LT®3085 500mA dropout linear regulator that paralleled increase output

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LT®3085 500mA dropout linear regulator that paralleled increase output

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LT3085 Adjustable 500mA Single Resistor Dropout Regulator DESCRIPTION
LT®3085 500mA dropout linear regulator that paralleled increase output current spread heat surface mounted boards. Designed precision current source voltage follower, this regulator finds many applications requiring high current, adjustability zero, heat sink. device also brings collector pass transistor allow dropout operation-down 275mV-when used with second supply. feature LT3085 capability supply wide output voltage range. using reference current through single resistor, output voltage programmed level between zero 36V. LT3085 stable with 2.2F capacitance output, uses small ceramic capacitors that require additional common with other regulators. Internal protection circuitry includes current limiting thermal limiting. LT3085 offered 8-lead MSOP profile (0.75mm) 6-lead package (both with Exposed better thermal characteristics).
Lare registered trademarks Linear Technology Corporation. other trademarks property their respective owners.
Outputs Paralleled Higher Current Heat Spreading Output Current: 500mA Single Resistor Programs Output Voltage Initial Accuracy Current Output Adjustable Current Limit Constant with Temperature Output Noise: 40VRMS (10Hz 100kHz) Wide Input Voltage Range: 1.2V Dropout Voltage: 275mV Load Regulation 0.001%/ Line Regulation Minimum Load Current: 0.5mA Stable with Minimum 2.2F Ceramic Capacitor Current Limit with Foldback Overtemperature Protected 8-Lead MSOP, 6-Lead Packages
APPLICATIONS
High Current Surface Mount Supply High Efficiency Linear Regulator Post Regulator Switching Supplies Parts Count Variable Voltage Supply Output Voltage Power Supplies
TYPICAL APPLICATION
Variable Output Voltage 500mA Supply
1.2V VCONTROL LT3085 1676
VOUT 2.2F 9.80 10.00 10.20 9.90 10.10 CURRENT DISTRIBUTION
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RSET VOUT RSET
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LT3085 ABSOLUTE MAXIMUM RATINGS
(Note Voltages Relative VOUT
VCONTROL Voltage 40V, -0.3V Voltage 40V, -0.3V Current (Note ±15mA Voltage (Relative OUT) .±10V Output Short-Circuit Duration Indefinite
Operating Junction Temperature Range (Notes Grade -40°C 125°C Grade. -55°C 125°C Storage Temperature Range. -65°C 150°C Lead Temperature (Soldering, sec) MS8E Package Only 300°C
CONFIGURATION
VIEW VIEW VCONTROL VCONTROL
PACKAGE 6-LEAD (2mm 3mm) PLASTIC TJMAX 125°C, 73°C/W, 10.6°C/W EXPOSED (PIN OUT, MUST SOLDERED VOUT APPLICATIONS INFORMATION SECTION
MS8E PACKAGE 8-LEAD PLASTIC MSOP TJMAX 125°C, 60°C/W, 10°C/W EXPOSED (PIN OUT, MUST SOLDERED VOUT APPLICATIONS INFORMATION SECTION
ORDER INFORMATION
LEAD FREE FINISH LT3085EDCB#PBF LT3085EMS8E#PBF LT3085IDCB#PBF LT3085IMS8E#PBF LT3085MPMS8E#PBF LEAD BASED FINISH LT3085EDCB LT3085EMS8E LT3085IDCB LT3085IMS8E LT3085MPMS8E TAPE REEL LT3085EDCB#TRPBF LT3085EMS8E#TRPBF LT3085IDCB#TRPBF LT3085IMS8E#TRPBF LT3085MPMS8E#TRPBF TAPE REEL LT3085EDCB#TR LT3085EMS8E#TR LT3085IDCB#TR LT3085IMS8E#TR LT3085MPMS8E#TR PART MARKING* LDQQ LTDQP LDQQ LTDQP LTDWQ PART MARKING* LDQQ LTDQP LDQQ LTDQP LTDWQ PACKAGE DESCRIPTION 6-Lead (2mm 3mm) Plastic 8-Lead Plastic MSOP 6-Lead (2mm 3mm) Plastic 8-Lead Plastic MSOP 8-Lead Plastic MSOP PACKAGE DESCRIPTION 6-Lead (2mm 3mm) Plastic 8-Lead Plastic MSOP 6-Lead (2mm 3mm) Plastic 8-Lead Plastic MSOP 8-Lead Plastic MSOP TEMPERATURE RANGE -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -55°C 125°C TEMPERATURE RANGE -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C -55°C 125°C
Consult Marketing parts specified with wider operating temperature ranges. *The temperature grade identified label shipping container. more information lead free part marking, http://www.linear.com/leadfree/ more information tape reel specifications,
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LT3085 ELECTRICAL CHARACTERISTICS
PARAMETER Current Output Offset Voltage (VOUT VSET) Load Regulation Line Regulation Minimum Load Current (Notes VCONTROL Dropout Voltage (Note Dropout Voltage (Note VCONTROL Current (Note Current Limit (Note Error Amplifier Output Noise (Note Ripple Rejection CONDITIONS ISET VCONTROL ILOAD 1mA, 25°C VCONTROL ILOAD 500mA (Note VCONTROL ILOAD 1mA, 25°C VCONTROL ILOAD ISET ILOAD 500mA ILOAD 500mA (Note ISET 36V, VCONTROL 36V, ILOAD 36V, VCONTROL 36V, ILOAD VCONTROL VCONTROL ILOAD 100mA ILOAD 500mA ILOAD 100mA ILOAD 500mA ILOAD 100mA ILOAD 500mA VCONTROL VSET VOUT -0.1V ILOAD 500mA, 10Hzf100kHz, COUT=10F CSET=0.1F f=120Hz, VRIPPLE=0.5VP-P, ILOAD=0.1A, CSET=0.1F, COUT=2.2F f=10kHz f=1MHz 10ms Pulse
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C (Note
-1.5 -0.1 -0.6 0.003 1.35 0.003 10.1 10.2 UNITS nA/V mV/V VRMS nARMS
Reference Current Output Noise (Note 10Hzf100kHz
Thermal Regulation, ISET
Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note Unless otherwise specified, voltages with respect VOUT. LT3085 tested specified under pulse load conditions such that LT3085E 100% tested 25°C. Performance LT3085E over full -40°C 125°C operating junction temperature range assured design, characterization, correlation with statistical process controls. LT3085I regulators guaranteed over full -40°C 125°C operating junction temperature range. LT3085 grade) 100% tested guaranteed over -55°C 125°C operating junction temperature range. Note Minimum load current equivalent quiescent current part. Since quiescent drive current delivered output part, minimum load current minimum current required maintain regulation. Note LT3085, dropout caused either minimum control voltage (VCONTROL) minimum input voltage (VIN). Both parameters specified with respect output voltage. specifications represent minimum input-to-output differential voltage required maintain regulation.
Note VCONTROL current drive current required output transistor. This current will track output current with roughly 1:60 ratio. minimum value equal quiescent current device. Note Output noise lowered adding small capacitor across voltage setting resistor. Adding this capacitor bypasses voltage setting resistor shot noise reference current noise; output noise then equal error amplifier noise (see Applications Information section). Note clamped output with diodes through resistors. These resistors diodes will only carry current under transient overloads. Note Load regulation Kelvin sensed package. Note Current limit includes foldback protection circuitry. Current limit decreases higher input-to-output differential voltages. Typical Performance Characteristics graphs more information. Note This includes over-temperature protection that intended protect device during momentary overload conditions. Junction temperature will exceed maximum operating junction temperature when over-temperature protection active. Continuous operation above specified maximum operating junction temperature impair device reliability.
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LT3085 TYPICAL PERFORMANCE CHARACTERISTICS
Current
10.20 10.15 CURRENT 10.10 10.05 10.00 9.95 9.90 9.85 9.80 TEMPERATURE (°C)
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Current Distribution
1676 OFFSET VOLTAGE (mV) 9.80 10.00 10.20 9.90 10.10 CURRENT DISTRIBUTION
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Offset Voltage (VOUT VSET)
-0.5 -1.0 -1.5 -2.0 TEMPERATURE (°C)
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Offset Voltage Distribution
1.00 1676 OFFSET VOLTAGE (mV) 0.75
Offset Voltage
0.25 ILOAD
Offset Voltage
25°C 0.25 -0.25 -0.50 -0.75 -1.00 DISTRIBUTION (mV)
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OFFSET VOLTAGE (mV)
0.50
-0.25 -0.50 125°C -0.75 -1.00 -1.25 -1.50
INPUT-TO-OUTPUT VOLTAGE
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-1.75 LOAD CURRENT (mA)
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Load Regulation
CHANGE OFFSET VOLTAGE WITH LOAD (mV) -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 CHANGE OFFSET VOLTAGE (VOUT VSET) ILOAD 500mA VOUT CHANGE REFERENCE CURRENT MINIMUM LOAD CURRENT (mA) CHANGE REFERENCE CURRENT WITH LOAD (nA)
Minimum Load Current
VIN, CONTROL VOUT MINIMUM VOLTAGE (VIN VOUT) (mV)
Dropout Voltage (Minimum Voltage)
125°C 25°C LOAD CURRENT (mA)
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VIN, CONTROL VOUT 1.5V
TEMPERATURE (°C)
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TEMPERATURE (°C)
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LT3085 TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage (Minimum Voltage)
MINIMUM VOLTAGE (VIN VOUT) (mV) ILOAD 500mA TEMPERATURE (°C)
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Dropout Voltage (Minimum VCONTROL Voltage)
MINIMUM CONTROL VOLTAGE (VCONTROL VOUT) 125°C 25°C LOAD CURRENT (mA)
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Dropout Voltage (Minimum VCONTROL Voltage)
MINIMUM CONTROL VOLTAGE (VCONTROL VOUT) TEMPERATURE (°C)
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-50°C
ILOAD 500mA ILOAD 100mA
ILOAD 100mA
Current Limit
CURRENT LIMIT (mA) CURRENT LIMIT (mA) VOUT
Current Limit
OUTPUT VOLTAGE DEVIATION (mV) 25°C LOAD CURRENT (mA)
Load Transient Response
VOUT 1.5V CSET 0.1F VCONTROL
COUT CERAMIC COUT 2.2F CERAMIC
TEMPERATURE (°C)
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INPUT-TO-OUTPUT DIFFERENTIAL
TIME
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Load Transient Response
OUTPUT VOLTAGE DEVIATION (mV) COUT 2.2F CERAMIC COUT CERAMIC OUTPUT VOLTAGE DEVIATION (mV)
Line Transient Response
OUTPUT VOLTAGE IN/CONTROL VOLTAGE
Turn-On Response
-100
LOAD CURRENT (mA)
-100 VCONTROL VOUT 1.5V CSET 0.1F TIME
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IN/CONTROL VOLTAGE
VOUT 1.5V ILOAD 10mA COUT 2.2F CERAMIC CSET 0.1F CERAMIC
COUT 2.2F CERAMIC RSET 100k CSET RLOAD
TIME
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TIME
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LT3085 TYPICAL PERFORMANCE CHARACTERISTICS
VCONTROL Currrent
CONTROL CURRENT (mA) ILOAD INPUT-TO-OUTPUT DIFFERENTIAL LOAD CURRENT
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VCONTROL Current
CONTROL CURRENT (mA) 25°C VCONTROL VOUT -50°C OUTPUT VOLTAGE (mV)
Residual Output Voltage with Less Than Minimum Load
VOUT RTEST
ILOAD 500mA
DEVICE CURRENT LIMIT
125°C
RTEST
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Ripple Rejection Single Supply
RIPPLE REJECTION (dB) VCONTROL VOUT (NOMINAL) RIPPLE 50mVP-P COUT 2.2F CERAMIC CSET 0.1F CERAMIC FREQUENCY (Hz) 100k
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Ripple Rejection Dual Supply VCONTROL
RIPPLE REJECTION (dB) ILOAD 100mA RIPPLE REJECTION (dB) FREQUENCY (Hz) 100k
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Ripple Rejection Dual Supply
ILOAD 100mA
ILOAD 100mA ILOAD 500mA
VOUT (NOMINAL) VCONTROL VOUT (NOMINAL) RIPPLE 50mVP-P COUT 2.2F CERAMIC CSET 0.1F CERAMIC ILOAD 500mA
ILOAD 500mA
VCONTROL VCONTROL VOUT (NOMINAL) RIPPLE 50mVP-P COUT 2.2F CERAMIC CSET 0.1F CERAMIC FREQUENCY (Hz) 100k
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Ripple Rejection (120Hz)
Noise Spectral Density
Output Voltage Noise
REFERENCE CURRENT NOISE SPECTRAL DENSITY (pA/
ERROR AMPLIFIER NOISE SPECTRAL DENSITY (nV/Hz)
RIPPLE REJECTION (dB)
SINGLE SUPPLY OPERATION VOUT (NOMINAL) RIPPLE 50mVP-P, 120Hz ILOAD 0.1A COUT 2.2F, CSET 0.1F FREQUENCY (Hz)
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VOUT 100V/DIV
TIME 1ms/DIV VOUT RSET 100k CSET O.1F COUT ILOAD 1.1A
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FREQUENCY (Hz)
100k
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LT3085 TYPICAL PERFORMANCE CHARACTERISTICS
Error Amplifier Gain Phase
GAIN (dB) ILOAD 100mA FREQUENCY (Hz) 100k ILOAD 500mA ILOAD 100mA ILOAD 500mA RIPPLE REJECTION (dB) PHASE (deg) -144 -216 -288 -360 -432 -504
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Ripple Rejection Current
RSET 100k VCONTROL VOUT (NOMINAL) RIPPLE 50mVP-P FREQUENCY (Hz) 100k
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CSET 0.1F
CSET
FUNCTIONS
(DCB/MS8E)
VCONTROL (Pin 4/Pin This supply control circuitry device. current flow into this about 1.7% output current. device regulate, this voltage must more than 1.2V 1.35V greater than output voltage (see VCONTROL Dropout Voltage Electrical Characteristics table graphs Typical Performance Characteristics). LT3085 requires bypass capacitor VCONTROL more than inches away from main input filter capacitor. output impedance battery rises with frequency, include bypass capacitor battery-powered circuits. bypass capacitor range suffices. (Pins 6/Pins This collector power device LT3085. output load current supplied through this pin. device regulate, voltage this must more than 0.1V 0.5V greater than output voltage (see Dropout Voltage Electrical Characteristics table graphs Typical Performance Characteristics). LT3085 requires bypass capacitor more than inches away from main input filter capacitor. output impedance battery
rises with frequency, include bypass capacitor battery-powered circuits. bypass capacitor range suffices. (NA/Pin Connection. Connect connection internal circuitry tied VIN, VCONTROL, VOUT, GND, floated. (Pins 2/Pins This power output device. There must minimum load current output regulate. minimum 2.2F output capacitor required stability. SET(Pin 3/Pin This non-inverting input error amplifier regulation point device. fixed current flows this through single external resistor, which programs output voltage device. Output voltage range zero absolute maximum rated output voltage. Transient performance improved output noise decreased adding small capacitor from ground. Exposed (Pin 7/Pin OUT. directly Pins Pins directly PCB.
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LT3085 BLOCK DIAGRAM
VCONTROL
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APPLICATIONS INFORMATION
LT3085 regulator easy protection features expected high performance regulators. Included short-circuit protection safe operating area protection, well thermal shutdown. LT3085 especially well suited applications needing multiple rails. architecture adjusts down zero with single resistor, handling modern voltage digital IC's well allowing easy parallel operation thermal management without heat sinks. Adjusting "zero" output allows shutting powered circuitry when input pre-regulated such 3.3V input supply external resistors help spread heat. precision internal current source connected non-inverting input power operational amplifier. power operational amplifier provides impedance buffered output voltage non-inverting input. single resistor from non-inverting input ground sets output voltage this resistor zero, zero output results. seen, output voltage obtained from zero maximum defined input power supply. What obvious from this architecture benefits using true internal current source reference opposed bootstrapped reference older regulators. true current source allows regulator have gain frequency response independent impedance positive input. Older adjustable regulators, such LT1086, have change loop gain with output voltage well bandwidth changes when adjustment bypassed ground. LT3085, loop gain unchanged changing output voltage bypassing. Output regulation fixed percentage output voltage fixed fraction millivolts. true current source allows gain buffer amplifier provide regulation none that gain needed amplify reference higher output voltage. LT3085 collector output transistor connected separate from control input. Since dropout collector pin) only 275mV, supplies used power LT3085 reduce dissipation: higher voltage supply control circuitry lower voltage supply collector. This increases efficiency reduces dissipation. further spread heat, resistor inserted series with collector move some heat spread board.
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LT3085 APPLICATIONS INFORMATION
LT3085 operated modes. Three terminal mode control connected power input which gives limitation 1.35V dropout. Alternatively, "control" tied higher voltage power lower voltage giving 275mV dropout minimizing power dissipation. This allows 500mA supply regulating from 2.5VIN 1.8VOUT 1.8VIN 1.2VOUT with dissipation. Setting Output Voltage LT3085 generates reference current that flows pin. Connecting resistor from ground generates voltage that becomes reference point error amplifier (see Figure reference voltage straight multiplication current value resistor. voltage generated there minimum output voltage regulator. Table lists many common output voltages standard resistor values used generate that output voltage. minimum load current required maintain regulation regardless output voltage. true zero voltage output operation, this load current must returned negative supply voltage.
VCONTROL LT3085
With level current used generate reference voltage, leakage paths from create errors reference output voltages. High quality insulation should used (e.g., Teflon, Kel-F); cleaning insulating surfaces remove fluxes other residues will probably required. Surface coating necessary provide moisture barrier high humidity environments.
Table Resistors Common Output Voltages
VOUT 1.2V 1.5V 1.8V 2.5V 3.3V RSET 100k 121k 150k 182k 249k 332k 499k
VCONTROL
RSET CSET
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Board leakage minimized encircling circuitry with guardring operated potential close itself; guardring should tied pin. Guarding both sides circuit board required. Bulk leakage reduction depends guard ring width. nanoamperes leakage into associated circuitry creates 0.1% error reference voltage. Leakages this magnitude, coupled with other sources leakage, cause significant offset voltage reference drift, especially over wide temperature range. guardring techniques used, this bootstraps stray capacitance pin. Since high impedance node, unwanted signals couple into cause erratic behavior. This will most noticeable when operating with minimum output capacitors full load current. easiest remedy this bypass with small amount capacitance from ground, 10pF 20pF sufficient.
VOUT RSET
Figure Basic Adjustable Regulator
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LT3085 APPLICATIONS INFORMATION
Input Capacitance Stability LT3085 designed stable with minimum capacitance each input pin. Ceramic capacitors with available bypass these pins, cases where long wires connect LT3085 inputs power supply (and also from ground LT3085 circuitry back power supply ground), this causes instabilities. This happens wire inductance forming tank circuit with input capacitor result instability LT3085. self-inductance, isolated inductance, wire directly proportional length. diameter does have major influence self-inductance. example, self-inductance 2-AWG isolated wire with diameter 0.26in. approximately half self-inductance 30-AWG wire with diameter 0.01in. foot 30-AWG wire 465nH self-inductance. overall self-inductance wire reduced ways. divide current flowing towards LT3085 between parallel conductors. this case, farther apart wires from each other, more self-inductance reduced, reduction when placed inches apart. Splitting wires basically connects equal inductors parallel, placing them close proximity gives wires mutual inductance adding self-inductance. second most effective reduce overall inductance place both forward- return-current conductors (the wire input wire ground) very close proximity. 30-AWG wires separated only 0.02in. used forward- return-current conductors reduce overall self-inductance approximately one-fifth that single isolated wire. LT3085 powered battery mounted close proximity same circuit board, 2.2F input capacitor sufficient stability. When powering from distant supplies, larger input capacitor based guideline plus another inches wire length. power supply impedance does vary, amount capacitance needed stabilize your application will also vary. Extra capacitance placed directly output power supply requires order magnitude more capacitance opposed placing extra capacitance close LT3085. Using series resistance between power supply input LT3085 also stabilizes application. little 0.5, often less, that needed provide damping circuit. extra impedance between power supply input unacceptable, placing resistors series with capacitors will provide damping prevent resonance from causing full-blown oscillation. Stability Output Capacitance LT3085 requires output capacitor stability. designed stable with most capacitors (typically ceramic, tantalum electrolytic). minimum output capacitor 2.2F with less recommended prevent oscillations. Larger values output capacitance decrease peak deviations provide improved transient response larger load current changes. Bypass capacitors, used decouple individual components powered LT3085, increase effective output capacitor value.
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LT3085 APPLICATIONS INFORMATION
improvement transient performance, place capacitor across voltage setting resistor. Capacitors used. This bypass capacitor reduces system noise well, start-up time proportional time constant voltage setting resistor (RSET Figure bypass capacitor. Extra consideration must given ceramic capacitors. Ceramic capacitors manufactured with variety dielectrics, each with different behavior across temperature applied voltage. most common dielectrics used specified with temperature characteristic codes Z5U, Y5V, X7R. dielectrics good providing high capacitances small package, they tend have strong voltage temperature coefficients shown Figures When used with regulator, capacitor exhibit effective value bias voltage applied over operating temperature range. dielectrics result more stable characteristics more suitable output capacitor. type better stability across temperature, while less expensive available higher values. Care still must exercised when using capacitors; codes only specify operating temperature range maximum capacitance change over temperature. Capacitance change bias with capacitors better than capacitors, still significant enough drop capacitor values below appropriate levels. Capacitor bias characteristics tend improve component case size increases, expected capacitance operating voltage should verified.
CHANGE VALUE -100 BOTH CAPACITORS 16V, 1210 CASE SIZE,
BIAS VOLTAGE
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Figure Ceramic Capacitor Bias Characteristics
CHANGE VALUE BOTH CAPACITORS 16V, 1210 CASE SIZE, TEMPERATURE (°C)
-100
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Figure Ceramic Capacitor Temperature Characteristics
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LT3085 APPLICATIONS INFORMATION
Voltage temperature coefficients only sources problems. Some ceramic capacitors have piezoelectric response. piezoelectric device generates voltage across terminals mechanical stress, ceramic capacitor stress induced vibrations system thermal transients. Paralleling Devices LT3085's paralleled with other LT308X devices obtain higher output current. pins tied together pins tied together. This same whether it's three terminal mode separate input supplies. outputs connected common using small piece trace ballast resistor equalize currents. trace resistance milliohms/inch shown Table Only tiny area needed ballasting.
Table Board Trace Resistance
WEIGHT (oz) WIDTH 54.3 27.1 WIDTH 27.1 13.6
4.8V VCONTROL
course, more than LT308X's paralleled even higher output current. They spread board, spreading heat. Input resistors further spread heat input-to-output difference high. Thermal Performance
this example, LT3085 devices mounted copper 4-layer board. They placed approximately inches apart board mounted vertically convection cooling. tests were measure cooling performance current sharing these devices.
VCONTROL LT3080
Trace resistance measured m/in
LT3085
worst-case offset between output only ±1.5mV allows very small ballast resistors used. shown Figure devices have small ballast resistors, which full output current gives better than equalized sharing current. external resistance (6.6m devices parallel) only adds about 10mV output regulation drop output 1.5A. Even with output voltage this only adds regulation.
165k
VOUT 3.3V 1.5A
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Figure Parallel Devices
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LT3085 APPLICATIONS INFORMATION
first test done with approximately 1.6V input- to-output 0.5A device. This gave 800mW dissipation each device output current. temperature rise above ambient approximately 28°C both devices were within plus minus 1°C. Both thermal electrical sharing these devices excellent. thermograph Figure shows temperature distribution between these devices board reaches ambient temperature within about half inch from devices. power then increased with 3.4V across each device. This gives watts dissipation each device device temperature about 90°C, about 65°C above ambient shown Figure Again, temperature matching between devices within 2°C, showing excellent tracking between devices. board temperature reached approximately 40°C within about 0.75 inches each device. While 90°C acceptable operating temperature these devices, this 25°C ambient. higher ambients, temperature must controlled prevent device temperature from exceeding 125°C. 3-meter-per-second airflow across devices will decrease device temperature about 20°C providing margin higher operating ambient temperatures. Both power relatively high power levels devices paralleled higher output current. Current sharing thermal sharing excellent, showing that acceptable operation while keeping peak temperatures below excessive operating temperatures board. This technique allows higher operating current linear regulation used systems where could never used before.
Quieting Noise LT3085 offers numerous advantages when comes dealing with noise. There several sources noise linear regulator. most critical noise source reference; from there, noise contribution from error amplifier must considered, gain created using resistor divider cannot forgotten. Traditional noise regulators bring voltage reference external (usually through large value resistor) allow bypassing noise reduction reference noise. LT3085 does traditional voltage reference like other linear regulators, instead uses reference current. That current operates with typical noise current levels 2.3pA/Hz (0.7nARMS over 10Hz 100kHz bandwidth). voltage noise this equal noise current multiplied resistor value.
Figure Temperature Rise 800mW Dissipation
Figure Temperature Rise 1.7W Dissipation
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LT3085 APPLICATIONS INFORMATION
resistor generates spot noise equal to4kTR Boltzmann's constant, 1.38 10-23 J/°K, absolute temperature) which summed with reference current noise. lower reference noise, voltage setting resistor bypassed with capacitor, though this causes start-up time increase factor time constant. LT3085 uses unity-gain follower from drive output, there requirement resistor output voltage. high accuracy voltage reference placed remove errors output voltage reference current tolerance resistor tolerance. Active driving acceptable; limitations creativity ingenuity circuit designer. problem that normal linear regulator sees with reference voltage noise that noise gained along with output when using resistor divider operate levels higher than normal reference voltage. With LT3085, unity-gain follower presents gain whatsoever from output, noise figures increase accordingly. Error amplifier noise typically 100nV/Hz (33VRMS over 10Hz 100kHz bandwidth); this another factor that summed give final noise figure regulator. Curves Typical Performance Characteristics show noise spectral density peak-to-peak noise characteristics both reference current error amplifier over 10Hz 100kHz bandwidth. Overload Recovery Like many power regulators, LT3085 safe operating area (SOA) protection. protection decreases current limit input-to-output voltage increases keeps power dissipation safe levels values input-to-output voltage. LT3085 provides some output current values input-to-output voltage device breakdown. Current Limit curve Typical Performance Characteristics. When power first turned input voltage rises output follows input, allowing regulator start into very heavy loads. During start-up, input voltage rising, input-to-output voltage differential small, allowing regulator supply large output currents. With high input voltage, problem occur wherein removal output short will allow output voltage recover. Other regulators, such LT1085 LT1764A, also exhibit this phenomenon unique LT3085. problem occurs with heavy output load when input voltage high output voltage low. Common situations immediately after removal short circuit. load line such load intersect output current curve points. this happens, there stable operating points regulator. With this double intersection, input power supply need cycled down zero brought again make output recover. Load Regulation Because LT3085 floating device (there ground part, quiescent drive current delivered load), possible provide true remote load sensing. Load regulation will limited resistance connections between regulator load. data sheet specification load regulation Kelvin sensed pins package. Negative side sensing true Kelvin connection, with bottom voltage setting resistor returned negative side load (see Figure Connected shown, system load regulation will LT3085 load regulation parasitic line resistance multiplied output current. important keep positive connection between regulator load short possible large wire board traces.
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LT3085 APPLICATIONS INFORMATION
VCONTROL LT3085
RSET
PARASITIC RESISTANCE
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LOAD
Figure Connections Best Load Regulation
Protection diodes otherwise needed between pin. internal diodes handle microsecond surge currents 50A. Even with large output capacitors, obtaining surge currents those magnitudes difficult normal operation. Only with large output capacitors, such 1000F 5000F with instantaneously shorted ground will damage occur. crowbar circuit capable generating those levels currents, then protection diodes from recommended. Normal power supply cycling system "hot plugging unplugging" does damage. protection diode between VCONTROL usually needed. internal parasitic diode VCONTROL LT3085 handles microsecond surge currents 10A. Again, this only occurs when using crowbar circuits with large value output capacitors. Since VCONTROL usually current supply, this unlikely. Still, protection diode recommended VCONTROL instantaneously shorted ground. Normal power supply cycling system "hot plugging unplugging" does damage. LT3085 configured three-terminal (single supply) regulator with VCONTROL shorted together, internal diode will protect VCONTROL pin. Like other regulator, exceeding maximum inputto-output differential causes internal transistors break down then none internal protection circuitry functional. Thermal Considerations LT3085 internal power thermal limiting circuitry designed protect under overload conditions. continuous normal load conditions, maximum junction temperature must exceeded. important give consideration sources thermal resistance
Internal Parasitic Diodes Protection Diodes normal operation, LT3085 does require protection diodes. Older three-terminal regulators require protection diodes between VOUT input between VOUT prevent overstress. LT3085, internal resistors diodes limit current paths pin. Even with bypass capacitors pin, protection diode needed ensure device safety under short-circuit conditions. handles ±10V (either transient with respect without device degradation. Internal parasitic diodes exist between inputs. Negative input voltages transferred output damage sensitive loads. Reverse-biasing either input will turn these parasitic diodes allow current flow. This current flow will bias internal nodes LT3085 levels that possibly cause errors when suddenly returning normal operating conditions expecting device start operate. Prediction results bias fault impossible, immediate return normal operating conditions just difficult after bias fault. Suffice that extra wait time, power cycling, protection diodes needed allow LT3085 return normal operating mode quickly possible.
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LT3085 APPLICATIONS INFORMATION
from junction ambient. This includes junction-to-case, case-to-heat sink interface, heat sink resistance circuit board-to-ambient application dictates. Additional heat sources nearby must also considered. surface mount devices, heat sinking accomplished using heat spreading capabilities board copper traces. Surface mount heat sinks plated through-holes also used spread heat generated power devices. Boards specified thermal resistance tables have vias plated through-holes from topside backside. Junction-to-case thermal resistance specified from junction bottom case directly below die. This lowest resistance path heat flow. Proper mounting required ensure best possible thermal flow from this area package heat sinking material. Note that Exposed electrically connected output. following tables list thermal resistance several different copper areas given fixed board size. measurements were taken still two-sided 1/16" FR-4 board with ounce copper.
layers, copper weight, board layout thermal vias affect resultant thermal resistance. Although Tables provide thermal resistance numbers 2-layer board with ounce copper, modern multi-layer PCBs provide better performance than found these tables. example, 4-layer, ounce copper board with thermal vias from MSOP exposed backside inner layers (connected VOUT) achieves 40°C/W thermal resistance. Demo circuit 1401A's board layout achieves this 40°C/W performance. This approximately improvement over numbers shown Tables
Table Package, 8-Lead MSOP
COPPER AREA TOPSIDE* 2500mm2 1000mm2 225mm2 100mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 55°C/W 57°C/W 60°C/W 65°C/W
*Device mounted topside
Table Package, 6-Lead
COPPER AREA TOPSIDE* 2500mm2 1000mm2 225mm2 100mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 68°C/W 70°C/W 73°C/W 78°C/W
*Device mounted topside future information thermal resistance using thermal information, refer JEDEC standard JESD51, notably JESD51-12.
Calculating Junction Temperature Example: Given output voltage 0.9V, VCONTROL voltage 3.3V ±10%, voltage 1.5V ±5%, output current range from 0.5A maximum ambient temperature 50°C, what will maximum junction temperature package 2500mm2 board with topside copper area 500mm2? power drive circuit equals: PDRIVE (VCONTROL VOUT)(ICONTROL) where ICONTROL equal IOUT/60. ICONTROL function output current. curve ICONTROL IOUT found Typical Performance Characteristics curves.
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LT3085 APPLICATIONS INFORMATION
power output transistor equals: POUTPUT (VIN VOUT)(IOUT) total power equals: PTOTAL PDRIVE POUTPUT current delivered negligible ignored. VCONTROL(MAX CONTINUOUS) 3.630V (3.3V 10%) VIN(MAX CONTINUOUS) 1.575V (1.5V VOUT 0.9V, IOUT 0.5A, 50°C Power dissipation under these conditions equal PDRIVE (VCONTROL VOUT)(ICONTROL) 0.5A ICONTROL 8.3mA PDRIVE (3.630V 0.9V)(8.3mA) 23mW POUTPUT (VIN VOUT)(IOUT) POUTPUT (1.575V 0.9V)(0.5A) 337mW Total Power Dissipation 360mW Junction Temperature will equal PTOTAL (approximated using tables) 50°C 360mW 73°C/W 76°C this case, junction temperature below maximum rating, ensuring reliable operation. example, assume: VCONTROL VOUT 3.3V IOUT(MAX) 0.5A. formulas from Calculating Junction Temperature section previously discussed.
Figure Reducing Power Dissipation Using Series Resistor
RSET VCONTROL LT3085
Reducing Power Dissipation some applications necessary reduce power dissipation LT3085 package without sacrificing output current capability. techniques available. first technique, illustrated Figure employs resistor series with regulator's input. voltage drop across decreases LT3085's IN-to-OUT differential voltage correspondingly decreases LT3085's power dissipation.
3085
VOUT
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LT3085 APPLICATIONS INFORMATION
Without series resistor power dissipation LT3085 equals: 0.5A 3.3V 0.5A PTOTAL 3.3V 0.86W voltage differential (VDIFF) across pass transistor chosen 0.5V, then equals: 3.3V 0.5V 0.5A Calculating yields: 5.5V 3.2V 7.30 315mA Standard value maximum total power dissipation (5.5V 3.2V) 0.5A 1.2W. However LT3085 supplies only: 0.5A 5.5V 3.2V 0.193A
Therefore, LT3085's power dissipation only: PDIS (5.5V 3.2V) 0.193A 0.44W dissipates 0.71W power. with first technique, choose appropriate wattage resistors handle dissipate power properly. With this configuration, LT3085 supplies only 0.36A. Therefore, load current increase 0.3A 0.143A while keeping LT3085 normal operating range.
VCONTROL LT3085
Power dissipation LT3085 equals:
0.5A PTOTAL 3.3V 0.5V 0.5A 0.26W
LT3085's power dissipation only compared series resistor. dissipates 0.6W power. Choose appropriate wattage resistors handle dissipate power properly. second technique reducing power dissipation, shown Figure uses resistor parallel with LT3085. This resistor provides parallel path current flow, reducing current flowing through LT3085. This technique works well input voltage reasonably constant output load current changes small. This technique also increases maximum available output current expense minimum load requirements. example, assume: VCONTROL VIN(MAX) 5.5V, VOUT 3.3V, VOUT(MIN) 3.2V, IOUT(MAX) 0.5A IOUT(MIN) 0.35A. Also, assuming that carries more than IOUT(MIN) 630mA.
RSET
VOUT
3085
Figure Reducing Power Dissipation Using Parallel Resistor
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LT3085 TYPICAL APPLICATIONS
Higher Output Current
MJ4502
LT3085
100F
VCONTROL
4.7F
VOUT 3.3V 100F
332k
3085 TA02
Current Source
VCONTROL LT3085
100k
0.5W
IOUT 0.5A 4.7F
3085 TA03
Power Oscillator
VCONTROL LT3085
6.3V, 150mA LIGHT BULB 47nF 2.21k 8.45k 499k 8.45k 220n 47nF
3085 TA22
VOUT 400Hz 4VACP-P
4.7F
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LT3085 TYPICAL APPLICATIONS
Adding Shutdown
LT3085
Dropout Voltage Driver
VCONTROL LT3085 100mA
VCONTROL
VN2222LL SHUTDOWN INSURES ZERO OUTPUT ABSENCE OUTPUT LOAD.
3085 TA04
VOUT VN2222LL
24.9k
2.49
3085 TA05
Using Lower Value Resistor
VCONTROL LT3085
49.9k RSET
3085 TA06
VOUT 0.5V VOUT 0.5V RSET COUT 4.7F
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LT3085 TYPICAL APPLICATIONS
Adding Soft-Start
4.8V VCONTROL 1N4148 LT3085
VOUT 3.3V 0.5A COUT 4.7F
0.01F
332k
3085 TA07
Coincident Tracking
VCONTROL VCONTROL VCONTROL LT3085 LT3085 LT3085
169k VOUT2 3.3V 0.5A
80.6k 4.7F
VOUT3 0.5A 4.7F
3085 TA08
1.5F
249k
4.7F VOUT1 2.5V 0.5A
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LT3085 TYPICAL APPLICATIONS
Supply
VCONTROL LT3085 VCONTROL LT3085
0.25W
VOUT
0.5A
4.7F
100F
3085 TA09
High Voltage Regulator
1N4148 BUZ11 VCONTROL 6.1V
LT3085
VOUT 0.5A 4.7F VOUT VOUT RSET
RSET
3085 TA10
Ramp Generator
VCONTROL LT3085
VN2222LL VN2222LL VOUT 4.7F
3085 TA12
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LT3085 TYPICAL APPLICATIONS
Reference Buffer
VCONTROL LT3085
INPUT LT1019 OUTPUT VOUT* 4.7F
3085 TA11
*MIN LOAD 0.5mA
Ground Clamp
VCONTROL
LT3085
VEXT
1N4148
VOUT
4.7F
3085 TA13
Boosting Fixed Output Regulators
VCONTROL LT3085
LT1963-3.3
3085 TA20
3.3VOUT
*4mV DROP ENSURES LT3085 WITH LOAD MULTIPLE LT3085'S USED
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LT3085 TYPICAL APPLICATIONS
Voltage, High Current Adjustable High Efficiency Regulator*
0.47H PVIN 2.7V 5.5V 100F LTC3414 PGOOD RUN/SS 1000pF 78.7k SYNC/MODE SGND PGND 124k 294k 12.1k
470pF
2.2MEG 100k
SVIN
100F 2N3906
VCONTROL
LT3085
VCONTROL LT3085
*DIFFERENTIAL VOLTAGE LT3085 0.6V 2N3906
MAXIMUM OUTPUT VOLTAGE 1.5V
BELOW INPUT VOLTAGE
VCONTROL
LT3085
VCONTROL
LT3085
100k
3085 TA18
100F
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LT3085 TYPICAL APPLICATIONS
Adjustable High Efficiency Regulator*
CMDSH-4E
4.5V 100k
BOOST LT3493 0.1F MBRM140 TP0610L 1MEG
3085 TA19
SHDN 0.1F
VCONTROL
LT3085
0.5A 4.7F
*DIFFERENTIAL VOLTAGE LT3085 1.4V TPO610L P-CHANNEL THRESHOLD. MAXIMUM OUTPUT VOLTAGE BELOW INPUT VOLTAGE
Terminal Current Source
CCOMP*
VCONTROL
LT3085
100k
3085 TA21
IOUT
*CCOMP 2.2F
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LT3085 PACKAGE DESCRIPTION
Package 6-Lead Plastic (2mm 3mm)
(Reference 05-08-1698)
0.70
0.05
3.55
0.05 2.15
1.65 0.05 SIDES) 0.05 PACKAGE OUTLINE
0.25 0.50 1.35 0.05 SIDES)
0.05
RECOMMENDED SOLDER PITCH DIMENSIONS 2.00 0.10 SIDES) 0.115 0.05 0.40 0.10
3.00 0.10 SIDES) MARK (SEE NOTE
1.65 0.10 SIDES) NOTCH R0.20 0.25 CHAMFER 0.25 0.50 1.35 0.10 SIDES)
(DCB6) 0405
0.05
0.200
0.75
0.05
0.00 0.05
BOTTOM VIEW-EXPOSED
NOTE: DRAWING MADE JEDEC PACKAGE OUTLINE M0-229 VARIATION (TBD) DRAWING SCALE DIMENSIONS MILLIMETERS DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.15mm SIDE EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
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LT3085 PACKAGE DESCRIPTION
MS8E Package 8-Lead Plastic MSOP
(Reference 05-08-1662)
BOTTOM VIEW EXPOSED OPTION 2.06 (.081 1.83 (.072 0.102 .004) 0.102 .004)
2.794 (.110
0.102 .004)
0.889 (.035
0.127 .005)
5.23 (.206)
2.083 (.082
0.102 3.20 3.45 .004) (.126 .136)
0.42 0.038 (.0165 .0015)
0.65 (.0256)
3.00 0.102 (.118 .004) (NOTE
0.52 (.0205)
RECOMMENDED SOLDER LAYOUT
DETAIL 4.90 0.152 (.193 .006) 3.00 0.102 (.118 .004) (NOTE
0.254 (.010) GAUGE PLANE
0.53 0.152 (.021 .006) DETAIL 0.18 (.007) SEATING PLANE 0.22 0.38 (.009 .015) 1.10 (.043)
0.86 (.034)
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")
0.65 (.0256)
0.1016 (.004
0.0508 .002)
MSOP (MS8E) 0307
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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.
LT3085 TYPICAL APPLICATION
Paralleling Regulators
VCONTROL LT3080
4.8V
VCONTROL
LT3085
165k
VOUT 3.3V 1.5A
3085 TA14
RELATED PARTS
PART NUMBER LDOs LT1086 LT1763 LT3021 LT3080 1.5A Dropout Regulator 500mA, Noise 500mA VLDO Regulator 1.1A, Parallelable, Noise, Dropout Linear Regulator Fixed 2.85V, 3.3V, 3.6V, Output 300mV Dropout Voltage, Noise 20VRMS, VIN: 1.8V 20V, SO-8 Package VIN: 0.9V 10V, Dropout Voltage 190mV, VADJ 200mV, DFN-16, SO-8 Packages 300mV Dropout Voltage (2-Supply Operation), Noise 40VRMS, VIN: 1.2V 36V, VOUT 35.7V, Current-Based Reference with 1-Resistor VOUT Set, Directly Parallelable Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP Packages 300mV Dropout Voltage (2-Supply Operation), Noise 40VRMS, VIN: 1.2V 36V, VOUT 35.7V, Current-Based Reference with 1-Resistor VOUT Set, Directly Parallelable Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP Packages. LT3080-1 Version Integrated Ballast Resistor 340mV Dropout Voltage, Noise 40VRMS, VIN: 2.5V 20V, TO-220, SOT-223 SO-8 Packages 290mV Dropout Voltage, Noise 40VRMS, VIN: 1.8V 20V, VOUT 1.2V 19.5V, Stable with Ceramic Caps TO-220, DDPak, MSOP Packages VIN: 1.14V 3.5V (Boost Enabled), 1.14V 5.5V (with External 5V), 0.1V, 950A, Stable with Ceramic Capacitors, 10-Lead MSOP Packages DESCRIPTION COMMENTS
LT3080-1
Parallelable 1.1A Adjustable Single Resistor Dropout Regulator (with Internal Ballast 1.5A Noise, Fast Transient Response 1.1A Noise 1.5A Input Voltage VLDORegulator
LT1963A LT1965 LTC®3026 Switching Regulators
High Voltage, 1.5A Step-Down 200kHz, 100A, TSSOP-16E Package Switching Regulator Efficiency, VIN: 2.25V 5.5V, VOUT(MIN) 0.8V, TSSOP Package LTC3414 (IOUT), 4MHz Synchronous Step-Down DC/DC Converter LTC3406/LTC3406B 600mA (IOUT), 1.5MHz Synchronous Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 20A, Step-Down DC/DC Converter ThinSOT Package Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 0.8V, 60A, 10-Lead LTC3411 1.25A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter Packages VLDO ThinSOT trademarks Linear Technology Corporation. LT1976
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Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1008 PRINTED
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2008

LT®3085 500mA dropout linear regulator that paralleled increase output

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