Power Products Richard Markell, Editor INTRODUCTION Application Note f
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Linear Technology Magazine Circuit Collection, Volume
Power Products Richard Markell, Editor INTRODUCTION Application Note fourth series that excerpts useful circuits from Linear Technology magazine preserve them posterity. This application note highlights "power" circuits from issue VI:1 (February 1996) through issue VIII:4 (November 1998). Another application note will feature data conversion, interface signal processing circuits from same era. Like predecessor, this Application Note includes circuits that power most system imagine, from "server" power supplies that generate excess amps micropower systems portable handheld equipment. Also included power converters that voltage programmed using Intel's code. Charge pump converters, linear regulators battery charger circuits included here, with Li-Ion batteries receiving extra attention. There are, course, circuits that cannot simply categorized. Come browse. I'll authors describe their creations. Note: Article Titles appear this application note exactly they originally appeared Linear Technology magazine. This result some inconsistency usage terminology.
TABLE CONTENTS Introduction REGULATORS-SWITCHING (BUCK) LTC®1435-LTC1439 DC/DC Controllers Feature Value Performance LTC1266 Operates From Provides 3.3V LTC1435 Makes Great Microprocessor Core Voltage Regulator LTC1433/LTC1434: High Efficiency, Constant-Frequency Monolithic Buck Converter. Volt Volt Converter Provides Amps LTC1553 Synchronous Regulator Controller Powers Pentium® Other Processors Synchronizing LTC1430s Reduced Ripple Combine Switching Regulator UltraFastLinear Regulator High Performance 3.3V Supply LTC1624: Versatile, High Efficiency, SO-8 N-Channel Switching Regulator Controller Cost 3.3V 1.xV Power Supply LT®1374: 500kHz, 4.5A Monolithic Buck Converter. LTC1504: Flexible, Efficient Synchronous Switching Regulator Source Sink 500mA High Efficiency Distributed Power Converter Features Synchronous Rectification Fixed Frequency, 500kHz, 4.5A Step-Down Converter SO-8 Operates from Input Voltage Programmer Intel Mobile Processors. DC/DC Controller Enables High Step-Down Ratios LTC1627 Monolithic Synchronous Step-Down Regulator Maximizes Single Dual Li-Ion Battery Life LTC1625 Current Mode DC/DC Controller Eliminates Sense Resistor PolyPhaseSwitching Regulators Offer High Efficiency Voltage, High Current Applications LTC1622: Input Voltage, Current Mode Buck Converter.
AN84-1
Application Note
Wide Input Range, High Efficiency Step-Down Switching Regulators REGULATORS-SWITCHING (BOOST) Volt Output from LT1377 LT1370: 500kHz, Monolithic Boost Converter Bootstrapped Synchronous Boost Converter Operates 1.8V Input REGULATORS (SWITCHING)-BUCK-BOOST 500kHz Buck-Boost Converter Needs Heat Sink Battery-Powered Buck-Boost Converter Requires Magnetics REGULATORS-SWITCHING (INVERTING) Making 14-Bit Quiet Negative-to-Positive Telecommunication Supply Positive-to-Negative Converter Powers -48V Telecom Circuits Noise LT1614 DC/DC Converter Delivers 200mA from Input -48V DC/DC Converter Operates from Telephone Line REGULATORS-SWITCHING (FLYBACK) LT1425 Isolated Flyback Controller High Isolation Converter Uses Off-the-Shelf Magnetics Wide-Input-Range, Voltage Flyback Regulator REGULATORS-SWITCHING (LOW NOISE) LT1533 Heralds Class Noise Switching Regulators LT1533 Ultralow Noise Switching Regulator High Voltage High Current Applications REGULATORS-SWITCHING (MULTIOUTPUT) LTC1538-AUX: Addition LTC's Adaptive PowerController Family High Efficiency, Power, 3-Output DC/DC Converter Dual-Output Voltage Regulator Switcher Generates Bias Voltages without Transformer Features Reduce from Switching Regulator Circuits REGULATORS-SWITCHING (MICROPOWER) Power Management High Efficiency Switcher Maximize Nine-Volt Battery Life LT1307 Micropower DC/DC Converter Eliminates Electrolytic Capacitors Ultralow Quiescent Current, Boost Regulator. Capacitive Charge Pump Powers from Source LTC1474 LTC1475 High Efficiency Switching Regulators Draw Only 10µA Supply Current Free Digital Panel Meters from Oppressive Yoke Batteries LTC1514/LTC1515 Provide Power Step-Up/Step-Down DC/DC Conversion without Inductors LTC1626 Voltage Monolithic Step-Down Converter Operates from Single Li-Ion Cell Wall Cube 5V/400mA DC/DC Converter Efficient. Micropower 600kHz Fixed-Frequency DC/DC Converters Step from 1-Cell 2-Cell Battery LT1610 Micropower Step-Up DC/DC Converter Runs 1.7MHz Noise Varactor Bias Supply LTC1516 Converts Cells with High Efficiency Extremely Light Loads REGULATORS-LINEAR Dropout Regulator Driver Handles Fast Load Transients Operates Single 3V-10V Input
AN84-2
Application Note
LT1575/LT1577 UltraFast Linear Regulator Controllers Eliminate Bulk Tantalum/Electrolytic Output Capacitors LT1579 Battery-Backup Regulator Provides Uninterruptible Power BATTERY CHARGERS LT1511 Battery Charger Charges Battery Types, Including Lithium-Ion LT1512/LT1513 Battery Chargers Operate with Input Voltages Above Below Battery Voltage Li-Ion Battery Charger Does Require Precision Resistors LT1510 Charger with Termination Constant-Voltage Load Battery Simulation. High Efficiency, Dropout Lithium-Ion Battery Charger Charges Five Cells Amps More Battery Charger Also Serve Main Step-Down Converter LT1635 Shunt Charger 800mA Li-Ion Battery Charger Occupies Less Volume than Stacked Quarters Single-Cell Li-Ion Battery Supervisor POWER MANAGEMENT LTC1479 PowerPathController Simplifies Portable Power Management Design LTC1473 Dual PowerPath Switch Driver Simplifies Portable Power Management Design Short-Circuit-Proof Isolated High-Side Switch Tiny MSOP Dual Switch Driver SMBus Controlled LTC1710: Switches with SMBus Control into Tiny MSOP-8 Package MISCELLANEOUS Voltage Programmer Intel Mobile Processors. Battery Charger Doubles Current Sensor 100V, Constant-Voltage/ Constant-Current Bench Supply Complete Battery Backup Solution Using Rechargeable NiCd Cell What Efficiency Curves Don't Tell APPENDIX COMPONENT VENDOR CONTACTS INDEX
LTC, registered trademarks Linear Technology Corporation; Adaptive Power, Burst Mode, RSENSE, PolyPhase, PowerPath UltraFast trademarks Linear Technology Corporation. Gelcell trademark Johnson Controls, Inc.; Kool registered trademark Magnetics, Inc.; Pentium registered trademark Intel Corp.; VERSA-PAC trademark Coiltronics, Inc.
AN84-3
Application Note
Regulators-Switching (Buck) LTC1435-LTC1439 DC/DC CONTROLLERS FEATURE VALUE PERFORMANCE Randy Flatness, Steve Hobrecht Milton Wilcox Introduction LTC1435-LTC1439 multiple-output DC/DC controllers bring unprecedented levels value supplies notebook computers other battery-powered equipment, while eliminating previous performance barriers.
(MAX)
example, Adaptive Poweroutput stage allows previously incompatible parameters, constant frequency operation good current efficiency, coexist same power supply. second breakthrough allows N-channel power MOSFETs used exclusively, while maintaining dropout operation previously available only with P-channel MOSFETs. Other innovations include auxiliary linear regulator loop, phase-locked loop (PLL) synchronize oscillator external source, self-contained power-on-reset (POR) timer programmable delays useful staging output voltages.
2.2µF VPROG 56pF COSC EXT. CLOCK 0.01µF IRF7403 BOOST 0.1µF IRLML2803 MBRS1100 IRF7403 *CMDSH-3
22µF
MBRS140
SENSE+ LTC1437 1000pF SENSE VOSENSE 0.033
3.3µF
51pF 0.1µF RUN/SS 510pF
0.1µF
VOUT1 5V/3A 100µF
ZETEX FZT749
SGND PGND
1MEG
VOUT2 12V/200mA 4.7µF
100k
DALE LPE-8562-A092 (650) 665-9301 *CENTRAL SEMICONDUCTOR (516) 435-1110
Figure High Efficiency, Constant Frequency, Dual-Output Supply Delivers 250mA
AN84-4
Application Note
Cost Effective LTC1437 Switcher/Linear Combination with 5V/3A 12V/200mA Outputs main switcher loop, shown schematic Figure strapping VPROG high. Other output options include 3.3V (VPROG low) adjustable (VPROG open). output Figure circuit provided auxiliary linear regulator operating conjunction with secondary winding feedback loop using pin. turns ratio transformer 1:2.2, resulting
5.2V-25V
secondary output voltage approximately 15V. secondary resistive divider causes voltage drop below internal 1.19V reference secondary output loaded output little load. This forces continuous operation necessary guarantee sufficient headroom linear regulator maintain regulation independent load. auxiliary output turned with pin. auxiliary regulator also used adjustable mode, determined voltage pin. When voltage higher than 9.5V,
0.1µF *CMDSH-3 SFB1 BOOST1 TGL1 IRLML2803 0.1µF MBRS140 Si4412DY 0.033 1000pF SENSE1- 1000pF 220pF 1000pF ITH1 0.1µF RUN/SS1 4.7nF COSC EXT. CLOCK 0.01µF SGND PGND POR2 221k 316k 51pF MMBT2907ALT1 ZETEX ZTX849 VOUT3 2.9V/2.5A 330µF 6.3V RUN/SS2 56pF ITH2 0.05µF 220pF LTC1439 SENSE2- VOSENSE2 1000pF SENSE1+ SENSE2+ Si4410DY 1000pF 0.02 VOUT2 3.3V/3A 0.1µF MBRS140 VPROG1 VPROG2 BOOST2 TGL2 IRLML2803 0.1µF 10µH *CMDSH-3
2.2µF
Si4410
Si4412DY 22µF 10µH
22µF
TGS1
TGS2
100µF
100µF
VOUT1 5V/3A *CENTRAL SEMICONDUCTOR (516) 435-1110
Figure High Efficiency, Constant-Frequency, Triple-Output Supply Features 200mV Dropout
AN84-5
Application Note
case Figure regulator automatically configures itself fixed operation using internal resistive divider. When less than 8.5V, internal divider removed user adjust output voltage external divider referenced 1.19V. external auxiliary regulator pass transistor sized desired output current; this case SOT-223 device used deliver 200mA. signal present, goes low, causing oscillator minimum frequency (fMIN 180kHz with COSC 56pF). Applying 3.3V logic signal duty cycle will cause oscillator frequency lock external frequency track maximum fMAX fMIN. logic signal also coupled effect frequency shift, provided that initial frequency been less than 200kHz. Figure photograph showing 3.3V output staged start 10ms before output when power first applied Figure circuit. internal regulation monitor continually monitoring main controller output LTC1436/LTC1437, controller output (3.3V Figure LTC1438/ LTC1439. When regulation shutdown mode, open drain output pulls low. start-up, once output voltage reached final value, internal timer started, after which released. timer accomplished counting oscillator cycles, yielding delay-to-release reset approximately 300ms typical application. normally connected output allow power derived from regulator itself. Quiescent current then reduced because driver control currents scaled factor approximately equal controller duty cycle. also connected other external high efficiency sources, maximum 10V.
Synchronizable, Triple-Output, Dropout Supply LTC1439-based supply shown Figure example three logic supply voltages, 3.3V 2.9V, easily derived using only simple inductors. main DC/DC controller loops used supply 5V/3A 3.3V/5.5A. 2.5A 3.3V output current then used supply 2.9V output using adjustable capability auxiliary linear regulator. 2.9V output also illustrates external pass transistor with auxiliary regulator. Because only 0.4V dropped across transistor, 2.9V efficiency remains range. thanks duty cycle capability switcher loops, Figure supply maintain three output voltages regulation down 5.2V with load output. phase-locked loops built into LTC1437/LTC1436PLL LTC1439 offer convenient means synchronization applications Figures internal oscillator actually voltage-controlled oscillator (VCO) controlled voltage pin. When
Figure Start-Up 3.3V Supplies Easily Staged Upon Initial Application Input Power
AN84-6
Application Note
LTC1266 OPERATES FROM PROVIDES 3.3V Craig Varga Circuit Description Operation design Figure relies floating high-side driver that provides enough gate-drive capability easily switch large power MOSFET. LTC1266 configured drive P-channel MOSFET tying (PINV) ground. This required because there will inversion floating driver. controls driver stage provides gate-discharge capability through When low-side switches charges through When LTC1266 signals turn turned off. provides base current which, conjunction with acts like SCR. Once fired, regenerative behavior rapidly charges gate Since referenced source rises above supply rail turns forcing gate
nearly above ground. When LTC1266 takes high, turns pulling charge from gate capacitance through This back biases baseemitter junction forcing pull-up circuit, therefore off. Since input voltage high relative output, nominal duty factor high-side switch small this case approximately 31%). result, current through relatively low. contrast, low-side switches nearly time, therefore much higher current. This explains lowside switch employs MOSFETs, whereas high-side switch uses only one. Schottky diode used help keep body diodes from turning during short dead time before switching transitions. These body diodes exhibit relatively long reverse recovery times, contributing commutation losses. Schottky diode improves overall efficiency several percent, circuit will function correctly without Switching losses
MBR120T3 4.3k 2N3906 MPS2222 VN2222LL Si4410 0.1µF
100µF,
MBR0520LT3 0.001µF
0.015 0.015
300pF 1000pF
TDRV PWRVIN PINV BINH SENSE-
BDRV PGND
VOUT 3.3V
LBIN LTC1266 SGND Si4410
330µF, 6.3V
SENSE+ 1000pF
Si4410
MBRS320T3 6.04k,
3300pF
POLARIZED CAPACITORS TYPE (207) 282-5111 EQUIVALENT
Figure 3.3V/12A Supply
AN84-7
Application Note
low-side switches nearly zero, since these devices turned into nearly zero volts (the forward drop Schottky). There fundamental limitation high maximum input voltage with this approach. drive level shift limited breakdown rating Obviously, power transistors input capacitors must rated intended input voltage. power supply needed provide power LTC1266 voltage bootstrap supply. Figure shows input design. input supply voltage increased, thing watch potential overlap high- low-side turn-on/turn-off transitions. LTC1266 designed prevent shootthrough actually waiting until gate voltage switch before allowing other switch turned Using floating driver defeats this capability, this condition must checked for. high-side drive turnon time reduced lowering value R11. Using larger device will speed turn-off transition. value also need larger reduced limit drooping bootstrap supply voltage.
MPS2222A MBR0540LT3 4.3k 2N3906 MPS2222 VN2222LL MBR0520LT3 0.001µF 0.1µF 330µF NOTE
330µF NOTE
Si4410
0.015 0.015
1N759
1.0, 1/4W
TDRV PWRVIN PINV BINH SENSE-
BDRV PGND
VOUT 3.3V
LBIN LTC1266 SGND Si4410
330µF 6.3V MBRS340T3 6.04k,
SENSE+ 1000pF
470pF 1000pF 3300pF
Si4410
POLARIZED CAPACITORS TYPE EQUIVALENT UNLESS NOTED OTHERWISE. (207) 282-5111 CONSISTS TURNS MAGNETICS, INC. 77848-A7 Kool CORE (800) 245-3984 PANASONIC TYPE EQUIVALENT (201) 348-7522
Figure 3.3V/12A Supply
LTC1435 MAKES GREAT MICROPROCESSOR CORE VOLTAGE REGULATOR John Seago Current microprocessor architectures require different voltages core ring. portable computer applications, microprocessor core voltage reduced lower power consumption. Three high current
regulated voltages, 3.3V 2.9V, commonly required. Several manufacturers offer two-output controllers, like LTC1438, which normally used 3.3V. Another controller required generate 2.9V. Figure shows simple circuit using LTC1435 provide 2.9V 2.65 amps Intel portable Pentium® processor.
AN84-8
Application Note
circuit's 165kHz switching frequency selected compromise between transient response circuit efficiency. This frequency determined value Output voltage transient response shown Figure transient response adjusted other applications changing values compensation components C14. Efficiency curves different input voltages load currents amps shown Figure Another feature LTC1435 option maintain constant switching frequency under load conditions select Burst Modeoperation highest efficiency light loads. Pulling high enables Burst Mode when load current drops value. However, Burst Mode degrade transient response input voltages should used pulsed load applications where good transient response input voltage required.
5.5V INPUT INPUT INPUT
100mVP-P 50mV/DIV
EFFICIENCY
0.0A
2A/DIV
INPUT INPUT
500µs/DIV
0.01A
0.1A
1.0A
Figure Output Voltage Transient Response
5.5V-28V
Figure LTC1435 Efficiency Curves Different Input Voltages
68pF 0.1µF 47pF LTC1435 100pF SGND 0.1µF 330pF RUN/SS BOOST COSC
22µF
22µF SI4412
0.1µF
10µH
0.033
2.9V/ 2.65A 35.7k
MBRS0530 470pF
100µF
VOSENS
SI4412
0.001µF
SENSE-
PGND
4.7µF MBRS140T3 24.9k
100µF
SENSE+
C12,
AVX, TPSE226M035 SUMIDA, CDRH125-10 AVX, TPSD107M010 SILICONIX, SI4412DY MOTOROLA, MBRS0530 IRC, LR2010-01-R033-F MOTOROLA, MBRS140T3
Figure 2.9V Regulator Portable Pentium Processor
AN84-9
Application Note
2.9V 1V/DIV 0.0V 0.0V 1.25A 0.0A 200µs/DIV 1A/DIV 0.0A 2A/DIV 2µs/DIV 5V/DIV
Figure Inductor Input Voltage Current Waveforms
Figure Soft-Start Output Voltage Inductor Current
circuit Figure grounded, which will defeat Burst Mode ensure constant frequency operation. sometimes necessary shut down power load. RUN/SS dual-function LTC1435 that provides both output voltage on/off control output current soft-start capability. When RUN/SS (pin pulled open collector open drain device, output voltage turned controller shuts down. soft-start feature takes over when removed from Figure shows output voltage under no-load conditions turn-on, with soft-start capacitor equal 0.1µF. This simulates start conditions microprocessor held standby until after input voltage stabilized. regulator started under full-load conditions, output current ramp time will approximately 0.5s/µF soft-start capacitance. output voltLTC1433/LTC1434: HIGH EFFICIENCY, CONSTANTFREQUENCY MONOLITHIC BUCK CONVERTER San-Hwa Chee Typical Application: Buck Converter Supplies 3.3V 600mA Figure shows practical LTC1433 circuit that used cellular telephone applications. Efficiency curves this circuit various input voltages shown Figure Note that efficiency reaches supply voltage load current about 150mA. This high efficiency makes LTC1433 LTC1434 attractive power-sensitive applications. circuit works down 3.6V load current 250mA before dropping oscillator frequency constant 210kHz down 20mA load current.
during this soft-start period depends load impedance. soft-start required, capacitor used current limit setting regulator determines maximum load current during start-up. order properly enhance MOSFET (Q1), level shifted charge pumping capacitor minus diode drop. provides power turn off. LTC1435 regulated will increase with higher voltage applied VCC, maximum 10V. outputs between 10V, output should connected VCC. power loss linear regulator will replaced more efficient switcher output gate-drive voltage both MOSFETs will increased lower "ON" resistance. Figure shows input voltage current with volt input, volt output, 2.65 load current.
Typical Application: Positive-to-Negative Converter Both LTC1433 LTC1434 easily negative output voltage. Figure shows schematic using LTC1433. efficiency curve shown Figure This circuit that output taken from device ground. Components that normally referenced back device ground, such Run/SS capacitor, oscillator frequency capacitor compensation network, connected output instead circuit ground.
AN84-10
Application Note
0.1µF MBRS130LT3 COILCRAFT DO3316-104 TPSD107M010R0100 TPSE686M020R0150 68µF
VOUT 3.3V
INPUT VOLTAGE 3.6V
EFFICIENCY
100µH L1**
100µF
PWRVIN PGND SVIN
LTC1433 SGND RUN/SS 0.1µF VOSENSE VPROG
POWER RESET 680pF 5.1k 47pF 6800pF
0.001 0.01 0.10 1.00
LOAD CURRENT
Figure LTC1433 Typical Application: 3.3V Output 600mA
Figure Efficiency Load Current Figure 11's Circuit
MOTOROLA MBRS130LT3 COILCRAFT DO3316 SERIES TPSD107M010R0100 TPSE107M016R0100
L1** 68µH
SGND RUN/SS
PWRVIN PGND SVIN
680pF 5.1k 6800pF 100pF 100µF
INPUT VOLTAGE 7.5V
VOUT -5.0V IOUT (mA)
0.1µF
100µF
LTC1433
COSC VOSENSE VPROG
0.01µF
Figure Positive-to-Negative (-5.0V) Converter
0.001
EFFICIENCY
3.5V
VOUT -5.0V COSC 100pF 0.01 0.10 1.00
LOAD CURRENT
Figure Efficiency Curves Figure 13's Positive-to-Negative Converter
AN84-11
Application Note
VOLT VOLT CONVERTER PROVIDES AMPS John Seago Combining LTC1435 with large geometry power MOSFET good layout allows large currents processed easily efficiently. With current sense transformer, output voltages greater than implemented. circuit Figure shows LTC1435 configured conventional buck regulator using single N-channel MOSFET control output voltage greater than with load current exceeding amps. efficiency breadboard measured with input, output load current. maximum
INPUT
efficiency required, adding second power MOSFET synchronous switching will improve efficiency about This circuit's 100kHz switching frequency selected reduce switching losses that mounted heat sinks could used without requiring additional flow. switching frequency from 50kHz 400kHz selecting appropriate value current sense transformer uses 1:100 turns ratio scale down buck inductor input current develop voltage across used ±SENSE inputs regulation. Shortcircuit protection provided When current transformer secondary voltage developed across
1N4148
1000µF
1000µF
100T 100pF
0.62
0.001µF 2N3906 VN2222LL
1N758 2N3904
1N751 10µH
0.001µF
100k
120pF 0.1µF 330pF 47pF 100pF 11.8k COSC RUN/SS SGND VOSENS SENSE SENSE BOOST LTC1435 0.001µF 0.1µF 0.1µF 2N3906
127k 470µF
470pF
PGND
4.7µF 1N4148
470µF
R12,
2N3904
2.2k
0.01µF
0.001µF
C10, NICHICON, UPL1V102MHH6 (847) 843-7500 C13, NICHICON, UPL1E471MHH6 MOTOROLA, MBRS0540 (800) 441-2447 MOTOROLA MBR2045 WITH THERMALLOY #7020 HEAT SINK INTERNATIONAL RECTIFIER, IRL3803 (310) 322-3331 WITH THERMALLOY #6299 HEAT SINK (972) 243-4321 CORE MAGNETICS, 55930-AZ (800) 245-3984 WINDING BIFILAR CORE MAGNETICS W-41406-TC WINDING 100T
Figure 14V, Buck Regulator
AN84-12
Application Note
SWITCH VOLTAGE 20V/DIV CURRENT 10A/DIV 0.0V
0.0A PRIMARY CURRENT 10A/DIV 0.0A OUTPUT VOLTAGE RIPPLE 14VDC 0.2V/DIV
2µS/DIV
Figure Buck Regulator Circuit Waveforms
enough turn temporarily pulls RUN/SS low, turning regulator. Output current soft-starts when releases RUN/SS pin. This results frequent attempts establish output voltage short exists, without high current continuously flowing through power elements. power elements consist input capacitors C11, Current sense transformer buck inductor power MOSFET commutating diode output capacitors C14. Although wide 3.6V-36V input voltage range duty cycle operation LTC1435 ideal battery/ wall adapter input applications, operating above duty cycle causes problems current sense transformer. avoid transformer saturation, stage limits duty cycle approximately 90%. Current through tries
charge base voltage switch cycle terminates less than duty cycle, reset duty cycle exceeds 90%, charges until turns ending switch cycle. Switch voltage, inductor current, primary current, output voltage ripple waveforms shown Figure These waveforms were measured with input, output, load current. When MOSFET turns switch voltage (Trace goes high, inductor current (Trace increases, does primary current (Trace output ripple voltage (Trace When turns off, switch voltage goes low, inductor current decreases stored energy supplies load current through primary current goes zero output voltage decreases slightly. power converter requirements while minimizing number external components. on-chip 5-bit digital-toanalog converter (DAC) provides output voltages conforming Intel's specifications. This allows LTC1553 read code sent processor provide with requested voltage. LTC1553 also provides power-good indication (PWRGD) system. There also on-chip overvoltage protection circuit that latches regulator state output voltage ever rises more above DAC-requested voltage. applications with other processors, four inputs routed jumper block, zero resistors
LTC1553 SYNCHRONOUS REGULATOR CONTROLLER POWERS PENTIUM OTHER PROCESSORS Y.L. Teo, S.H. Craig Varga LTC1553 provides current-limit short-circuit protection without external sense resistor. excellent (±1%) output regulation over temperature, line voltage load current variations. compliment main voltage-feedback loop, LTC1553 includes additional feedback loops provide good large-signal transient response. LTC1553 adds additional internal circuits conform Intel Pentium processor
AN84-13
Application Note
Typical Application switch, hard wired, desired output voltage. This allows output voltage programmed easily steps while eliminating need stock assortment precision resistors. This flexibility output voltage setting cheap insurance against last-minute power supply voltage changes microprocessor manufacturers. LTC1553 Overview on-chip, 5-bit digital-to-analog converter (DAC) allows output voltage adjusted from 1.80V 3.5V, shown Table Current limiting maintained sensing voltage drop across RDS(ON) high-side MOSFET. accuracy, initial reference voltage tolerance internal feedback resistor tolerances result maximum initial output voltage error selected output voltage. line load regulation plus temperature drift over 70°C temperature range will contribute another output error budget. This gives total static operating error less than ±2%, providing sufficient headroom (3%) dynamic response remain within output voltage tolerance, while still requiring reasonable amount output capacitance. typical application LTC1553 converting 1.8V-3.5V Pentium processor based personal computer. supply form voltage regulator module (VRM) implemented directly motherboard. output used power Pentium processor input taken from system's supply. circuit shown Figure provides 1.80V-3.5V while maintaining output regulation within ±1%. output voltage determined connecting five inputs pins processor. power MOSFETs sized minimize board space allow operation without need heat sink. With proper airflow, ambient temperature conditions Celsius acceptable. Typical efficiency above from 3.3V out. (see Figure 18). Achieving higher output currents from LTC1553 based designs simply matter selecting appropriate MOSFETs passive components. pays look regulator design from perspectives: electrical thermal. Most processor applications operate average currents that approximately less specified peak current. such, thermal
0.1µF 5.6k 5.6k 5.6k 10µF RIMAX
1N5817
990µF 330µF
PWRGD Pentium Processor SYSTEM FAULT LTC1553 VID0-VID4
IMAX
PVCC
0.1µF
Q1A, PARALLEL) 2.0µH/18A
VOUT
1.8k CONNECTING VID0-VID4 SWITCH VOUT DALE NTHS-1206N02 (605) 665-9301
OUTEN COMP 100pF 0.01µF PGND
SENSE
2310µF 330µF
0.01µF 0.1µF Q1A, Q1B, MOTOROLA MTD20N03HDL (800) 441-2447
1552_06.eps
Figure Typical 1.8V-3.5V/14A LTC1553 Application
AN84-14
Application Note
Table Output Voltage VIDx Code
VID4 VID3 VID2 VID1 VID0 *Reserved future expansion (VDC) 1.80 1.85 1.90 1.95 2.00 2.05
EFFICIENCY LOAD CURRENT
1552_07.eps
Figure Efficiency Plot Figure 17's Circuit
load results huge, most likely unnecessary, design margin. good understanding your system requirements result substantial savings size cost power supply. RIMAX sets current limit desired level. one-half inductor ripple current maximum load current determine peak switch current. Multiply this current maximum on-resistance selected MOSFET switch determine minimum current limit threshold voltage. It's good idea least margin this limit. Also, sure on-resistance MOSFET. multiplier about times room temperature RDS(ON) should used determine resistance. case parallel MTD20N03HDLs (Q1A Q1B), cold resistance approximately 0.035 each; therefore, assume resistance approximately 0.050. Divide this because FETs parallel. threshold voltage programmed multiplying IMAX pin's sink current value RIMAX. Since determine required threshold, need calculate value RIMAX. specified minimum sink current, 150µA, calculate resistor value. soft-start time programmed 0.01µF connected pin. larger value this capacitor, slower turn-on ramp. Inductor sized handle full load current, onset current limit, without saturating. value between adequate most processor supply designs. careful overspecify inductor.
design based lower current level. Higher currents, while present, typically sufficient duration significantly heat power devices. design does, however, need capable delivering peak current without entering current limit resulting device failures. Keep mind that power dissipation resistive element, such MOSFET, varies square load current. such, raising load current from 100% translates approximately more power dissipation (1/0.82). Designing this higher ther-
AN84-15
Application Note
inductor need retain no-load inductance current-limit threshold. inductor still retains order initial inductance under worst-case short-circuit current conditions, circuit should prove reliable. However, want ensure that approximately initial inductance retained nominal full load. Excessive inductance roll-off will result higher than expected output ripple voltage high loads, along with increased dissipation power FETs inductor itself. Proper loop compensation critical obtaining optimum transient response while ensuring good stability margins. compensation network shown here gives good response when used with inductor output capacitors values shown Figure Several capacitors placed parallel reduce total output ESR, resulting lower output ripple improved transient performance. Generally speaking, ESR, high value output capacitors should chosen optimize board space. However, value given capacitor value, loop stability problems occur. feedback loop depends frequency "zero" being well below loop crossover frequency. There positive phase shift frequency where capacitive reactance equals capacitor. Without this phase shift, loop would impossible stabilize. ESR, TPS-series tantalum capacitors very good compromise between ESR, capacitance value physical size. Input capacitors included suppress input switching noise keep input supply variation minimum during ON/OFF cycle. Excessive conSYNCHRONIZING LTC1430s REDUCED RIPPLE Craig Varga recent move split-plane microprocessors several makers inclusion multiple switching regulators many motherboard designs. These regulators typically provide 3.3V system logic separate supply processor core. Current requirements 5A-10A more supply unusual. LTC1430 synchronous buck regulator commonly used provide these tightly regulated supplies. nature, input current waveform buck topology discontinuous, ducted emissions usually traced back inadequate input capacitance poor layout power-path traces. crucial parameter input capacitors ripple current rating. reasonable rule thumb says that input capacitor ripple current going approximately load current. Therefore, typical Pentium processor application, input capacitors should rated close 7ARMS. excellent choice input capacitors Sanyo OS-CONs equivalent. They have extremely high ripple current ratings their size have demonstrated excellent reliability this type application. aluminium electrolytic capacitors viable option from both input output. Although lower cost than OS-CONs tantalum capacitors, their long-term reliability good. Using 105°C capacitors keeping operating temperatures will help obtain reasonable capacitor life. combination Dale NTHS-1206N02 thermistor 1.8k resistor overtemperature monitoring. flag trips ambient temperature reaches about 90°C; 100°C drivers stop operating. system monitors flag, there should ample time take precautions, saving data system configuration information prior overtemperature shutdown. Alternatively, activity could reduced, lowering power supply current allowing supply cool down. PWRGD gives rail-voltage indication. reason, output regulation falls limit (including overtemperature shutdown), PWRGD will provide logic signal system monitor.
resulting large input ripple current. synchronizing pair supplies phase, possible achieve degree ripple current cancellation. This results less stress input capacitors (the number input capacitors could reduced) lower EMI. ripple easier filter since frequency effectively doubled peak-to-peak current reduced. extremely simple synchronize pair LTC1430s appropriate phase relationship. Simply connect resistor divider from gate drive "master"
AN84-16
Application Note
LTC1430 130k PVCC2 FSET IMAX COMP PVCC1 PGND -SENS +SENS
MASTER
SLAVE
SGND
LTC1430
Figure Phase Relations Between Switching Nodes Regulators
FSET IMAX COMP
PGND -SENS +SENS
PVCC2
PVCC1
DI1430_01.eps
approximately 300kHz 130k resistor from FSET ground) slave left natural frequency 200kHz. slave frequency will forced that master. sync function LTC1430 works follows: when shutdown pulled low, high-side switch turns off; normal duty factor control determines when highside switch will turn back long shutdown held less than approximately 40µs, chip will shut down. simplified schematic (Figure shows synchronization circuitry. detailed description LTC1430based regulator designs, LTC1430 data sheet. scope photo (Figure shows voltage common connection FETs each regulator.
SGND
Figure Simplified Schematic Diagram Synchronization Circuitry
regulator sync "slave" regulator. resistors should divide gate-drive voltage down something slightly less than supply slave regulator, typically from down approximately 4.5V. Total divider resistance adequate. Also, slave regulator must free slower than master regulator. example, master configured
AN84-17
Application Note
COMBINE SWITCHING REGULATOR ULTRAFAST LINEAR REGULATOR HIGH PERFORMANCE 3.3V SUPPLY Craig Varga Introduction becoming increasingly necessary provide voltage power microprocessor loads very high current levels. Many processors also exhibit high speed load transients. Pentium® processor from Intel exhibits both these requirements. This processor requires 3.3V approximately peak average) capable making transition from
power state full load several clock cycles. Generally, switching regulators used supply such high power devices, because unacceptable power losses associated with linear regulators. Unfortunately, switching regulators exhibit much slower transient response than linear regulators. This greatly increases output capacitor requirements switchers. Circuit Operation circuit shown Figure takes advantage new, ultrahigh speed linear regulator combined with switching regulator best both worlds. LTC1435 synchronous buck regulator combined with LT1575
150µF
150µF
150µF
BOOST INTVCC LTC1435 CMDSH-3 0.1µF 7.5m
C14, 150µF, 68pF 0.1µF C10, 1000pF 1500pF 16.5k EXTVCC COSC RUN/SS SGND PGND
1000µF
1000µF 1000µF
1000pF
0.1µF MBRS330T3 35.7k
4.7µF
COILTRONICS CTX01-13199-X2 (561) 241-7876 SILICONIX SUD50N03-10 (800) 544-5565
IPOS
INEG LT1575 GATE C21, 10pF COMP
IRLZ44
0.1µF
1000pF
2.1k, 3.3V VCORE CERAMIC 0805 CASE
470pF 1.21k
DI1575_01.eps
Figure 3.3V/9A (14A Peak) Hybrid Regulator
AN84-18
Application Note
SWITCHER EFFICIENCY
EFFICIENCY
50mV/DIV
TOTAL EFFICIENCY
LOAD CURRENT
200µs/DIV
Figure Efficiency Figure 21's Circuit
DI1575_02.eps
Figure Transient Response Figure 21's Circuit Load Step
linear regulator generate 3.3V output from input with overall conversion efficiency approximately 72%. output capable current slew rates approximately microsecond. LT1575 uses IRLZ44 MOSFET pass transistor, allowing dropout voltage less than 550mV. Setting switching supply's output only 700mV above output linear regulator ensures output regulation. switcher therefore deliver 4.0V from supply. Conversion efficiency switcher around (depending load), whereas LT1575's efficiency 82.5% (see Figure 22). input current only about 5.5A. average current power dissipation linear pass transistor only 6.3W. small stamped aluminum heat sink adequate. LTC1624: VERSATILE, HIGH EFFICIENCY, SO-8 N-CHANNEL SWITCHING REGULATOR CONTROLLER Randy Flatness Introduction LTC1624 current mode switching regulator controller operating internally frequency 200kHz. This versatile 8-pin controller uses same constant frequency current mode architecture Burst Mode operation LTC1435-LTC1439 controllers, without synchronous switch. LTC1624, like other members family, drives cost-effective, external Nchannel MOSFET topside switch maintains dropout operation previously available only with P-channel MOSFETs.
Figure shows transient response load step with rise time approximately 50ns. only output capacitance ceramic capacitors. additional bulk capacitance required processor. circuit eliminates approximately dozen tantalum capacitors load, which would required without linear postregulator. switching supply's output decoupled with three aluminum electrolytic capacitors. Because transient response this point much less critical than load, long-term degradation aluminum capacitors will detrimental circuit's performance would they were used load decoupling.
LTC1624 configured operate standard switching configurations, including boost, step-down, inverting, SEPIC flyback, without limitation output voltage. wide input voltage range 3.5V allows operation from variety power sources, from four NiCd cells though high voltage wall adapters. Tight load regulation, coupled with reference voltage trimmed provides very accurate output voltage control. Application Circuits LTC1624 used wide variety switching regulator applications, most common being stepdown converter. Other switching regulator architectures discussed here include step-up SEPIC converters.
AN84-19
Application Note
1000pF 4.5V 5.1k SENSE BOOST 570pF /RUN 100pF RSENSE 0.05 Si4412DY 10µH VOUT 3.3V/2A 35.7k
EFFICIENCY
0.1µF MBRS340T3
LTC1624
22µF
COUT 100µF
10mA
100mA LOAD CURRENT
1624_07.eps
1624_06.eps
Figure Efficiency Plot Figure 24's Circuit
Figure High Performance 3.3V/2A Step-Down DC/DC Converter
basic step-down converter shown Figure This application shows 3.3V/2A converter operating from input voltage range 4.5V 25V. efficiency this circuit shown Figure Step-up SEPIC applications require low-side switch pulling inductor ground (see Figures 28). Since source MOSFET must grounded, switch (SW) LTC1624 also grounded order driver supply gate-to-source signal control MOSFET. these applications, voltage boost constant resulting 0V-5V gate-drive level. capacitor from boost switch still required, since this capacitor supplies gate-charge currents.
basic step-up converter shown Figure LTC1624 used create 12V/1A from source with efficiency shown Figure Efficiency above from 20mA close full load, dropping only order allow input voltages both above below output voltage, SEPIC converter used. example LTC1624 used 12V/0.5A SEPIC converter operating from input range shown Figure
330pF 100pF SENSE ITH/RUN BOOST 0.1µF Si4412DY 1000pF RSENSE 0.04 20µH
22µF
VOUT 12V/1A MBRS130LT3
LTC1624
35.7k
1624_08.eps
3.92k
COUT 100µF
Figure 12V/1A Step-Up Converter
AN84-20
Application Note
EFFICIENCY
10mA 100mA LOAD CURRENT
1624_09.eps
Figure Efficiency Plot Figure 26's Circuit
22µF MBRS130LT3 VOUT 12V/0.5A
1000pF 330pF 100pF SENSE ITH/RUN BOOST 0.1µF
RSENSE 0.082
LTC1624
Si4412DY
22µF
L1a, L1b:CTX50-4
35.7k
1624_10.eps
3.92k
COUT 100µF
Figure 12V/0.5A DC/DC Converter Operates from 5V-15V Inputs
COST 3.3V 1.XV POWER SUPPLY Nork voltage requirements microprocessors drop, need high power DC/DC conversion from 3.xV supply lower voltage keeps growing. LTC1430 very attractive choice such DC/DC applications, cost, high efficiency high output power capability. However, there problems: first, 3.xV does provide enough gate drive ensure RDS(ON) using external logic-level FETs; second, LTC1430 minimum input requirement. These obstacles both overcome using LTC1517-5 regulated charge pump generate input voltage LTC1430.
circuit shown Figure uses LTC1430 produce synchronous 3.3V 1.9V step-down DC/DC converter. circuit achieves 90.5% efficiency amps output current maximum output capability. (Refer LTC1430 data sheet detailed description LTC1430-based designs). Power LTC1430 derived from output LTC1517-5. LTC1517-5 switched capacitor charge pump available tiny, 5-pin SOT-23 package. part uses Burst Mode operation generate output from 2.7V input.The regulated supply powers internal circuitry LTC1430 ensures that LTC1430
AN84-21
Application Note
provide adequate gate drive external N-channel FETs. With insufficient gate drive, output power efficiency will significantly reduced high RDS(ON) FETs. this circuit, typical supply current drawn LTC1430 between 25mA 30mA, vast majority which needed charge discharge external FETs. Because LTC1517-5 maximum effective output impedance this current comfortably supplied from 3.3V input. input voltage drops lower, LTC1517-5 output also drop. However, with FETs shown Figure LTC1517-5 will provide 4.5V minimum supply LTC1430 input voltages down circuit's efficiency shown Figure Pulling SHDN LTC1430 will shut down power supply. will forced LTC1430 quiescent current will drop 1µA. Although LTC1517-5 does have shutdown feature, no-load operating current extremely 6µA. This keeps overall shutdown current below 10µA plus external leakage. (For further reductions shutdown current, 8pin LTC1522 used place LTC1517-5; LTC1522 same LTC1517-5 with shutdown.) additional LTC1517-5 circuitry will take much board space. entire circuit consumes only 0.045 in2.
3.3V VOUT 1.9V
EFFICIENCY
LOAD CURRENT
1517_02.EPS
Figure Efficiency Figure 29's Circuit
CERAMIC 3.3µF CERAMIC 10µF 0.1µF BAT54 LTC1517-5 0.22µF
3.3V
330µF 6.3V 0.1µF
2.4µH, SUMIDA CDRH127-2R4 MBRS120 4.99K
Si4410
LTC1430CS PVCC1 PVCC2 PGND SENSE IMAX FREQSET SENSE COMP SHDN 0.1µF
Si4410
VOUT 1.9V
0.018µF
330µF 6.3V
5.2k 0.012µF
390pF
10µF
1517 TA03
*AVX TANTALUM (207) 282-5111
Figure 3.3V 1.9V/6A Power Supply
AN84-22
Application Note
LT1374: 500kHz, 4.5A MONOLITHIC BUCK CONVERTER Karl Edwards Introduction LT1374 4.5A buck converter using on-chip switch. With 500kHz operating frequency integral switch, only external, surface mount components required produce complete switching regulator. LT1374's features include current mode control, external synchronization current (typically 20µA) shutdown mode. Improvements have been made reduce start-up headroom switching noise. novel power device layout makes possible high speed, bipolar, switch into surface mount SO-8 package. LT1374 also available TO-220 packages higher power applications. Application: 5V/4.25A Buck Converter With input 4.5A minimum switch current, LT1374 will into wide range applications. Figure shows typical buck converter with input range, output 4.25A output current capability. on-resistance switch, efficiency remains high over wide range currents, shown Figure reduce power dissipation, both BIAS boost circuit supplied from output. Several factors, including maximum current, core copper losses, size cost, affect choice inductor, high value, high current inductor gives highest output current with lowest ripple, expense large physical size cost. Lower inductance values tend physically smaller, have higher current ratings cheaper, output ripple current, hence ripple voltage, increases. input capacitor, experiences very high ripple currents, IOUT/2, tantalum capacitors needed. 4.25A output current, capacitors parallel required meet ripple current requirement. ripple current output capacitor, lower, still needs limit output voltage ripple. voltage drop across catch diode, significant effect overall converter efficiency, especially higher input voltages when switch duty cycle low. ability survive short-circuit conditions increase power rating. good electrical performance, must placed close LT1374. power dissipated will raise board's temperature around LT1374. This must taken into account when modeling taking bench measurements temperature.
1N914
0.27µF LT1374-5 BIAS SHDN 3.3nF MBRS330T3 L1** OUTPUT** 5V/4.25A
INPUT
BOOST
EFFICIENCY
10µF 50µF
100µF, SOLID TANTALUM
RIPPLE CURRENT RATING IOUT/2 COILTRONICS UP2-4R7; (561) 241-7876 INCREASE 10µH LOAD CURRENTS ABOVE 3.5A 20µH ABOVE
1374_02.EPS
LOAD CURRENT
1374_03
Figure Buck Converter
Figure Efficiency Figure 31's Circuit:
AN84-23
Application Note
Layout loop compensation capacitor, produces pole frequency response 240Hz. Unity-gain phase margin further improved with addition resistor, typically series with adding zero frequency response. This, however, cause largesignal subharmonic problem loop. output ripple voltage feeds back through error amplifier pin, changing current trip point next cycle. This changes voltage ripple output, loop closed. Adding second capacitor directly from ground form pole one-fifth switching frequency solves problem. high current, high speed circuits require careful layout obtain optimum performance. When laying PCB, keep trace length around high frequency switching components short possible. This minimizes radiation from loop created this path. These traces have parasitic inductance approximately 20nH/inch, which cause additional problem higher operating voltages. switch-off, current flowing trace inductance causes voltage spike. This addition input voltage across switch transistor. higher currents, additional voltage potentially cause output switching transistor exceed absolute maximum voltage rating. included. diminutive SO-8 package minimizes amount space LTC1504 fills while allowing adequate thermal dissipation 500mA load current levels. LTC1504 allows previously impossible least awkward) tasks completed with ease.
LTC1504: FLEXIBLE, EFFICIENT SYNCHRONOUS SWITCHING REGULATOR SOURCE SINK 500mA Dave Dwelley Introduction LTC1504 8-pin step-down switching regulator. consists 200kHz fixed frequency, voltage-feedback, buck-mode switching regulator controller pair power switches 8-pin package. LTC1504 also includes synchronous rectifier on-chip, maximizing efficiency minimizing external parts count while allowing output both sink source current: source sink 500mA with input voltages from 3.3V output voltages 1.26V. LT1504 achieve 100% duty cycle output switch, maximizing dropout performance with input-to-output voltage differentials. LTC1504 includes onboard precision reference user-programmable currentlimit soft-start circuits, allowing implementation full-featured power conversion circuits with minimum external components. LTC1504 architecture optimized maximum efficiency loads above 50mA does include light-load Burst Modecircuit. This penalizes efficiency very light loads allows device seamlessly shift between sourcing sinking current, opening whole class applications. micropower shutdown mode
Minimum Component-Count Circuits Figure shows fully functional LTC1504 3.3V regulator, including current limit soft-start, using fixed-output LTC1504-3.3 only external components. Efficiency above with load currents between
RIMAX** SHUTDOWN
IMAX
SHDN SENSE COMP
LEXT 47µH VOUT 3.3V/500mA
22µF
LTC1504-3.3
COUT 100µF
CSS* O.1µF
1000pF
TPSC226M016R0375 COUT SANYO 16CV100GX LEXT SUMIDA CD54-470 OPTIONAL: DELETE DISABLE SOFT START OPTIONAL: DELETE DISABLE CURRENT LIMIT
1504_01.EPS
Figure Minimum Parts-Count 5V-3.3V Converter
AN84-24
Application Note
RIMAX SHUTDOWN
IMAX
IMAX SHDN SENSE COMP LEXT 47µH VOUT 3.3V/500mA
SHDN SHDN
LEXT 47µH
TERMPWR 10µF CERAMIC
LINES
22µF
LTC1504-3.3
COUT 100µF
LTC1504 LTC1504 SENSE COMP COMP
COUT 100µF
O.1µF
7.5k 0.01µF
7.5k
220pF
1504_02EPS
220pF
1540_03.EPS
COUT TPSC107M006R0150 LEXT SUMIDA CD54-470
0.01µF
TPSC226M016R0375 COUT TPSE107M016R0125 LEXT SUMIDA CD54-470
Figure SCSI-2 Active Terminator
Figure Improved Transient Response
50mA 200mA, peaking 100mA remaining above maximum 500mA load. Current limit 500mA this example; reduced lowering value RIMAX. sets startup time approximately 25ms. circuit Figure relies output capacitor maintain loop stability with just single capacitor COMP pin. Figure uses surface mount electrolytic capacitor with about 400m ESR. tantalum output capacitor improve transient response output requires more complex compensation network COMP (Figure 34). There tradeoff made here: minimum component count solution simplest uses least expensive components pays penalty transient response. circuit Figure improved transient response actually uses less board space: tantalum output capacitor smaller than electrolytic device used Figure additional compensation components tiny 0603 surface mount devices. Note that input bypass capacitor both Figures type, relatively costly surge-tested tantalum capacitor. This small, surface mount device that surge current rating adequate support 500mA maximum load current LTC1504. Buck regulators (like LTC1504) inherently draw large currents from input bypass capacitor, capacitor type chosen must capable withstanding this current
without overheating. with switching regulator circuits, layout critical obtaining maximum performance; doubt, contact Applications Department component selection layout advice. Sink/Source Capability Improves SCSI Terminators Supply Splitters Figure shows adjustable-output LTC1504 connected 2.85V regulator SCSI terminator. ability LTC1504 circuit sink current makes ideal terminator applications, where load just likely putting current into regulator taking out. synchronous-buck architecture LTC1504 allows shift cleanly between sourcing sinking current, making ideal such applications. small number tiny external components required minimizes space used terminator circuit. output capacitor used along with optimized compensation network improve output transient response maintain maximum data fidelity.
SHUTDOWN IMAX 10µF CERAMIC SHDN SHDN 11.8k LEXT 47µH (22µH)* SPLIT SUPPLY 2.5V ±500mA
LTC1504 LTC1504 SENSE COMP COMP 7.5k 0.01µF
COUT 47µF
12.1k
220pF
1540_04.EPS
COUT TAJC476M016R LEXT SUMIDA CDRH73-470 (LOWER RIPPLE/HIGHER EFFICIENCY) *CDRH73-220 (FASTER TRANSIENT RESPONSE)
Figure Supply Splitter
AN84-25
Application Note
Substituting different feedback resistors (Figure creates supply splitter, which creates 2.5V "ground" allow analog circuitry operate from split supplies. circuits data converters like HIGH EFFICIENCY DISTRIBUTED POWER CONVERTER FEATURES SYNCHRONOUS RECTIFICATION Dale Eagar Introducing LT1339 LT1339 buck/boost converter that needs steroids. full-featured switching controller, LT1339 incorporates features needed system-level solutions. LT1339 innovative slope-compensation function that allows circuit designer freedom controlling both slope offset slope-compensation ramp. Additionally, LT1339 average current limit loop that yields constant output current limit, regardless input and/or output voltage. LT1339's actually input precision comparator, giving designer freedom select undervoltage lockout point hysteresis appropriate design. SYNC (soft-start) pins allow simple solutions system-level design considerations. Like Linear Technology controllers, LT1339 anti-shootthrough circuitry that ensures robustness that demanded real-world applications medium high power conversion.
operate from dual supplies, sink/source capability LTC1504 allows load currents returned directly 2.5V "ground" supply.
input voltages ranging from output voltages ranging from 1.3V 36V, LT1339 simple, robust solution your power-conversion problems. LT1339 ideal power levels ranging from tens watts tens kilowatts. LT1339 straightforward remarkably easy use. This power converter that's afraid 20A, even 150A load current. Distributed Power Figure details typical voltage buck converter. This circuit range with configurable output current voltage. This simple circuit delivers 250W load power into load while maintaining efficiencies mid-nineties. Higher Input Voltages circuit shown Figure limited because maximum rating (Abs Max) LT1339 pin. input voltage extended above inserting Zener diode where asterisk shown Figure This will extend input voltage Figure 37's circuit (the rating MOSFETs).
CINPUT 1000µF OS-CON
100k
1N914 BOOST LT1339 SENSE SENSE
1N5817 IRL3803 10µH RSENSE 0.002
RSENSE 0.01 0.005 0.002
ILIMIT
12VIN 5VREF SLOPE IAVG VREF
Q2-Q5 IRL3103D2
1500pF
COUTPUT 2200µF 6.3V OS-CON
1N5817
CAVG 2200pF RCOMP 4.7k CCOMP 2200pF 0.1µF
SYNC SGND PGND
RREF
1.66K 1.25K
1339_01.EPS
VOUT 3.3V 2.8V 1.8V 1.3V
*SEE TEXT
Figure 10V-18V 5V/50A Buck Converter
AN84-26
Application Note
(SUPPLIED SEPARATELY) 1N914 FMMT619 RSENSE CINPUT 0.01 1500µF 0.005 Q1-Q2 0.002 IRFZ44 10µH RSENSE 0.002
47µF
100k
ILIMIT
BOOST
FMMT720 FMMT619
1500pF CAVG 2200pF RCOMP 4.7k 2200pF 0.1µF
12VIN 5VREF SLOPE
3.3V Q3-Q6 IRFZ44
COUT 2200µF 6.3V OS-CON
LT1339 IAVG VREF SENSE SENSE
FMMT720
1N914
RREF
SYNC SGND PGND
1339_02.EPS
18.2K 8.66K 1.66k 1.25k
VOUT 3.3V 2.8V
Figure 5V/50A Out, High Power Buck Converter
15V-25V
1000µF
FZT849
RSENSE 0.02 1/2W 22µF
PRIMARY GROUND
ISOLATION BARRIER
SECONDARY GROUND
100k 0.1µF
MURS120 MURS 3.3µF Si4450 Si4450
0.1µF
12VIN 5VREF SLOPE SENSE+ SENSE- BOOST IAVG PHASE VREF SYNC SGND PGND LT1339
VOUT 5V/6A
IN4148
COUT 220µF OS-CON
T2** Si4539DY 0.1µF 1N914 1N914
230pF CAVG 2.2nF
CNY17-3 220pF
2.49k
SUD50N03 TURNS AWG20 77130-A7 POWER TRANSFORMER GATE-DRIVE TRANSFORMER (SEE FIGURE DETAILS)
COLL
LT1431 GND-F RREF 2.49k
GND-S
Figure Galvanically Isolated Synchronous Forward Converter (see Figure Details
AN84-27
Application Note
PHILIPS EFD20-3F3 CORE 93µH, 1150nH/T2 GAP) SECONDARY, TURNS TRIFILAR 26AWG PRIMARY, TURNS TRIFILAR 26AWG COILTRONICS VP1-1400 (500V ISOLATION) 2MIL POLYESTER FILM
1500VDC ISOLATION TUCK TAPE ENDS
localized gate voltages above threshold voltage bottom MOSFET. defeat physicists, 3.3V negative offset bottom gate drive, effectively making threshold bottom MOSFETs 3.3V harder reach (see Figure 38). This offset provided 3.3V Zener, capacitor, resistor 1N914 diode preceding gate bottom MOSFETs. Synchronous Forward Converter Figure details Galvanically isolated LT1339 synchronous forward converter. Operating rated load this circuit achieves efficiency with input efficiency with input. Figure shows details transformers used Figure 39's circuit. Synchronous Boost Converter
1339 .eps
Figure Transformer Details Figure 39's Circuit
Blame Physicists input voltage approaches 30V, bottom MOSFETs will begin exhibit "phantom turn-on." This phenomenon driven instantaneous voltage step drain, ratio CMILLER CINPUT, yields
LT1339 becomes synchronous boost controller when PHASE grounded. Figure details 250W boost converter that outputs from supply.
IRF3205 FMMT720 RSENSE 0.002 40µH FMMT619 1N914 BOOST FMMT619 IRF3205 FMMT720 10pF 0.1µF AWG12 77437-A7 SENSE+ SENSE- VREF PHASE IAVG RCOMP 7.5k CCOMP 1.5nF LT1339 5VREF SLOPE 2200pF RREF 1.2k (SUPPLIED SEPARATELY)
VOUT 28V/8.5A
12VIN 100k 47µF
COUT 2200µF
5V/60A CINPUT 220µF 6.3V
SYNC PGND SGND
10µF
CAVG 2.2nF
Figure This Synchronous Boost Converter Limits Input Current (DC)
AN84-28
Application Note
FIXED FREQUENCY, 500kHz, 4.5A STEP-DOWN CONVERTER SO-8 OPERATES FROM INPUT Karl Edwards Introduction LT1506 500kHz monolithic buck mode switching regulator, functionally identical LT1374 optimized lower input voltage applications. high 4.5A switch rating makes this device suitable primary regulator small medium power systems. small SO-8 footprint input operating range ideal local onboard regulators operating from system supplies. 4.5A switch included die, along with necessary oscillator, control logic circuitry simplify design. part's high switching frequency allows considerable reduction size external components, providing compact overall solution. LT1506 available standard 7-pin fusedlead SO-8 packages. maintains high efficiency over wide output current range keeping quiescent supply current using supply-boost capacitor saturate power switch. topology current mode fast transient response good loop stability. Full cycle-by-cycle short-circuit protection thermal shutdown provided. Both fixed 3.3V adjustable output voltage parts available. 3.3V Buck Converter circuit Figure step-down converter suitable local regulator supply 3.3V logic from power bus. high efficiency, shown Figure removes need bulky heat sinks separate power devices, allowing circuit placed confined locations. Since boost circuit only needs operate, boost diode still connected output, improving efficiency. Figure 42's circuit shows shutdown option. this pulled logic low, output disabled part goes into shutdown mode, reducing supply current 20µA. internal pull-up ensures correct operation when left open. SYNC pin, option package, used synchronize internal oscillator system clock. logic-level clock signal applied SYNC synchronize switching frequency range 580kHz 1MHz.
Current Sharing Multiphase Supply circuit Figure uses multiple LT1506s produce power supply. There several advantages using multiple switcher approach compared single larger switcher. inductor size considerably reduced. Inductor size proportional energy that needs stored core. Three inductors store less energy (1/2Li2) than single coil, they much smaller. addition, synchronizing three converters 120° phase with each other reduces input output ripple currents. This reduces ripple rating, size cost filter capacitors.
1N914 0.68µF INPUT BOOST LT1506-3.3 SHDN SENSE 1.5nF
10µF 50µF CERAMIC
OPEN HIGH
EFFICIENCY
OUTPUT 3.3V
MBRS330T3
100µF, SOLID TANTALUM
1506 TA01
LOAD CURRENT
Figure 3.3V Step-Down Converter
Figure Efficiency Load Current Figure 42's Circuit
AN84-29
Application Note
3-BIT RING COUNTER 1.8MHz MARCON THCS50E1E106Z ROHM RB051L-40 1N914 DO3316P-682
LT1506-SYNC SYNC BOOST
LT1506-SYNC SYNC BOOST
LT1506-SYNC SYNC BOOST 5.36k 10µF
INPUT
10µF
10µF
68nF
10µF
4.99k
6.8µH
330nF
Current Sharing/Split Input Supplies Current sharing accomplished connecting pins common compensation capacitor. output error amplifier stage, number devices connected together. effective composite error amplifier product individual devices. Figure compensation capacitor, been increased Tolerances reference voltages cause small offset currents flow between pins. overall effect that loop regulates output voltage somewhere between minimum maximum references devices used. Switch-current matching between devices will typically better than 300mA over full current range. negative temperature coefficient VC-to-switch-current transconductance prevents current hogging. common voltage forces each LT1506 operate same switch current, same duty cycle. Each device operates duty cycle defined input voltage. This useful feature distributed power system. input voltage each device could vary drops across backplane, copper losses, connectors common signal ensures that loading still shared between devices.
6.8µH
330nF
Figure Current-Sharing 5V/12A Supply
6.8µH
330nF
Synchronized Ripple Currents ring counter generates three synchronization signals 600kHz, duty cycle, phased 120° apart. sync input will operate over wide range duty cycles, further pulse conditioning needed. full load, each device's input ripple current trapezoidal wave 600kHz, shown Figure Summing these waveforms gives effective input ripple complete system. resultant waveform, shown bottom Figure remains frequency increased 1.8MHz. higher frequency eases requirements value input filter without increase ripple current rating that would normally occur. Although only single input capacitor required, practical layout restrictions usually dictate individual capacitor each device. Figure shows output ripple current waveforms. resultant 1.8MHz triangular waveform maximum amplitude 350mA input voltage 10V. This significantly lower than would expected output. Interestingly, inputs 7.6V 15V, theoretical summed output ripple current cancels completely. reduce board space ripple voltage, ceramic capacitors. Loop compensation capacitor must adjusted when using ceramic output capacitors, lack effective series resistance (ESR).
1506
AN84-30
Application Note
Redundant Operation typical tantalum compensation value 1.5nF increased 22nF ceramic output capacitor. synchronization used internal oscillators free run, circuit will operate correctly, ripple cancellation will occur. Input output capacitors must ripple rated individual output currents. circuit shown Figure fault tolerant when operating less than output current. power stage fails open circuit, output will remain regulation. feedback loop will compensate raising voltage pin, increasing switch current remaining devices.
PHASE
PHASE CURRENT
TIME
CURRENT
TIME
PHASE
PHASE CURRENT
TIME
CURRENT
TIME PHASE CURRENT
PHASE
CURRENT
TIME TOTAL
TIME TOTAL
CURRENT
TIME
CURRENT
TIME
Figure Input Current
Figure Output Current
AN84-31
Application Note
VOLTAGE PROGRAMMER INTEL MOBILE PROCESSORS Peter Guan Figure shows VID-programmed DC/DC converter Intel mobile processor that uses LTC1435A LTC1706-19 deliver output current with programmable VOUT 1.3V 2.0V from 4.5V 22V. Simply connecting LTC1706-19's SENSE pins LTC1435A's VOSENSE SENSE- pins, respectively, closes loop between output voltage sense feedback inputs LTC1435A regulator with appropriate resistive divider network, which controlled LTC1706-19's four input pins.
4.5V COSC 43pF 0.1µF LTC1435A COSC RUN/SS INTVCC 51pF SGND VOSENSE BOOST PGND 0.22µF 3.3µH SENSE 0.1µF
Each must grounded driven produce digital input, whereas digital high input generated either floating connecting VCC. LTC1706-19 fully compatible operational over input voltage range that much higher than VCC. Table shows inputs their corresponding output voltages. VID3 most significant (MSB) VID0 least significant (LSB). When four inputs low, LTC1706-19 sets regulator output voltage 2.00V. Each increasing binary count equivalent decreasing output voltage 50mV. Therefore,
Si4410DY
10µF,
SENSE
0.015
VOUT 1.30V 2.00V/7A
220pF
1000pF
MBRS -140T3 LTC1706-19
4.7µF Si4410DY CMDSH-3
COUT 820µF
SENSE- SENSE+ 1000pF
FROM
COILCRAFT D05022P-332HC
Figure Intel Mobil Pentium Power Converter
4.8V 2.7V 5.5V LTC1706-19 0.1µF VID0 SENSE VID1 100pF VID2 VID3 470pF 6.8k LTC1624 1000pF SENSE- 0.1µF 10µH MBRS340T3 SUMIDA CDRH125-10 RSENSE 0.033 Si4412DY
ITH/RUN BOOST
22µF VOUT 1.3V-3.0V
COUT 100µF
Figure High Efficiency SO-8, N-Channel Switching Regulator with Programmable Output
AN84-32
Application Note
Table Inputs Coresponding Output Voltages
Code 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 VID3 Float Float Float Float Float Float Float VID2 Float Float Float Float Float Float Float VID1 Float Float Float Float Float Float Float VID0 Float Float Float Float Float Float Float Output 2.00V 1.95V 1.90V 1.85V 1.80V 1.75V 1.70V 1.65V 1.60V 1.55V 1.50V 1.45V 1.40V 1.35V 1.30V
Figure shows combination LTC1624 LTC1706-19 configured high efficiency step-down switching regulator with programmable output 1.3V 2.0V from input 4.8V 20V. Using only N-channel power MOSFET, SO-8 packaged parts offer extremely versatile, efficient, compact regulated power supply. Figure shows LTC1436A-PLL LTC1706-19, combination that yields high efficiency noise synchronous step-down switching regulator with programmable 1.3V outputs external frequency synchronization capability. Besides family 1.19V-referenced DC/DC converters, LTC1706-19 also used program output voltages regulators with different onboard references. Figure shows LTC1706-19 programming output LT1575, UltraFasttransient response, dropout regulator that ideal today's powerhungry desktop microprocessors. However, since LT1575 1.21V reference instead 1.19V reference, output will range from 1.27V 2.03V steps 50.8mV.
obtain 1.30V output, three MSBs left floating while only VID0 grounded. cases where four inputs tied high left floating, such when processor present system, regulated 1.25V output generated VSENSE.
EXTERNAL FREQUENCY SYNCHRONIZATION 4.5V-22V
0.1µF
COSC 39pF 0.1µF
PLLIN COSC RUN/SS
0.22µF IRLML2803 Si4412DY 3.3µH
22µF, RSENSE 0.02
LTC1436A-PLL INTVCC
VOUT 1.30V- 2.00V/5A SENSE
510pF 100pF SGND VOSENSE
BOOST PGND
MBRS -140T3 LTC1706-19
4.7µF Si4412DY CMDSH-3
COUT 100µF
SENSE- SENSE+ 1000pF
FROM
Figure High Efficiency, Noise, Synchronous Step-Down Switching Regulator with Adjustable Output Voltage
AN84-33
Application Note
3.3V LTC1706-19 VID0 SENSE VID1 VID2 VID3 LT1575 SHDN IPOS INEG GATE COMP IRFZ24 220µF 3.3V
VOUT 1.27V 2.03 50.8mV STEPS
7.5k 10pF 1000pF
24µF
Figure UltraFast Transient Response, Dropout Regulator with Adjustable Output Voltage
DC/DC CONTROLLER ENABLES HIGH STEP-DOWN RATIOS Greg Dittmer Capabilities LTC1435 LTC1435 high efficiency synchronous DC/DC controller been extremely popular notebook computers other battery-powered equipment noise, constant-frequency operation dual N-channel drive outstanding high current efficiency without sacrificing dropout operation. However, 400ns 500ns minimum on-time requires lower operating frequencies (<150kHz) regulate output voltages below 2.0V
LTC1435A MOSFET LIMIT 1.25 LTC1435
high. This occurs because VOUT/(VIN thus, duty ratios, frequency must decreased keep tON(MIN). Lowering operating frequency usually desirable because increases noise componnent size. What happens minimum on-time violated LTC1435? increased that on-time falls below tON(MIN), LTC1435 will begin skip cycles remain regulation. During this "cycle-skipping" mode, output remains regulation operating frequency decreases, causing inductor ripple current output ripple voltage increase.
RECOMMENDED REGION ON-TIME EFFICIENCY
MINIMUM ON-TIME (ns)
MAXIMUM
250kHz ILOAD 4.7µH 25°C 1.75 2.25 OUTPUT VOLTAGE
AN70
IMAX INDUCTOR RIPPLE CURRENT IMAX)
AN70
RSENSE
Figure LTC1435/LTC1435A Maximum Comparison
Figure LTC1435A Minimum On-Time Inductor Ripple Current
AN84-34
Application Note
COSC 43pF 0.1µF LTC1435A 330pF 51pF COSC RUN/SS INTVCC 100pF SGND VOSENSE BOOST PGND 4.5V
4.7µH 0.1µF Si44412DY
10µF, VOUT 1.60V/3A 35.7k 102k COUT 100µF, 6.3V
RSENSE 0.033
4.7µF Si44412DY
MBRS -140T3
SENSE- SENSE+ 1000pF
CMDSH-3 CENTRAL (516) 435-1110
Figure LTC1435A 1.6V/3A Converter 250kHz)
Enter LTC1435A operating envelope been substantially expanded with introduction LTC1435A DC/DC controller, which outstanding features LTC1435 with reduced minimum on-time 300ns less improved noise immunity output voltages. With these improvements, high performance output voltages down 1.3V achieved with operating frequencies excess 250kHz from input supply voltages above 22V. Figure shows resulting improvement maximum output voltage result reduced minimum on-time. LTC1435A's minimum on-time dependent speed internal current comparator, which turn dependent amplitude signal comparator monitoring: inductor ripple current. Thus, higher ripple current, lower minimum on-time. Figure shows minimum on-time varies function inductor ripple amplitude. higher amplitudes, tON(MIN) less than 250ns; amplitudes 350ns more. This means that duty cycle applications where on-time approaching tON(MIN), there minimum ripple current amplitude, hence, maximum inductance necessary prevent cycle skipping. expressed differently, lower inductance, higher maximum that achieved before minimum on-time violated cycle skipping occurs. most applications, ripple only reduces minimum on-time also optimizes efficiency.
1.6V Converter 250kHz Figure shows LTC1435A configured N-channel synchronous buck topology 1.6V/ converter running 250kHz. 43pF COSC capacitor sets internal oscillator frequency 250kHz sense resistor sets maximum load current 1.6V converter, on-time required
1.6/(22 250kHz) 291ns
LTC1435A this? maximum inductor ripple
VOUT VOUT/VIN) 1.6/22) 250kHz 4.7µH 1.3A
which maximum load. From Figure ripple gives minimum on-time 235ns, which well below 291ns required this application, cycle skipping will occur. 10µH inductor used, ripple amplitude drops 0.6A minimum on-time increases 280ns. This does provide much margin below 291ns on-time required, thus 4.7µH inductor better choice.
AN84-35
Application Note
Intel Mobile Processor Power Converter Figure shows LTC1435A used with LTC1706-19 implement Intel Mobile Pentium® Processor power converter. This DC/DC converter provides digitally selectable output voltages over range 1.3V 2.0V
4.5V COSC 43pF 0.1µF
50mV increments 250kHz load current. selectable output voltage implemented replacing conventional feedback resistor network with LTC1706-19, which provides appropriate feedback resistor ratios internally. proper ratio selected with 4-bit digital input pins.
LTC1435A COSC RUN/SS INTVCC
0.1µF
Si4410DY 3.3µH
10µF,
SENSE
0.015 0.22µF LTC1706-19 SENSE
VOUT 1.30V 2.00V/7A
220pF
1000pF 51pF SGND VOSENSE
BOOST PGND
4.7µF Si4410DY CMDSH-3 CENTRAL (516) 435-1110 MBRS -140T3
COUT 820µF
SENSE- SENSE+ 1000pF
FROM
FIgure Intel Mobil Pentium Power Converter
LTC1627 MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR MAXIMIZES SINGLE DUAL LI-ION BATTERY LIFE Jaime Tseng Introduction LTC1627 addition growing family power management products optimized Li-Ion batteries. Li-Ion batteries, with their high energy density, becoming chemistry choice many handheld products. demand longer battery operating time continues increase operating voltages submicron DSPs microcontrollers decreases, more demands placed DC/DC conversion. LTC1627 monolithic, current mode synchronous buck regulator specifically designed meet these demands. LTC1627, with operating supply range 2.65V 8.5V, operate from Li-Ion batteries well 6-cell NiCd NiMH battery packs.
LTC1627 incorporates power saving Burst Mode operation 100% duty cycle dropout maximize battery operating time. Burst Mode operation, both power MOSFETs turned increasing intervals load current drops. Along with gate-charge savings, unused circuitry shut down between burst intervals, reducing quiescent current 200µA. This extends operating efficiencies exceeding over decades output load range. Typical Applications LTC1627, with synchronous switching attendant circuitry, provides means easily constructing secondary flyback regulator, shown Figure This flyback regulator regulated secondary feedback resistive divider tied SYNC/FCB pin. This forces continuous operation whenever drops below groundreferenced threshold 0.8V. Power then drawn from secondary flyback regulator whether main output loaded not.
AN84-36
Application Note
CITH 47pF 0.1µF CIN* 22µF SYNC/ 249k
80.6k MBR0520LT1
8.5V
RUN/SS LTC1627
VSEC 3.3V/100mA 22µF*** 6.3V 1.8V VOUT 1.8V/0.3A
25µH 100k
TPSC226M016R0375 TPSC107M006R0150 TAJA226M006R (207) 282-5111
COILTRONICS CTX25-1
COUT** 100µF 6.3V
(561) 241-7876 MMSZ4678T1 10mA LOAD CURRENT RECOMMENDED
80.6k
Figure Dual-Output 1.8V/0.3A 3.3V/100mA Application
Li-Ion Step-Down Converter
Figure schematic diagram showing LTC1627 being powered Li-Ion batteries. components shown this schematic surface mount have been selected minimize board space height. output voltage 3.3V, easily programmed other voltages.
CITH 47pF 0.1µF SYNC/
8.4V
RUN/SS LTC1627
25µH* 249k 80.6k
Single Li-Ion Step-Down Converter
circuit Figure intended input voltages below 4.5V, making ideal single Li-Ion battery applications. Diodes capacitors comprise bootstrapped charge pump realize negative supply pin, return P-channel MOSFET driver. This allows Figure 57's circuit maintain switch RDS(ON) down UVLO trip voltage.
CITH 47pF 0.1µF 2.8V-4.5V BAT54S** 22µF SYNC/
22µF *SUMIDA CD54-250 (847) 956-0666 TPSC107M006R0150 TPSC226M016R0375 (207) 282-5111
VOUT 3.3V/0.5A
COUT 100µF 6.3V
Figure Lithium-Ion 3.3V/0.5A regulator
0.1µF
RUN/SS LTC1627 0.1µF
SUMIDA CD54-150 (847) 956-0666 ZETEX BAT54S (516) 543-7100 TPSC107M006R0150 TPSC226M016R0375 (207) 282-5111 15µH* 169k 80.6k VOUT 2.5V/0.5A
100µF 6.3V
Figure Single Lithium-Ion 2.5V/0.5A Regulator
AN84-37
Application Note
LTC1625 CURRENT MODE DC/DC CONTROLLER ELIMINATES SENSE RESISTOR
VOUT 2.5V LTC1625 LTC1435
Christopher Umminger
Introduction Power supply designers have tool their quest ever higher efficiencies. past, when designing step-down DC/DC converter, choose between high efficiency voltage mode control many benefits current mode control. Although voltage mode control offers high efficiency simple topology, difficult compensate, poor rejection inputvoltage transients does inherently limit output current under fault conditions, such output short circuit. Current mode control overcomes these problems adding control loop regulate inductor current addition output voltage. Unfortunately, sense resistor required measure this current, which adds cost complexity while reducing converter efficiency. However, with LTC1625 RSENSEcontroller, enjoy benefits current mode control without penalties using sense resistor. LTC1625 step-down DC/DC switching regulator controller that capable wide range operation with inputs from 3.7V 36V. Fixed output voltages 3.3V selected external resistive divider used obtain output voltages from 1.19V nearly
EFFICIENCY
LOAD CURRENT
DI_1068_02a.
Figure Efficiency Load Current
full input voltage. controller provides synchronous drive N-channel power MOSFETs retains advantage dropout operation typically associated with P-channel MOSFETs. Burst Modeoperation maintains efficiency load currents, overridden assist secondary-winding regulation forcing continuous operation. addition eliminating sense resistor, LTC1625 further reduces external parts count incorporating oscillator timing capacitor. oscillator frequency 150kHz, 225kHz, injection locked frequency between these points.
Design Examples Figure shows LTC1625 application supplying 2.5V output using external feedback divider. Si4410DY MOSFETs from Siliconix allow this converter deliver
0.1µF
Si4410DY
LTC1625 EXTVCC SYNC RUN/SS SGND VOSENSE VPROG
10µF
0.1µF
820pF
O.22µF
MBRS140T3
VOUT 2.5V/5A COUT 100µF 0.065
BOOST INTVCC PGND
220pF
CVCC 4.7µF
Si4410DY
CMDSH-3
Figure 2.5V/5A Adjustable-Output Supply
AN84-38
Application Note
0.1µF
Si4412DY
INTVCC 0.1µF 220pF
LTC1625 EXTVCC SYNC RUN/SS SGND VOSENSE VPROG BOOST INTVCC PGND **DB
22µF
O.1µF
39µH MBRS140T3 35.7k 3.92k Si4412DY
VOUT 12V/2.2A COUT 100µF 0.030
CVCC 4.7µF
SUMIDA CDRH127-390MC CMDSH-3
Figure 12V/2.2A Adjustable-Output Supply
load current. Ripple current 1.8A (36% full load) current limit occurs around Note also that EXTVCC connected external supply. This increases efficiency drawing roughly gate charge current from supply lower than VIN. efficiency plot this circuit shown Figure LTC1435 with identical components power path also plotted comparison. lower output voltages such this, sense resistor responsible increasing share total power loss. eliminating this source loss, LTC1625 easily able deliver efficiency PolyPhase SWITCHING REGULATORS OFFER HIGH EFFICIENCY VOLTAGE, HIGH CURRENT APPLICATIONS Craig Varga Introduction recent years, there been tendency digital world toward smaller device geometries higher gate counts. This requirements lower voltages higher currents logic supplies. this trend continues, levels under over 30A, conventional buck regulator approach ceases viable. Switch currents high single device handle, inductor energy storage exceeds what available surface mount technology ripple current requirements input capacitors dictate many capacitors parallel. Although this seem like enough challenge,
greater than high load current. benefit reduced loss readily apparent highest loads. controller makes transition Burst Mode operation below around which keeps efficiency high moderate loads. circuit demonstrating wide output range LTC1625 shown Figure This application uses Si4412DY MOSFETs deliver output 2.2A. Note that SYNC tied high 225kHz operation order reduce inductor size ripple current. transient response requirements also become much more severe. question that arises there topology that solve these problems simultaneously? answer "PolyPhaseTM." What PolyPhase, Anyway? Since apparent that multiple FETs need paralleled handle current requirements, question whether there drive them intelligently, rather than brute force. solution stagger turn-on times that dead bands input current waveform "filled up," speak. simplest implementation, there essentially independent synchronous buck regulators operating 180° phase. effect this that input output ripple currents channels tend cancel during steady-state operation. This results significant reductions both input
AN84-39
BAW56LT1 SYNC1 SYNC2 0.002 TRACE +VIN MMBT3906LT1 470µF 6.3V 470µF 6.3V 0.8µH ETQP1F0R8LB 6800pF 470µF 6.3V
AN84-40
BAT54 ISENSE1 47µF CHARGE PUMP OPTIONAL BAT54 0.47µF
Si4410DY Si4410DY
Application Note
SYNC1
CLOCK LTC1430ACS8 Si4410DY
22µF
Si4410DY
PVCC2 SHDN COMP PVCC1
1000pF
0.1µF
470µF 6.3V 9.76k 10k,
180pF
100pF, NPO, 1500pF
+VOUT 2.5V/30A OUTPUT
CHARGE PUMP OPTIONAL BAT54 C27, 0.47µF
3.09k Si4410DY Si4410DY
CD4047
(POWER FROM
ISENSE2
0.002 TRACE
0.8µH ETQP1F0R8LB
470µF 6.3V
470µF 6.3V
+VIN INPUT
Figure 2-Phase Synchronous Buck Regulator
SYNC2 PVCC2 SHDN COMP PVCC1 LTC1430ACS8 1500pF Si4410DY Si4410DY
0.022µF 180pF
6800pF 470µF 6.3V
470µF 6.3V
9.76k
1000pF
22µF
4.3k
ISENSE2
3300pF
ISENSE1 0.022µF
3300pF
4.3k
LT1006 SHARE AMPLIFIER
NOTES: RESISTORS UNLESS NOTED OTHERWISE. INPUT/OUTPUT CAPACITORS KEMET T510 SERIES TRACE RESISTORS R11, 0.1" WIDE 0.675" LONG
(408) 986-0424
Application Note
VOUT 3.3V EFFICIENCY VOUT VOUT 2.5V 100mV/DIV 160mV
CURRENT
10µs/DIV
Figure Efficiency Figure 61's Circuit,
DC201 F01b
Figure Transient Response with Load Step (100ns Rise Time)
output capacitor requirements. There also fourfold reduction total inductor energy storage requirement, which means much smaller inductors vastly improved transient dynamics. During large load step, channels operate maximum duty factor attempt maintain desired output voltage. Both inductor currents slew rapidly additive, since they going same direction. Hence, slew rate double what single channel could equal inductor values. However, ripple current cancellation during steady-state conditions, inductors reduced approximately one-half value that single channel design would require equal ripple currents. Since during slew they appear operating parallel, actual slew rate four times that single channel design with equal steady-state output ripple current. Both input output ripple frequencies double those single-channel design, further simplifying filtering requirements.
Stop Two? channels good, aren't more channels better? word, yes. principle, there limit number parallel channels that added. number channels, increases, ripple frequency increases times single-channel frequency. Input output ripple currents continue decrease. Diminishing returns reached rises above three. three stages, ripple reductions very substantial dynamic performance excellent. Adding more channels produces slight improvements dramatic gains will have been realized only real penalty added complexity. bottom line that PolyPhase designs offer considerable reduction cost volume power devices expense little added complexity control circuitry.
CHANNEL 5A/DIV CHANNEL TOTAL INPUT RIPPLE CURRENT, UNFILTERED CHANNEL 5A/DIV 306kHz 2.5V 2µs/DIV 2µs/DIV
20mV/DIV
Figure Output Ripple with Load
Figure Ripple Cancellation-Input
AN84-41
Application Note
nize LTC1430s. Unfortunately, simply connecting regulators parallel recipe instant disaster. output voltages regulators will slightly different normal component tolerances. Therefore, higher output voltage channel will attempt supply full load current, while lower voltage output will sink current from output desperate attempt reduce output voltage where thinks should result like chasing tail, with large currents running around circle going nowhere. solves this problem. Because channels identical, output currents same, input currents will also. value sense resistors included input power path allow circuit measure input current. then forces input current channel match input current channel making small adjustments channel two's output voltage. does this adding subtracting small amount current from channel two's feedback divider. sense resistors short lengths trace only need ratiometrically accurate. absolute value these resistors important (see Linear Technology Application Note Appendix discussion design trace resistors). only remaining trick circuit role associated circuitry. start-up, LTC1430's clock frequency slowed down approximately 10kHz until output voltage rises approximately desired level. during this start-up phase, attempt made synchronize controller very high frequency, oscillator ramp amplitude never rises level sufficiently high trip comparator enable drivers. Therefore, output gets stuck ground. fixes this forcing sync signals high during turn-on transient. Once output voltage nears final level, clock signals allowed synchronize controllers.
5A/DIV CHANNEL CHANNEL
2µs/DIV
Figure Ripple Cancellation-Output
2-Phase Design Example circuit shown Figure 2-phase, voltage mode- control, synchronous buck regulator designed input output voltages below 3.3V. intended power large memory arrays, ASICs, FPGAs like server workstation applications. output capable more than amps continuous outputs 2.5V below, with peak current capability greater than amps. design entirely surface mount maximum height above board 5.5mm. Overall board area only 4.24 in2. Efficiency excellent, seen curve Figure Output ripple voltage shown Figure circuit's dynamic response load step shown Figure response dominated output capacitor's shows output voltage recovered original level under 10µs. Figures show input output ripple currents cancel. Circuit Operation basic design consists LTC1430CS8-based synchronous buck regulators connected parallel operated 180° phase. CD4047 oscillator, used generate required clock signals synchro-
AN84-42
Application Note
LTC1622: INPUT VOLTAGE, CURRENT MODE BUCK CONVERTER San-Hwa Chee
EFFICIENCY
4.2V 3.3V 8.4V
Introduction 8-pin LTC1622 step-down DC/DC controller designed help system designers harness available energy from lithium-ion batteries several ways. wide operating input-voltage range (2.0V absolute maximum 10V) 100% duty cycle allows dropout maximum energy extraction from battery. part's quiescent current, 400µA, with shutdown current 15µA, extends battery life. user-selectable Burst Mode operation enhances efficiency load current. portable applications where board space premium, LTC1622 operates constant frequency 550kHz synchronized frequencies 750kHz. High frequency operation allows small inductors, making this part ideal communications products. LTC1622 comes tiny 8-lead MSOP package, providing complete power solution while occupying only small area. 2.5V/1.5A Step-Down Regulator typical application circuit using LTC1622 shown Figure This circuit supplies 1.5A load 2.5V with input supply between 2.7V 8.5V. 0.03 sense resistor selected ensure that circuit capable
0.001
VOUT 2.5V RSENSE 0.03 0.100 0.010 LOAD CURRENT 1.000
Figure Efficiency Load Current Figure 67's Circuit (Burst Mode Operation Enabled)
supplying 1.5A input voltage. addition, sublogic threshold MOSFET used, since circuit operates input voltages 2.7V. circuit operates internally frequency 550kHz. 4.7µH inductor chosen that inductor's current remains continuous during burst periods load current. output voltage ripple, capacitor (100m) used. Efficiency Considerations efficiency curves Figure 67's circuit shown Figures Figure shows efficiency with Burst Mode enabled, whereas Figure Burst Mode defeated. (Burst Mode defeated connecting SYNC/Mode ground.) Note that, load currents, efficiency higher with Burst Mode operation. However, constant frequency operation still achievable
0.03
2.5V-8.5V
220pF
10µF
LTC1622 SENSE- PDRV SYNC/MODE RUN/SS 470pF
Si3443DV 4.7µH 159k VOUT
2.5V/1.5A 47µF
MURATA CERAMIC GRM235Y5V106Z (814) 236-1431 SANYO POSCAP 6TPA47M (619) 661-6835 MURATA LQN6C-4R7M04 (814) 237-1431
IR10BQ015 (310) 322-3331 DALE, 0.25W (605) 665-9301
Figure LTC1622 Typical Application: 2.5V/1.5A Converter
AN84-43
Application Note
4.2V EFFICIENCY 0.001 8.4V VOUT 2.5V RSENSE 0.03 0.010 0.100 1.000 0.1ms/DIV OUTPUT VOLTAGE COUPLED) 0.1V/DIV 3.3V
LOAD CURRENT
Figure Efficiency Load Current Figure 66's Circuit (Burst Mode Operation Disabled)
Figure Transient Response with Burst Mode Operation Enabled; Load Step 50mA 1.2A
lower load currents with Burst Mode operation defeated. kinks efficiency curves indicate transition Burst Mode operation. components Figure have been carefully chosen provide amount output power using minimum board space. Efficiency also prime consideration selecting components, illustrated Figures Figures show transient response VOUT with load step from 50mA 1.2A. Figure Burst Mode enabled, while Figure defeated. Note that output voltage ripple middle portion photographs) higher Burst Mode operation than with Burst Mode disabled 50mA load current. Applications that require better transient response circuit Figure whose components selected specifically this requirement. Figures show response with without Burst Mode operation, respectively. Note that transient response been
0.03
enhanced significantly. However, this comes expense slightly reduced efficiency load currents, indicated efficiency curves Figures
OUTPUT VOLTAGE COUPLED) 0.1V/DIV
0.1ms/DIV
Figure Transient Response with Burst Mode Operation Inhibited; Load Step 50mA 1.2A
2.5V 8.5V
47µF
100pF
LTC1622 SENSE- PDRV SYNC/MODE RUN/SS
Si3443DV 1.3µH
TPSD476M016R0150 (803) 946-0362 TPSD476M016R0065 MURATA LQN6C-1R5M04 (814) 237-1431
IR10BQ015 (310) 322-3331 DALE, 0.25W (605) 665-9301
159k
VOUT 2.5V/1.5A 100µF
470pF
Figure 2.5V/1.5A Converter with Improved Transient Response
AN84-44
Application Note
OUTPUT VOLTAGE COUPLED) 0.1V/DIV
OUTPUT VOLTAGE COUPLED) 0.1V/DIV
0.1ms/DIV
0.1ms/DIV
Figure Transient Response with Burst Mode Operation Enabled; Load Step 50mA 1.2A
Figure Transient Response with Burst Mode Operation Inhibited; Load Step 50mA 1.2A
EFFICIENCY
4.2V
3.3V
3.3V 0.001 VOUT 2.5V RSENSE 0.03 0.010 0.100 LOAD CURRENT 1.000 8.4V 4.2V
8.4V 0.001 VOUT 2.5V RSENSE 0.03 0.010 0.100 LOAD CURRENT 1.000
Figure Efficiency Load Current Figure 72's Circuit (Burst Mode Operation Enabled)
Figure Efficiency Load Current Figure 72's Circuit (Burst Mode Operation Disabled)
EFFICIENCY
AN84-45
Application Note
WIDE INPUT RANGE, HIGH EFFICIENCY STEP-DOWN SWITCHING REGULATORS Jeff Schenkel Introduction LT1676/LT1776 current mode switching regulator optimized high efficiency operation high input voltage, output voltage buck topologies. These parts pin-for-pin compatible virtually identical operation, only difference being their internal oscillator frequencies-100kHz LT1676 200kHz LT1776. They operate fixed frequency mode opposed constant off-time on-time, instance) externally synchronized higher switching frequency. internal output switch rated nominal peak current 700mA, which typically accommodates output currents 500mA. input voltage range 7.4V 60V. Maintaining acceptable efficiency upper half this input voltage range requires very fast output-switch edge rates. LT1676/LT1776 contain specialized output circuitry deliver this performance. Additionally, they contain circuitry monitor output load level reduce leading-edge switch rate (turn-on) when output load light. This arrangement helps avoid pulse skipping light load, with consequent subharmonic behavior.
True current mode operation supported, with well known advantages switching regulator operation. shutdown implements pair functions. Pulling down near ground turns part almost completely reduces quiescent current tens microamperes. second shutdown function acts threshold roughly 1.25V. Below this level, part operates normally, except that output switching action inhibited. This allows implementation undervoltage lockout function instance, external resistor divider. LT1676/LT1776 available both 8-pin PDIP packages. Applications
Minimum Component-Count Application
Figure shows basic "minimum component count" application using LT1676. circuit produces 5.0V 500mA IOUT with input voltages range 48V. typical POUT/PIN efficiency shown Figure pulse skipping observed down zero external load. (The several milliamperes drawn acts sufficient preload.) shown, SHDN SYNC pins unused, however either both) optionally driven external signals desired.
39µF 100pF
SHDN LT1676 SYNC 2200pF MBRS1100 220µH
100µF
EFFICIENCY
36.5k 12.1k
VOUT 500mA
100pF 3.3V VOUT VERSION: 24.3k, 14.7k 150µH, DO3316P-154 IOUT: 500mA
PANASONIC (201) 348-7522 CASE TPSD107M010R0080 (803) 946-0362 COG/NPO MOTOROLA 100V, SCHOTTKY (800) 441-2447 COILCRAFT DO3316P-224 (847) 936-6400
1676 F04a
LOAD CURRENT (mA)
1000
1676 F04b
Figure Minimum Component-Count Application
Figure Efficiency Figure 77's Circuit
AN84-46
Application Note
100pF
15µF
SHDN LT1776 SYNC 68µH 100µF VOUT 400mA
EFFICIENCY
MBRS1100 2200pF 100pF
36.5k 12.1k
CASE 15µF TPSD156M035R0300 (803) 946-0362 CASE 100µF TPSD107M010R0080 2200pF, 100pF, COG/NPO
MOTOROLA 100V, SCHOTTKY MBRS1100 (800) 441-2447 COILCRAFT DO1608C-683 (847) 936-6400
1776 F07a
LOAD CURRENT (mA) 1000
1776 F07b
3.3V VOUT VERSION: IOUT: 500mA 47µH, DO1608C-473 24.3k, 14.7k
Figure Minimum Board Application
Figure Efficiency Figure 79's Circuit
Minimum Board Area Application
previous application example used LT1676 demonstrate simultaneously maximum input voltage output current capability. such, input bypass capacitor choice high frequency aluminum electrolytic type, rated 63V. Also, 100kHz switching rate LT1676 requires inductor about 220µH. DO3316 device size chosen support output current requirements. However, both these components physically large. application example Figure shows circuit that much smaller physically than previous minimum component count application. nominal 200kHz switching frequency LT1776 allows physically smaller 68µH inductor-a Coilcraft DO1608C-683. This inductor will support output current 400mA However, part incapable withstanding indefinite short circuit ground. (Momentary shorts seconds less still tolerated.) Additionally, bulky aluminum electrolytic capacitor previously been replaced compact 35V-rated tantalum type. result postage-stamp-sized circuit with efficiency shown Figure load current. This surprising, LT1676 itself represents fixed power overhead. possible improve light load efficiency Burst Modeoperation. Figure shows LT1676 configured Burst Mode operation. Output voltage regulation provided "bang-bang" digital manner, comparator LTC1440. Resistor divider R4/R5 provides scaled version output voltage, which compared against U2's internal reference. Intentional hysteresis divider. output voltage falls below regulation range, LT1676 turned output voltage rises and, climbs above regulation range, LT1676 turned off. Efficiency maximized LT1676 only powered while providing heavy output current. Figure shows that efficiency typically maintained better down load current 10mA. Even load current 2mA, efficiency still respectable (depending VIN). Resistor divider R1/R2 still present, does directly influence output voltage. chosen ensure that LT1676 delivers high output current throughout voltage regulation range. presence also required maintain proper short-circuit protection. Transistors resistor form high VIN, quiescent current voltage regulator power
Burst Mode Application
minimum component count application demonstrates that power supply efficiency degrades with lower output
AN84-47
Application Note
PN2484 2N2369
39µF
SYNC LT1676 SHDN 220µH MBRS1100
100µF
323k
VOUT
100pF
PANASONIC (201) 348-2552 CASE TPSD107M010R0080 (803) 946-0362) COG/NPO MOTOROLA 100V, SCHOTTKY (800) 441-2447 COILCRAFT DO3316-224 (847) 639-6400
LTC1440 HYST
100k
1676
2.4M
Figure Burst Mode Operation Configuration
Battery Charger Application
Figure shows LT1776 configured battery charger. LT1620 railto-rail current sense amplifier (U2) monitors differential voltage across current sense resistor this equals exceeds voltage across resistor R5/R6 divider, LT1620 responds sinking current IOUT pin. This connected control node LT1776 therefore acts reduce amount power delivered load. overall behavior seen Figure
EFFICIENCY LOAD CURRENT (mA) 1000
1676 F07b
Target voltage current limits independently programmable. output voltage 7.2V, which corresponds charging voltage 3-cell lead-acid battery, R1/R2 divider internal reference LT1776. Output current, presently 200mA, current sense resistor R5/R6 divider. 16-pin version LT1620 that implements end-of-cycle detection also available. This useful implementing lead-acid battery "top-off" charger behavior like. LT1620 data sheet further information.) circuit shown accommodates input voltage range 30V. upper input voltage limit determined LT1776, LT1121-5 regulator (U3). regulated required LT1620.) This regulator chosen micropower behavior, which helps maintain good overall efficiency. However, basic catalog part only rated 30V. Substitution industry standard LM317, example, extends allowable input voltage more with version), greater quiescent current drain degrades efficiency from that shown.
Figure Efficiency Figure 81's Circuit
AN84-48
Application Note
(SEE TEXT)
39µF
100pF SHDN
LT1776 SYNC
100µH MBRS1100
7.2V
100pF
2200pF
100µF
57.6k 12.1k
3-CELL LEAD-ACID BATTERY
LT1121-5
0.33µF
0.1µF
IOUT
LT1620 PROG SENSE
1776 TA02
PANASONIC (201) 348-7522 TPSD107M010R0080 (803) 946-0362 COILCRAFT DO3316P-104 (847) 639-6400
Figure Wide Range, High Efficiency Battery Charger
Dual Output SEPIC Converter
previous applications provide single positive output voltage. Real world situations often require dual supply voltages. SEPIC topology (single-ended primary inductance converter) offers cost-effective simultaneously generate negative voltage with single piece magnetics. circuit Figure uses LT1776 generate both positive negative inductors shown actually just windings standard Coiltronics inductor. Capacitor creates SEPIC topology, which improves regulation reduces ripple current best negative supply voltage regulation, this output should have preload least maximum positive load. Total available current from both outputs limited 500mA. Maximum negative supply current limited positive load. typical limit one-half positive current, more exact calculation includes input voltage. this further details this topology, Linear Technology Design Note 100.
Positive-to-Negative Converter
previous example used dual inductor create pair output voltages, positive other negative. positive-to-negative converter topology illustrated Figure generates single negative output voltage from positive input voltage, using just ordinary inductor. topology somewhat similar original stepdown arrangement, inductor grounded LT1776 ground referred negative output voltage. Note that integrated circuit must rated
OUTPUT VOLTAGE
OUTPUT CURRENT (mA)
1776 TA05
Figure Battery Charger Output Voltage Output Current Figure 83's Circuit
AN84-49
Application Note
worst case input voltage plus absolute value output voltage. relatively high input voltage rating LT1676/LT1776 parts along with their good efficiency under such conditions make them excellent choice implementing this topology. circuit shown converts input voltage range output. Available output current 300mA worst case 10V. user should exercise caution modifying this circuit other applications. positive-to-negative topology straightforward step-down topology. actually more like flyback topology, that current delivered output discrete pulses. output capacitor must supply entire load current least portion switching cycle, output capacitor ripple current rating issue. Maximum available output current will usually strong function input voltage. Supporting VIN-to-VOUT ratios require additional components maintaining controlloop stability. detailed theoretical analysis this topology behavior found Linear Technology Application Note
15µF SHDN
SYNC 100pF 100µH MBR1100 100µF
100pF
LT1776
VOUT 36.5k 12.1k VOUT
2200pF
TOTAL AVAILABLE CURRENT LIMITED 500mA (SEE TEXT)
Figure Dual-Output SEPIC Converter
15µF SHDN
100µH 36.5k 12.1k
100pF CASE TPSD156M035R0300 (803) 946-0362 CASE TPSD107M010R0080 COG/NPO MOTOROLA MBRS1100 100V, SCHOTTKY (800) 441-2447 COILCRAFT D03316-104 (847) 639-6400
LT1776 SYNC
2200pF 100pF
MBRS1100
Figure Positive-to-Negative Converter
AN84-50
CASE TPSD156M035R0300 (803) 946-0362 CASE TPSD107M010R0080 COG/NPO MOTOROLA MBRS1100 100V, SCHOTTKY (800) 441-2447 *L1: COILTRONICS CTX100-3 SINGLE CORE WITH WINDINGS (561) 241-7876
100µF
MBR1100 100µH
100µF
100µF
VOUT 300mA
Application Note
Regulators-Switching (Boost)
VOLT OUTPUT FROM LT1377 John Seago Many applications positive negative voltages, with only voltage requiring tight regulation. Often, cost board space more important than regulation second output. equal output opposite polarity added boost configuration means negative charge pump. This two-output configuration shown Figure 1MHz switching frequency LT1377 decreases required board space, availability both positive negative feedback amplifiers allows regulation either positive negative output. circuit Figure LT1377 with make positive boost circuit. internal power switch turns voltage goes energy stored inductor When power switch turns off, transfers energy through diodes capacitor positive output load. supplies load current when power switch Resistors provide feedback from positive output. provide loop compensation. input capacitor provides local decoupling charge pump consists capacitors, diodes small inductor. When power switch turns off, also replenishes charge forward biasing When power switch turns charge reverse biases forward biases supplies energy negative output load. attenuates capacitive current spikes. added that voltage drop across both would approximately equal voltage drops saturation voltage power switch LT1377. This makes both output voltages approximately equal opposite polarity. replaced with single Schottky diode equal outputs required. Voltage current waveforms internal power switch shown Figure These measurements were taken LT1377 with circuit powered from supply. Figure shows ripple voltage from each output. high frequency spikes attenuated with small filter necessary. circuit Figure intended operate from supply provide ±12V outputs 100mA each. operates over input range load current variations from 15mA 100mA. regulated positive output voltage remains constant changes input
INPUT
10µH
MURS110 MURS110
OUTPUT
10µF 0.47µF
LT1377 PGND
86.6k
10µF
2.2µF
SGND
0.0047µF
0.047µF
MBRS130L
1E106ZY5U-C205-M, TOKIN (408) 432-8020 1E225ZY5U-C203. TOKIN (408) 432-8020 CTX10-1P, COILTRONICS (407) 241-7876 PM20-R047M, GARRETT (805) 922-0594
MBRS130L
0.047µH
2.2µF -12V OUTPUT
Figure Positive Output Regulated Supply
AN84-51
Application Note
-13.00 -12.75 -12.50
SWITCH VOLTAGE 5V/DIV
±15mA LOAD ±50mA LOAD ±100mA LOAD
OUTPUT VOLTAGE
-12.25 -12.00 -11.75 -11.50 -11.25 -11.00 -10.75
SWITCH CURRENT 0.5A/DIV
INPUT VOLTAGE
0.5µs/DIV
Figure Switch Voltage Current Waveforms
Figure Unregulated Negative Output Voltage with Positive Output Voltage Regulated
13.00 12.75
OUTPUT VOLTAGE
OUTPUT RIPPLE 0.1V/DIV COUPLED
12.50 12.25 12.00 11.75 11.50 11.25 11.00 10.75 INPUT VOLTAGE ±100mA LOAD ±50mA LOAD ±15mA LOAD
-12V OUTPUT RIPPLE 0.1V/DIV COUPLED
0.5µs/DIV
Figure Output Ripple Voltage
10µH
Figure Unregulated Positive Output Voltage with Negative Output Voltage Regulated
MURS110 MURS110 OUTPUT
INPUT
10µF 0.47µF
LT1377 SGND PGND
10µF MBRS130L 2.21k 8.25k
2.2µF
0.0047µF
0.047µF
1E106ZY5U-C205-M, TOKIN (408) 432-8020 1E225ZY5U-C203, TOKIN (408) 432-8020 CTX10-1P, COILTRONICS (407) 241-7876 PM20-R047M, GARRETT (805) 922-0594
MBRS130L 0.047µH
2.2µF -12V OUTPUT
Figure Negative Output Regulated Dual Supply
AN84-52
Application Note
voltage load current, while voltage unregulated negative output changes shown Figure Line load regulation unregulated output will improve with smaller changes input voltage load current. common requirement positive output regulate majority power while negative output supplies much smaller, unregulated bias current. Measurements taken test circuit Figure showed unregulated -12V output less than variation fixed 15mA load while input voltage changed from LT1370: 500kHz, MONOLITHIC BOOST CONVERTER Karl Edwards Introduction LT1370 500kHz, boost converter. on-resistance, maximum switch voltage 500kHz switching frequency, LT1370 used wide range output voltage current applications. high efficiency switch included die, along with oscillator, control protection circuitry necessary complete switching regulator. This part combines convenience parts count monolithic solution with switching capabilities discrete power device controller. LT1370, features cur5V MBRD835L VOUT 53.6k
with load current change 15mA 200mA regulated positive output. Occasionally, more important regulate negative output than positive output. circuit Figure same that shown Figure except feedback resistors have different values provide feedback from negative output negative feedback amplifier LT1377. Figure shows variation unregulated positive output input voltage load current variations. rent mode operation, external synchronization current shutdown mode (12µA typical). Only surface mount components needed complete small, high efficiency DC/DC converter. LT1370 will operate standard switching configurations, including boost, buck, flyback, forward, inverting SEPIC. Boost Converter Figure shows typical boost application. feedback divider network been selected give desired output voltage. long less than input bias current ignored. inductor needs chosen carefully meet both peak average current values. output capacitor high ripple currents-often, this application, higher than ripple rating single capacitor. This requires surface mount tantalums parallel; both capacitors should same value manufacturer. input capacitor does have endure such high ripple currents
LT1370
0.047µF
6.19k 0.0047µF
1370_02.EPS
EFFICIENCY
C1** 22µF
C4** 22µF
*COILTRONICS (561) 241-7876 UP2-4R7 (4.7µH) UP4-100 (10µH) **AVX TPSD226M025R0200
IOUT IOUT 4.7µH 1.8A 10µH 2.0A
OUTPUT CURRENT
1370_03
Figure Boost Converter
Figure Output Efficiency
AN84-53
Application Note
2.7V
Positive-to-Negative Converter
P6KE-15A 1N4148
100µF
100µF 2.49k 2.49k -VOUT
LT1370
MBRD835L
0.047µF *PULSE PE-53719 (619) 674-8100 IOUT 1.75A 2.25A 3.0A
0.0047µF
1370_04.EPS
Figure Positive-to-Negative Converter with Direct Feedback
single capacitor will normally suffice. catch diode, must rated output voltage average output current. compensation capacitor, normally forms pole with internal part 20Hz range. also creates zero conjunction with series resistor 1kHz 5kHz. second capacitor, sometimes required prevent erratic switching. Ripple current output capacitor's causes voltage ripple. This feeds back through error pin, changing current-trip threshold cycle-to-cycle. problem appears subharmonic oscillation. Adding typically one-tenth value main compensation capacitor, reduces loop gain switching frequency, preventing oscillation. ground return from compensation network must separate from high current switch ground. drops ground trace switch current cause dip, premature switch-off will occur. This effect appears poor load regulation. solution this return compensation network pin. this example driven logical on/off signal, input forcing LT1370 into 12µA shutdown mode. Figure shows overall converter efficiency. Note that peak efficiency over 90%; efficiency stays above device's maximum operating current.
(negative feedback) allows negative output regulators designed with direct feedback. circuit shown Figure 2.7V input, output converter, output monitored simple divider network. complex level shifting unusual grounding techniques required. regular left open circuit divider network, calculated based -2.49V reference voltage 30µA input current. switch-clamp diodes, prevent leakage spike from transformer, from exceeding switch's absolute maximum voltage rating. Zener voltage must higher than output voltage, enough that input voltage clamp voltage does exceed switch voltage rating. SEPIC Converter Figure shows SEPIC converter. advantages SEPIC topology that input voltage range from below above output voltage. Figure input voltage range from with output. magnetic coupling inductors critical operation, generally they wound same core. couples inductors together eliminates
L1A* 6.8µH LT1370
4.7µF
MBRD835L 18.7k
VOUT
33µF
L1B* 6.8µH 0.047µF 0.0047µF
6.19k
100µF
1370_05.EPS
TPSD 336M020R0200 TOKIN 1E475ZY5U-C304 TPSD107M010R0100 ELECTRONICS 501-0726 (612) 894-9590 INPUT VOLTAGE GREATER LESS THAN OUTPUT VOLTAGE
IOUT 1.8A 2.6A 2.9A
Figure Li-Ion Cells SEPIC Converter
AN84-54
Application Note
need switch snubber network. must have very ESR, because ripple current equal ISW/2. capacitance value critical significant effect loop stability. voltage across equal BOOTSTRAPPED SYNCHRONOUS BOOST CONVERTER OPERATES 1.8V INPUT Gross Some applications, such those powered batteries solar cells, their input voltage decrease they operate. Many regulators that could operate with high input voltages cease function input voltage decreases. circuit Figure maintains maximum load current input voltage drops. regulator boosts 2.5V-4.2V input maximum load current (10W output power). circuit bootstrapped synchronous boost regulator using LTC1266 synchronous regulator controller. Diodes through allow ci
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