LT3085 Adjustable 500mA Single Resistor Low Dropout Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n Outputs May be Paralleled for Higher Current and Heat Spreading Output Current: 500mA Single Resistor Programs Output Voltage 1% Initial Accuracy of SET Pin Current Output Adjustable to 0V Current Limit Constant with Temperature Low Output Noise: 40μVRMS (10Hz to 100kHz) Wide Input Voltage Range: 1.2V to 36V Low Dropout Voltage: 275mV < 1mV Load Regulation < 0.001%/ V Line Regulation Minimum Load Current: 0.5mA Stable with Minimum 2.2μF Ceramic Capacitor Current Limit with Foldback and Overtemperature Protected 8-Lead MSOP, and 6-Lead 2mm × 3mm DFN Packages n n n n A key feature of the LT3085 is the capability to supply a wide output voltage range. By using a reference current through a single resistor, the output voltage is programmed to any level between zero and 36V. The LT3085 is stable with 2.2μF of capacitance on the output, and the IC uses small ceramic capacitors that do not require additional ESR as is common with other regulators. Internal protection circuitry includes current limiting and thermal limiting. The LT3085 is offered in the 8-lead MSOP and a low profile (0.75mm) 6-lead 2mm × 3mm DFN package (both with an Exposed Pad for better thermal characteristics). APPLICATIONS n The LT®3085 is a 500mA low dropout linear regulator that can be paralleled to increase output current or spread heat on surface mounted boards. Designed as a precision current source and voltage follower, this new regulator finds use in many applications requiring high current, adjustability to zero, and no heat sink. The device also brings out the collector of the pass transistor to allow low dropout operation—down to 275mV—when used with a second supply. High Current All Surface Mount Supply High Efficiency Linear Regulator Post Regulator for Switching Supplies Low Parts Count Variable Voltage Supply Low Output Voltage Power Supplies L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and VLDO and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Variable Output Voltage 500mA Supply LT3085 IN VIN 1.2V TO 36V N = 1676 VCONTROL + – 1μF OUT VOUT SET RSET VOUT = RSET • 10μA 3085 TA01a 2.2μF 9.80 10.00 10.20 9.90 10.10 SET PIN CURRENT DISTRIBUTION (μA) 3085 TA01b 3085fb 1 LT3085 ABSOLUTE MAXIMUM RATINGS (Note 1) All Voltages Relative to VOUT VCONTROL Pin Voltage ..................................... 40V, –0.3V IN Pin Voltage ................................................ 40V, –0.3V SET Pin Current (Note 7) .................................... ±15mA SET Pin Voltage (Relative to OUT) ..........................±10V Output Short-Circuit Duration .......................... Indefinite Operating Junction Temperature Range (Notes 2, 10) E, I Grade ........................................... –40°C to 125°C MP Grade........................................... –55°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) MS8E Package Only .......................................... 300°C PIN CONFIGURATION TOP VIEW TOP VIEW 6 IN OUT 1 OUT 2 7 OUT OUT OUT SET 5 IN 4 VCONTROL SET 3 1 2 3 4 9 8 7 6 5 IN IN NC VCONTROL MS8E PACKAGE 8-LEAD PLASTIC MSOP DCB PACKAGE 6-LEAD (2mm s 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 73°C/W, θJC = 10.6°C/W EXPOSED PAD (PIN 7) IS OUT, MUST BE SOLDERED TO VOUT ON PCB SEE THE APPLICATIONS INFORMATION SECTION TJMAX = 125°C, θJA = 60°C/W, θJC = 10°C/W EXPOSED PAD (PIN 9) IS OUT, MUST BE SOLDERED TO VOUT ON PCB SEE THE APPLICATIONS INFORMATION SECTION ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3085EDCB#PBF LT3085EDCB#TRPBF LDQQ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LT3085EMS8E#PBF LT3085EMS8E#TRPBF LTDQP 8-Lead Plastic MSOP –40°C to 125°C LT3085IDCB#PBF LT3085IDCB#TRPBF LDQQ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LT3085IMS8E#PBF LT3085IMS8E#TRPBF LTDQP 8-Lead Plastic MSOP –40°C to 125°C LT3085MPMS8E#PBF LT3085MPMS8E#TRPBF LTDWQ 8-Lead Plastic MSOP –55°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3085EDCB LT3085EDCB#TR LDQQ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LT3085EMS8E LT3085EMS8E#TR LTDQP 8-Lead Plastic MSOP –40°C to 125°C LT3085IDCB LT3085IDCB#TR LDQQ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LT3085IMS8E LT3085IMS8E#TR LTDQP 8-Lead Plastic MSOP –40°C to 125°C LT3085MPMS8E LT3085MPMS8E#TR LTDWQ 8-Lead Plastic MSOP –55°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3085fb 2 LT3085 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 2). PARAMETER CONDITIONS MIN TYP MAX UNITS 10 10 10.1 10.2 μA μA 1.5 3 mV mV –1 nA mV SET Pin Current ISET VIN = 1V, VCONTROL = 2V, ILOAD = 1mA, TJ = 25°C VIN ≥ 1V, VCONTROL ≥ 2V, 1mA ≤ ILOAD ≤ 500mA (Note 9) l 9.9 9.8 Output Offset Voltage (VOUT – VSET) VOS VIN = 1V, VCONTROL = 2V, ILOAD = 1mA, TJ = 25°C VIN = 1V, VCONTROL = 2V, ILOAD = 1mA l –1.5 –3 Load Regulation ΔISET ΔILOAD = 1mA to 500mA ΔVOS ΔILOAD = 1mA to 500mA (Note 8) –0.1 –0.6 l ΔISET ΔVIN = 1V to 36V, ΔVCONTROL = 2V to 36V, ILOAD = 1mA ΔVOS ΔVIN = 1V to 36V, ΔVCONTROL = 2V to 36V, ILOAD = 1mA Minimum Load Current (Notes 3, 9) VIN = VCONTROL = 10V VIN = VCONTROL = 36V Line Regulation VCONTROL Dropout Voltage (Note 4) l l 0.1 0.003 0.5 nA/V mV/V 300 500 1 μA mA ILOAD = 100mA ILOAD = 500mA l 1.2 1.35 1.6 V V VIN Dropout Voltage (Note 4) ILOAD = 100mA ILOAD = 500mA l l 85 275 150 450 mV mV VCONTROL Pin Current (Note 5) ILOAD = 100mA ILOAD = 500mA l l 3 8 6 15 mA mA Current Limit (Note 9) VIN = 5V, VCONTROL = 5V, VSET = 0V, VOUT = –0.1V l Error Amplifier RMS Output Noise (Note 6) ILOAD = 500mA, 10Hz ≤ f ≤ 100kHz, COUT = 10μF, CSET = 0.1μF 650 mA 33 μVRMS Reference Current RMS Output Noise (Note 6) 10Hz ≤ f≤ 100kHz 0.7 nARMS Ripple Rejection f = 120Hz, VRIPPLE = 0.5VP-P, ILOAD = 0.1A, CSET = 0.1μF, COUT = 2.2μF f=10kHz f=1MHz 90 75 20 dB dB dB Thermal Regulation, ISET 10ms Pulse Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2. Unless otherwise specified, all voltages are with respect to VOUT. The LT3085 is tested and specified under pulse load conditions such that TJ ≅ TA. The LT3085E is 100% tested at TA = 25°C. Performance of the LT3085E over the full –40°C to 125°C operating junction temperature range is assured by design, characterization, and correlation with statistical process controls. The LT3085I regulators are guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3085 (MP grade) is 100% tested and guaranteed over the –55°C to 125°C operating junction temperature range. Note 3. Minimum load current is equivalent to the quiescent current of the part. Since all quiescent and drive current is delivered to the output of the part, the minimum load current is the minimum current required to maintain regulation. Note 4. For the LT3085, dropout is caused by either minimum control voltage (VCONTROL) or minimum input voltage (VIN). Both parameters are specified with respect to the output voltage. The specifications represent the minimum input-to-output differential voltage required to maintain regulation. 500 0.003 %/W Note 5. The VCONTROL pin current is the drive current required for the output transistor. This current will track output current with roughly a 1:60 ratio. The minimum value is equal to the quiescent current of the device. Note 6. Output noise is lowered by adding a small capacitor across the voltage setting resistor. Adding this capacitor bypasses the voltage setting resistor shot noise and reference current noise; output noise is then equal to error amplifier noise (see Applications Information section). Note 7. The SET pin is clamped to the output with diodes through 1k resistors. These resistors and diodes will only carry current under transient overloads. Note 8. Load regulation is Kelvin sensed at the package. Note 9. Current limit includes foldback protection circuitry. Current limit decreases at higher input-to-output differential voltages. See the Typical Performance Characteristics graphs for more information. Note 10. This IC includes over-temperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed the maximum operating junction temperature when over-temperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 3085fb 3 LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Set Pin Current Set Pin Current Distribution Offset Voltage (VOUT – VSET) 10.20 2.0 N = 1676 1.5 10.10 OFFSET VOLTAGE (mV) SET PIN CURRENT (μA) 10.15 10.05 10.00 9.95 9.90 9.85 1.0 0.5 0 –0.5 –1.0 –1.5 9.80 –50 –25 0 9.80 25 50 75 100 125 150 TEMPERATURE (°C) –2.0 –50 –25 10.00 10.20 9.90 10.10 SET PIN CURRENT DISTRIBUTION (μA) 0 25 50 75 100 125 150 TEMPERATURE (°C) 3085 G02 3085 G01 Offset Voltage Distribution 3085 G03 Offset Voltage Offset Voltage 1.00 0.25 ILOAD = 1mA N = 1676 0.75 0 0.50 –0.25 OFFSET VOLTAGE (mV) OFFSET VOLTAGE (mV) TJ = 25°C 0.25 0 –0.25 –0.50 –0.75 –1.00 2 6 24 30 18 INPUT-TO-OUTPUT VOLTAGE (V) 0 12 0 –0.3 –10 –0.4 –20 –0.5 –30 (VOUT – VSET) –0.6 –40 –50 CHANGE IN OFFSET VOLTAGE –60 25 50 75 100 125 150 TEMPERATURE (°C) 3085 G07 MINIMUM LOAD CURRENT (mA) 10 CHANGE IN REFERENCE CURRENT 0 –1.75 0 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 3085 G06 Dropout Voltage (Minimum IN Voltage) 400 0.8 CHANGE IN REFERENCE CURRENT WITH LOAD (nA) CHANGE IN OFFSET VOLTAGE WITH LOAD (mV) 20 ΔILOAD = 1mA TO 500mA VIN – VOUT = 2V –0.8 –50 –25 36 Minimum Load Current 0 –0.7 –1.25 3085 G05 Load Regulation –0.2 –1.00 –1.50 3085 G04 –0.1 TJ = 125°C –0.75 0.7 MINIMUM IN VOLTAGE (VIN – VOUT) (mV) 0 –1 1 VOS DISTRIBUTION (mV) –2 –0.50 VIN, CONTROL – VOUT = 36V 0.6 0.5 0.4 VIN, CONTROL – VOUT = 1.5V 0.3 0.2 0.1 0 –50 –25 350 TJ = 125°C 300 250 200 TJ = 25°C 150 100 50 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 3085 G08 0 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 3085 G09 3085fb 4 LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Dropout Voltage (Minimum IN Voltage) 1.6 1.6 1.4 MINIMUM CONTROL VOLTAGE (VCONTROL – VOUT) (V) 350 ILOAD = 500mA 300 250 200 150 ILOAD = 100mA 100 1.2 1.0 TJ = 125°C 0.8 TJ = 25°C 0.6 0.4 0.2 50 0 25 50 75 100 125 150 TEMPERATURE (°C) Current Limit 700 600 600 200 500 400 200 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 5 10 15 20 25 30 35 INPUT-TO-OUTPUT DIFFERENTIAL (V) Load Transient Response OUTPUT VOLTAGE DEVIATION (mV) OUTPUT VOLTAGE DEVIATION (mV) 0 IN/CONTROL VOLTAGE (V) LOAD CURRENT (mA) –100 VIN = VCONTROL = 3V VOUT = 1.5V CSET = 0.1μF 0 VOUT = 1.5V ILOAD = 10mA COUT = 2.2μF CERAMIC CSET = 0.1μF CERAMIC –50 6 4 2 0 0 10 20 30 40 50 60 70 80 90 100 TIME (μs) 3085 G16 COUT = 10μF CERAMIC COUT = 2.2μF CERAMIC 200 100 0 0 20 40 60 80 100 120 140 160 180 200 TIME (μs) 3085 G15 Turn-On Response 50 –100 COUT = 2.2μF CERAMIC 250 –20 Line Transient Response 50 0 40 100 150 500 0 3085 G14 3085 G13 –50 20 –40 100 COUT = 10μF CERAMIC VOUT = 1.5V CSET = 0.1μF VIN = VCONTROL = 3V 40 300 100 100 25 50 75 100 125 150 TEMPERATURE (°C) Load Transient Response LOAD CURRENT (mA) 300 0 3085 G12 OUTPUT VOLTAGE DEVIATION (mV) CURRENT LIMIT (mA) CURRENT LIMIT (mA) VIN = 7V VOUT = 0V 0 0.4 60 TJ = 25°C 0 –50 –25 0.6 Current Limit 700 400 0.8 3085 G11 3085 G10 500 ILOAD = 100mA 1.0 0 –50 –25 0 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 0 10 20 30 40 50 60 70 80 90 100 TIME (μs) 3085 G17 OUTPUT VOLTAGE (V) 0 1.2 0.2 1.5 1 COUT = 2.2μF CERAMIC RSET = 100k CSET = 0 RLOAD = 2Ω 0.5 0 8 IN/CONTROL VOLTAGE (V) 0 –50 –25 ILOAD = 500mA 1.4 TJ = –50°C MINIMUM CONTROL VOLTAGE (VCONTROL – VOUT) (V) 400 MINIMUM IN VOLTAGE (VIN – VOUT) (mV) Dropout Voltage (Minimum VCONTROL Pin Voltage) Dropout Voltage (Minimum VCONTROL Pin Voltage) 6 4 2 0 0 2 4 6 8 10 12 14 16 18 20 TIME (μs) 3085 G18 3085fb 5 LT3085 TYPICAL PERFORMANCE CHARACTERISTICS VCONTROL Pin Current 8 7 CONTROL PIN CURRENT (mA) CONTROL PIN CURRENT (mA) 18 800 VIN = VCONTROL = 2V VIN = VOUT = 1V 16 14 ILOAD = 500mA 12 10 DEVICE IN CURRENT LIMIT 8 6 4 TJ = –50°C 6 TJ = 25°C 5 4 TJ = 125°C 3 2 VOUT VIN = 20V RTEST 500 400 VIN = 10V 300 VIN = 5V 200 100 ILOAD = 1mA 0 0 30 12 18 24 6 INPUT-TO-OUTPUT DIFFERENTIAL (V) 0 0 36 0.1 0.2 0.3 LOAD CURRENT (A) 0.4 100 90 90 80 80 RIPPLE REJECTION (dB) ILOAD = 100mA 60 50 40 30 VIN = VCONTROL = VOUT (NOMINAL) +2V RIPPLE = 50mVP–P COUT = 2.2μF CERAMIC CSET = 0.1μF CERAMIC 20 10 0 10 100 1k 10k FREQUENCY (Hz) 100k 2k Ripple Rejection - Dual Supply - IN Pin 100 90 ILOAD = 100mA 70 60 ILOAD = 500mA 50 40 VIN = VOUT (NOMINAL) + 1V VCONTROL = VOUT (NOMINAL) +2V RIPPLE = 50mVP–P COUT = 2.2μF CERAMIC CSET = 0.1μF CERAMIC 30 20 10 70 60 ILOAD = 500mA 50 40 VIN = VCONTROL +2V VCONTROL = VOUT (NOMINAL) +2V RIPPLE = 50mVP–P COUT = 2.2μF CERAMIC CSET = 0.1μF CERAMIC 30 20 10 0 1M ILOAD = 100mA 80 RIPPLE REJECTION (dB) 100 ILOAD = 500mA 1k RTEST (Ω) 3085 G21 Ripple Rejection - Dual Supply - VCONTROL Pin Ripple Rejection - Single Supply 70 0 0.5 3085 G20 3085 G19 RIPPLE REJECTION (dB) VIN 600 1 2 SET PIN = 0V 700 OUTPUT VOLTAGE (mV) 20 0 Residual Output Voltage with Less Than Minimum Load VCONTROL Pin Current 0 10 100 1k 10k FREQUENCY (Hz) 100k 3085 G22 1M 10 100 10k 1k FREQUENCY (Hz) 100k 3085 G23 Ripple Rejection (120Hz) 3085 G24 Noise Spectral Density 85 1M Output Voltage Noise 10k 1k 1k 100 ERROR AMPLIFIER NOISE SPECTRAL DENSITY (nV/√Hz) 83 82 81 80 79 78 SINGLE SUPPLY OPERATION VIN = VOUT (NOMINAL) +2V RIPPLE = 50mVP–P, f = 120Hz ILOAD = 0.1A COUT = 2.2μF, CSET = 0.1μF 77 –50 –25 0 25 50 75 100 125 150 FREQUENCY (Hz) 3085 G25 100 10 10 1 10 1.0 100 1k 10k FREQUENCY (Hz) REFERENCE CURRENT NOISE SPECTRAL DENSITY (pA/ √Hz) RIPPLE REJECTION (dB) 84 VOUT 100μV/DIV TIME 1ms/DIV 3085 G27 VOUT = 1V RSET = 100k CSET = O.1μF COUT = 10μF ILOAD = 0.5A 0.1 100k 3085 G26 3085fb 6 LT3085 TYPICAL PERFORMANCE CHARACTERISTICS Error Amplifier Gain and Phase Ripple Rejection - SET Pin Current 150 144 135 15 72 120 12 0 ILOAD = 500mA 9 –72 ILOAD = 100mA 6 –144 ILOAD = 500mA 3 –216 0 –288 –3 ILOAD = 100mA –6 –9 PHASE (deg) GAIN (dB) 18 10 100 10k 1k FREQUENCY (Hz) 100k 90 75 CSET = 0 60 45 30 –432 15 –504 1M CSET = 0.1μF 105 –360 3085 G28 PIN FUNCTIONS RIPPLE REJECTION (dB) 216 21 0 10 RSET = 100k VIN = VCONTROL = VOUT (NOMINAL) +2V RIPPLE = 50mVP–P 100 1k 10k FREQUENCY (Hz) 100k 1M 3085 G29 (DCB/MS8E) VCONTROL (Pin 4/Pin 5): This pin is the supply pin for the control circuitry of the device. The current flow into this pin is about 1.7% of the output current. For the device to regulate, this voltage must be more than 1.2V to 1.35V greater than the output voltage (see VCONTROL Dropout Voltage in the Electrical Characteristics table and graphs in the Typical Performance Characteristics). The LT3085 requires a bypass capacitor at VCONTROL if more than six inches away from the main input filter capacitor. The output impedance of a battery rises with frequency, so include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1μF to 10μF suffices. IN (Pins 5, 6/Pins 7, 8): This is the collector to the power device of the LT3085. The output load current is supplied through this pin. For the device to regulate, the voltage at this pin must be more than 0.1V to 0.5V greater than the output voltage (see VIN Dropout Voltage in the Electrical Characteristics table and graphs in the Typical Performance Characteristics). The LT3085 requires a bypass capacitor at IN if more than six inches away from the main input filter capacitor. The output impedance of a battery rises with frequency, so include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1μF to 10μF suffices. NC (NA/Pin 6): No Connection. The No Connect pin has no connection to internal circuitry and may be tied to VIN, VCONTROL, VOUT, GND, or floated. OUT (Pins 1, 2/Pins 1, 2, 3): This is the power output of the device. There must be a minimum load current of 1mA or the output may not regulate. A minimum 2.2μF output capacitor is required for stability. SET (Pin 3/Pin 4): This pin is the non-inverting input to the error amplifier and the regulation set point for the device. A fixed current of 10μA flows out of this pin through a single external resistor, which programs the output voltage of the device. Output voltage range is zero to the absolute maximum rated output voltage. Transient performance can be improved and output noise can be decreased by adding a small capacitor from the SET pin to ground. Exposed Pad (Pin 7/Pin 9): OUT. Tie directly to Pins 1, 2/ Pins 2, 3 directly at the PCB. 3085fb 7 LT3085 BLOCK DIAGRAM IN VCONTROL 10μA + – 3085 BD SET OUT APPLICATIONS INFORMATION The LT3085 regulator is easy to use and has all the protection features expected in high performance regulators. Included are short-circuit protection and safe operating area protection, as well as thermal shutdown. The LT3085 is especially well suited to applications needing multiple rails. The new architecture adjusts down to zero with a single resistor, handling modern low voltage digital IC’s as well as allowing easy parallel operation and thermal management without heat sinks. Adjusting to “zero” output allows shutting off the powered circuitry and when the input is pre-regulated – such as a 5V or 3.3V input supply – external resistors can help spread the heat. A precision “0” TC 10μA internal current source is connected to the non-inverting input of a power operational amplifier. The power operational amplifier provides a low impedance buffered output to the voltage on the non-inverting input. A single resistor from the non-inverting input to ground sets the output voltage and if this resistor is set to zero, zero output results. As can be seen, any output voltage can be obtained from zero up to the maximum defined by the input power supply. What is not so obvious from this architecture are the benefits of using a true internal current source as the reference as opposed to a bootstrapped reference in older regulators. A true current source allows the regulator to have gain and frequency response independent of the impedance on the positive input. Older adjustable regulators, such as the LT1086, have a change in loop gain with output voltage as well as bandwidth changes when the adjustment pin is bypassed to ground. For the LT3085, the loop gain is unchanged by changing the output voltage or bypassing. Output regulation is not fixed at a percentage of the output voltage but is a fixed fraction of millivolts. Use of a true current source allows all the gain in the buffer amplifier to provide regulation and none of that gain is needed to amplify up the reference to a higher output voltage. The LT3085 has the collector of the output transistor connected to a separate pin from the control input. Since the dropout on the collector (IN pin) is only 275mV, two supplies can be used to power the LT3085 to reduce dissipation: a higher voltage supply for the control circuitry and a lower voltage supply for the collector. This increases efficiency and reduces dissipation. To further spread the heat, a resistor can be inserted in series with the collector to move some of the heat out of the IC and spread it on the PC board. 3085fb 8 LT3085 APPLICATIONS INFORMATION The LT3085 can be operated in two modes. Three terminal mode has the control pin connected to the power input pin which gives a limitation of 1.35V dropout. Alternatively, the “control” pin can be tied to a higher voltage and the power IN pin to a lower voltage giving 275mV dropout on the IN pin and minimizing the power dissipation. This allows for a 500mA supply regulating from 2.5VIN to 1.8VOUT or 1.8VIN to 1.2VOUT with low dissipation. With the low level current used to generate the reference voltage, leakage paths to or from the SET pin can create errors in the reference and output voltages. High quality insulation should be used (e.g., Teflon, Kel-F); cleaning of all insulating surfaces to remove fluxes and other residues will probably be required. Surface coating may be necessary to provide a moisture barrier in high humidity environments. Setting Output Voltage Table 1. 1% Resistors for Common Output Voltages The LT3085 generates a 10μA reference current that flows out of the SET pin. Connecting a resistor from SET to ground generates a voltage that becomes the reference point for the error amplifier (see Figure 1). The reference voltage is a straight multiplication of the SET pin current and the value of the resistor. Any voltage can be generated and there is no minimum output voltage for the regulator. Table 1 lists many common output voltages and standard 1% resistor values used to generate that output voltage. A minimum load current of 1mA is required to maintain regulation regardless of output voltage. For true zero voltage output operation, this 1mA load current must be returned to a negative supply voltage. LT3085 IN VCONTROL 10μA + VIN + – + VCONTROL OUT VOUT SET COUT RSET CSET 3085 F01 VOUT = RSET • 10μA Figure 1. Basic Adjustable Regulator VOUT RSET 1V 100k 1.2V 121k 1.5V 150k 1.8V 182k 2.5V 249k 3.3V 332k 5V 499k Board leakage can be minimized by encircling the SET pin and circuitry with a guardring operated at a potential close to itself; the guardring should be tied to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. Ten nanoamperes of leakage into or out of the SET pin and associated circuitry creates a 0.1% error in the reference voltage. Leakages of this magnitude, coupled with other sources of leakage, can cause significant offset voltage and reference drift, especially over a wide temperature range. If guardring techniques are used, this bootstraps any stray capacitance at the SET pin. Since the SET pin is a high impedance node, unwanted signals may couple into the SET pin and cause erratic behavior. This will be most noticeable when operating with minimum output capacitors at full load current. The easiest way to remedy this is to bypass the SET pin with a small amount of capacitance from SET to ground, 10pF to 20pF is sufficient. 3085fb 9 LT3085 APPLICATIONS INFORMATION Input Capacitance and Stability The LT3085 is designed to be stable with a minimum capacitance of 1μF at each input pin. Ceramic capacitors with low ESR are available for use to bypass these pins, but in cases where long wires connect the LT3085 inputs to a power supply (and also from ground of the LT3085 circuitry back to power supply ground), this causes instabilities. This happens due to the wire inductance forming an LC tank circuit with the input capacitor and not as a result of instability on the LT3085. The self-inductance, or isolated inductance, of a wire is directly proportional to its length. The diameter does not have a major influence on its self-inductance. As an example, the self-inductance of a 2-AWG isolated wire with a diameter of 0.26in. is approximately half the self-inductance of a 30-AWG wire with a diameter of 0.01in. One foot of 30-AWG wire has 465nH of self-inductance. The overall self-inductance of a wire is reduced in one of two ways. One is to divide the current flowing towards the LT3085 between two parallel conductors. In this case, the farther apart the wires are from each other, the more the self-inductance is reduced, up to a 50% reduction when placed a few inches apart. Splitting the wires basically connects two equal inductors in parallel, but placing them in close proximity gives the wires mutual inductance adding to the self-inductance. The second and most effective way to reduce overall inductance is to place both forward- and return-current conductors (the wire for the input and the wire for ground) in very close proximity. Two 30-AWG wires separated by only 0.02in. used as forward- and return-current conductors reduce the overall self-inductance to approximately one-fifth that of a single isolated wire. If the LT3085 is powered by a battery mounted in close proximity on the same circuit board, a 2.2μF input capacitor is sufficient for stability. When powering from distant supplies, use a larger input capacitor based on a guideline of 1μF plus another 1μF per 8 inches of wire length. As power supply impedance does vary, the amount of capacitance needed to stabilize your application will also vary. Extra capacitance placed directly on the output of the power supply requires an order of magnitude more capacitance as opposed to placing extra capacitance close to the LT3085. Using series resistance between the power supply and the input of the LT3085 also stabilizes the application. As little as 0.1Ω to 0.5Ω, often less, is all that is needed to provide damping in the circuit. If the extra impedance between the power supply and the input is unacceptable, placing the resistors in series with the capacitors will provide damping to prevent the LC resonance from causing full-blown oscillation. Stability and Output Capacitance The LT3085 requires an output capacitor for stability. It is designed to be stable with most low ESR capacitors (typically ceramic, tantalum or low ESR electrolytic). A minimum output capacitor of 2.2μF with an ESR of 0.5Ω or less is recommended to prevent oscillations. Larger values of output capacitance decrease peak deviations and provide improved transient response for larger load current changes. Bypass capacitors, used to decouple individual components powered by the LT3085, increase the effective output capacitor value. For improvement in transient performance, place a capacitor across the voltage setting resistor. Capacitors up to 1μF can be used. This bypass capacitor reduces system noise as well, but start-up time is proportional to the time constant of the voltage setting resistor (RSET in Figure 1) and SET pin bypass capacitor. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics used are specified with EIA temperature characteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances 3085fb 10 LT3085 APPLICATIONS INFORMATION in a small package, but they tend to have strong voltage and temperature coefficients as shown in Figures 2 and 3. When used with a 5V regulator, a 16V 10μF Y5V capacitor can exhibit an effective value as low as 1μF to 2μF for the DC bias voltage applied and over the operating temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is available in higher values. Care still must be exercised when using X5R and X7R capacitors; the X5R and X7R codes only specify operating temperature range and maximum capacitance change over temperature. Capacitance change due to DC bias with X5R and X7R capacitors is better than Y5V and Z5U capacitors, but can still be significant enough to drop capacitor values below appropriate levels. Capacitor DC bias characteristics tend to improve as component case size increases, but expected capacitance at operating voltage should be verified. Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. Paralleling Devices LT3085’s may be paralleled with other LT308X devices to obtain higher output current. The SET pins are tied together and the IN pins are tied together. This is the same whether it’s in three terminal mode or has separate input supplies. The outputs are connected in common using a small piece of PC trace as a ballast resistor to equalize the currents. PC trace resistance in milliohms/inch is shown in Table 1. Only a tiny area is needed for ballasting. Table 1. PC Board Trace Resistance WEIGHT (oz) 10 mil WIDTH 20 mil WIDTH 1 54.3 27.1 2 27.1 13.6 Trace resistance is measured in mΩ/in 40 20 20 CHANGE IN VALUE (%) BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF CHANGE IN VALUE (%) 0 X5R –20 –40 –60 –80 –100 –20 –40 Y5V –60 –80 Y5V X5R 0 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF –100 –50 –25 0 2 4 8 6 10 12 DC BIAS VOLTAGE (V) 14 16 3085 F02 50 25 75 0 TEMPERATURE (°C) 100 125 3085 F03 Figure 3. Ceramic Capacitor Temperature Characteristics Figure 2. Ceramic Capacitor DC Bias Characteristics 3085fb 11 LT3085 APPLICATIONS INFORMATION The worst-case offset between the SET pin and the output of only ±1.5mV allows very small ballast resistors to be used. As shown in Figure 4, the two devices have a small 10mΩ and 20mΩ ballast resistors, which at full output current gives better than 80% equalized sharing of the current. The external resistance of 20mΩ (6.6mΩ for the two devices in parallel) only adds about 10mV of output regulation drop at an output of 1.5A. Even with an output voltage as low as 1V, this only adds 1% to the regulation. Of course, more than two LT308X’s can be paralleled for even higher output current. They are spread out on the PC board, spreading the heat. Input resistors can further spread the heat if the input-to-output difference is high. Thermal Performance The first test was done with approximately 1.6V input- to-output and 0.5A per device. This gave a 800mW dissipation in each device and a 1A output current. The temperature rise above ambient is approximately 28°C and both devices were within plus or minus 1°C. Both the thermal and electrical sharing of these devices is excellent. The thermograph in Figure 5 shows the temperature distribution between these devices and the PC board reaches ambient temperature within about a half an inch from the devices. The power is then increased with 3.4V across each device. This gives 1.7 watts dissipation in each device and a device temperature of about 90°C, about 65°C above ambient as shown in Figure 6. Again, the temperature matching In this example, two LT3085 2mm × 3mm DFN devices are mounted on a 1oz copper 4-layer PC board. They are placed approximately 1.5 inches apart and the board is mounted vertically for convection cooling. Two tests were set up to measure the cooling performance and current sharing of these devices. VIN LT3080 VCONTROL + – OUT 10mΩ Figure 5. Temperature Rise at 800mW Dissipation SET VIN 4.8V TO 28V VIN LT3085 VCONTROL + – 1μF OUT 20mΩ SET VOUT 3.3V 1.5A 10μF 165k 3085 F04 Figure 4. Parallel Devices Figure 6. Temperature Rise at 1.7W Dissipation 3085fb 12 LT3085 APPLICATIONS INFORMATION between the devices is within 2°C, showing excellent tracking between the devices. The board temperature has reached approximately 40°C within about 0.75 inches of each device. While 90°C is an acceptable operating temperature for these devices, this is in 25°C ambient. For higher ambients, the temperature must be controlled to prevent device temperature from exceeding 125°C. A 3-meter-per-second airflow across the devices will decrease the device temperature about 20°C providing a margin for higher operating ambient temperatures. Both at low power and relatively high power levels devices can be paralleled for higher output current. Current sharing and thermal sharing is excellent, showing that acceptable operation can be had while keeping the peak temperatures below excessive operating temperatures on a board. This technique allows higher operating current linear regulation to be used in systems where it could never be used before. Quieting the Noise The LT3085 offers numerous advantages when it comes to dealing with noise. There are several sources of noise in a linear regulator. The most critical noise source for any LDO is the reference; from there, the noise contribution from the error amplifier must be considered, and the gain created by using a resistor divider cannot be forgotten. Traditional low noise regulators bring the voltage reference out to an external pin (usually through a large value resistor) to allow for bypassing and noise reduction of reference noise. The LT3085 does not use a traditional voltage reference like other linear regulators, but instead uses a reference current. That current operates with typical noise current levels of 2.3pA/√Hz (0.7nARMS over the 10Hz to 100kHz bandwidth). The voltage noise of this is equal to the noise current multiplied by the resistor value. The resistor generates spot noise equal to√4kTR (k = Boltzmann’s constant, 1.38 • 10-23 J/°K, and T is absolute temperature) which is RMS summed with the reference current noise. To lower reference noise, the voltage setting resistor may be bypassed with a capacitor, though this causes start-up time to increase as a factor of the RC time constant. The LT3085 uses a unity-gain follower from the SET pin to drive the output, and there is no requirement to use a resistor to set the output voltage. Use a high accuracy voltage reference placed at the SET pin to remove the errors in output voltage due to reference current tolerance and resistor tolerance. Active driving of the SET pin is acceptable; the limitations are the creativity and ingenuity of the circuit designer. One problem that a normal linear regulator sees with reference voltage noise is that noise is gained up along with the output when using a resistor divider to operate at levels higher than the normal reference voltage. With the LT3085, the unity-gain follower presents no gain whatsoever from the SET pin to the output, so noise figures do not increase accordingly. Error amplifier noise is typically 100nV/√Hz (33μVRMS over the 10Hz to 100kHz bandwidth); this is another factor that is RMS summed in to give a final noise figure for the regulator. Curves in the Typical Performance Characteristics show noise spectral density and peak-to-peak noise characteristics for both the reference current and error amplifier over the 10Hz to 100kHz bandwidth. Overload Recovery Like many IC power regulators, the LT3085 has safe operating area (SOA) protection. The SOA protection decreases current limit as the input-to-output voltage increases and keeps the power dissipation at safe levels for all values of input-to-output voltage. The LT3085 provides some output current at all values of input-to-output voltage up to the device breakdown. See the Current Limit curve in the Typical Performance Characteristics. When power is first turned on, the input voltage rises and the output follows the input, allowing the regulator to start into very heavy loads. During start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output currents. With a high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. Other regulators, such as the LT1085 and LT1764A, also exhibit this phenomenon so it is not unique to the LT3085. 3085fb 13 LT3085 APPLICATIONS INFORMATION The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations are immediately after the removal of a short circuit. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable operating points for the regulator. With this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. Load Regulation Because the LT3085 is a floating device (there is no ground pin on the part, all quiescent and drive current is delivered to the load), it is not possible to provide true remote load sensing. Load regulation will be limited by the resistance of the connections between the regulator and the load. The data sheet specification for load regulation is Kelvin sensed at the pins of the package. Negative side sensing is a true Kelvin connection, with the bottom of the voltage setting resistor returned to the negative side of the load (see Figure 7). Connected as shown, system load regulation will be the sum of the LT3085 load regulation and the parasitic line resistance multiplied by the output current. It is important to keep the positive connection between the regulator and load as short as possible and use large wire or PC board traces. Internal Parasitic Diodes and Protection Diodes In normal operation, the LT3085 does not require protection diodes. Older three-terminal regulators require protection diodes between the VOUT pin and the input pin or between the ADJ pin and the VOUT pin to prevent die overstress. IN LT3085 VCONTROL PARASITIC RESISTANCE + – OUT SET RSET RP RP LOAD RP 3085 F07 On the LT3085, internal resistors and diodes limit current paths on the SET pin. Even with bypass capacitors on the SET pin, no protection diode is needed to ensure device safety under short-circuit conditions. The SET pin handles ±10V (either transient or DC) with respect to OUT without any device degradation. Internal parasitic diodes exist between OUT and the two inputs. Negative input voltages are transferred to the output and may damage sensitive loads. Reverse-biasing either input to OUT will turn on these parasitic diodes and allow current flow. This current flow will bias internal nodes of the LT3085 to levels that possibly cause errors when suddenly returning to normal operating conditions and expecting the device to start and operate. Prediction of results of a bias fault is impossible, immediate return to normal operating conditions can be just as difficult after a bias fault. Suffice it to say that extra wait time, power cycling, or protection diodes may be needed to allow the LT3085 to return to a normal operating mode as quickly as possible. Protection diodes are not otherwise needed between the OUT pin and IN pin. The internal diodes can handle microsecond surge currents of up to 50A. Even with large output capacitors, obtaining surge currents of those magnitudes is difficult in normal operation. Only with large output capacitors, such as 1000μF to 5000μF, and with IN instantaneously shorted to ground will damage occur. A crowbar circuit at IN is capable of generating those levels of currents, and then protection diodes from OUT to IN are recommended. Normal power supply cycling or system “hot plugging and unplugging” does not do any damage. A protection diode between OUT and VCONTROL is usually not needed. The internal parasitic diode on VCONTROL of the LT3085 handles microsecond surge currents of 1A to 10A. Again, this only occurs when using crowbar circuits with large value output capacitors. Since the VCONTROL pin is usually a low current supply, this is unlikely. Still, a protection diode is recommended if VCONTROL can be instantaneously shorted to ground. Normal power supply cycling or system “hot plugging and unplugging” does not do any damage. Figure 7. Connections for Best Load Regulation 3085fb 14 LT3085 APPLICATIONS INFORMATION If the LT3085 is configured as a three-terminal (single supply) regulator with IN and VCONTROL shorted together, the internal diode of the IN pin will protect the VCONTROL pin. Like any other regulator, exceeding the maximum inputto-output differential causes internal transistors to break down and then none of the internal protection circuitry is functional. Thermal Considerations The LT3085 has internal power and thermal limiting circuitry designed to protect it under overload conditions. For continuous normal load conditions, maximum junction temperature must not be exceeded. It is important to give consideration to all sources of thermal resistance from junction to ambient. This includes junction-to-case, case-to-heat sink interface, heat sink resistance or circuit board-to-ambient as the application dictates. Additional heat sources nearby must also be considered. For surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Surface mount heat sinks and plated through-holes can also be used to spread the heat generated by power devices. Boards specified in thermal resistance tables have no vias on plated through-holes from topside to backside. Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die. This is the lowest resistance path for heat flow. Proper mounting is required to ensure the best possible thermal flow from this area of the package to the heat sinking material. Note that the Exposed Pad is electrically connected to the output. The following tables list thermal resistance for several different copper areas given a fixed board size. All measurements were taken in still air on two-sided 1/16” FR-4 board with one ounce copper. PCB layers, copper weight, board layout and thermal vias affect the resultant thermal resistance. Although Tables 2 and 3 provide thermal resistance numbers for 2-layer board with 1 ounce copper, modern multi-layer PCBs provide better performance than found in these tables. For example, a 4-layer, 1 ounce copper PCB board with 5 thermal vias from the DFN or MSOP exposed backside pad to inner layers (connected to VOUT) achieves 40°C/W thermal resistance. Demo circuit 1401A’s board layout achieves this 40°C/W performance. This is approximately a 45% improvement over the numbers shown in Tables 2 and 3. Table 2. MSE Package, 8-Lead MSOP COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 55°C/W 1000mm2 2500mm2 2500mm2 57°C/W 225mm2 2500mm2 2500mm2 60°C/W 100mm2 2500mm2 2500mm2 65°C/W *Device is mounted on topside Table 3. DCB Package, 6-Lead DFN COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 68°C/W 1000mm2 2500mm2 2500mm2 70°C/W 225mm2 2500mm2 2500mm2 73°C/W 100mm2 2500mm2 2500mm2 78°C/W *Device is mounted on topside For future information on the thermal resistance and using thermal information, refer to JEDEC standard JESD51, notably JESD51-12. Calculating Junction Temperature Example: Given an output voltage of 0.9V, a VCONTROL voltage of 3.3V ±10%, an IN voltage of 1.5V ±5%, output current range from 1mA to 0.5A and a maximum ambient temperature of 50°C, what will the maximum junction temperature be for the DFN package on a 2500mm2 board with topside copper area of 500mm2? The power in the drive circuit equals: PDRIVE = (VCONTROL – VOUT)(ICONTROL) where ICONTROL is equal to IOUT/60. ICONTROL is a function of output current. A curve of ICONTROL vs IOUT can be found in the Typical Performance Characteristics curves. 3085fb 15 LT3085 APPLICATIONS INFORMATION The power in the output transistor equals: POUTPUT = (VIN – VOUT)(IOUT) The total power equals: PTOTAL = PDRIVE + POUTPUT The current delivered to the SET pin is negligible and can be ignored. VCONTROL(MAX CONTINUOUS) = 3.630V (3.3V + 10%) Reducing Power Dissipation In some applications it may be necessary to reduce the power dissipation in the LT3085 package without sacrificing output current capability. Two techniques are available. The first technique, illustrated in Figure 8, employs a resistor in series with the regulator’s input. The voltage drop across RS decreases the LT3085’s IN-to-OUT differential voltage and correspondingly decreases the LT3085’s power dissipation. VIN(MAX CONTINUOUS) = 1.575V (1.5V + 5%) VOUT = 0.9V, IOUT = 0.5A, TA = 50°C VIN C1 VCONTROL LT3085 RS IN VINa Power dissipation under these conditions is equal to: PDRIVE = (VCONTROL – VOUT)(ICONTROL) I 0.5A ICONTROL = OUT = = 8.3mA 60 60 PDRIVE = (3.630V – 0.9V)(8.3mA) = 23mW + – OUT SET RSET VOUT C2 3085 F08 POUTPUT = (VIN – VOUT)(IOUT) POUTPUT = (1.575V – 0.9V)(0.5A) = 337mW Figure 8. Reducing Power Dissipation Using a Series Resistor Total Power Dissipation = 360mW Junction Temperature will be equal to: TJ = TA + PTOTAL • θJA (approximated using tables) TJ = 50°C + 360mW • 73°C/W = 76°C As an example, assume: VIN = VCONTROL = 5V, VOUT = 3.3V and IOUT(MAX) = 0.5A. Use the formulas from the Calculating Junction Temperature section previously discussed. In this case, the junction temperature is below the maximum rating, ensuring reliable operation. 3085fb 16 LT3085 APPLICATIONS INFORMATION Without series resistor RS, power dissipation in the LT3085 equals: 0.5A PTOTAL = ( 5V – 3.3V ) • + ( 5V – 3.3V ) • 0.5A 60 = 0.86W If the voltage differential (VDIFF) across the NPN pass transistor is chosen as 0.5V, then RS equals: RS = 5V – 3.3V − 0.5V = 2.4Ω 0.5A Power dissipation in the LT3085 now equals: PTOTAL = ( 5V – 3.3V ) • 0.5A + ( 0.5V ) • 0.5A = 0.26W 60 The LT3085’s power dissipation is now only 30% compared to no series resistor. RS dissipates 0.6W of power. Choose appropriate wattage resistors to handle and dissipate the power properly. The second technique for reducing power dissipation, shown in Figure 9, uses a resistor in parallel with the LT3085. This resistor provides a parallel path for current flow, reducing the current flowing through the LT3085. This technique works well if input voltage is reasonably constant and output load current changes are small. This technique also increases the maximum available output current at the expense of minimum load requirements. As an example, assume: VIN = VCONTROL = 5V, VIN(MAX) = 5.5V, VOUT = 3.3V, VOUT(MIN) = 3.2V, IOUT(MAX) = 0.5A and IOUT(MIN) = 0.35A. Also, assuming that RP carries no more than 90% of IOUT(MIN) = 630mA. Calculating RP yields: 5.5V – 3.2V = 7.30Ω 315mA (5% Standard value = 7.Ω) RP = The maximum total power dissipation is (5.5V – 3.2V) • 0.5A = 1.2W. However the LT3085 supplies only: 0.5A – 5.5V – 3.2V = 0.193A 7.5Ω Therefore, the LT3085’s power dissipation is only: PDIS = (5.5V – 3.2V) • 0.193A = 0.44W RP dissipates 0.71W of power. As with the first technique, choose appropriate wattage resistors to handle and dissipate the power properly. With this configuration, the LT3085 supplies only 0.36A. Therefore, load current can increase by 0.3A to 0.143A while keeping the LT3085 in its normal operating range. VIN C1 VCONTROL LT3085 IN RP + – OUT SET RSET VOUT C2 3085 F09 Figure 9. Reducing Power Dissipation Using a Parallel Resistor 3085fb 17 LT3085 TYPICAL APPLICATIONS Higher Output Current MJ4502 VIN 6V 50Ω LT3085 IN VCONTROL + + – 100μF 1μF VOUT 3.3V 5A OUT + SET 4.7μF 100μF 332k 3085 TA02 Current Source LT3085 IN VIN 10V VCONTROL + – 1μF OUT 2Ω 0.5W SET IOUT 0A TO 0.5A 4.7μF 100k 3085 TA03 Power Oscillator VIN LT3085 IN VCONTROL + – VOUT 400Hz 4VACP-P OUT SET 10μF 6.3V, 150mA LIGHT BULB #47 47nF 2.21k 4.7μF 8.45k 20Ω 499k 8.45k 220n 47nF 121Ω 3085 TA22 3085fb 18 LT3085 TYPICAL APPLICATIONS Adding Shutdown VIN LT3085 IN VIN Low Dropout Voltage LED Driver C1 LT3085 VCONTROL + – 3085 TA04 SET ON OFF IN OUT Q2* VN2222LL R1 100mA D1 + – OUT VOUT Q1 VN2222LL VCONTROL SET R1 24.9k SHUTDOWN R2 2.49Ω 3085 TA05 *Q2 INSURES ZERO OUTPUT IN THE ABSENCE OF ANY OUTPUT LOAD. Using a Lower Value SET Resistor IN VIN 12V LT3085 VCONTROL C1 1μF + – OUT SET R1 49.9k 1% 1mA VOUT 0.5V TO 10V R2 499Ω 1% VOUT = 0.5V + 1mA • RSET COUT 4.7μF RSET 10k 3085 TA06 3085fb 19 LT3085 TYPICAL APPLICATIONS Adding Soft-Start LT3085 IN VIN 4.8V to 28V VCONTROL C1 1μF + – D1 1N4148 OUT SET C2 0.01μF VOUT 3.3V 0.5A COUT 4.7μF R1 332k 3085 TA07 Coincident Tracking LT3085 IN VCONTROL IN LT3085 + – VCONTROL VIN 7V TO 28V IN LT3085 + – VCONTROL C1 1.5μF OUT SET 169k OUT + – OUT SET R1 249k SET R2 80.6k C2 4.7μF C3 4.7μF VOUT2 3.3V 0.5A VOUT3 5V 0.5A 4.7μF 3085 TA08 VOUT1 2.5V 0.5A 3085fb 20 LT3085 TYPICAL APPLICATIONS Lab Supply LT3085 IN VIN 12V TO 18V LT3085 IN VCONTROL VCONTROL + – + 15μF + – 1Ω OUT 0.25W OUT + SET 50k 0A TO 0.5A + SET 15μF VOUT 0V TO 10V 4.7μF R4 1M 100μF 3085 TA09 High Voltage Regulator 6.1V 10k VIN 50V 1N4148 IN LT3085 BUZ11 VCONTROL + + – 10μF OUT SET RSET 2M + 15μF VOUT 0.5A 4.7μF VOUT = 20V VOUT = 10μA • RSET 3085 TA10 Ramp Generator IN VIN 5V LT3085 VCONTROL + – 1μF OUT VOUT SET VN2222LL 1μF VN2222LL 4.7μF 3085 TA12 3085fb 21 LT3085 TYPICAL APPLICATIONS Reference Buffer LT3085 IN VIN VCONTROL + – OUT VOUT* C2 4.7μF INPUT SET OUTPUT LT1019 C1 1μF GND 3085 TA11 *MIN LOAD 0.5mA Ground Clamp LT3085 IN VIN VEXT VCONTROL 20Ω + – OUT 1μF SET VOUT 1N4148 4.7μF 5k 3085 TA13 Boosting Fixed Output Regulators IN LT3085 VCONTROL + – OUT 20mΩ SET 20mΩ 5V 3.3VOUT 2A LT1963-3.3 10μF 42Ω* 47μF 3085 TA20 33k *4mV DROP ENSURES LT3085 IS OFF WITH NO LOAD MULTIPLE LT3085’S CAN BE USED 3085fb 22 LT3085 TYPICAL APPLICATIONS Low Voltage, High Current Adjustable High Efficiency Regulator* 0.47μH 2.7V TO 5.5V† 100μF ×2 + 2.2MEG 100k PVIN SW SVIN ITH LTC3414 10k + 12.1k RT 470pF 294k PGOOD 100μF ×2 2N3906 LT3085 IN VCONTROL RUN/SS + – VFB 1000pF OUT 78.7k SGND PGND 20mΩ SET SYNC/MODE 124k LT3085 IN VCONTROL + – *DIFFERENTIAL VOLTAGE ON LT3085 IS 0.6V SET BY THE VBE OF THE 2N3906 PNP. OUT †MAXIMUM OUTPUT VOLTAGE IS 1.5V BELOW INPUT VOLTAGE 20mΩ SET 0V TO 4V† 2A LT3085 IN VCONTROL + – OUT 20mΩ SET LT3085 IN VCONTROL + – OUT 3085 TA18 SET 100k 20mΩ + 100μF 3085fb 23 LT3085 TYPICAL APPLICATIONS Adjustable High Efficiency Regulator* CMDSH-4E 4.5V TO 25V† VIN 10μF 1μF 100k BOOST LT3493 SHDN 0.1μF 10μH 0.1μF MBRM140 GND LT3085 IN SW 68μF 200k TP0610L VCONTROL + – FB OUT 10k 3085 TA19 SET 0V TO 10V† 0.5A 4.7μF 1MEG *DIFFERENTIAL VOLTAGE ON LT3085 ≈ 1.4V SET BY THE TPO610L P-CHANNEL THRESHOLD. †MAXIMUM OUTPUT VOLTAGE IS 2V BELOW INPUT VOLTAGE 10k 2 Terminal Current Source CCOMP* IN LT3085 VCONTROL + – OUT R1 SET 100k 3085 TA21 IOUT = 1V R1 *CCOMP R1 ≤ 10Ω 10μF R1 ≥ 10Ω 2.2μF 3085fb 24 LT3085 PACKAGE DESCRIPTION DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 p0.05 3.55 p0.05 1.65 p0.05 (2 SIDES) 2.15 p0.05 PACKAGE OUTLINE 0.25 p0.05 0.50 BSC 1.35 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP R = 0.05 TYP 2.00 p0.10 (2 SIDES) 3.00 p0.10 (2 SIDES) 0.40 p0.10 4 6 1.65 p0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.25 s 45° CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) 3 0.200 REF 0.75 p0.05 1 (DCB6) DFN 0405 0.25 p0.05 0.50 BSC 1.35 p0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (TBD) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3085fb 25 LT3085 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 0.889 p 0.127 (.035 p .005) 1.88 p 0.102 (.074 p .004) 0.29 REF 1.68 (.066) 0.05 REF 5.23 (.206) MIN DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 p 0.102 3.20 – 3.45 (.066 p .004) (.126 – .136) 8 0.42 p 0.038 (.0165 p .0015) TYP 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0o – 6o TYP GAUGE PLANE 1 0.53 p 0.152 (.021 p .006) DETAIL “A” 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 0.65 (.0256) BSC 0.1016 p 0.0508 (.004 p .002) MSOP (MS8E) 0210 REV F NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 3085fb 26 LT3085 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 6/10 Updated trademarks 1 Revised Conditions in Electrical Characteristics table 3 Changed ILOAD value on curve G27 in Typical Performance Characteristics section 6 Revised Figure 1 9 Added 200k resistor to drawing 3085 TA19 in Typical Applications section Updated Package Description drawings 24 25, 26 3085fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 27 LT3085 TYPICAL APPLICATION Paralleling Regulators IN LT3080 VCONTROL + – OUT 10mΩ SET IN VIN 4.8V TO 36V LT3085 VCONTROL + – 1μF OUT 20mΩ VOUT 3.3V 1.5A SET 10μF 165k 3085 TA14 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS 1.5A Low Dropout Regulator Fixed 2.85V, 3.3V, 3.6V, 5V and 12V Output LDOs LT1086 LT1763 500mA, Low Noise LDO 300mV Dropout Voltage, Low Noise = 20μVRMS, VIN: 1.8V to 20V, SO-8 Package LT3021 500mA VLDO Regulator LT3080 1.1A, Parallelable, Low Noise, Low Dropout Linear Regulator LT3080-1 Parallelable 1.1A Adjustable Single Resistor Low Dropout Regulator (with Internal Ballast R) LT1963A 1.5A Low Noise, Fast Transient Response LDO 1.1A Low Noise LDO VIN: 0.9V to 10V, Dropout Voltage = 190mV, VADJ = 200mV, 5mm × 5mm DFN-16, SO-8 Packages 300mV Dropout Voltage (2-Supply Operation), Low Noise = 40μVRMS, VIN: 1.2V to 36V, VOUT : 0V to 35.7V, Current-Based Reference with 1-Resistor VOUT Set, Directly Parallelable (No Op Amp Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP and 3mm × 3mm DFN Packages 300mV Dropout Voltage (2-Supply Operation), Low Noise = 40μVRMS, VIN: 1.2V to 36V, VOUT : 0V to 35.7V, Current-Based Reference with 1-Resistor VOUT Set, Directly Parallelable (No Op Amp Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP and 3mm × 3mm DFN Packages. LT3080-1 Version Has Integrated Ballast Resistor 340mV Dropout Voltage, Low Noise = 40μVRMS, VIN: 2.5V to 20V, TO-220, DD, SOT-223 and SO-8 Packages 290mV Dropout Voltage, Low Noise = 40μVRMS, VIN: 1.8V to 20V, VOUT : 1.2V to 19.5V, Stable with Ceramic Caps TO-220, DDPak, MSOP and 3mm × 3mm DFN Packages VIN: 1.14V to 3.5V (Boost Enabled), 1.14V to 5.5V (with External 5V), VDO = 0.1V, IQ = 950μA, Stable with 10μF Ceramic Capacitors, 10-Lead MSOP and DFN Packages LT1965 LTC®3026 1.5A Low Input Voltage VLDOTM Regulator Switching Regulators LT1976 LTC3414 LTC3406/LTC3406B LTC3411 High Voltage, 1.5A Step-Down Switching Regulator 4A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter 600mA (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter 1.25A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter f = 200kHz, IQ = 100μA, TSSOP-16E Package 95% Efficiency, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, TSSOP Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT TM Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 10-Lead MS or DFN Packages 3085fb 28 Linear Technology Corporation LT 0610 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008