models used Intel (Not Vendor Specifications).36
Pentium® Processor Power Distribution Guidelines
Introduction
computer performance demands increase, new, higher-speed logic with increased density developed fulfill these needs. reduce their overall power dissipation, modern microprocessors being designed with lower voltage implementations. This turn requires power supplies provide lower voltages with higher current capability. Because this, processor power becoming significant portion system design, demands special attention. more than ever, power distribution requires careful design practices. Pentium processors have unique requirements voltages supplied them. Their implementation, called AGTL+, requires voltage supply own. most personal computer designs, power plane with high frequency bulk decoupling capacitors spread evenly across system board low-cost ensure sufficient power distribution. current differences between power state high power state increase, cost power distribution system becomes significant enough merit careful calculation. Centralized distribution power, example, longer most cost effective solution power distribution. Another side effect lowering voltages some components existence multiple voltages within system. basic Pentium processor-based system board there will AGTL+ termination, processor, CMOS non-AGTL+ signals, chipset cache, other components. possibility that these voltages "come before another must taken into account. This discussed Section 3.3.
Terminology
"Power-Good" "PWRGOOD" active high signal) indicates that supplies clocks within system stabilized. PWRGOOD should active some constant time after VCC_CORE stable should inactive time these voltages fail their specifications. time constant should such that, working system, clocks other supply levels have reached stable condition before PWRGOOD goes active. "VCC_CORE" processor core's VCC. VCC_CORE voltage level varies different Pentium processors. "VCC_L2", Pentium processor's cache supply voltage, always "AGTL+", "Host bus", "System bus." these references refer main processor uses communicate with chipset. AGTL+, host bus, system synonymous purposes this document. Pentium processor system operates same manner Pentium processor system bus. Pentium processor system uses variant GTL+ signaling technology called Assisted Gunning Transceiver Logic (AGTL+) signaling technology. AGTL+ buffers open-drain require pull-up resistors providing high logic level termination. processor AGTL+ output buffers differ from GTL+ buffers with addition active pMOS pull-up transistor "assist" pull-up resistors during first clock low-to-high voltage transition. Additionally, processor S.E.C.C. contains pull-up resistors provide termination each load."VTT" AGTL+ termination voltage Pentium processor always "S.E.C Cartridge S.E.C.C. "Single Edge Contact Cartridge processor packaging technology utilized Pentium Pentium processors. "242-Contact Slot connector", "SC242 connector", physical interconnect that S.E.C. cartridge plugs into, just Pentium processor utilizes interconnect called Socket
Pentium® Processor Power Distribution Guidelines
References
Copies documents which have ordering number referenced this document, other Intel literature obtained calling 1-800-548-4725 visiting Intel's website http://www.intel.com.
Title Intel Order Number 244452 243335 243337 243773 243735 243332 found www.teleport.com/~atx found www.teleport.com/~nlx
Pentium Processor datasheet Pentium Processor MHz, MHz, datasheet Pentium Processor MHz, datasheet DC-DC Converter Design Guidelines AGTL+ Layout Guidelines Pentium® Processor Intel® 440BX AGPset Slot Processor Power Distribution Guidelines Intel Power Supply Design Guide Power Supply Recommendations
Typical Power Distribution
Power distribution generally thought getting power parts that need Occasionally, digital designers begin assuming that ideal supply will provided, plan their schematics with little thought power distribution until end. printed circuit board (PCB) designers attempt create ideal supply with power planes using large width traces distribute power. High frequency noise created when logic gates switch controlled with high frequency ceramic capacitors, which turn recharged from bulk capacitors (such tantalum capacitors). Various `rule thumb' methods exist determining amount each type capacitance that required. Pentium processor designs, system designer needs reach beyond rule thumb architect power distribution system with specifications Pentium processor mind. Figure shows ideal power model. However, real SC242 connector system, power distribution scheme typically appears Figure This system physical components such cables, connectors, PCB, processor package. this figure, recommended solution involving local voltage regulator modules.
Figure Ideal Pentium® Processor Power Supply Scheme
Processor
Pentium® Processor Power Distribution Guidelines
completely model this system, must include inductance resistance which exists cables, connectors, PCB, pins body components such resistors capacitors edge fingers contacts processor voltage regulator. more detailed model showing these effects shown Figure past, voltage drops inductance Ldi/ resistance have been nearly negligible relative tolerance components most systems. This caused creation simple rules decoupling. example, with current tolerance could easily ignore effects resistance distribution path. However, this drop equal tolerance. Similarly, inductance typically ignored power distribution system, unless current transients A/ns exist, they when using Pentium processors. Ldi/dt drop this case also equal Figure Physical Power Distribution Pentium System
Local Voltage Regulation
A6850-01
Figure Detailed Power Distribution Model
Power Supply CABLE
CABLE
Voltage Regulator
CONN CBULK CONN
BOARD BOARD
BOARD
Processor
CABLE
CABLE
CONN
CONN
BOARD
VCC_CORE requires switching regulator. VCC_L2 each more cost-effective linear converter.
Table
Pentium® Processor Power Delivery Models
Supply VCC_CORE VCC_L2 Regulator Capacitance 6000 3000 Regulator Inductance Regulator Resistance Motherboard Inductance 0.35 Motherboard Resistance 0.15
Pentium® Processor Power Distribution Guidelines
Section 10.0 includes power distribution network models VCC_CORE, VCC_L2, that applicable Pentium Pentium processor S.E.C.C. designs. Table contains summary those models. high value Pentium processor's current high rate change current must both taken into account successful design. Section describes power requirements Pentium processor. Section discusses meeting these power requirements.
Pentium® Processor Power Requirements
This section describes issues related supplying power Pentium processor using approximate values from processor specifications. However, please review appropriate datasheets that referenced Section 1.2, actual specifications. Pentium processor currently operates Pentium processor operates These supply voltages compare with Pentium Pro, Pentium processor, previous Intel processors. Pentium Pentium processors require approximately three times average current Pentium processor. VCC_CORE maximum current requirements range from nearly addition, these processors shut unused units conserve power, include features such Stop Clock AutoHALT, which create load-change transients high microsecond VCC_CORE. this document, load-change transient change from current requirement (averaged over many clocks) another. Future Pentium processors require higher current different voltages processor. System developers must terminate AGTL+ each voltage source called VTT. nominally with recommended tolerance three percent during steady state operations. This implementation allows loads eight loads MHz. While support higher device loading, SC242 connector implementation limited three loads MHz. Just processor start stop executing within clock cycles, usage will follow. following sections discuss each these concepts. Section Section discuss AGTL+ power requirements.
Voltage Tolerance
ease measurement VCC_CORE supply, Intel specifies tolerances either side SC242 connector; i.e., either input (motherboard) side SC242 connector processor's edge fingers. specific tolerances, review appropriate datasheets. Voltage tolerances detailed Pentium Processor datasheet, Pentium Processor MHz, MHz, datasheet, Pentium Processor MHz, datasheet. Failure meet these specifications results transistors slowing down meeting timing specifications. meeting specifications high induce electromigration, causing damage reducing life processor.
Pentium® Processor Power Distribution Guidelines
Multiple Voltages
While current Pentium processor core runs cache runs Future Pentium processors will different voltages. Reference Table details.
Figure Pentium® Processor Substrate
Processor Core Cache
VCC_CORE VCC_L2
A6852-01
SC242 connector pinout supports cache including cache support pins package. These pins called VCC_L2, while primary voltage supplied VCC_CORE pins. Figure location these pins. Pentium processor with discrete cache requires well decoupled supply connected VCC_L2 pins. Intel expects future cache current requirements exceed maximum average current (over many cycles) maximum power Pentium processor specified maximum power substrate, maximum current specification each voltage source. This fact that components maximum power simultaneously. system designer planning upgrade potential should also aware that future devices beyond current Pentium Pentium processors will require VCC_CORE other than support this level upgrade potential, power source main processor supply should designed with ability easily configured. Intel recommends using processor's Voltage (VID) pins with resistor tree digital-to-analog converter (DAC). voltage scheme described Pentium Processor datasheet well DC-DC Converter Design Guidelines. Intel worked with power supply vendors create replaceable voltage regulators which support voltage selection. Please your local field applications engineer assistance. AGTL+ also requires another voltage called (1.5 Section discusses this voltage further detail.
Voltage Sequencing
When designing system with multiple voltages, there always issue ensuring that damage occurs system during voltage sequencing. Voltage sequencing timing relationship between more voltages, such AGTL+ signals VCC_CORE. Sequencing applies when user turns power supply, system enters failure condition. Sequencing applies power voltage levels levels certain other crucial signals.
Pentium® Processor Power Distribution Guidelines
Figure SC242 Connector Power Pins, View (Through SC242 Connector)
VCC_VTT VCC_CORE VCC_L2 VCC5 Other
A121
B121
Figure shows example power voltage sequencing. Here voltage levels shown trade places with each other. During power voltage differential between greater than that nominal levels. During power-off, voltage input actually higher than voltage input some period time. Intel designed Pentium processors, AGTL+ bus, Intel's chipsets such that additional circuitry required power system ensure order voltage sequencing. However, systems should designed such that neither supply stays permanently while other off. Excessive exposure these conditions compromise long term component reliability. System designers need aware motherboard devices which sensitive voltage sequencing conditions. further information, Intel Power Supply Design Guide http://www.teleport.com/~atx/ Power Supply Recommendations http://www.teleport.com/~nlx.
Pentium® Processor Power Distribution Guidelines
Figure Voltage Sequencing Example
rising first, falling first ANom
BNom Volts Rises later, falls later ANom-BNom Time
following discussion simplified assuming worst case, which voltage while other off. Figure Figure highly simplified models buffers that show protection diodes. This model provided discussion purposes only meant imply implementation scheme. Figure Non-AGTL+ Diodes
VCC_CORE
Package Boundary
Diodes
Lpin
Figure AGTL+ Diodes
VCC_CORE
Diode Package Boundary
Driver
Pentium® Processor Power Distribution Guidelines
3.3.1
Non-AGTL+ Signals
non-AGTL+ buffers open drain. When VCC_CORE supply non-AGTL+ supply (2.5 off, protection diodes buffers reverse biased power supplied signal lines. processor sees RESET#, outputs switch high inactive state contention after comes avoided. supply while VCC_CORE supply off, supply delivers current Pentium processor core through string three protection diodes connecting pads VCC_CORE. pull-up used high level signals, then ohms will allow maximum only current supplied core cell. inputs driven CMOS output, then current from output should limited maximum output current Pentium processor pin.
3.3.2
AGTL+ Signals
AGTL+ outputs also open drain. When VCC_CORE supply off, inputs appear there will current flowing AGTL+ bus. VCC_CORE off, AGTL+ attempts power core through protection diode. resulting VCC_CORE level will enough that significant current will consumed core. Note: Every device must have power AGTL+ operate properly.
3.3.3
Memory Side Signals
Intel's chipset's tolerant signals internally buffered similar manner. When using DRAM there memory side sequencing issues. When supply DRAM memory controller supply off, lines float. This could cause DRAM drive signals component that voltage applied. system should provide weak pull-ups lines prevent DRAM devices from driving inputs when there power memory controller. providing memory controller with PWRGOOD signal, will drive lines DRAM inactive, reset data buffers soon receives This holds DRAM outputs keeps chipset buffer components reset during period power supply stabilization. This includes poor that would prevent AGTL+ RESET# signal from being created correctly. This action protects these devices from producing contention between themselves.
3.3.4
Side Signals
PCIRST# tells devices remain tri-state condition. controller holds this signal active when controller receives power PWR_OK signal inactive. controller also tri-states outputs during this time. addition, inputs input their protection. This eliminates issue with turning diodes.
3.3.5
Clock Input
clock input frequency must never exceed intended final value while PWRGOOD signal processor active. (See terminology Section 1.1)
Pentium® Processor Power Distribution Guidelines
PWRGOOD should inactive anytime that VCC_CORE, VCC_L2 invalid. This accomplished logically OR-ing `power good' signal from supplies, connecting this output chipset Pentium processor's PWRGOOD input reset generation. this case, `power good' signal from each supply that indicates stable voltage levels that within tolerance.)
Meeting Pentium® Processor Power Requirements
Pentium processor power supply design requires trade-offs between power supply, distribution decoupling technologies. This section discusses step step design system using more accurate power distribution model shown Figure
Voltage Budgeting
Before beginning design power distribution system must have idea budget tolerance specifications each components involved. This provides target each component helps reduce iterations reach solution. high frequency decoupling found Pentium processor eliminates need calculate high frequency budget.
Table
Sample Frequency Budget
Component Regulator Point Tolerance Bulk Capacitance ESR/ Capacitance Resistive Losses Board Ripple, Noise SC242 Connector Total Budget (mV) -125
Table provides estimation effects factors that system designers need consider when calculating frequency voltage budget.
Supplying Power
power distribution system starts with source power, power supply. central power supply unit create required voltages. Another option, local regulation, create voltages closer load. section below discusses tradeoffs involved. higher current requirements order maintain power supply tolerance, Pentium processor requires local regulation. loss occurs over power distribution system resistance such things cables, power planes, connectors. Local regulation provides most effective means overcome these losses.
Pentium® Processor Power Distribution Guidelines
formula represents this loss. Where voltage loss, current effective resistance distribution system. system with consistent current demand, setting voltage slightly higher than nominal value overcomes resistance distribution system. This ensures that voltage farthest reaches system remains within specification. However, systems where current change significantly between high state (i.e. high), changes significantly well. formula represents this change voltage. tighter tolerance specification Pentium processors make this loss significant. Intel recommends local regulation (the supply regulator near load) create voltage needed. example, local DC-to-DC converter, placed close load, converts higher voltage lower level using either linear switching regulator. Distributing lower current higher voltage converter minimizes unwanted losses (Power companies this same method high tension lines distribute electricity from generating source local residential use.) More importantly however, discrete regulator regulates voltage locally which minimizes line losses eliminating RCABLE reducing RBOARD processor voltage. Power supplies with remote sense work local regulation appropriate. power supply typically regulates voltage terminals before cabling board. Again, changing distribution losses based current demand make difficult hold tight tolerance load. remote sense, shown Figure solve this problem running separate connection from near load feedback loop power supply. feedback loop very current draw microamp range) does suffer from line losses described above. This allows supply regulate output based voltage level load that affected line losses. Remote-sense supplies suffer from added inductance cabling power supply noise induced remote sense feedback signal. Section explains this issue. system designer must also deal with finding representative load point that applies processors multi-processor system. Figure System Design Model
LCable RCable Power Supply
LBoard RBoard
Processor
CBulk
LCable RCable
LBoard RBoard
Figure Remote Sense
Amps (Large Power Source µAmps (Small Load
Pentium® Processor Power Distribution Guidelines
Either method regulation easily maintain accuracy, plus small ripple noise budget, under stable load. However, further demands Pentium processor abilities remote-sense supply. large current transients Pentium processor means that system designer must exercise extreme care eliminate noise coupling ringing when using remote sense feedback.
4.2.1
Local DC-to-DC Converters Centralized Power Supply
Most desktop computers today utilize self-contained multiple output power supply. This convenient cost effective strategy isolates issues power generation from system designer allows creation large reusable sub-system. However, lower operating voltages increased transient response make long distribution schemes self-contained supplies less suitable resistance inductance distribution scheme. distributed local DC-to-DC converters provides another alternative. Distributed local DC-to-DC converters improve upgrade potential. Sockets allow these converters added replaced required. Furthermore, self-adjusting regulators meet varying needs processor socket. While decision lies hands system designer, Intel recommends local regulators. Converter sockets meeting specifications DC-DC Converter Design Guidelines, future design guides, then installed each empty Pentium processor socket provide inexpensive upgrade strategy. socketed regulator regulator with selected output levels power Pentium processors.
4.2.2
Input Voltage
Pentium processor voltage created directly from line voltage from voltage central power supply. Creating voltage from voltage generally easier than converting from level another. DC-to-DC voltage converter must first chop voltage order create alternating voltage before converter step that voltage down. Typically however, power supplies today provide voltage taps system. Creating additional voltage from line voltage requires addition extra winding line transformer. This incurs additional costs suffers from issues distribution explained next sections. Changing output voltage this system requires changing transformer, which makes design less versatile. Creating additional voltage from existing voltage requires DC-to-DC converter. These converters work well systems they work existing taps typical power supplies, manufactured high volumes. System designers place DC-to-DC converters near Pentium processor (thus reducing distribution loss) design them into existing power supply case. They also design DC-to-DC converters have selectable output voltages, well.
4.2.3
Linear Regulators Switching Regulators
linear regulator drops variable voltage across itself order maintain output voltage within tolerance regardless load changes (within specifications). their simplicity, linear regulators respond load changes fairly quickly (about response time). linear regulator's efficiency drops input voltage output voltage become farther separated evidenced Equation
Pentium® Processor Power Distribution Guidelines
Equation Loss Within Linear Regulator
PLOSS (VIN-VOUT)
older linear regulator designs require minimum drop from input output about diode drop (0.5 making impossible have small changes from VOUT. Many linear designs today utilize dropout controllers coupled with FETs which require only FETRDS (Resistance Drain-to-Source) input output drop. formula efficiency VOUT/VIN approximates efficiency linear regulator. Table illustrates significant power loss poor efficiency linear regulator fixed output current amps. Table Efficiency Linear Regulator
VOUT Efficiency with Power Loss Amps
Linear regulators tend have faster reaction times than switching regulators. However, high power loss linear regulator, designers should consider switching regulators high output current ratings required Pentium processors. switching regulator achieve efficiency switching regulator first chops input voltage make AC-like. faster switches chops, faster converter's reaction time. faster reaction time reduces capacitance requirements. switching regulators operate switching rate, while high devices start MHz.
Decoupling Technologies Transient Response
shown earlier, inductance also issue distribution power. inductance system cables power planes further slows power supply's ability respond quickly current transient. Decoupling power plane broken into several independent parts. Figure shows each locations where capacitance could theoretically applied. closer load capacitor placed, more inductance that bypassed. bypassing inductance leads, power planes etc., less capacitance required. However, closer load there less room capacitance. Therefore trade-offs must made. Typically digital component causes switching transients. These sharp surges current occur each clock edge taper cycle. Intel designed Pentium processor such that manages highest frequency components current transients. Intel accomplished this adding capacitance S.E.C. cartridge well directly (CDIE). lower SC242 connector substrate inductance CONN LSUB) well board inductance
Pentium® Processor Power Distribution Guidelines
(LBOARD), Pentium processor core designed with approximately ground pins power pins. These processor design considerations reduce current slew rate order 20A/ (30A/µs Pentium processor). Note: voltage regulator designer will need determine they intend support Pentium Pentium III, both processors voltage, current di/dt requirements vary these processor families. Pentium processors require external high frequency capacitance, since sufficient lower di/dt 20A/µs. Note that 20A/µs only processor VCC_CORE. VCC_L2 VTT/ VREF (AGTL+) have different maximum di/dt (please refer datasheet specifics). Larger bulk storage (CBULK), such electrolytic capacitors, supply current during longer lasting changes current demand component, such coming idle condition. Similarly, they storage well current when entering idle condition from running condition. Figure Location Capacitance Power Model with DC-to-DC Converter
Cartridge
LBOARD LCONN DC-to-DC Converter CBULK LBOARD LCONN LSUB CDIE LSUB
this power bypassing required relatively slow speed which power supply DC-to-DC converter react. typical voltage converter reaction time order while processor's current transients order Bulk capacitance supplies energy from time high frequency decoupling capacitors drained until power supply react demand. More correctly, bulk capacitors system slow transient requirement seen power source rate that able supply, while high frequency capacitors slow transient requirement seen bulk capacitors rate that they supply. Figure shows poorly controlled supply versus well-controlled supply during increase current demand. Notice poorly controlled supply dips below allowed tolerance specification. similar situation exists current demand decreases. load-change transient occurs when coming entering power mode. Pentium processor this load-change transient order 15.3 more. These only quick changes current demand, long lasting average current requirements. This occurs when STPCLK# asserted de-asserted during AutoHALT. processor general goes from Stop-Clock high power state automatically. AutoHALT power state that processor enters when HALT op-code executed. Note that even during normal operation current demand still change much more activity levels change within processor component. Maintaining voltage tolerance, during these changes current, requires high-density bulk capacitors with Effective Series Resistance (ESR). thorough analysis when choosing these components.
Pentium® Processor Power Distribution Guidelines
4.3.1
Bulk Capacitance
understand just adding more capacitance always effective, must consider capacitance being added. This inherent resistance capacitor plate material. understand where comes from, recognize capacitor, analyze cylindrical capacitor. unrolling metal capacitor appears sheet. This sheet some linear resistance /inch. longer sheet (bigger diameter capacitor) increases ESR. wider sheet (taller capacitor) decreases ESR.
Figure Effect Transients Power Supply
3.10 3.05 3.00 2.95 2.90 2.85 2.80
Current Transients
Well Controlled Supply
Voltage (Volts)
Poorly Controlled Supply
Time (ns)
Figure Cylindrical Capacitor
Length Width
Another effect fairly high inductance bulk capacitors. These elements modeled shown Figure Figure Capacitor Model
Current
Pentium® Processor Power Distribution Guidelines
Overcoming discussed here while assuming that inductance effect will addressed high frequency decoupling capacitors discussed Section 4.3.2. Figure shows relationship between current delivered (with budget) capacitors. Even with infinite capacitance, drops full budget shown Equation Figure Required Various Current Demands
required ohms
0.030 0.025 0.020 0.015 0.010 0.005 0.000 2.000 4.000 6.000 8.000 10.000
Amps
Equation Allowed Budget
Another useful formula estimating amount bulk capacitance required shown Equation This ignores component furnishes amount capacitance that would required from ideal component. Equation Capacitance Ideal Capacitor
represents current that bulk capacitance must able deliver source. This equal difference between high current states since power supply will initially continue supply same current that been prior load change. allowable voltage change budgeted bulk capacitive (discharge) over period reaction time power source duration which capacitors must supply current. Assuming some representative numbers capacitance required shown Equation Equation Capacitance Needed Ohms
4250 0.060V
Combining above formulas remove resistive drop from budget bulk capacitance gives Equation
Pentium® Processor Power Distribution Guidelines
Equation Capacitance
This equation leads capacitance graph shown Figure when assumed assumed 8.5A, reaction time power source shaded area graph covers capacitance types that insufficient this application. Again this provides figure that used feel type capacitors required. example, satisfy this equation could twelve 1000 capacitors each parallel resistance capacitors would parallel capacitance would 12,000 which falls white zone graph Figure Figure Capacitance Required 8.5A,
30000
Capacitance (µF)
25000 20000 15000 10000 5000 0.000 0.001 0.002 0.003 0.004 0.005 0.006
This fairly conservative analysis. Using reaction time power source assumes that power source does compensate change current demand until passed, then immediately capable delivering that demand. Also, unnecessarily conservative assume that drop full drop whole period which capacitor discharges. analyze power distribution system more detail requires running simulation from power source model Pentium processor power model, including board, cable, capacitor effects. Section more information component models Section 11.0 Pentium processor power model.
4.3.2
High Frequency Decoupling
Pentium processors contain capacitors necessary high frequency decoupling properly designed system. This section discusses high frequency decoupling background purposes only. recommended that many high frequency capacitors sites possible placed close SC242 connector. Since bulk storage only contains effective series resistance, also fairly high inductance, these capacitors need assisted other capacitors that have lower inductance (but typically less capacitance). These high frequency capacitors control switching transients hold-over power planes during average load change until higher inductance capacitors react. 1206 surface mount package fairly inductance package, actually lower than inductance 0603 package geometry board interconnects. even lower inductance 0612 package since board interconnect area gets even larger. 0612 same size 1206 pads along long edge. cost these significantly higher however complexity mass producing them. 1206 package capacitors other hand readily available lower cost.
Pentium® Processor Power Distribution Guidelines
difficulty simulating with high frequency capacitors however, that vendors readily offer specification inductance their parts. Section some measured values from capacitors that Intel investigated which should verified against vendors' parts that will actually used design. After calculating number capacitors required, look impact that averaging tolerances over many measured components design design appropriately with additional components. Since capacitor inductance package related, choose largest value available package that been chosen. highest capacitance obtainable will most beneficial design since amount capacitance behind this inductance still critical. This simple inductance useful example estimating number high frequency capacitors required: Equation Simple Inductance
voltage drop that will seen inductance. di/dt value expressed inductance series combination via, trace, high frequency capacitors parallel. Section ideas reducing trace inductance. Once allowable inductance budgeted voltage drop (due high frequency transitions) calculated, number capacitors required estimated Equation Number Capacitors Required
where inductance single capacitor inductance required that calculated above. example, meet A/ns di/dt produce more than noise high frequency capacitor inductance (1.9 from Table would simply plug into Equation Equation Equation Inductance Allowed
0.060V
Equation Number Capacitors
10capacitors
above analysis also include resistance high frequency capacitors.
More capacitors will actually required achieve necessary capacitance prior voltage regulator module limited space within 1206 package. number capacitors required Pentium processor therefore "capacitance dependent".
Pentium® Processor Power Distribution Guidelines
While above calculation provides theoretical number capacitors required meet di/dt requirement, high frequency noise persist. More capacitors necessary control noise from other sources. However, mixing additional values design create higher resonance points should useful since capacitors described (1206 package) have very high resonant frequencies already. This shown using values from Table Equation Equation Resonant Frequency
7.3MHz 0.47
Note that 1206 capacitors will have basically same inductance value that smaller components actually have more inductance. Also, inductance vias larger contributors cause resonance more like MHz. Note that many packaging technologies available that 1206 capacitors just example. Check with capacitor vendors optimal designs.
Power Planes Islands
imperfections power planes themselves have been ignored. These also introduce unwanted resistance inductance into power distribution system. complex model Figure refers these imperfections RBOARD LBOARD. Figure illustrates Intel's recommendation layers four layer Pentium processor baseboard. Route VCC_CORE VCC_L2 layer.
Figure Baseboard Layer Definition
Signal Signal
A6847-01
Power should definitely distributed plane. This plane constructed island layer used other signals, supply plane with other power islands, dedicated layer PCB. Processor power should never distributed traces alone. Figure Figure examples voltage islands. fact that Pentium processor voltage unique most system designs, voltage island, islands, will probably most cost effective means distributing power processors. This island should continuous from source power load. should also completely surround pins source pins load.
Pentium® Processor Power Distribution Guidelines
Figure Pentium® Processor VCC_CORE Voltage Island
Pentium® Processor Power Distribution Guidelines
Figure Pentium® Processor VCC_L2 Voltage Island
4.4.1
Location High Frequency Decoupling
Pentium processor contains high frequency decoupling required properly designed system. Where needed, high frequency decoupling should placed close power pins load physically possible. both sides board necessary placing components order achieve optimum proximity power pins. This vital inductance board's metal plane layers could cancel usefulness these inductance components. Another method lower inductance that should considered shorten path from capacitor pads pins that decoupling. possible, place vias connecting planes within capacitor. this possible, keep traces short feasible., place them within outline capacitor order minimize loop inductance. Possibly both ends capacitor connected directly processor without
Pentium® Processor Power Distribution Guidelines
via. Even simulation results look good, these practical suggestions used create even better decoupling situation where they applied layout. Figure illustrates these concepts.
4.4.2
Location Bulk Decoupling
location bulk capacitance critical since more inductance already expected these components. However, knowing their location inductance values involved will useful simulation. this example bulk capacitance voltage converter module electrically behind inductance converter pins. This Intel's recommended solution.
4.4.3
Impedance Emission Effects Power Islands
There impedance consequences signals that cross over under edges power island that exists another layer. While neither these necessary most designs, there reasonable options consider which protect system from these consequences. Pentium processor power islands isolated from signals solid power plane layers such ground layer. This forces particular stack-up model. Another option that helps, does completely eliminate radiation effects, decouple edges processor power islands ground regular intervals about using good high frequency decoupling capacitors. This requires more components does require particular board stack-up. either event, controlling emissions, planes islands should well decoupled. amount decoupling required controlling emission will determined exact board layout, chassis design. should plan ahead allowing additional pads capacitors added case they discovered necessary during initial testing.
AGTL+ Power Requirements
Pentium processor varies from Pentium processor output buffer implementation. buffers that drive system signals Pentium processor actively driven VCC_CORE clock cycle after high transition improve rise times. These signals should still considered open-drain require termination supply that provides high signal level. Because this specification different from standard GTL+ specification, referred AGTL+ this other documentation. AGTL+ logic GTL+ logic compatible with each other both used same system bus. more information AGTL+ routing, AP-906, AGTL+ Layout Guidelines Pentium® Processor Intel® 440BX AGPset (Order Number 245086). Intel recommends terminating both ends AGTL+ voltage level called (1.5 supplies current when output drivers turn There approximately AGTL+ lines Pentium processor system design. AGTL+ power requirements present different situation than creating power Pentium processors. While AGTL+ requires less current than processor, still tight tolerance specification. Just processor start stop executing within clock cycles, usage follows, which turns causes load changes transients power supply. must available termination resistors both ends bus. This accomplished having sources distributing VTT.
Pentium® Processor Power Distribution Guidelines
AGTL+ buffer sinks maximum When considering duty cycle signals, AGTL+ signals draw maximum about 5.38 100% utilization bus. Table illustrates AGTL+ current draw using relatively conservative duty cycles. Utilization bus, value AGTL+ termination resistors, chipset functionality motherboard design limit actual current draw. Power supply designers need take these benefits into account well. Figure Capacitor Layouts
Good Good Very Good Excellent
Vias
Pads
Capacitors
Table
Estimating Current
Signal Group Data Address Parity Arbitration Request Error Response Other Total Quantity Signals Duty Cycle Average Current 3.24 1.06 0.32 0.21 0.05 0.09 0.41 5.38
Tolerance
processor edge fingers must held ±9%. recommended that regulator that maintain current draw used order guarantee over conditions. again important note that this tolerance specification covers voltage anomalies including power supply ripple, power supply tolerance, current transient response, noise. meeting specification high will change rise fall time specifications. Failure meet this specification will also result reduced margins AGTL+ buffers thus making more difficult meet timing specifications.
Reference Voltage
AGTL+ requires Voltage Reference called VREF well. Pentium processor generates copy VREF. VREF voltage level needed chipset. simple voltage divider resistors meet VREF current requirements, very current draw this signal most device). Bear mind that leakage current varies significant when building voltage divider.
Pentium® Processor Power Distribution Guidelines
Meeting AGTL+ Power Requirements
different nature powering AGTL+ versus powering processor, meeting requirements addressed different way.
Generating
Intel recommends terminating both ends AGTL+ bus. Since each Pentium processor contains termination side bus, dual-processor (DP) motherboard needs terminating resistors. Depending layout ATGL+ bus, uni-processor (UP) motherboard requires least terminating resistors (referred SET, singled-ended termination). Simulation results will determine whether motherboard required provide second termination resistors (referred DET, dual-ended termination). Designers wish generate each line. this case, each supply only needs provide half current necessary AGTL+ drivers. larger AGTL+ supply suffice both ends fairly near each other. Designs utilizing single ended termination only need provide half current necessary AGTL+ drivers. When powering from single regulator, design techniques closely resemble those Section 4.0. Motherboard designers should full analysis. current required each AGTL+ regulator, dual regulator AGTL+ supply, means that linear regulators used. Linear regulators faster devices than switching regulators therefore require less output decoupling. dual regulator AGTL+ supply also results lower supply components. Intel recommends conducting proper analysis described Section 4.0. Analysis techniques remain same, reaction time supply current levels differ. regulators need track each other long each keeps tolerance. naturally performs averaging function these supplies. VREF discussed Section 6.3) must also track these supplies.
Distributing
Only VREF AGTL+ termination resistors need VTT. distance termination resistors small, distributing with wide trace should sufficient. wide trace VREF generation point keeps inductance minimum. Intel recommends plane, especially single AGTL+ supply used ends AGTL+ near each other. This helps offset distribution resistive inductive losses. Again, separate smaller linear regulators each alleviate possible need power plane. example TT/VREF voltage island Figure
Pentium® Processor Power Distribution Guidelines
Figure Pentium Processor VTT/VREF Voltage Island
Note:
When using resistor networks with single corner connection AGTL+ termination, beware inductive packages. Intel found that these packages cause significant voltage drops inductance SOIC packages being used this purpose.
Generating Distributing VREF
VREF current input (about device) differential receivers within each components AGTL+ bus. Each Pentium processor generates VREF. simple voltage divider generate VREF. Because VREF used only input buffers, does need
Pentium® Processor Power Distribution Guidelines
maintain tight tolerance from component component. does however, need meet specification VREF inputs. VREF should track averaging dual regulated AGTL+ supply. Equation uses generate VREF nominal value VTT. Figure illustrates using resistors generate VREF specification Figure Simple Circuit Generating VREF
VREF IREF
Equation Creating VREF
VREF
should small enough values that current drawn VREF inputs (IREF) negligible versus current caused complete analysis this circuit's currents into center node, Equation will provide final VREF circuit. number IREF inputs supplied divider. Equation Node Analysis
Plugging currents rearranging, gives: Equation Node Analysis Terms Voltage
VREF VREF
Which leads
Pentium® Processor Power Distribution Guidelines
Equation Solving VREF
VREF
worst case VREF should analyzed with IREF maximum minimum values determined number loads being provided voltage. number loads change from model model because upgrades, this should taken into account well. Analyze Equation Solving VREF with extremes their tolerance specifications.
6.3.1
Distributing VREF
system board designer choose distribute place resistor divider each component voltage regulator generate VREF then distribute each devices. wide isolated traces VREF reduce noise loss. When using regulators generate VTT, VREF must track averaging from both sources. Generate separate VREF, each regulator, every four loads. Connect VREFs together with wide trace. closer this VREF signal tracks path signals, better matches average voltage AGTL+ bus. Route VREF separate layer reduce cross-talk.
Recommendations
Intel recommends using simulation design verify Pentium processor based systems. With above estimates, model power source, model Pentium processor provided Section 11.0, system developers begin analog modeling. Intel recommends following starting point benchmark:
VCC_L2
VCC_L2, typical power supply with tap. Ensure sufficient current supply power system chipset, AGTL+ regulator other logic system caches that exist system. chipset specification chipset power requirements. voltage current specifications Pentium Processor datasheet requirements cache. Bulk decoupling requirements depend reaction time power supply. Pentium processor contains sufficient high frequency decoupling, provided that system well designed power supply.
VCC_CORE
VCC_CORE, Intel recommends starting with socketed local DC-to-DC converter shown Figure This removes cable inductance from distribution, reduces board inductance, allows cost upgrade strategy well. Regulator sockets provided upgradable processor sockets rather than shipping with full current capability already available. Another
Pentium® Processor Power Distribution Guidelines
benefit using separate regulators processor ability vary processor types system, allowed product line future. output this regulator should adjustable allow changes voltage specification products become available. Figure Local Regulation
Intel recommends placing bulk decoupling DC-to-DC converter module. Since these capacitors tend large available surface mount technology, makes sense isolate these smaller module that different manufacturing environment than typical system board designs. These bulk capacitors would supplement bulk devices placed near processor SC242 connector. Pentium processor S.E.C.C.2 package contains high frequency decoupling required properly designed system.
7.2.1
Main Power Supply
main supply must provide power DC-to-DC converter well rest system. should ensure that input voltage converter meets converter's requirements, that DC-to-DC converter does create transient problem outputs main supply. Voltage Regulator Module (VRM) DC-to-DC converter specifications describe guidelines given DC-to-DC converter industry. Intel located these specifications site Table below defines logic levels Pentium processor's pins. Intel recommends connecting pins described appropriate DC-to-DC converter specification.
Pentium® Processor Power Distribution Guidelines
Table
Voltage Identification Code
Processor Pins VID4 A121 VID3 B119 VID2 A119 VID1 A120 VID0 B120 VCCCORE 1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05 Core
NOTES: Processor connected VSS. Open processor; pulled motherboard. Required support variations Pentium processors. Required support variations Pentium Pentium processors.
Since losses linear regulator directly proportional VIN-VOUT, power supply makes good choice input voltage regulator. processor voltage (VCC_CORE) seem like better choice since lower than varies from
Pentium® Processor Power Distribution Guidelines
Pentium processor variant next. This would lead design change each generation Pentium processor. Also, Linear regulators require minimum voltage drop order operate. This becomes issue Pentium processor voltages decrease. Separate linear regulators contain voltage distribution very local region. layout where both ends physically near each other, regulator supply both sets termination resistors. this situation, trace (the wider better) should distribute power termination resistors. Linear regulators fairly common produced many vendors. your local field applications engineer visit assistance locating vendor. Reaction time specifications regulator determine bulk capacitance. capacitance must hold-over regulator during switch from estimated Table until regulator reacts. addition, Intel recommends capacitors each termination resistor package high frequency decoupling. Place these capacitors near termination resistors possible.
7.3.1
Termination Resistors
Discrete resistors employed, however assembly time associated with placing about resistors system should taken into account. lower part count implementation uses resistor networks. Note: When using resistor networks with single corner connection AGTL+ termination, beware inductive packages. Intel found that these packages cause significant voltage drops inductance SOIC packages being used this purpose. better option resistor networks which both ends each resistor available pins.
VREF
Intel recommends voltage divider each component. Pentium processor generates VREF internally. Therefore, most motherboards require only VREF voltage dividers. Assume maximum leakage current load. Note that these leakage currents positive negative. following discussion illustrates using single voltage divider support both VREF loads. Using resistors voltage divider Figure make resistor, This creates static usage (1.5 voltage divider. After looking combinations (above below tolerance) IREF (±30 µA), worst case solution Equation found with IREF tolerance specification (148.5 high tolerance specification (75.75 This yields:
Pentium® Processor Power Distribution Guidelines
Equation Resistor Tolerance Analysis
VREF 1.5/75.75 .000030 0.99V 1/75.75 1/148.5
Since target 1.00 this setting within 0.97% point satisfies specification. spreadsheet program allows reader easily verify other corners. Varying over tolerance range minimal effect. These values chosen have additional benefits: parallel combination terminates VREF line This generally available resistance value reduces resistor cost. Decouple VREF each VREF input voltage divider with 0.001 capacitor VSS. Decoupling VREF voltage dividers with 0.001 capacitor further enhance ability VREF track VTT. actual benefit this decoupling controversial. When routing VREF loads, 30-50 trace (The wider better) keep other signals least mils away from VREF trace. This provides impedance line without cost additional plane island.
Component Models
When making component selection decisions, assure that capacitor does degrade with temperature, time voltage applied. Acquire component models from their manufacturers. Intel guarantee specifications another manufacturer's components. This section contains some models developed Intel simulations. Designers also need route minimize current loop inductance. Pentium processor model found Section 11.0.
Table
Various Component Models used Intel (Not Vendor Specifications)
Component Simulation Ceramic 0603 package Ceramic 1206 package (2.05"x0.71") Tantalum Case Aluminum Electrolytic 1000 Aluminum Electrolytic 1000 Aluminum Electrolytic OS-CON Electrolytic LBOARD. used VSS, VCC_CORE. This estimate accommodates traces vias, planes socket connections plane. 0.100 0.120 0.005 0.100 0.143 0.053 0.031 0.012 0.000 (nH) 1.60 0.47 0.30 0.602 2.37 0.40 ESL+ Trace (nH)
Pentium® Processor Power Distribution Guidelines
Measuring Transients
measure transients voltage island, requires clean connection. Achieve this placing coaxial connection directly into power island during layout. type connector used should placed near centrum voltage island. Cable signal directly into oscilloscope take reading with oscilloscope bandwidth limited MHz. This filters components noise that processor also filters out. There need decouple frequencies above this range since Pentium processor S.E.C.C.2 cartridge filters them out.
Existing Technology Pentium® Processor System Design
Solutions VCC_CORE
Intel assisted development many industry DC-to-DC converter modules. Designers should understand these components specific design. Intel guarantee DC-to-DC converter specific designs. general, vendor component assists designers usage their component. your local field office, visit list possible vendor solutions. Another solution that simple extension discussion this paper integrate components DC-to-DC converter, including bulk capacitance, onto system PCB. Intel helped power silicon vendors well designing Pentium processor specific solutions. Again, your local field office list possible vendor solutions.
Linear Regulators
Linear regulators widely available. Switching regulators also used generate VTT.
Termination Resistors
Intel recommends resistor networks reduce part count processor board assembly. best resistor networks have separate access each side every resistor package. This minimizes inductance crosstalk within package. When using resistor networks with single corner connection AGTL+ termination, beware inductive packages. These packages cause significant voltage drops inductance SOIC packages being used this purpose.
Pentium® Processor Power Distribution Guidelines
10.0
Pentium® Processor Power Distribution Network Modeling
Intel provides electrical models which shown Figure Figure Figure Figure simulation transient response Pentium processor power delivery systems. tool capability limitations, these models have been greatly simplified provided rough illustration Pentium processor power delivery systems.
Figure VCC_CORE Power Delivery Model Transient Response Systems
Lmb_vc R_vcs 11mOhm 0.35nH
Rmb_vc 0.15mOhm
Iac_load L_vcs 3.0nH C_vcs Vc(0+) 2.8V 6000uF 400ns Vac_out
0.35nH Lmb_vs
0.15mOhm Rmb_vs
A6861-01
Figure VCC_CORE Power Delivery Model Transient Response Systems
Lmb_vc R_vcs 11mOhm 0.23nH
Rmb_vc 0.19nOhm
Iac_load L_vcs C_vcs Vc(0+) 2.0V 9000uF 400ns Vax_out
0.23nH Lmb_vs
0.19Ohm Rmb_vs
A6846-01
Pentium® Processor Power Distribution Guidelines
Figure VCC_L2 Power Delivery Model Transient Response
Lmb_vc R_vcs 25mOhm
Rmb_vc 1mOhm
Iac_load L_vcs 2.0nH C_vcs Vc(0+) 3.3V 200uF 1.4A 1400ns Vac_out
Lmb_vs
1mOhm Rmb_vs
A6862-01
Figure Power Delivery Model Transient Response
Lmb_vc R_vcs 25mOhm
Rmb_vc 1.5mOhm
Iac_load L_vcs 2.0nH C_vcs Vc(0+) 1.5V 3000uF 2.7A 270ns Vac_out
Lmb_vs
1.5mOhm Rmb_vs
A6863-01
exponential waveform form: exp(-t/tr)) represents Pentium processor current source. Motherboard inductance impedance characteristics modeled Lmb_vc, Lmb_vs, Rmb_vc Rmb_vs. Finally source impedance, inductance capacitance characteristics modeled R_vcs, L_vcs, C_vcs. values
Pentium® Processor Power Distribution Guidelines
provided below motherboard source characteristics example purposes source motherboard characteristics should reflect actual values system under analysis.
11.0
Right Angle Connector Power Delivery Considerations
System developers considering right angle SC242 connector (RAC) need keep mind following constraints: added delay increases risk both higher frequency implementations implementations that single ended termination. System designers must take into account added resistance inductance RAC. System designers will need perform static dynamic analysis their solution. detailed analysis Pentium processor-based systems utilizing available AP-587: Slot Processor Power Distribution Guidelines application note (Order Number: 243332) used basis analyzing other SC242 designs.
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