LT1946
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LT1946 - LT1946
LT1945* - LT1945*
LT1946 - LT1946
LT1946 1.2MHz Boost DC/DC Converter with 1.5A Switch Soft-Start
DESCRIPTIO
1.5A, Internal Switch 1.2MHz Switching Frequency Integrated Soft-Start Function Output Voltage VCESAT Switch: 300mV 1.5A (Typ) 430mA from 3.3V Input Small 8-Lead MSOP Package
APPLICATIO
TFT-LCD Bias Supplies Receivers Modems Local Power Supplies
LT®1946 fixed frequency step-up DC/DC converter containing internal 1.5A, switch. Capable generating 430mA from 3.3V input, LT1946 ideal large TFT-LCD panel power supplies. LT1946 switches 1.2MHz, allowing tiny, profile inductors value ceramic capacitors. Loop compensation either internal external, giving user flexibility setting loop compensation allowing optimized transient response with ceramic output capacitors. Soft-start controlled with external capacitor, which determines input current ramp rate during start-up. 8-lead MSOP package high switching frequency ensure profile overall solution less than 1.2mm high.
registered trademarks Linear Technology Corporation. other trademarks property their respective owners.
TYPICAL APPLICATIO
3.3V 2.2µF 49.9k 470pF 100nF SHDN LT1946 COMP 4.7µH
VOUT 430mA
EFFICIENCY
28.7k
20µF 5.23k
2.2µF, X7R, 6.3V 10µF, X7R, MICROSEMI UPS120 EQUIVALENT RLF5018T-4R7M1R4
1946
Figure 3.3V 430mA Step-Up DC/DC Converter
Efficiency
LOAD CURRENT (mA)
1946 F01b
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LT1946
ABSOLUTE
(Note
RATI
Maximum Junction Temperature 125°C Operating Temperature Range (Note 40°C 85°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
Voltage Voltage 0.4V Voltage 2.5V SHDN Voltage Current Into ±1mA
PACKAGE/ORDER ATIO
VIEW SHDN COMP
ORDER PART NUMBER LT1946EMS8E PART MARKING LTBNW
SHDN
MS8E PACKAGE 8-LEAD PLASTIC MSOP EXPOSED (PIN GROUND (MUST SOLDERED PCB)
TJMAX 125°C, 40°C/W, 10°C/W
Consult Marketing parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage CONDITIONS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VSHDN unless otherwise specified. (Note
2.45 1.230 1.220 1.250 VSHDN 2.5V, Switching VSHDN 2.6V
Bias Current Error Transconductance Error Voltage Gain Quiescent Current Quiescent Current Shutdown Reference Line Regulation Switching Frequency Switching Frequency Foldback Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current Soft-Start Charging Current
1.250V (Note
(Note 0.5V
VIEW COMP
ORDER PART NUMBER LT1946EMS8 PART MARKING LTUG
PACKAGE 8-LEAD PLASTIC MSOP
TJMAX 125°C, 125°C/W (4-LAYER BOARD)
1.270 1.270
UNITS µmhos
0.01 0.01
0.05
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LT1946
ELECTRICAL CHARACTERISTICS
SYMBOL SHDN Input Voltage High SHDN Input Voltage SHDN Bias Current VSHDN VSHDN CONDITIONS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VSHDN unless otherwise specified. (Note
UNITS
Note Absolute Maximum Ratings those values beyond which life device impaired. Note LT1946E guaranteed meet performance specifications from 70°C. Specifications over -40°C 85°C operating temperature range assured design, characterization correlation with statistical process controls.
Note Current flows pin. Note Current limit guaranteed design and/or correlation static test. Current limit independent duty cycle guaranteed design.
TYPICAL PERFOR CHARACTERISTICS
Feedback Voltage
1.28
OSCILLATOR FREQUENCY (kHz)
1.27
FEEDBACK VOLTAGE
1.26 1.25 1.24 1.23 1.22 1.21 1.20 TEMPERATURE (°C)
-30°C
100°C 25°C
CURRENT LIMIT
Switch Saturation Voltage
0.35 0.30 0.25
VCESAT
QUIESCENT CURRENT (mA)
0.20 0.15 0.10 0.05 SWITCH CURRENT
1946
1946
Oscillator Frequency
1400 1200 1000
Current Limit
FEEDBACK VOLTAGE
1946
TEMPERATURE (°C)
1946
Quiescent Current
TEMPERATURE (°C)
Switching Waveforms Figure Circuit
VOUT 20mV/DIV COUPLED 5V/DIV 0.5A/DIV COUPLED 0.5µs/DIV
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LT1946
CTIO
(Pin Error Amplifier Output Pin. external compensation network this pin, internal compensation network shorting COMP pin. (Pin Feedback Pin. Reference voltage 1.250V. Connect resistive divider here. Minimize trace area VOUT according VOUT 1.250(1 R1/R2). SHDN (Pin Shutdown Pin. 2.4V more enable device. Ground shut down. float this pin. (Pin Ground. directly local ground plane. (Pin Switch Pin. This collector internal power switch. Minimize metal trace area connected this minimize EMI. (Pin Input Supply Pin. Must locally bypassed. COMP (Pin Internal Compensation Pin. Provides internal compensation network. directly internal compensation. used. (Pin Soft-Start Pin. Place soft-start capacitor here. Upon start-up, current charges capacitor 1.5V. larger capacitor slower start-up. Leave floating use. Exposed (MS8E, Ground. Must soldered PCB.
BLOCK DIAGRA
1.250V REFERENCE
RAMP GENERATOR
VOUT (EXTERNAL) (EXTERNAL) 0.5V
1.2MHz OSCILLATOR
SHUTDOWN SHDN
Figure Block Diagram
COMP 120k
90pF
COMPARATOR DRIVER
0.01
(MSE8 ONLY)
1946
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LT1946
OPERATIO
LT1946 uses constant frequency, current mode control scheme provide excellent line load regulation. Please refer Figure following description part's operation. start oscillator cycle, latch set, turning power switch switch current flows through internal current sense resistor generating voltage. This voltage added stabilizing ramp resulting into positive terminal comparator When this voltage exceeds level negative input latch reset, turning power switch. level negative input pin) error amplifier (A1) simply amplified version difference between feedback voltage reference voltage 1.250V. this manner, error amplifier sets correct peak current level keep output regulation. functions provided enable very clean start-up LT1946. Frequency foldback used reduce oscillator frequency factor when
APPLICATIO ATIO
Inductor Selection
Several inductors that work well with LT1946 listed Table This table exclusive; there many other manufacturers inductors that used. Consult each manufacturer more detailed information their entire selection related parts, many different sizes shapes available. Ferrite core inductors should used obtain best efficiency, core losses 1.2MHz much lower ferrite cores than cheaper powdered-iron ones. Choose inductor that handle least 1.5A without saturating, ensure that inductor (copper wire resistance) minimize power losses. 4.7µH 10µH inductor will best choice most LT1946 designs. Note that some applications, current handling requirements inductor lower, such SEPIC topology where each inductor only carries one-half total switch current.
below nominal value 0.5V. This accomplished comparator This feature reduces minimum duty cycle that part achieve thus allowing better control switch current during start-up. When voltage exceeds 0.5V, oscillator returns normal frequency 1.2MHz. soft-start function also provided LT1946. When part brought shutdown, current sourced pin. connecting external capacitor pin, rate voltage rise set. Typical values soft-start capacitor range from 10nF 200nF. directly limits rate rise pin, which turn limits peak switch current. Current limit shown Figure switch current constantly monitored allowed exceed nominal value 2.1A. switch current reaches 2.1A, latch reset regardless output comparator This current limit helps protect power switch well external components connected LT1946. inductors shown Table were chosen small size. better efficiency, similar valued inductors with larger volume.
Table Recommended Inductors
(µH) SIZE (mm) PART CDRH5D18-4R1 CDRH5D18-5R4 CDRH5D28-5R3 CDRH5D28-6R2 CDRH5D28-8R2 ELL6SH-4R7M ELL6SH-5R6M ELL6SH-6R8M RLF5018T4R7M1R4 VENDOR Sumida (847) 956-0666 www.sumida.com Panasonic (408) 945-5660 www.panasonic.com (847) 803-6100 www.tdk.com
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LT1946
APPLICATIO ATIO
Capacitor Selection (equivalent series resistance) capacitors should used output minimize output ripple voltage. Multilayer ceramic capacitors excellent choice, they have extremely available very small packages. dielectrics preferred, these materials retain capacitance over wide voltage temperature ranges. 4.7µF 20µF output capacitor sufficient most applications, systems with very output currents need only 2.2µF output capacitor. Solid tantalum OS-CON capacitors used, they will occupy more board area than ceramic will have higher ESR. Always capacitor with sufficient voltage rating. Ceramic capacitors also make good choice input decoupling capacitor, which should placed close possible LT1946. 2.2µF 4.7µF input capacitor sufficient most applications. Table shows list several ceramic capacitor manufacturers. Consult manufacturers detailed information their entire selection ceramic parts.
Table Ceramic Capacitor Manufacturers
Taiyo Yuden Murata (408) 573-4150 www.t-yuden.com (803) 448-9411 www.avxcorp.com (714) 852-2001 www.murata.com
VOUT 20mV/DIV COUPLED
Compensation-Adjustment compensate feedback loop LT1946, series resistor-capacitor network should connected from COMP GND. most applications, capacitor range 220pF 680pF will suffice. good starting value compensation capacitor, 470pF. compensation resistor, usually range 100k. good technique compensate application 100k potentiometer place 470pF capacitor adjusting potentiometer while observing transient response, optimum value found. Figures illustrate this process circuit Figure with load current stepped from 250mA 300mA. Figure shows transient response with equal 7.5k. phase margin
0.5A/DIV COUPLED 49.9k 200µs/DIV
1946 F03b
0.5A/DIV COUPLED 7.5k 200µs/DIV
1946 F03a
Figure Transient Response Shows Excessive Ringing
VOUT 20mV/DIV COUPLED
0.5A/DIV COUPLED 200µs/DIV
1946 F03b
Figure Transient Response Better
VOUT 20mV/DIV COUPLED
Figure Transient Response Well Damped
poor evidenced excessive ringing output voltage inductor current. Figure value increased 18k, which results more damped response. Figure shows results when increased further 49.9k. transient response nicely damped compensation procedure complete. COMP provides access internal resistor (120k) capacitor (90pF). some applications, these values will suffice external will needed.
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LT1946
APPLICATIO ATIO
Compensation-Theory
Like other current mode switching regulators, LT1946 needs compensated stable efficient operation. feedback loops used LT1946: fast current loop which does require compensation, slower voltage loop which does. Standard Bode plot analysis used understand adjust voltage feedback loop. with feedback loop, identifying gain phase contribution various elements loop critical. Figure shows equivalent elements boost converter. Because fast current control loop, power stage inductor diode have been replaced equivalent transconductance amplifier gmp. acts current source where output current proportional voltage. Note that maximum output current finite current limit From Figure gain, poles zeroes calculated follows:
COMPENSATION CAPACITOR COUT: OUTPUT CAPACITOR gma: TRANSCONDUCTANCE AMPLIFIER INSIDE gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER COMPENSATION RESISTOR OUTPUT RESISTANCE DEFINED VOUT DIVIDED ILOAD(MAX) OUTPUT RESISTANCE FEEDBACK RESISTOR DIVIDER NETWORK
Figure Boost Converter Equivalent Model
Current Mode zero right half plane zero which issue feedback control design, manageable with proper external component selection. Using circuit Figure example, following table shows parameters used generate Bode plot shown Figure
Table Bode Plot Parameters
Parameter COUT VOUT Value 18.6 49.9 Units µmho Comment Application Specific Application Specific Adjustable Adjustable Adjustable Application Specific Application Specific Adjustable Adjustable Application Specific Adjustable
Output Pole: COUT Error Pole: Error Zero: 1.25VIN GAIN: VOUT Zero: COUT Zero:
VOUT High Frequency Pole:
From Figure phase 120° when gain reaches giving phase margin 60°. This more than adequate. crossover frequency 25kHz, which about three times lower than frequency right half plane zero important that crossover frequency least three times lower than frequency zero achieve adequate phase margin.
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COUT VOUT
1.250V REFERENCE
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LT1946
APPLICATIO ATIO
GAIN (dB)
100k FREQUENCY (Hz)
1946 F05a
PHASE (DEG)
-100
-180 -200 100k FREQUENCY (Hz)
1946 F05b
Figure Bode Plot Figure Circuit
GROUND PLANE
SHUTDOWN MULTIPLE VIAs VOUT LT1946
Figure Recommended Component Placement Boost Converter. Note Direct High Current Paths Using Wide Traces. Minimize Trace Area (VC) (FB). Multiple Vias Copper Ground Plane. Vias Location Only Avoid Introducing Switching Currents Into Ground Plane
1946fa
Diode Selection Schottky diode recommended with LT1946. Microsemi UPS120 very good choice. Where input output voltage differential exceeds 20V, UPS140 diode). These diodes rated handle average forward current applications where average forward current diode less than 0.5A, Semiconductor MBR0520 diode used Setting Output Voltage output voltage, select values (see Figure according following equation: 1.25V good range from 30k. Layout Hints high speed operation LT1946 demands careful attention board layout. will advertised performance with careless layout. Figure shows recommended component placement boost converter.
1946
LT1946
TYPICAL APPLICATIO
Profile, Triple Output Supply (10V, -10V, 20V)
3.3V
4.7µF 100nF
4.7µF, 6.3V 10µF, 1µF, 2.2µF, 0.1µF, MICROSEMI UPS120 EQUIVALENT ZETEX BAT54S EQUIVALENT SUMIDA CDRH5D18-5R4
Efficiency
EFFICIENCY
3.3V
LOAD VOFF LOAD 10mA AVDD LOAD CURRENT (mA)
1946 TA01a
0.1µF 5.4µH SHDN LT1946 10.5k AVDD 450mA, 275mA, 3.3V 20µF
COMP 33.3k 470pF
0.1µF
2.2µF VOFF -10V 10mA
1946 TA01
Transient Response
AVDD 50mV/DIV COUPLED
0.5A/DIV
AVDD 150mA LOAD 100mA
100µs/DIV
1946 TA01b
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LT1946
TYPICAL APPLICATIO
Output Boost Converter
4.7µH SHDN LT1946 100nF COMP 9.76k
3.3V
Efficiency
3.3V
EFFICIENCY
LOAD CURRENT (mA)
1946 TA02a
VOUT 410mA, 275mA, 3.3V 84.5k 4.7µF
4.7µF 33.3k 470pF
4.7µF, X7R, 6.3V 4.7µF, X7R, MICROSEMI UPS120 EQUIVALENT RLF5018T-4R7M1R4
1946 TA02
Transient Response
VOUT 100mV/DIV COUPLED
0.5A/DIV
ILOAD 175mA 100mA 3.3V 100µs/DIV
1946 TA02b
1946fa
LT1946
PACKAGE DESCRIPTIO
Package 8-Lead Plastic MSOP
(Reference 05-08-1660)
3.00 0.102 (.118 .004) (NOTE 0.497 0.076 (.0196 .003) 0.254 (.010) GAUGE PLANE DETAIL 4.90 0.152 (.193 .006) 3.00 0.102 (.118 .004) (NOTE 0.53 0.152 (.021 .006) DETAIL 0.18 (.007) 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") SEATING PLANE 0.17 0.27 (.007 .011) 0.127 0.076 (.005 .003)
MSOP (MS) 0603
0.889 0.127 (.035 .005)
5.23 (.206)
3.20 3.45 (.126 .136)
0.50 0.305 0.038 (.0197) (.0120 .0015) RECOMMENDED SOLDER LAYOUT
1.10 (.043) 0.86 (.034)
0.50 (.0197)
MS8E Package 8-Lead Plastic MSOP
(Reference 05-08-1662)
BOTTOM VIEW EXPOSED OPTION 0.52 (.0205) 2.06 0.102 (.081 .004) 1.83 0.102 (.072 .004)
2.794 0.102 (.110 .004)
0.889 0.127 (.035 .005)
3.00 0.102 (.118 .004) (NOTE
5.23 (.206)
2.083 0.102 3.20 3.45 (.082 .004) (.126 .136) 0.254 (.010)
DETAIL
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE
0.42 0.038 (.0165 .0015)
0.65 (.0256)
GAUGE PLANE
0.86 (.034)
RECOMMENDED SOLDER LAYOUT
DETAIL 0.18 (.007) 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")
0.53 0.152 (.021 .006)
1.10 (.043)
SEATING PLANE
0.22 0.38 (.009 .015)
0.65 (.0256)
0.127 0.076 (.005 .003)
MSOP (MS8E) 0603
1946fa
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.
LT1946
TYPICAL APPLICATIO
Profile, Triple Output Supply (8V, 23V)
0.1µF 0.1µF 0.1µF 5.4µH SHDN LT1946 5.23k 28.7k 20µF AVDD 375mA COMP 49.9k 470pF 0.1µF 2.2µF VOFF 10mA
1946 TA03
3.3V
4.7µF 100nF
4.7µF, 6.3V 10µF, 2.2µF, 1µF, 0.1µF, 0.1µF, MICROSEMI UPS120 EQUIVALENT ZETEX BAT54S EQUIVALENT SUMIDA CDRH5D18-5R4
Efficiency
EFFICIENCY AVDD 2V/DIV
Start-Up Waveforms
AVDD LOAD CURRENT (mA) LOAD VOFF LOAD 10mA
10V/DIV VOFF 5V/DIV
200mA/V 1ms/DIV
1946 TA03a
1946 TA04
RELATED PARTS
PART NUMBER LT1613 LT1615 LT1930/LT1930A LT1944/LT1944-1 LT1945 LT1946A LT1947 DESCRIPTION 1.4MHz Switching Regulator 5-Lead ThinSOT
COMMENTS 200mA from 3.3V Input, ThinSOT Package 12mA from 2.5V, ThinSOT Package 300mA from Input, ThinSOT Package 1.2V 15V, VOUT 34V, MS10 Package 1.2V 15V, VOUT ±34V, MS10 Package 2.45V 16V, VOUT 34V, MS8E Package 200mA from 3.3V Input, 10-Lead MSOP Package
1946fa LT/TP 0205 PRINTED
Micropower Constant Off-Time DC/DC Converter 5-Lead ThinSOT 1.2MHz/2.2MHz, Switching Regulator 5-Lead ThinSOT Dual 350mA Boost Converter Dual ±250mA Boost Converter 2.7MHz, 1.5A Boost DC/DC Converter 3MHz, Dual Switching Regulator
ThinSOT trademark Linear Technology Corporation.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2001
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