2-Phase Dual Output Synchronous Buck Control MIC2150/1 simple 2-p

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2-Phase Dual Output Synchronous Buck Control MIC2150/1 simple 2-p

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MIC2150/MIC2151
2-Phase Dual Output Synchronous Buck Control
MIC2150/1 simple 2-phase dual-output synchronous buck control featuring small size high efficiency. implement control 500kHz (MIC2150) 300kHz (MIC2151), with outputs switching 180° phase. result out-of-phase operation 1MHz input ripple frequency with ripple current cancellation, minimizing required input filter capacitance. output voltage tolerance allows maximum level system performance. Internal drivers with adaptive gate drive allow highest efficiency with minimum external components. dual threshold enable pin, matched soft-start pins, power good output provided, allowing high level control. MIC2150/1 available small size 24-pin MLF® package. MIC2150/1 junction operating range from -40°C +125°C. Data sheets support documentation found Micrel's site www.micrel.com.
Features
Dual Synchronous Buck Control with outputs switching degree out-of-phase 4.5V 14.5V input voltage range Adjustable output voltages down 0.7V output voltage accuracy MIC2150: 500kHz operation MIC2151: 300kHz operation Adaptive gate drive allows efficiencies over Adjustable current limit with sense resistor Senses low-side MOSFET current Internal drivers allow phase Power Good output allow simple sequencing Dual threshold enable Independent programmable soft-start pins Output over-voltage protection Input UVLO Works with ceramic output capacitors Tiny 24-Pin MLF® package Junction temperature range -40°C +125°C
Applications
Multi-output power supplies with sequencing DSP, FPGA, ASIC power supplies Telecom Networking equipment Servers
Typical Application
MicroLead Frame registered trademarks Amkor Technology, Inc. Micrel Inc. 2180 Fortune Drive Jose, 95131 (408) 944-0800 (408) 474-1000 http://www.micrel.com
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Ordering Information
Part Number MIC2150YML MIC2151YML Frequency 500kHz 300kHz Voltage Adj. Adj. Junction Temp. Range -40°C +125°C -40°C +125°C Lead Finish Pb-Free Pb-Free Package 24-pin
24-pin MLF®
Configuration
24-Pin MLF® (ML)
Description
Number Name HSD1 Function Boost 1(Input): Provides voltage high-side MOSFET driver gate drive voltage higher than source voltage minus diode drop. High-Side Drive (Output): High current output-driver ext. high-side MOSFET. Switch Node 1(Output): High current output driver return HSD1. Current Sense (Input): Current-limit comparator non-inverting input. current limit sensed across low-side during ON-time. Current limit resistor series with pin. Soft-start, Output 1(Input): Controls turn-on time output voltage. Active power-up, Enable Current Limit recovery. Compensation (Input): external compensation, Channel Analog Ground (Signal): Signal path return PGOOD, AVDD, COMP. Feedback (Input): Input Channel error amplifier. Regulates 0.7V. Analog Supply Voltage (Input): Connect ext. bypass capacitor. Feedback (Input): Input Channel error amplifier. Regulates 0.7V. Power Good (Output): Indicates Channel output Channel output Nominal. Compensation (Input): external compensation, Channel
COMP1 AGND AVDD PGOOD COMP2
August 2009
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Micrel, Inc.
Number Name Function
MIC2150
Soft-start, Output 2(Input): Controls turn-on time output voltage. Active power-up, Enable Current Limit recovery. Current Limit (Input): Current-limit comparator non-inverting input. current limit sensed across low-side during time. Current limit resistor series with pin. Switch node (Output): High current output driver return HSD2. High-Side Drive (Output): High current output-driver high-side MOSFET. Boost (Input): Provides voltage high-side MOSFET driver gate drive voltage higher than source voltage minus diode drop. Power Ground High current return low-side driver CS2. Low-Side Drive (Output): High-current driver output external MOSFET. Internal Linear Regulator from (Output): ext. MOSFET gate drive supply voltage internal supply When <5V, this regulator operates drop-out mode. Connect external bypass capacitor. Enable (Input): Dual threshold enable pin. Logic turns off. Exceeding lower threshold enables Channel exceeding higher threshold then enables Channel dual threshold function allows option power sequencing from single pin. Both channels must turned together. enable must driven higher than 2.8V proper operation. Supply voltage Channel (Input): 4.5V Low-Side Drive (Output): High-current driver output external MOSFET. Power Ground High current return low-side driver CS1. Exposed (Power): Must make full connection plane maximize thermal performance package.
HSD2 PGND2 LSD2
EPAD
LSD1 PGND1
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Absolute Maximum Ratings(1)
Supply Voltage (VIN) -0.3V Bootstrap Voltage (BST HSD) COMP, VDD, AVDD -0.3V -0.3V Power Good (PGOOD) AVDD 0.3V Storage Temperature (TS).-65°C +150°C Lead Temperature (Soldering seconds) 260°C Rating(3) .HBM 2kV, 200V,
Operating Ratings(2)
Supply Voltage (VIN). +4.5V +14.5V Output Voltage Range. 0.7V Junction Temperature Range -40°C +125°C Package Thermal Resistance MLF® (JA).60°C/W MLF® (JC).6°C/W
Electrical Characteristics(4)
25°C; 12V; unless otherwise specified. Bold values indicate -40°C +125°C Parameter VEN, Supply Total Supply Current, mode supply current Shutdown Current UVLO Start Voltage UVLO Stop Voltage UVLO Hysteresis UVLO Start Voltage UVLO Stop Voltage UVLO Hysteresis Threshold Threshold Hysteresis Internal Bias Voltages (VDD) Load Current (each threshold) IVDD -50mA 14.5V 5.5V Oscillator Section Frequency design note Maximum Duty Cycle (Each Channel) Minimum On-Time
Notes: Exceeding absolute maximum rating damage device. device guaranteed function outside operating rating. Devices sensitive. Handling precautions recommended. Human body model, 1.5k series with 100pF. Specification packaged product only. Minimum on-time before automatic cycle skipping begins. applications section. Guaranteed design.
(5,6)
Condition 0.7V (both O/Ps) (Outputs switching excluding external MOSFET gate current.) rising falling rising falling
Units
2.03
(Internal Oscillator frequency)
MIC2150 MIC2151 MIC2150 MIC2151
(Each Channel)
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Parameter Regulation Feedback Voltage Reference Feedback Bias Current Output Voltage Line Regulation Gain
Condition (Each Channel) 25oC (Each Channel) -40°C +125°C (Each Channel) (Each Channel)
0.03
Units
Error Amplifier (Each Channel) (Latches High) 1.25 2.75 %Nom
Output Over voltage Protection (each channel) threshold Delay Blanking time Soft-Start Internal Soft-Start source current (each channel) Soft-Start source current matching between channels Internal Soft-Start discharge current (each channel) Over Current Trip Point program current comparator sense threshold Power Good threshold PGOOD voltage Upper Threshold, VFB_OVT Lower Threshold, VFB_UVT Gate Drivers Rise/Fall Time Low-Side Drive Resistance High-Side Drive Resistance
Notes: Guaranteed design.
During Soft Current Limit
Current Sense (Each Channel)
4.5V, IPGOOD (relative VFB). (relative VFB).
+6.5 -6.5
%Nom
Output Dynamic Correction Thresholds
Into 3000pF
Rise Fall Source Sink
Source Sink
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M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Parameter Driver non-overlap time (adaptive)(6) Driver non-overlap time between low-side high-side on(6)
Notes: Guaranteed design.
Condition
MIC2150 MIC2151
Units
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Typical Characteristics
Current Source
Source Current Temperature
(µA) 14.5V
Input Current Input Voltage
INPUT VOLTAGE (µA) INPUT VOLTAGE
(µA)
TEMPERATURE (°C)
INPUT CURRENT (mA)
Input Current Input Voltage
ENABLED
Regulator Temperature
ENABLE THRESHOLD
1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80
Enable Thresholds Input Voltage
2.5V 1.5V
-50mA
INPUT VOLTAGE
TEMPERATURE (°C)
INPUT VOLTAGE
TRANSITION VREF)
Enable Thresholds Input Voltage
2.30 TRIP VOLTAGE VREF) ENABLE THRESHOLD 2.20 2.10 2.00 1.90 1.80 1.70 INPUT VOLTAGE 130% 128% 126% 124% 122% 120% 118% 116% 114% 112% 110%
Threshold Reaction Time
Power Good Thresholds Input Voltage
HIGH
TPULSE (µs)
1000
INPUT VOLTAGE
EFFICIENCY
Efficiency Output Current
EFFICIENCY
Efficiency Output Current
Max. Duty Cycle
DUTY CYCLE
1.8V
VOUT 3.3V OUTPUT CURRENT
OUTPUT CURRENT
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M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Functional Characteristics
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Functional Diagram
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Functional Description
MIC2150 dual channel, synchronous buck controller built with latest BiCMOS process optimum speed efficiency. Both channels operate 180o phase with each other minimize input capacitor ripple current input noise. control loop stages regulation. During steady state medium output disturbances, loop operates fixed frequency, mode while, during large voltage disturbance (~±6.5% nominal), loop becomes hysteretic; meaning that short period, switching MOSFETs switched continuously until output voltage returns nominal level. This maximizes transient response large load steps, while operating nominally fixed frequency mode. Voltage mode control used allow maximum flexibility maintain good transient regulation. operating voltage range 4.5V 14.5V output voltage down 0.7V. Start-up surges prevented using built soft-start circuitry well resistor-less current sensing overload protection. Other protection features include UVLO, dual level enable thresholds, over voltage latch protection, power good signal dual level over current protection. Theory Operation output voltage converter sensed inverting input error amplifier. This connected VOUT feedback resistors. non-inverting input connected internal 0.7V reference compared produce error voltage. This error voltage then into non-inverting input comparator compared 1.5V voltage ramp create pulses. pulses propagate through MOSFET drivers which drive external MOSFETs create power switching waveform (duty cycle). This then filtered power inductor capacitor produce output voltage where VOUT example, load increase input voltage drop, output voltage will instantaneously drop. This will cause
M9999-082809-A (408) 944-0800
August 2009
Micrel, Inc. error voltage rise, resulting wider pulses output comparator. higher Duty Cycle power switching waveform will cause associated rise output voltage will continue rise until feedback voltage equal reference loop again equilibrium. necessary reduce bandwidth this feedback loop order keep system stable. This result relatively poor transient regulation performance. However, MIC2150 further hysteretic feedback loop which operates during large transients reduce this effect. Hysteretic mode invoked when output voltage detected ±6.5% nominal level. input voltage step output load step large enough cause 6.5% deviation VOUT, then additional control loop functions return output voltage nominal point fastest time possible. This limited only time constant power inductor output capacitor. This scheme used during normal operation because creates switching waveform whose frequency dependant upon VIN, passive component values load current. large noise spectrum, only used during surges keep switching noise known, fixed frequency. Soft-start
MIC2150
Figure Soft-Start
startup, Soft-start MOSFET (SSFET) released starts charge rate transistor's emitter (COMP) starts track that rate until reaches lower ramp waveform. This around 950mV where switching pulses will begin drive power MOSFETs. This ramp continues COMP until loop reaches it's regulation point which dependant upon duty cycle required regulation anywhere from 1.4V 2.9V. will however, continue rise base-emitter junction becomes reverse biased. During large over current short circuit conditions, i.e., where current limit detected VOUT <75% nominal, SSFET momentarily switched This discharges ~150mV which point, re-starts soft-start cycle once again. During soft-start, hysteretic comparators disabled until -6.5% comparator been set. Soft-start time Where value CCOMP same magnitude CSS, then there additional delay associated error amplifier charges CCOMP capacitor. Current Limit MIC2150 uses RDSON low-side MOSFET sense over current conditions. lower MOSFET used displays much lower parasitic oscillations during switching then upper MOSFET. Using MOSFET RDSON most accurate method current measurement, adequate method circuit protection without adding additional cost board space that would taken discrete current sense resistors. Generally, MIC2150 current limit
M9999-082809-A (408) 944-0800
Figure Hysteretic Block Diagram
Figure Hysteretic Waveforms
August 2009
Micrel, Inc. circuit acts provide fixed maximum output current until resistance load that voltage across longer within regulation limits. this point (75% nominal output voltage), Hiccup current mode initiated protect down-stream loads from excessive current during hard short circuits also reduces overall power dissipation converter components during fault. Before hiccup current mode occurs, `brick wall' current limiting provided prevent system shutdown disturbance overload only marginal.
MIC2150 pulse missed Thus reducing overall energy transferred output VOUT starts fall. this successive missing pulses results effectively lower switching frequency, power inductor ripple currents very high left unlimited. MIC2150 therefore limits Duty Cycle during current limit prevent currents building power inductor output capacitors. Current-Limit Setting current limit circuit responds peak inductor current flowing through low-side FET. value estimated with "simple" method more accurately calculated taking inductor ripple current into account. Simple Method Current limit quickly estimated with following equation:
Figure Overcurrent Sensing
During normal operation synchronous Buck regulator, lower MOSFET switched drain voltage will become negative with respect ground inductor current continues flow from Source Drain. This negative voltage proportional output load current, inductor ripple current MOSFET RDSON.
Where: RDSON maximum on-resistance side operating junction temperature Accurate Method designs where ripple current significant when compared IOUT duty cycle operation, calculating current setting resistor should take into account that sensing peak inductor current that there blanking delay approximately 100ns.
Figure Current Sensing Waveforms
larger inductor current, more negative becomes. This utilized detection over current passing known fixed current source (200µA) through resistor which sets offset voltage When (Source Drain equal this voltage, MIC2150's over current trigger set. This disables next high-side gate drive pulse. After missing high-side pulse, over current (OC) trigger reset. next low-side drive cycle, current still high i.e., another high-side
Figure Overcurrent-Circuit Waveform
Calculate peak switch current
IOUT IRIPPLE
Where: IRIPPLE
VOUT
calculate actual point allow 100ns delay.
August 2009
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Micrel, Inc.
ISET VOUT TDLY
MIC2150 regardless state CH1. functionality required only, driven externally above VREF enable operate only. Enable Sometimes, high currents, possible relatively large ground current peaks. These, turn, create voltage differentials between AGND points. order prevent these from affecting converter operation, good practice drive enable 0.5V higher than maximum threshold i.e., >2.8V both channels. Regulator internal regulator provides regulated supplying analogue circuit power (AVDD) MOSFET driver power from input supply (VIN). While this designed operate dropout input voltages down driver current will limited while regulator dropout. therefore recommended that ranges MOSFET gate current should kept less than 50mA. AVDD supply should connected through filter provide decoupling switching noise generated MOSFET drivers taking large current steps from regulator. Gate Drivers MIC2150 designed drive both high-side low-side N-Channel MOSFETs enable high switching speeds lowest possible losses. high-side MOSFET driver supplied bootstrapping switching voltage Drain lower MOSFET VDD. This provides high-side MOSFET with constant drive voltage equal VDD.
calculated using:
ISET RDSON(MAX
Where: Duty Cycle Switching Frequency Power inductor value TDLY Current limit blanking time 100ns ICS(min) 180µA Example Consider 3.3V converter with 0.5µH power inductor efficiency full load.
VOUT Efficiency
IRIPPLE
0.31) 9.11A 500kHz 0.5µH 9.11 9.55 3.3v 100ns ISET 9.55 8.89 0.5µH 8.89 180µA
Using simple method here would result current limit point much lower than expected. This equation sets minimum current limit point converter, maximum will depend actual inductor value RDSON MOSFET under current limit conditions. This could region higher should considered ensure that power components within their thermal limits unless thermal protection implemented separately. recommended connect 22pF capacitor from AGND close pins prevent adjacent channel switching noise from affecting current limit behavior. Over Voltage Protection voltage detected higher than nominal >2µs, channel stopped from switching immediately latched off. Switching re-started taking below channel's enable threshold re-enabling re-cycling power Power Good Output power good output (PG) will high only when both Channel outputs above their nominal output voltage. disabled (EN<2V), then will August 2009
Figure High-Side Gate Drive Circuit Waveform
When goes high, this turns high-side MOSFET node rises sharply. This coupled through bootstrap capacitor CBST Diode DBST becomes reverse biased. MOSFET Gate held 0.5V above Source long CBST remains charged. bias current high-side driver <10mA 100nF sufficient hold gate voltage with minimal droop power stroke (High-side
M9999-082809-A (408) 944-0800
Micrel, Inc. switching) cycle. i.e., 100nF 160mV. most applications, 220nF should used achieve improved, lower droop. When low-side driver turns every switching cycle, lost charge from CBST replaced DBST becomes forward biased. Therefore minimum voltage 0.5V. Low-side driver supplied directly from nominal Adaptive Gate Drive
MIC2150 There period when both driver outputs held (`dead time') prevent shoot-through current flowing. Shoot-through current flows both MOSFETS momentarily cycle's crossover. This dead time must kept minimum reduce losses catch diode which could either external Schottky diode placed across lower MOSFET internal Schottky diode implemented some MOSFETs. recommended high current designs, rely intrinsic body diode power MOSFET; these typically have large values slow reverse recovery characteristic which will significant losses regulator. Dependent MOSFETs used, dead time could required 150ns 20ns. MIC2150 solves this variability issue using adaptive gate-drive scheme: When high-side driver turned off, naturally inductor forces voltage switching node (lowside MOSFET drain) towards ground keep current flowing. When detected have reached 1.5V, MOSFET assumed low-side driver output immediately turned There also short delay between low-side drive turning high-side driver turning This fixed ~60ns 100ns allow large gate charge MOSFETs used.
Figure Adaptive Gate Drive Diagram
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
VOUTPK IRIPPLE IRIPPLE COUT
Application Information
Passive Component Selection Guide Inductor Selection inductor value responsible ripple current which causes some proportion resistive losses power components. These losses proportional IRIPPLE2. Minimizing inductor ripple current therefore reduce current flowing power components generally improve efficiency; this achieved choosing larger value inductor. Having said this, actual value inductance realistically defined space limitations, rating (IRMS) saturation current (ISAT) available inductors. looks newer flat wire inductors example, these typically have higher ISAT ratings than IRMS lower values. Also, inductance value increases, these figures tend closer value. This mirrors what happens converter with ISAT analogous maximum peak switch current IRMS analogous output current. inductance increases, ISWITCH(PK) tends towards IOUT. This characteristic that makes these types inductor optimal with high power buck converters such MIC2150. determine ISAT IRMS rating inductor, should start with nominal value ripple current. This should typically more than IOUT(MAX)/2 minimize MOSFET losses ripple current mentioned earlier. Therefore: LMIN
VOUT VOUT IOUT Efficiency
therefore, need output voltage noise (e.g., output voltage converters), VOUT ripple directly reduced increasing inductor value, output capacitor value reducing ESR. tantalum capacitors, typically >40m which usually makes loop stabilization easier utilizing pole-zero (type compensator. many advantages multi-layer ceramic capacitors, among them, cost, size, ripple rating ESR, useful choose these many cases. However, disadvantage product. This lower than tantalum. mixture tantalum ceramic good compromise which still utilize simple type compensator. With ceramic output capacitors only, double-pole, double-zero (type III) compensator required ensure system stability. Loop compensation described more detail later data sheet. Ensure ripple current rating capacitor above improve reliability. Input Capacitor Selection ripple rating single phase converter typically IOUT/2 under worst case duty cycle conditions 50%. This increases ~10% ripple current IOUT/2. When both cycles switching 180° phase, ripple reduce <50%
IRMSCIN
ILRMS ILSAT value chosen above LMIN will ensure these ratings exceeded. considering actual value choose, needs look effect ripple other components circuit. chosen inductor value will have ripple current IRIPPLE
VOUT
however, also advisable closely decouple Power MOSFETs with ceramic capacitors reduce ringing prevent noise related issues from causing problems layout regulator. ripple rating therefore, satisfied these decoupling capacitors; allowing perhaps more ceramic tantalum input capacitor input voltage node decouple input noise localize high di/dt signals regulator input. Power MOSFET Selection MIC2150 drives N-Channel MOSFETs both upper lower positions. This because switching speed given RDSON N-Channel device superior P-Channel device. There different criteria choosing upper lower MOSFETs these criteria more marked lower duty cycles such 1.8V conversion. such application, upper MOSFET required switch quickly possible minimize transition
This value should ideally kept minimum, within cost size constraints design, reduce unnecessary heat dissipation. Output Capacitor Selection output capacitor (COUT) will have full inductor ripple current IRIPPLERMS flowing through This creates output switching noise which consists main components:
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc. losses (power dissipated during rise fall times). Conversely, lower MOSFET switch slower, must handle larger currents. When duty cycle approaches 50%, then current carrying capability upper MOSFET starts become critical also sometimes benefit from external high current drivers achieve necessary switching speeds. MOSFET loss Static loss Transition loss Static loss (PS) Transition loss (PT) Where: Rise time Fall time worst case driver currents MIC2150, value simplifies (ns) (nC) found MOSFET characteristic curves
MIC2150 There many MOSFET packages available which have various values thermal resistance therefore, dissipate more power there sufficient airflow heat sink externally remove heat. However, this exercise, assume maximum dissipation 1.2W MOSFET package. This altered final design higher allowable package dissipation. Look lower MOSFET first: 1.2W low-side FET, small because VDSOFF clamped forward voltage drop Schottky diode. Therefore: RDSON(MAX) ~1.2 IFETRMS2 E.g. 1.8V RDSON(MAX) <14m important remember RDSON(MAX) figure MOSFET maximum temperature help prevent thermal runaway temperature increases, RDSON increases). Qgmax should limited that low-side MOSFET within fixed 80ns delay before high-side driver turns High-side MOSFET: high-side FET, losses should ideally evenly spread between transition static losses. center range balance losses. Therefore: Qgmax (IOUT RDSON calculated similarly high-side MOSFET: RDSON(MAX) ~0.6 IFETRMS2 Using previous example: Qgmax 20nC RDSON(MAX) Note that these maximum figures based upon thermal limits targeted highest efficiency. Selection lower values recommended achieve higher efficiency designs. Limits watch for: <1500 nC/VIN QgTOTAL (<2500nC/VIN MIC2151) Total both high-side low-side MOSFET values both channels. E.g. VIN(MAX) 13.2V: QgTOTAL 1500 13.2 114nC QgLOW <120nC (Per output)
Figure MOSFET Gate Charge Characteristic
VDSOFF Voltage across MOSFET when
IFETRMS
IOUT IRIPPLE/2 IOUT IRIPPLE/2 duty cycle since changes depending upon which MOSFET calculating losses for. Upper DC/FS lower MOSFET whole time that upper MOSFET fixed 80ns high-side driver delay. Therefore, there 80ns term subtracted from lower time equation. Lower DC)/FS 80ns
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M9999-082809-A (408) 944-0800
Micrel, Inc. Maximum turn gate charge each separate lowside MOSFET ensure proper turn before highside MOSFET switched Output Voltage Setting internal reference MIC2150 0.7V nominal. Therefore: VOUT R2)/R2 setting <10k 0.7)/0.7 input offset current 500nA. therefore recommended resistor values less than improve output accuracy Schottky Diode Snubbing Components When high-side switch turns there usually overshoot ringing associated with this fast edge. This induced perturbation tank circuit made combination trace lead inductances MOSFET Drain other parasitic capacitances. This cause unwanted stress driver circuitry left un-damped. Snubbing recommended reduce this ringing acts critically damp natural ringing frequency tank circuit. Technically, this achieved using single resistance dissipate ringing energy. However, practical terms, this would cause power loss. Therefore series used only edges waveform. There several methods calculating ideal values approach presented here estimate value then calculate This best left until final layout components available then accounts parasitic contributors that cause rising edge ringing. Estimating With snubbing, measure frequency ringing. This capacitor that results ring frequency Fo/2. This CSNUB. Calculating RSNUB Loop compensation loop voltage mode, buck converter contains main blocks considered; modulator, power stage compensator.
MIC2150 Modulator This section turns error signal from error amplifier into impedance square wave with pulse width proportional input. This section therefore includes ramp, comparator, drivers MOSFETs. Usually, moderate frequencies control loop, delays which appear phase between error amplifier output power stage small, significant allowing loop become unstable. average gain this stage therefore assumed linear with gain VIN/Ramp phase shift less than degrees. Power Stage This section essentially inductor, output capacitors load resistance. Unlike Modulator, frequency range loop, this complex system contains poles (i.e., -40dB/decade gain fall 1/2.LC total 180° phase lag) zero i.e., +20dB/Decade gain rise 1/2C.ESR total degree phase lead). zero created output capacitor's high affect poles then possible have conditions unstable loop without compensation. general, there types compensators that give good transient response (the measure fast regulation loop responds load step brings output voltage back steady state voltage): Double pole-Double Zero, Type compensator. This typically used ceramic output capacitor designs. Pole Zero pair, Type compensator. This typically used Tantalum electrolytic output capacitor designs.
Figure Loop Compensation Block Diagram
Compensator This section consists feedback resistors, error amplifier, compensation network reference. acts sample output voltage create frequency compensated error signal proportional difference between output voltage reference. this negative feedback system, this stage introduces phase shift degrees. output compensator then into modulator. What meant frequency compensated that adds phase gain where lost power stage also acts ensure gain high frequencies reduce susceptibility switching noise. goal compensation network achieve closed loop system that sufficient phase margin and/or gain margin ensure system stability across
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc. operating conditions. detailed analysis achieving this covered other texts will covered here. following method calculating correct values stability. Ceramic Output Capacitor Designs closed loop Bode plot response correctly compensated ceramic output capacitor design shown below.
MIC2150 margin (typically degrees will ensure system stability over conditions). Fs/5 degrees Place phase boost break frequencies such that maximum phase boost occurs desired crossover frequency Fco.
Sin(PM) Sin(PM) Sin(PM) Sin(PM)
must somewhere below equal FZ2. Placing half helps spread frequency range phase boost.
Finally, place noise suppression pole half switching frequency.
Figure Ceramic Output Capacitor Bode Plot
power inductor output capacitor create resonant frequency preferred make desired crossover frequency (loop bandwidth) greater than this with phase margin (PM) typically degrees. maximum phase boost, scale, occurs approximately half between highest zero (FZ2) lowest pole (FP1). precise, required compensation network this double pole, double zero type network shown Figure
calculation required components achieve FP1, FP2, this circuit ideal spreadsheet which available Micrel website. However, they also calculated using following method:
Collect Known Circuit Parameters Inductor value Output capacitor value COUT: ESR: Output capacitor ESR. Fco: Desired crossover frequency VRAMP: Internal ramp voltage 1.5V Internal reference voltage 0.7V VREF: Maximum input voltage converter VIN: Calculating Network Values
COUT
Choose value: This reasonable value 10k, order keep values within practical limits, this `factor' useful. 25k/Fo
Figure Type Compensation Network
Placement Poles Zeros Choose loop bandwidth/crossover frequency (Fco) less than fifth switching frequency phase August 2009
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Micrel, Inc.
MIC2150
COUT VRAMP
VREF VOUT VREF
Figure Type Compensation Network
Tantalum/Electrolytic Output Capacitor Designs closed loop bode plot response higher capacitor design looks something like figure below.
Pole Zero Positioning
COUT
introduce boost phase beyond resonance output filter (Fo), placed Together with phase boost associated with output capacitor zero, this will achieve degrees Phase margin. noise suppression pole half switching frequency.
Figure Tantalum Output Capacitor Bode Plot
output capacitor creating zero within range desired crossover frequency (Fco), this design only requires that adds zero associated pole. phase boost this case occurs between zero (FZ) pole (FP) compensator. Therefore, zero gain crossover frequency (Fco) will between these points. zero created pole should half switching frequency reduce noise sensitivity. plateau gain (gain between AvPLATEAU RC1/R1, this should modest gain five-to-ten improve transient response. This compensation network shown Figure
Calculating Network Values Choose <10k reduce susceptibility noise inaccuracies induced error amplifier bias current.
output voltage,
VREF VOUT VREF
plateau gain
Assuming FZ<<FP, approximated
August 2009
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Micrel, Inc.
MIC2150 bypass capacitor must used limit overvoltage spike seen input supply with power suddenly applied. additional Tantalum Electrolytic bypass input capacitor 22µF higher required input power connection. Keep inductor connection switch node (SW) short. route digital lines underneath close inductor. Keep switch node (SW) away from feedback (FB) pin. minimize noise, place ground plane underneath inductor. wide trace connect output capacitor ground terminal input capacitor ground terminal. Phase margin will change output capacitor value changes. Make sure stability calculations done minimum maximum tolerance values capacitor. feedback trace should separate from power trace connected close possible output capacitor. Sensing long high current load trace degrade load regulation. gate charge MOSFETs should used maximize efficiency, especially when operating lower output current. snubber from each switch node-to-ground recommended reduce ringing noise output minimize component stress. Place Schottky diode same side board MOSFETs input capacitor. connection from Schottky diode's Anode input capacitors ground terminal must short possible. diode's Cathode connection switch node (SW) must keep short possible. Connect current limiting resistor directly drain low-side MOSFET.
M9999-082809-A (408) 944-0800
Design Layout Guideline
Warning!!! minimize output noise, follow these layout recommendations.
Layout critical achieve reliable, stable efficient performance. ground plane required control minimize inductance power, signal return paths. following guidelines should followed insure proper operation MIC2150 MIC2151 converters.
(Integrated Circuit)
Inductor
Place point-of-load (POL).
MOSFETs
close
traces route input output power lines. Signal power grounds should kept separate connected only location. exposed (EP) bottom must connected PGND AGND pins Place feedback network close keep high impedance feedback trace short. Then route VOUT trace output. capacitor must placed close preferably connected directly through via. capacitor must located right terminal very noise sensitive placement capacitor very critical. Connections must made with wide trace. Place input capacitors same side board close MOSFETs possible. Keep both power connections short. Place several vias ground plane close input capacitor ground terminal. either dielectric input capacitors. type capacitors. replace ceramic input capacitor with other type capacitor. type capacitor placed parallel with input capacitor. Tantalum input capacitor placed parallel with input capacitor, must recommended switching regulator applications operating voltage must derated 50%. "Hot-Plug" applications, Tantalum Electrolytic
Output Capacitor
MOSFETs
Input Capacitor
Snubber
Schottky Diode (Optional)
Others
August 2009
Micrel, Inc. output voltage feedback resistors should placed close pin. side upper resistor should connect directly output node. this trace away from switch node traces inductor. bottom side lower voltage divider resistor should connect control compensation resistor capacitors should placed right next COMP other side should connect directly control rather than going ground plane. placeholders gate resistors top-side MOSFET gate drives. necessary, gate resistors less should used.
MIC2150
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
MIC2150 Evaluation Board Schematic
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Bill Materials
Item Part Number Manufacturer Description Qty.
C1,C3 C8,C10,C11, C12,C20 C13,C14 C7,C28,C29 C6,C9 C4,C5 C21,C22 C23,C24 C16,C17 D1,D2 D3,D4 Q1,Q4 Q5,Q8 R2,R3,R4 R10,R11 R9,R12
TR3D107K016C0100 GRM21BR61C106KE15L VJ0805Y106KXXAT 0805YD106K VJ0805Y104KXXAT VJ0603Y104KXXAT VJ0603Y105KXXAT VJ0805Y105KXXAT C3225X5R0J107M 12106D107KAT2A OPEN TR3D337K6R3C0100 TPSD337K006R0045 VJ0805Y102KXXAT VJ0603A181KXXAT VJ0603A121KXXAT VJ0603Y472KXXAT VJ0603A220KXXAT VJ0603Y222KXXAT OPEN SD103BWS-V-GS08 DFLS220L-7(Not Fitted) HC5-1R5 HC5-2R2 FDMS8680 SiR462DP FDMS8660AS Si7636DP Fitted Fitted CRCW06031002FKEA CRCW06034751FKEA CRCW06031001FKEA CRCW06032210FKEA CRCW12062R00FKEA CRCW06033011FKEA CRCW06033920FKEA CRCW06033651FKEA
Vishay
100µF/16V, case
Murata(2) Vishay(1) AVX(3) Vishay(1) Vishay
10µF/16V, 1210,
100nF/16V, 0805 100nF/16V, 0603 1µF/16V, 0603 1µF/16V, 0805 100µF/6.3V, 1210 OPEN,
Vishay Vishay
TDK(4) AVX(3) Vishay(1) AVX(3) Vishay(1) Vishay Vishay Vishay
330µF/6.3V, case 1nF/16V, 0805 180pF/16V, 0603 120pF/16V, 0603 4.7nF/16V, 0603 22pF/16V, 0603 2.2nF/16V, 0603 OPEN, SD103BWS
Vishay(1)
Vishay(1) Vishay
Diodes Inc. Cooper(6) Cooper
DFLS220L-7 1.5µH,17A 2.2µH,14A
Fairchild(7) Vishay(1) Fairchild(7) Vishay(1)
Vishay
0603 4.75k, 0603 0603 ohm, 0603 ohms, 1206 3.01k, 0603 ohms, 0603 3.65k, 0603
Vishay(1) Vishay Vishay Vishay
Vishay(1) Vishay Vishay
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Item
Part Number
Manufacturer
Description
Qty.
Notes:
CRCW06034991FKEA CRCW060310R0FKEA CRCW06033650FKEA OPEN
MIC2150YML
Vishay(1) Vishay Vishay
4.99k, 0603 ohms, 0603 ohms 0603 OPEN,
MIC2150 2-Phase Dual Output Synchronous Buck Control
Micrel Semiconductor
Vishay.: www.vishay.com Murata: www.murata.com AVX: www.avx.com TDK: www.tdk.com Diodes Inc.: www.diodes.com Cooper Electronics: www.cooperet.com Fairchild Semiconductor: www.fairchildsemi.com
Micrel, Inc.: www.micrel.com
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Recommended Layout
Copper
Bottom Copper
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Layer
Layer
August 2009
M9999-082809-A (408) 944-0800
Micrel, Inc.
MIC2150
Package Information
24-Lead (ML)
MICREL, INC. 2180 FORTUNE DRIVE JOSE, 95131
(408) 944-0800 (408) 474-1000 http://www.micrel.com
information furnished Micrel this data sheet believed accurate reliable. However, responsibility assumed Micrel use. Micrel reserves right change circuitry specifications time without notification customer. Micrel Products designed authorized components life support appliances, devices systems where malfunction product reasonably expected result personal injury. Life support devices systems devices systems that intended surgical implant into body support sustain life, whose failure perform reasonably expected result significant injury user. Purchaser's sale Micrel Products life support appliances, devices systems Purchaser's risk Purchaser agrees fully indemnify Micrel damages resulting from such sale. 2009 Micrel, Incorporated.
August 2009
M9999-082809-A (408) 944-0800

2-Phase Dual Output Synchronous Buck Control MIC2150/1 simple 2-p

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