DESCRIPTIO 1.5A Switch Small MSOP-8 Package Constant 1.25MHz Swit

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DESCRIPTIO 1.5A Switch Small MSOP-8 Package Constant 1.25MHz Swit

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LT1961 1.5A, 1.25MHz Step-Up Switching Regulator
DESCRIPTIO
1.5A Switch Small MSOP-8 Package Constant 1.25MHz Switching Frequency Wide Operating Voltage Range: High Efficiency Switch 1.2V Feedback Reference Voltage Overall Output Voltage Tolerance Uses Profile Surface Mount External Components Shutdown Current: Synchronizable from 1.5MHz 2MHz Current-Mode Loop Control Constant Maximum Switch Current Rating Duty Cycles* Thermally Enhanced Exposed Package
LT®1961 1.25MHz monolithic boost switching regulator. high efficiency 1.5A, switch included together with control circuitry required complete high frequency, current-mode switching regulator. Current-mode control provides fast transient response excellent loop stability. design techniques achieve high efficiency high switching frequencies over wide operating range. dropout internal regulator maintains consistent performance over wide range inputs from systems LiIon batteries. operating supply current maintains high efficiency, especially lower output currents. Shutdown reduces quiescent current 6µA. Maximum switch current remains constant duty cycles. Synchronization allows external logic level signal increase internal oscillator from 1.5MHz 2MHz. LT1961 available exposed pad, 8-pin MSOP package. Full cycle-by-cycle switch current limit protection thermal shutdown provided. High frequency operation allows reduction input output filtering components permits chip inductors.
registered trademarks Linear Technology Corporation. *Patent Pending
APPLICATIO
Modems Portable Computers Battery-Powered Systems Distributed Power
TYPICAL APPLICATIO
6.8µH
Boost Converter
UPS120 INPUT 2.2µF CERAMIC OPEN HIGH LT1961 SHDN SYNC 90.9k
EFFICIENCY
OUTPUT 0.5A*
6800pF 6.8k
100pF
10µF CERAMIC
*MAXIMUM OUTPUT CURRENT SUBJECT THERMAL DERATING.
1961 TA01
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
Efficiency Load Current
VOUT LOAD CURRENT (mA)
1961 TA01a
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LT1961
ABSOLUTE MAXIMUM RATINGS
(Note
PACKAGE/ORDER INFORMATION
VIEW SYNC SHDN
Input Voltage Switch Voltage SHDN Current SYNC Current Operating Junction Temperature Range (Note LT1961E 40°C 125°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
ORDER PART NUMBER LT1961EMS8E MS8E PART MARKING LTQY
MS8E PACKAGE 8-LEAD PLASTIC MSOP GROUND CONNECTED LARGE COPPER AREA TJMAX 125°C, 50°C/W
Consult Marketing parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Recommended Operating Voltage Maximum Switch Current Limit Oscillator Frequency Switch Voltage Drop Undervoltage Lockout Supply Current Supply Current/ISW Shutdown Supply Current Feedback Voltage Input Current Voltage Gain Transconductance Source Current Sink Current Switch Current Transconductance Minimum Switching Threshold 1.5A Threshold Maximum Switch Duty Cycle Duty Cycle 0.4V 0.9V ±10µA 1.4V 3.3V 1.5A (Note 1.5A CONDITION
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 15V, 0.8V, SHDN, SYNC switch open unless otherwise noted.
2.73 1.218 1.224 1300
UNITS mA/A µMho
2.47
VSHDN 25V,
25V, 0.4V 0.9V
1.182 1.176
1.2V, 100mA 1.2V, 25°C 125°C 1.2V, 25°C SHDN 60mV Above Threshold SHDN 100mV Below Threshold
1.28
1.35 1.42
SHDN Threshold Voltage SHDN Input Current (Shutting Down) SHDN Threshold Current Hysteresis SYNC Threshold Voltage SYNC Input Frequency SYNC Resistance ISYNC
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LT1961
ELECTRICAL CHARACTERISTICS
Note Absolute Maximum Ratings those values beyond which life device impaired. Note LT1961E guaranteed meet performance specifications from 125°C. Specifications over 40°C 125°C operating junction temperature range assured design, characterization correlation with statistical process controls. Note Minimum input voltage defined voltage where internal regulator enters lockout. Actual minimum input voltage maintain regulated output will depend output voltage load current. Applications Information.
TYPICAL PERFORMANCE CHARACTERISTICS
Temperature
1.22 125°C SWITCH VOLTAGE (mV) 1.21 1.18 TEMPERATURE (°C) SWITCH CURRENT
1961
1.20
-40°C
FREQUENCY (MHz)
VOLTAGE
1.19
SHDN Threshold Temperature
1.40
1.38
SHDN THRESHOLD CURRENT (µA) SHDN INPUT (µA)
1.36
1.34
1.32
1.30
TEMPERATURE (°C)
Switch Voltage Drop
Oscillator Frequency
25°C
SWITCH CURRENT
1961
1961
SHDN Supply Current
SHDN
SHDN Current Temperature
SHUTTING DOWN
STARTING
1961
TEMPERATURE (°C)
1961
1961G06
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LT1961 TYPICAL PERFOR CHARACTERISTICS
SHDN Supply Current
SWITCH PEAK CURRENT
CURRENT (µA)
CURRENT (µA)
SHUTDOWN VOLTAGE
FUNCTIONS
feedback used output voltage using external voltage divider that generates 1.2V with desired output voltage. required, current limit reduced during start when below 0.5V (see Current Limit Foldback graph Typical Performance Characteristics section). impedance less than needed this feature operate. VIN: This powers internal circuitry internal regulator. Keep external bypass capacitor close this pin. GND: Short pins exposed PCB. reference regulated output, load regulation will suffer "ground" load same voltage This condition occurs when load current flows through metal path between pins load ground point. Keep ground path short between pins load ground plane when possible. Keep path between input bypass pins short. exposed should attached large copper area improve thermal resistance. VSW: switch collector on-chip power switch large currents flowing through Keep traces switching components short possible minimize radiation voltage spikes. SYNC: sync used synchronize internal oscillator external signal. directly logic compatible driven with signal between duty cycle. synchronizing range equal initial operating frequency, 2MHz. Synchronization section Applications Information details. When use, this should grounded. SHDN: shutdown used turn regulator reduce input drain current microamperes. 1.35V threshold function accurate undervoltage lockout (UVLO), preventing regulator from operating until input voltage reached predetermined level. Float pull high regulator operating mode. output error amplifier input peak switch current comparator. normally used frequency compensation, double duty current clamp control loop override. This sits about 0.3V very light loads 0.9V maximum load.
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1961
Input Supply Current
1200 1000 INPUT VOLTAGE
1961
Current Limit Foldback
INPUT CURRENT (µA)
SWITCH CURRENT
MINIMUM INPUT VOLTAGE
CURRENT
FEEDBACK VOLTAGE
1961
LT1961
BLOCK DIAGRAM
LT1961 constant frequency, current-mode boost converter. This means that there internal clock feedback loops that control duty cycle power switch. addition normal error amplifier, there current sense amplifier that monitors switch current cycle-by-cycle basis. switch cycle starts with oscillator pulse which sets flip-flop turn switch When switch current reaches level inverting input comparator, flip-flop reset switch turns off. Output voltage control obtained using output error amplifier switch current trip point. This technique means that error
INPUT
2.5V BIAS REGULATOR
SYNC
SHUTDOWN COMPARATOR
1.33V
ERROR AMPLIFIER 850µMho
Figure Block Diagram
SHDN
amplifier commands current delivered output rather than voltage. voltage system will have phase shift resonant frequency inductor output capacitor, then abrupt 180° shift will occur. current system will have phase shift much lower frequency, will have additional shift until well beyond resonant frequency. This makes much easier frequency compensate feedback loop also gives much quicker transient response. comparator connected shutdown disables internal regulator, reducing supply current.
INTERNAL SLOPE COMP
0.3V
1.25MHz OSCILLATOR
CURRENT COMPARATOR FLIP-FLOP CURRENT SENSE AMPLIFIER VOLTAGE GAIN DRIVER CIRCUITRY
POWER SWITCH
0.01
1.2V
1767
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LT1961
APPLICATIONS INFORMATION
RESISTOR NETWORK suggested resistance (R2) from ground This reduces contribution input bias current output voltage less than 0.2%. formula resistor (R1) from VOUT
VOUT
R2(0.2µA)
LT1961 ERROR AMPLIFIER
OUTPUT
1.2V
1961
Figure Feedback Network
OUTPUT CAPACITOR Step-up regulators supply current output pulses. rise fall times these pulses very fast. output capacitor required reduce voltage ripple this causes. ripple current calculated from: IRIPPLE(RMS) IOUT
(VOUT VIN)
LT1961 will operate with both ceramic tantalum output capacitors. Ceramic capacitors generally chosen their small size, very (effective series resistance), good high frequency operation, reducing output ripple voltage. Their removes useful zero loop frequency response, common tantalum capacitors. compensate this, loop compensation pole frequency must typically reduced factor Typical ceramic output capacitors 10µF range. Since absolute value capacitance
defines pole frequency output stage, type ceramic, which have good temperature stability, recommended. Tantalum capacitors usually chosen their bulk capacitance properties, useful high transient load applications. rather than absolute value defines output ripple 1.25MHz. Values 22µF 100µF range generally needed minimize meet ripple current ratings. Care should taken ensure ripple ratings exceeded.
Table Surface Mount Solid Tantalum Capacitor Ripple Current Case Size (Max, Ripple Current
TPS, Sprague 593D Case Size TPS, Sprague 593D Case Size (typ) (typ)
INPUT CAPACITOR Unlike output capacitor, ripple current input capacitor normally enough that ripple current rating issue. current waveform triangular, with value given IRIPPLE(RMS) 0.29 VOUT
(L)(f)(VOUT
higher switching frequency, energy storage requirement input capacitor reduced values range 4.7µF suitable most applications. similar type ceramics used since absolute value capacitance less important significant effect loop stability. operation required close minimum input voltage required either output LT1961, larger value necessary. This prevent excessive ripple causing dips below minimum operating voltage resulting erratic operation.
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LT1961
APPLICATIONS INFORMATION
INDUCTOR CHOICE MAXIMUM OUTPUT CURRENT When choosing inductor, there conditions that limit minimum inductance; required output current, avoidance subharmonic oscillation. maximum output current LT1961 standard boost converter configuration with infinitely large inductor LMIN (VIN (VOUT 0.4(VOUT (IOUT )(f)
IOUT (MAX) 1.5A
VOUT
Where converter efficiency (typically 0.87 high current). value inductance reduced, ripple current increases IOUT(MAX) reduced. minimum inductance required output current given
LMIN (VOUT 2VOUT
second condition, avoidance subharmonic oscillation, must operating duty cycle greater than 50%. slope compensation circuit within LT1961 prevents subharmonic oscillation inductor ripple currents 0.7AP-P, defining minimum inductor value
LMIN
(VOUT 0.7VOUT
These conditions define absolute minimum inductance. However, generally recommended that prevent excessive output noise, difficulty obtaining stability, ripple current more than average inductor current. Since inductor ripple
RIPPLE VOUT (L)(f)
recommended minimum inductance
inductor value need further adjustment other factors such output voltage ripple filtering requirements. Remember also, inductance drop significantly with current manufacturing tolerance. inductor must have rating greater than peak operating current prevent saturation resulting efficiency loss. Peak inductor current given
ILPEAK (VOUT )(IOUT (VOUT 2VOUT (L)(f)
Also, consideration should given resistance inductor. Inductor resistance contributes directly efficiency losses overall converter. Suitable inductors available from Coilcraft, Coiltronics, Dale, Sumida, Toko, Murata, Panasonic other manufactures.
Table
PART NUMBER Coiltronics TP1-2R2 TP2-2R2 TP3-4R7 TP4- Murata LQH1C1R0M04 LQH3C1R0M24 LQH3C2R2M24 LQH4C1R5M04 Sumida CD73- CDRH4D18-2R2 CDRH5D18-6R2 CDRH5D28-100 Coilcraft 1008PS-272M LPO1704-222M LPO1704-332M 0.14 0.12 0.16
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VALUE (uH) ISAT(DC) (Amps) HEIGHT (mm) 0.51 0.79 1.44 1.32 0.188 0.111 0.181 0.146 0.28 0.06 0.09 0.080 0.058 0.071 0.048
LT1961
APPLICATIONS INFORMATION
CATCH DIODE suggested catch diode (D1) UPS120 1NS818 Schottky. rated average forward current 20V/30V reverse voltage. Typical forward voltage 0.5V diode conducts current only during switch time. Peak reverse voltage equal regulator output voltage. Average forward current normal operation equal output current. SHUTDOWN UNDERVOLTAGE LOCKOUT Figure shows undervoltage lockout (UVLO) LT1961. Typically, UVLO used situations where input supply current limited, relatively high source resistance. switching regulator draws constant power from source, source current increases source voltage drops. This looks like negative resistance load source cause source current limit latch under source voltage conditions. UVLO prevents regulator from operating source voltages where these problems might occur.
LT1961 INPUT SHDN 1.35V
1961
Figure Undervoltage Lockout
internal comparator will force part into shutdown below minimum 2.6V. This feature used prevent excessive discharge battery-operated systems. adjustable UVLO threshold required,
shutdown used. threshold voltage shutdown comparator 1.35V. internal current source defaults open condition operating (see Typical Performance Graphs). Current hysteresis added above SHDN threshold. This used voltage hysteresis UVLO using following:
1.35V)
1.35V
Turn-on threshold Turn-off threshold Example: switching should start until input above 4.75V stop input falls below 3.75V. 4.75V 3.75V 4.75V 3.75V 143k 1.35V 143k
(4.75V 1.35V)
50.4k
Keep connections from resistors SHDN short make sure that interplane surface capacitance switching nodes minimized. high resistor values used, SHDN should bypassed with capacitor prevent coupling problems from switch node.
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LT1961
APPLICATIONS INFORMATION
SYNCHRONIZATION SYNC pin, used synchronize internal oscillator external signal. SYNC input must pass from logic level low, through maximum synchronization threshold with duty cycle between 80%. input driven directly from logic level output. synchronizing range equal initial operating frequency 2MHz. This means that minimum practical sync frequency equal worst-case high self-oscillating frequency (1.5MHz), typical operating frequency 1.25MHz. Caution should used when synchronizing above 1.7MHz because higher sync frequencies amplitude internal slope compensation used prevent subharmonic switching reduced. Higher inductor values will tend eliminate this problem. Frequency Compensation section discussion entirely different cause subharmonic switching before assuming that cause insufficient slope compensation. Application Note more details theory slope compensation. LAYOUT CONSIDERATIONS with high frequency switchers, when considering layout, care must taken achieve optimal electrical, thermal noise performance. maximum efficiency, switch rise fall times typically nanosecond range. prevent noise both radiated conducted, high speed switching current path, shown Figure must kept short possible. This implemented suggested layout Figure Shortening this path will also reduce parasitic trace inductance approximately 25nH/inch. switch off, this parasitic inductance produces flyback spike across LT1961 switch. When operating higher currents output voltages, with poor layout, this spike generate voltages across LT1961 that exceed absolute maximum rating. ground plane should always used under switcher circuitry prevent interplane coupling overall noise. components should kept away possible from switch node. LT1961 pinout been designed this. ground these components should separated from switch current path. Failure will result poor stability subharmonic like oscillation. Board layout also significant effect thermal resistance. exposed copper plate that runs under LT1961 die. This best thermal path heat package. Soldering onto board will reduce temperature increase power capability LT1961. Provide much copper area possible around this pad. Adding multiple solder filled feedthroughs under around ground plane will also help. Similar treatment catch diode inductor terminations will reduce additional heating effects.
LT1961
Figure High Speed Switching Path
VOUT
HIGH FREQUENCY SWITCHING PATH
LOAD
1961
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LT1961
APPLICATIONS INFORMATION
6.8µH UPS120 INPUT 2.2µF CERAMIC OPEN HIGH LT1961 SHDN SYNC 10µF CERAMIC 90.9k
*MAXIMUM OUTPUT CURRENT SUBJECT THERMAL DERATING.
INPUT
MINIMIZE LT1961, LOOP
VOUT
KELVIN SENSE VOUT
Figure Typical Application Suggested Layout (Topside Only Shown)
OUTPUT 0.5A*
6800pF 6.8k
100pF
LT1961EMS8E
KEEP COMPONENTS AWAY FROM HIGH FREQUENCY, HIGH INPUT COMPONENTS
PLACE FEEDTHROUGHS AROUND GROUND GOOD THERMAL CONDUCTIVITY
SOLDER EXPOSED GROUND BOARD
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LT1961
APPLICATIONS INFORMATION
inductor must have rating greater than peak operating current prevent saturation resulting efficiency loss. Peak inductor current given thermal resistance number worst-case ambient temperature: (PTOT) true temperature required, measurement SYNC resistance used. SYNC resistance across temperature must first calibrated, with device power, oven. same measurement then used operation indicate temperature. FREQUENCY COMPENSATION Loop frequency compensation performed output error amplifier pin) with series network. main pole formed series capacitor output impedance (500k) error amplifier. pole falls range 20Hz. series resistor creates "zero" 1kHz 5kHz, which improves loop stability transient response. second capacitor, typically one-tenth size main compensation capacitor, sometimes used reduce switching frequency ripple pin. ripple caused output voltage ripple attenuated output divider multiplied error amplifier. Without second capacitor, ripple
ILPEAK
(VOUT )(IOUT (VOUT 2VOUT (L)(f)
Also, consideration should given resistance inductor. Inductor resistance contributes directly efficiency losses overall converter. THERMAL CALCULATIONS Power dissipation LT1961 chip comes from four sources: switch loss, switch loss, drive current, input quiescent current. following formulas show calculate each these losses. These formulas assume continuous mode operation, they should used calculating efficiency light load currents.
duty cycle (VOUT VOUT
Switch loss:
)(ISW (RSW VOUT
loss: )(DC PVIN 1mA(VIN Switch resistance 0.27 hot) Example: VOUT IOUT 0.5A
Total power dissipation 0.23 0.31 0.07 0.005 0.62W Thermal resistance LT1961 package influenced presence internal backside planes. With full plane under package, thermal resistance will about 50°C/W. calculate temperature, appropriate
Ripple
1.2(VRIPPLE)(gm)(RC) (VOUT)
VRIPPLE Output ripple (VP-P) Error amplifier transconductance (850µmho) Series resistor VOUT output voltage
prevent irregular switching, ripple should kept below 50mVP-P. Worst-case ripple occurs maximum output load current will also increased poor quality (high ESR) output capacitors used. addition 47pF capacitor reduces switching frequency ripple only millivolts. value will also reduce ripple, loop phase margin inadequate.
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LT1961
TYPICAL APPLICATIO
100pF
Dual Output Flyback Converter
115k UPS140 P6KE-20A LT1961 2.2nF *DALE LPE-4841-100MB
LT1961 TA02
4.7µF
VOUT 47µF
1N4148
47µF -VOUT -15V
UPS140
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LT1961
TYPICAL APPLICATIO
4.7µF
4V-9VIN 5VOUT SEPIC Converter**
VIN** L1A* 10µH LT1961
4.7µF
UPS120 31.6k
VOUT
L1B* 10µH
47µF
2.2nF
100pF
LT1961 TA03
ELECTRONICS 511-1012 INPUT VOLTAGE GREATER LESS THAN OUTPUT VOLTAGE
IOUT 0.59A 0.65A 0.70A 0.74A 0.80A
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LT1961
TYPICAL APPLICATIO
Single Li-Ion Cell
4.7µH
UPS120 VOUT 31.6k
SINGLE Li-Ion CELL LT1961
10µF
2.2nF 100pF
47µF
LT1961 TA04
IOUT 0.75A 2.7V 0.93A 3.3V 1.0A 3.6V
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LT1961
PACKAGE DESCRIPTION
MS8E Package 8-Lead Plastic MSOP
(Reference 05-08-1660)
2.794 0.102 (.110 .004)
5.23 (.206)
0.42 0.04 (.0165 .0015)
RECOMMENDED SOLDER LAYOUT DETAIL 4.88 (.192 .004) 3.00 0.102 (.118 .004) NOTE
0.254 (.010) GAUGE PLANE
0.18 (.077) SEATING PLANE 0.22 0.38 (.009 .015) 0.13 0.05 (.005 .002)
MSOP (MS8E) 1001
NOTE: DIMENSIONS MILLIMETER/(INCH) DRAWING SCALE DIMENSION DOES INCLUDE MOLD FLASH, PROTRUSIONS GATE BURRS. MOLD FLASH, PROTRUSIONS GATE BURRS SHALL EXCEED 0.152mm (.006") SIDE DIMENSION DOES INCLUDE INTERLEAD FLASH PROTRUSIONS. INTERLEAD FLASH PROTRUSIONS SHALL EXCEED 0.152mm (.006") SIDE LEAD COPLANARITY (BOTTOM LEADS AFTER FORMING) SHALL 0.102mm (.004")
BOTTOM VIEW EXPOSED OPTION 0.889 0.127 (.035 .005) 2.06 0.102 (.080 .004) 1.83 0.102 (.072 .004)
2.083 0.102 3.45 (.082 .004) (.126 .136) 0.65 (.0256) 3.00 0.102 (.118 .004) (NOTE 0.52 (.206)
0.53 0.015 (.021 .006) DETAIL
1.10 (.043)
0.86 (.34)
0.65 (.0256)
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LT1961
TYPICAL APPLICATIO
MUR405
2.2µF
RELATED PARTS
PART NUMBER LT1308A LT1310 LT1370 LT1371 LT1372/LT1377 LTC3400/ LTC3400B LTC3401 LTC3402 LTC3405/ LTC3405A DESCRIPTION 600kHz, Step-Up Regulator 4.5MHz, 1.5A Step-Up with Phase Lock Loop High Efficiency DC/DC Converter High Efficiency DC/DC Converter 500kHz 1MHz High Efficiency 1.5A Switching Regulators 1.2MHz, 600mA, Synchronous Step-Up Single Cell, High Current (1A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter Single Cell, High Current (2A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter 1.5MHz High Efficiency, IOUT 300mA, Monolithic Synchronous Step-Down Regulator COMMENTS 0.92V Battery Comparator, Package 2.75V 18V, VOUT 35V, MS10E Package 42V, 500kHz Switch, DD-Pak, TO-220 Package 35V, 500kHz Switch, DD-Pak, TO-220 Package Boost Topology, (MIN) 2.7V, Package 2.6V 16V, VOUT 34V, Integrated Package 0.85V Efficiency, ThinSOT Package 0.5V Efficiency Synchronizable Oscillator from 100kHz 3MHz, MS10 Package 0.7V Efficiency Synchronizable Oscillator from 100kHz 3MHz, MS10 Package 2.65V Efficiency, 100% Duty Cycle, 20µA, ThinSOT Package
LT1946/LT1946A 1.2MHz/2.7MHz, 1.5A, Monolithic Step-Up Regulator
ThinSOT trademark Linear Technology Corporation.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507
High Voltage Laser Power Supply
0.01µF 1800pF 10kV 1800pF 10kV DIODES LASER
2.2µF 0.47µF
10µH
LT1961
0.1µF
1N4002 (ALL) COILTRONICS CTX02-11128 ZETEX ZTX849 0.47µF WIMA 0.15µF TYPE MKP-20 DIODES SEMTECH-FM-50 LASER HUGHES 3121H-P COILTRONICS (407) 241-7876
10µF
LT1961 TA05
sn1961 1961is LT/TP 0602 1.5K PRINTED
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2001

DESCRIPTIO 1.5A Switch Small MSOP-8 Package Constant 1.25MHz Swit

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