LT3081 1.5A Single Resistor Rugged Linear Regulator with Monitors DESCRIPTION FEATURES n n n n n n n n n n n n n n n n Extended Safe Operating Area Maximum Output Current: 1.5A Stable with or without Input/Output Capacitors Wide Input Voltage Range: 1.2V to 36V Single Resistor Sets Output Voltage Output Current Monitor: IMON = IOUT/5000 Junction Temperature Monitor: 1µA/°C Output Adjustable to 0V 50µA SET Pin Current: 1% Initial Accuracy Output Voltage Noise: 27µVRMS Parallel Multiple Devices for Higher Current or Heat Spreading Programmable Current Limit Reverse-Battery and Reverse-Current Protection <1mV Load Regulation Typical Independent of VOUT <0.001%/V Line Regulation Typical Available in Thermally-Enhanced 12-Lead 4mm × 4mm DFN and 16-Lead TSSOP, 7-Lead DD-Pak and 7-Lead TO-220 APPLICATIONS n n n n n The LT®3081 is a 1.5A low dropout linear regulator designed for rugged industrial applications. Key features of the IC are the extended safe operating area (SOA), output current monitor, temperature monitor and programmable current limit. The LT3081 can be paralleled for higher output current or heat spreading. The device withstands reverse input and reverse output-to-input voltages without reverse current flow. The LT3081’s precision 50µA reference current source allows a single resistor to program output voltage to any level between zero and 34.5V. The current reference architecture makes load regulation independent of output voltage. The LT3081 is stable with or without input and output capacitors. The output current monitor (IOUT/5000) and die junction temperature output (1µA/°C) provide system monitoring and debug capability. In addition, a single resistor programs current limit. Internal protection circuitry includes reverse-battery and reverse-current protection, current limiting and thermal limiting. The LT3081 is offered in the 16-lead TSSOP (with exposed pad for improved thermal performance), 7-lead TO-220, 7-lead DD-Pak, and an 12-lead 4mm × 4mm DFN. All Surface Mount Power Supply Rugged Industrial Power Supply Post Regulator for Switching Supplies Low Output Voltage Supply Intrinsic Safety Applications L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION SET Pin Current 50.5 Wide Safe Operating Area Supply 50.4 VIN ISET 50µA + – TEMP RTEMP 1k OUT SET IMON RSET 30.1k ILIM RIMON 1k RILIM 6.04k COUT* 10µF IOUT 1.5V RLOAD* 1.5A 5mA MIN SET PIN CURRENT (µA) 50.3 IN LT3081 IL = 5mA 3081 TA01a *OPTIONAL 50.2 50.1 50.0 49.9 49.8 49.7 49.6 49.5 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3081 TA01b 3081f For more information www.linear.com/LT3081 1 LT3081 ABSOLUTE MAXIMUM RATINGS (Note 1) All voltages Relative to VOUT. IN Pin to OUT Pin Differential Voltage......................±40V SET Pin Current (Note 6)......................................±25mA SET Pin Voltage (Relative to OUT, Note 6)............... ±10V TEMP Pin Voltage (Relative to OUT)..................1V, –40V ILIM Pin Voltage (Relative to OUT)..........................±0.2V IMON Pin Voltage (Relative to OUT)....................1V, –40V Output Short-Circuit Duration........................... Indefinite Operating Junction Temperature Range (Note 2) E-, I-Grades........................................ –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) FE, R, T7 Packages Only.................................... 300°C PIN CONFIGURATION TOP VIEW OUT 1 16 OUT OUT 2 15 IN 11 IN OUT 3 10 IN OUT 4 9 IN OUT 5 ILIM 6 11 TEMP SET 7 10 IMON OUT 8 9 TOP VIEW 12 IN OUT 1 OUT 2 OUT 3 OUT 4 ILIM 5 8 TEMP SET 6 7 IMON 13 OUT DF PACKAGE 12-LEAD (4mm × 4mm) PLASTIC DFN TJMAX = 125°C, θJA = 32°C/W, θJC = 4°C/W EXPOSED PAD (PIN 13) IS OUT, MUST BE SOLDERED TO PCB TAB IS OUT 13 IN 12 IN OUT FE PACKAGE 16-LEAD PLASTIC TSSOP TJMAX = 125°C, θJA = 29°C/W, θJC = 8°C/W EXPOSED PAD (PIN 17) IS OUT, MUST BE SOLDERED TO PCB FRONT VIEW 7 6 5 4 3 2 1 14 IN 17 OUT FRONT VIEW NC IN TEMP OUT IMON SET ILIM TAB IS OUT 7 6 5 4 3 2 1 NC IN TEMP OUT IMON SET ILIM T7 PACKAGE 7-LEAD PLASTIC TO-220 TJMAX = 125°C, θJA = 40°C/W, θJC = 3°C/W R PACKAGE 7-LEAD PLASTIC DD TJMAX = 125°C, θJA = 15°C/W, θJC = 3°C/W 3081f 2 For more information www.linear.com/LT3081 LT3081 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3081EDF#PBF LT3081EDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C LT3081IDF#PBF LT3081IDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C LT3081EFE#PBF LT3081EFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C LT3081IFE#PBF LT3081IFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C LT3081ER#PBF LT3081ER#TRPBF LT3081R 7-Lead Plastic DD-Pak –40°C to 125°C LT3081IR#PBF LT3081IR#TRPBF LT3081R 7-Lead Plastic DD-Pak –40°C to 125°C LT3081ET7#PBF NA LT3081T7 7-Lead Plastic TO-220 –40°C to 125°C LT3081IT7#PBF NA LT3081T7 7-Lead Plastic TO-220 –40°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. Consult LTC Marketing for information on non-standard lead based finish parts. 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/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. (Note 2) PARAMETER SET Pin Current ISET Offset Voltage (VOUT – VSET) VOS ISET Load Regulation VOS Load Regulation (Note 7) CONDITIONS MIN TYP MAX UNITS VIN = 2V, ILOAD = 5mA 2V ≤ VIN ≤ 36V, 5mA ≤ ILOAD ≤ 1.5A l 49.5 48.75 50 50 50.5 51.25 µA µA VIN = 2V, ILOAD = 5mA VIN = 2V, ILOAD = 5mA l –1.5 –3.5 0 0 1.5 3.5 mV mV –0.1 ∆ILOAD = 5mA to 1.5A ∆ILOAD = 5mA to 1.5A Line Regulation ∆ISET ∆VOS nA DF, FE Packages l –0.5 –3 mV R, T7 Packages l –1.5 –4 mV 1.5 0.001 ∆VIN = 2V to 36V, ILOAD = 5mA ∆VIN = 2V to 36V, ILOAD = 5mA nA/V mV/V Minimum Load Current (Note 3) 2V ≤ VIN ≤ 36V l 1.1 5 Dropout Voltage (Note 4) ILOAD = 100mA ILOAD = 1.5A l 1.21 1.23 1.5 VIN = 5V, VSET = 0V, VOUT = –0.1V l 1.5 2 l 300 400 290 300 Internal Current Limit ILIM Programming Ratio ILIM Minimum Output Current Resistance ILOAD = 1.5A IMON Scale Factor 100mA ≤ ILOAD ≤ 1.5A 500 mA/kΩ 330 µA IMON Operating Range Ω 200 l VOUT – 40V V V A 400 IMON Full-Scale Output Current mA µA/A VOUT + 0.4V V 3081f For more information www.linear.com/LT3081 3 LT3081 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. (Note 2) PARAMETER CONDITIONS TEMP Output Current (Note 9) TJ > 5°C TEMP Output Current Absolute Error (Note 9) 0°C <TJ ≤ 125°C MIN TYP MAX 1 –10 UNITS µA/°C 10 µA Reference Current RMS Output Noise (Note 5) 10Hz ≤ f ≤ 100kHz 5.7 nARMS Error Amplifier RMS Output Noise (Note 5) ILOAD = 1.5A, 10Hz ≤ f ≤ 100kHz, COUT =10µF, CSET = 0.1µF 27 µVRMS Ripple Rejection VRIPPLE = 0.5VP-P, ILOAD = 0.1A, CSET = 0.1µF, COUT=10µF, VIN = VOUT(NOMINAL) + 3V f = 120Hz 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 LT3081 is tested and specified under pulse load conditions such that TJ ≈ TA. The LT3081E is tested at TA = 25°C and performance is guaranteed from 0°C to 125°C. Performance of the LT3081E over the full –40°C and 125°C operating temperature range is assured by design, characterization, and correlation with statistical process controls. The LT3081I is guaranteed over the full –40°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 LT3081, dropout is specified as the minimum input-tooutput voltage differential required supplying a given output current. 75 0.003 %/W Note 5: Adding a small capacitor across the reference current resistor lowers output noise. Adding this capacitor bypasses the resistor shot noise and reference current noise; output noise is then equal to error amplifier noise (see Applications Information section). Note 6: Diodes with series 400Ω resistors clamp the SET pin to the OUT pin. These diodes and resistors only carry current under transient overloads. Note 7: Load regulation is Kelvin sensed at the package. Note 8: This IC includes overtemperature protection that protects the device during momentary overload conditions. Junction temperature exceeds the maximum operating junction temperature when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 9: The TEMP pin output current represents the average die junction temperature. Due to power dissipation and thermal gradients across the die, the TEMP pin output current measurement does not guarantee that absolute maximum junction temperature is not exceeded. 3081f 4 For more information www.linear.com/LT3081 LT3081 TYPICAL PERFORMANCE CHARACTERISTICS SET Pin Current 50.5 50.4 TJ = 25°C unless otherwise specified. Offset Voltage (VOUT – VSET) SET Pin Current ILOAD = 5mA 2.0 N = 3195 OFFSET VOLTAGE (mV) SET PIN CURRENT (µA) 50.3 50.2 50.1 50.0 49.9 49.8 49.7 49.5 –50 –25 0 49 25 50 75 100 125 150 TEMPERATURE (°C) 50.5 49.5 50 SET PIN CURRENT DISTRIBUTION (µA) 0.5 0 –0.5 –1.0 –2.0 –50 –25 51 Offset Voltage Offset Voltage (VOUT – VSET) 0.2 ILOAD = 5mA 0.8 0 OFFSET VOLTAGE (mV) OFFSET VOLTAGE (mV) 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –1.0 2 TJ = 125°C –0.8 –1.0 0 0.25 0.5 0.75 1 150 –1.5 100 –2.0 50 –2.5 –3.0 25 50 75 100 125 150 TEMPERATURE (°C) Dropout Voltage 1.5 2.5 1.4 2.0 1.5 1.0 VIN – VOUT = 36V VIN – VOUT = 2V 0.5 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G07 3081 G08 DROPOUT VOLTAGE (V) –1.0 1.5 3081 G06 3.0 MINIMUM LOAD CURRENT (mA) 200 OFFSET VOLTAGE LOAD REGULATION (mV) –0.5 1.25 LOAD CURRENT (A) Minimum Load Current 0 250 0 –0.6 3081 G05 Load Regulation ∆ILOAD = 5mA TO 1.5A TJ = 25°C –0.4 –1.4 36 6 18 24 30 12 INPUT-TO-OUTPUT DIFFERENTIAL (V) 0 3081 G04 0 –50 –25 –0.2 –1.2 –0.8 1 –1 0 VOS DISTRIBUTION (mV) 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G03 Offset Voltage (VOUT – VSET) 1.0 N = 3195 –2 0 3081 G02 3081 G01 SET PIN CURRENT LOAD REGULATION (nA) 1.0 –1.5 49.6 300 ILOAD = 5mA 1.5 TJ = –50°C 1.3 TJ = 25°C TJ = 125°C 1.2 1.1 1.0 0 0.25 0.5 0.75 1 LOAD CURRENT (A) 1.25 1.5 3081 G09 3081f For more information www.linear.com/LT3081 5 LT3081 TYPICAL PERFORMANCE CHARACTERISTICS Internal Current Limit 1.5 3.0 2.5 CURRENT LIMIT (A) DROPOUT VOLTAGE (V) 1.4 1.3 ILOAD = 1.5A 1.2 ILOAD = 5mA 1.1 Internal Current Limit 2.0 VIN = 7V VOUT = 0V 1.8 1.6 CURRENT LIMIT (A) Dropout Voltage TJ = 25°C unless otherwise specified. 2.0 1.5 1.0 TO-220 AND DD-PAK 1.4 1.2 TSSOP AND DFN 1.0 0.8 0.6 0.4 0.5 0.2 1.0 –50 –25 0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 TO-220 Package Maximum Power Dissipation Programmable Current Limit POWER (W) 20 VIN – VOUT = 10V 15 10 VIN – VOUT = 5V 5 θJC = 3°C/W 1.4 RILIM = 4.53k 1.2 RILIM = 3.01k 1.0 0.8 0.6 RILIM = 1.50k 0.4 0 –50 –25 50 60 70 80 90 100 110 120 130 140 150 CASE TEMPERATURE (°C) VIN = 7V VOUT = 0V 0.2 0 RILIM 4.53k 0.6 0.4 0.2 0.5 1 1.5 OUTPUT CURRENT (A) 2 3081 G15 1 2 3 4 RILIM (kΩ) 5 350 140 300 120 100 80 60 40 0 –50 –25 6 IMON Pin Current 160 250 200 150 100 50 20 0 0 3081 G14 IMON PIN CURRENT (µA) 0.95 RILIM 3.01k TEMP PIN CURRENT (µA) RILIM 1.5k 0.5 TEMP Pin Current RSET = 20k 1.00 1.0 3081 G39 Programmable Current Limit 1.05 TJ = 25°C VIN = 7V VOUT = 0V 1.5 0 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G13 OUTPUT VOLTAGE (V) Programmable Current Limit 2.0 PROGRAMMED CURRENT LIMIT (A) PROGRAMMED CURRENT LIMIT (A) 25 0 3081 G12 1.6 30 VIN – VOUT = 20V LIMITED BY FOLDBACK CURRENT LIMIT 36 6 18 24 0 30 12 INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V) 3081 G11 3081 G10 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G16 0 0 0.3 0.6 0.9 1.2 1.5 LOAD CURRENT (A) 3081 G17 3081f 6 For more information www.linear.com/LT3081 LT3081 TYPICAL PERFORMANCE CHARACTERISTICS Linear Regulator Load Transient Response OUTPUT VOLTAGE DEVIATION (mV) 35 30 25 20 10 5 0 –50 36 6 18 24 0 30 12 INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V) ∆ILOAD = 100mA TO 500mA 200 0 20 40 60 80 100 120 140 160 180 200 TIME (µs) 400 tr = tf = 1µs 0 5 0 10 15 20 25 30 35 40 45 50 TIME (µs) 1.0 0.5 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 3 tr = tf = 1µs 0 5 10 15 20 25 30 35 40 45 50 TIME (µs) 100 50 0 100mA CURRENT SOURCE CONFIGURATION 0 5 10 15 20 25 30 35 40 45 50 TIME (µs) 3081 G24 20 40 60 80 100 120 140 160 180 200 TIME (µs) RSET = 20k 6 RLOAD = 0.67Ω COUT = 2.2µF CSET = 0.1µF 5 4 0.1 0 –0.1 –0.2 0 5 10 15 20 25 30 35 40 45 50 TIME (µs) 3081 G23 6 Linear Regulator Turn-On Response RSET = 6.04k ROUT = 0.3Ω COUT = 0 CSET = 30pF 5 4 3 1.2 1.0 0.8 0.6 4 3 2 1 0 2 OUTPUT CURRENT (A) OUTPUT CURRENT (mA) 2 150 0 7 Current Source Line Transient Response RSET = 6.04k ROUT = 3.01Ω COUT = 0 CSET = 30pF 4 0 3081 G22 Current Source Line Transient Response 5 1.0 3 ∆ILOAD = 500mA TO 1.5A 1.5 0 INPUT VOLTAGE (V) COUT = 0 3081 G21 6 ∆ILOAD = 500mA TO 1.5A 3081 G20 OUTPUT VOLTAGE DEVIATION (mV) ∆ILOAD = 100mA TO 500mA LOAD CURRENT (mA) LOAD CURRENT (mA) VIN = 3V 200 VOUT = 1V CSET = 30pF –400 –200 200 2.0 Linear Regulator Line Transient Response –200 –100 0 400 OUTPUT VOLTAGE DEVIATION (mV) OUTPUT VOLTAGE DEVIATION (mV) COUT = 0 0 600 0 Linear Regulator Load Transient Response Linear Regulator Load Transient Response VIN = 3V 100 VOUT = 1V CSET = 30pF 100 8081 G19 3791 TA02b 200 COUT = 2.2µF –200 400 0 VIN = 3V 200 VOUT = 1V CSET = 0.1µF –100 1A CURRENT SOURCE CONFIGURATION 0 5 10 15 20 25 30 35 40 45 50 TIME (µs) 3081 G25 OUTPUT VOLTAGE (V) 0 300 COUT = 2.2µF 50 –100 15 LOAD CURRENT (mA) IMON PIN CURRENT (µA) 40 VIN = 3V 100 VOUT = 1V CSET = 0.1µF INPUT VOLTAGE (V) 45 OUTPUT VOLTAGE DEVIATION (mV) 150 ILOAD = 200mA Linear Regulator Load Transient Response LOAD CURRENT (mA) IMON Pin Line Regulation 50 TJ = 25°C unless otherwise specified. 1.0 0.5 RSET = 20k RLOAD = 0.67Ω COUT = 2.2µF CERAMIC CSET = 0 0 –0.5 0 5 10 15 20 25 30 35 40 45 50 TIME (µs) 3081 G26 3081f For more information www.linear.com/LT3081 7 LT3081 TYPICAL PERFORMANCE CHARACTERISTICS Linear Regulator Turn-On Response 2 1 1.0 RSET = 20k RLOAD = 0.67Ω COUT = 2.2µF CERAMIC CSET = 0.1µF 2 1 RSET = 6.04k ROUT = 3.01Ω COUT = 0 CSET = 20pF 0 2 4 6 8 10 12 14 16 18 20 TIME (ms) 150 100 50 0 0 20 40 60 80 100 120 140 160 180 200 TIME (µs) Residual Output Voltage with Less Than Minimum Load VIN = 5V 400 SET PIN = 0V VIN 200 VOUT 0 0 500 1000 1500 60 50 40 30 0 2000 10 1k 10k 100k FREQUENCY (Hz) 100 Output Impedance CURRENT SOURCE CONFIGURATION RIPPLE REJECTION (dB) OUTPUT IMPEDANCE (Ω) 100k 10k 1k 100 100 1k 10k 100k FREQUENCY (Hz) 0 10M 3081 G33 COUT = 2.2µF CERAMIC CSET = 0.1µF ILOAD = 100mA 70 60 50 40 30 20 VIN = VOUT + 5V VIN = VOUT + 2V VIN = VOUT + 1.5V 10 1M 0 10M 10 1k 10k 100k FREQUENCY (Hz) 100 63 86 61 84 82 80 76 VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 120Hz ILOAD = 0.1A COUT = 2.2µF CSET = 0.1µF 70 –50 –25 0 10M Ripple Rejection (10kHz) 88 78 1M 3081 G32 65 72 1M 20 40 60 80 100 120 140 160 180 200 TIME (µs) 80 90 74 ISOURCE = 10mA ISOURCE = 100mA ISOURCE = 1A 10 0 Ripple Rejection (120Hz) 1M 1 0.5 3081 G31 3081 G30 10 1.0 90 ILOAD = 100mA ILOAD = 500mA ILOAD = 1.5A 10 RTEST (Ω) 10M 1.5 Ripple Rejection 70 20 RTEST 100 RSET = 6.04k ROUT = 0.3Ω COUT = 0 CSET = 20pF 100 RIPPLE REJECTION (dB) 80 RIPPLE REJECTION (dB) OUTPUT VOLTAGE (mV) VIN = 36V 300 1 3081 G29 COUT = 2.2µF CERAMIC CSET = 0.1µF VIN = VOUT(NOMINAL) + 2V 90 500 2 Ripple Rejection 100 800 600 1A CURRENT SOURCE CONFIGURATION 3 3081 G28 3081 G27 700 4 0 RIPPLE REJECTION (dB) 0 OUTPUT CURRENT (mA) OUTPUT VOLTAGE (V) 3 0 0 –0.5 100mA CURRENT SOURCE CONFIGURATION OUTPUT CURRENT (A) INPUT VOLTAGE (V) INPUT VOLTAGE (V) 3 4 Current Source Turn-On Response INPUT VOLTAGE (V) Current Source Turn-On Response 4 0.5 TJ = 25°C unless otherwise specified. 59 57 55 53 51 49 47 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G34 VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 10kHz ILOAD = 0.1A COUT = 2.2µF CSET = 0.1µF 45 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3081 G34 3081f 8 For more information www.linear.com/LT3081 LT3081 TYPICAL PERFORMANCE CHARACTERISTICS 10Hz to 100kHz Output Voltage Noise Noise Spectral Density Ripple Rejection (1MHz) 1000 26 100 ERROR AMPLIFIER NOISE SPECTRAL DENSITY (nV/√Hz) VIN = VOUT(NOMINAL) + 2V 24 RIPPLE = 200mVP-P f = 1MHz 22 ILOAD = 0.1A COUT = 2.2µF CERAMIC 20 CSET = 0.1µF 18 10 100 16 14 12 10 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 10 10 100 1k 10k FREQUENCY (Hz) 1 100k REFERENCE CURRENT NOISE SPECTRAL DENSITY (pA/√Hz) RIPPLE REJECTION (dB) TJ = 25°C unless otherwise specified. CSET = 0.1µF COUT = 4.7µF ILOAD = 1.5A VOUT 50µV/DIV NOISE INDEPENDENT OF OUTPUT VOLTAGE TIME 1ms/DIV 3081 G38 3981 G37 3081 G36 PIN FUNCTIONS IN: Input. This pin supplies power to regulate internal circuitry and supply output load current. For the device to operate properly and regulate, the voltage on this pin must be between the dropout voltage and 36V above the OUT pin (depending on output load current, see Dropout Voltage Specifications). OUT: Output. This is the power output of the device. The LT3081 requires a 5mA minimum load current for proper output regulation. TEMP: Temperature Output. This pin delivers a current proportional to the internal average junction temperature. Current output is 1µA/°C for temperatures above 5°C. The TEMP pin output current typically equals 25µA at 25°C. The output of the TEMP pin is valid for voltages from VOUT + 0.4V to VOUT – 40V. If unused, connect this pin to OUT. ILIM: Current Limit Program. A resistor between this pin and OUT programs output current limit to a level proportional to resistor value. Connect this resistor directly to OUT at the pins of the package. The typical ratio of current limit to resistor value is 400mA/kΩ. If programmable current limit is not used, leave this pin open; the internal current limit of the LT3081 is still active, keeping the device inside safe operating limits. External voltage drops between the current limit resistor and VOUT will affect the current limit. Keep drops below 1mV. IMON: Output Current Monitor. The IMON pin sources a current typically equal to ILOAD/5000 or 200µA per amp of output current. Terminating this pin with a resistor to GND produces a voltage proportional to ILOAD. For example, at ILOAD = 1.5A, IMON typically sources 300µA. With a 1k resistor to GND, this produces 300mV. The output of the IMON pin is valid for voltages from VOUT + 0.4V to VOUT – 40V. If unused, connect this pin to OUT. SET: Set. This pin is the error amplifier’s noninverting input and also sets the operating bias point of the circuit. A fixed 50μA current source flows out of this pin. A single external resistor programs VOUT. Output voltage range is 0V to 34.5V. Exposed Pad/Tab: Output. The exposed pad of the DF and FE packages and the tab of the R and T7 packages are tied internally to OUT. As such, tie them directly to OUT (Pins 1-4/Pins 1-5, 8, 9, 16/Pin 4/Pin 4) at the PCB. The amount of copper area and planes connected to OUT determine the effective thermal resistance of the packages. NC: No Connection. No connect pins have no connection to internal circuitry and may be tied to IN, OUT, GND or floated. 3081f For more information www.linear.com/LT3081 9 LT3081 BLOCK DIAGRAM IN 50µA CURRENT MONITOR IMON = ILOAD/5000 + TEMPERATURE DEPENDENT CURRENT SOURCE 1µA/°C – TEMP SET PROGRAMMABLE CURRENT LIMIT ILIM IMON OUT 3081 BD APPLICATIONS INFORMATION Introduction The LT3081 regulator is easy to use and has all the protection features expected in high performance regulators. Included are short-circuit protection, reverse-input protection and safe operating area protection, as well as thermal shutdown with hysteresis. Safe operating area (SOA) for the LT3081 is extended, allowing for use in harsh industrial and automotive environments where sudden spikes in input voltage lead to high power dissipation. The LT3081 fits well in applications needing multiple rails. This new architecture adjusts down to zero with a single resistor, handling modern low voltage digital ICs as well as allowing easy parallel operation and thermal management without heat sinks. Adjusting to zero output allows shutting off the powered circuitry. A precision “0” TC 50μA reference current source connects to the noninverting input of a power operational amplifier. The power operational amplifier provides a low impedance buffered output to the voltage on the noninverting input. A single resistor from the noninverting input to ground sets the output voltage. If this resistor is set to 0Ω, zero output voltage results. Therefore, any output voltage can be obtained between zero and the maximum defined by the input power supply is obtainable. The benefit of using a true internal current source as the reference, as opposed to a bootstrapped reference in older regulators, is not so obvious in this architecture. A true reference current source allows the regulator to have gain and frequency response independent of the impedance on the positive input. On older adjustable regulators, such as the LT1086 loop gain changes with output voltage and bandwidth changes if the adjustment pin is bypassed to ground. For the LT3081, the loop gain is unchanged with output voltage changes or bypassing. Output regulation is not a fixed percentage of output voltage, but is a fixed fraction of millivolts. Use of a true current source allows all of 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 LT3081 has many additional features that facilitate monitoring and control. Current limit is externally programmable via a single resistor between the ILIM pin and OUT. Shorting this resistor out disables all output current to the load, only bias currents remain. The IMON pin produces a current output proportional to load current. For every 1A of load current, the IMON pin sources 200µA of current. This can be sensed using an external resistor to monitor load requirements and detect potential faults. The IMON pin can operate at voltages above OUT, so it operates even during a short-circuit condition. One additional monitoring function is the TEMP pin, a current source that is proportional to average die temperature. For die temperatures above 0°C, the TEMP pin sources a current equal to 1µA/°C. This pin operates normally during output short-circuit conditions. 3081f 10 For more information www.linear.com/LT3081 LT3081 APPLICATIONS INFORMATION Programming Linear Regulator Output Voltage The LT3081 generates a 50μA 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 equals 50µA multiplied by the value of the SET pin resistor. Any voltage can be generated and there is no minimum output voltage for the regulator. Table 1 lists many common output voltages and the closest standard 1% resistor values used to generate that output voltage. Regulation of the output voltage requires a minimum load current of 5mA. For true zero voltage output operation, return this 5mA load current to a negative output voltage. Table 1. 1% Resistors for Common Output Voltages VOUT (V) RSET (kΩ) 1 20 1.2 24.3 1.5 30.1 1.8 35.7 2.5 49.9 3.3 66.5 5 100 With the 50µA current source 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 is required. Surface coating may be necessary to provide a moisture barrier in high humidity environments. OUT GND SET PIN 3081 F02 Figure 2. Guard Ring Layout Example of DF Package Configuring the LT3081 as a Current Source 50µA + – SET OUT VOUT = 50µA • RSET CSET If guard ring 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. LT3081 IN CIN Minimize board leakage by encircling the SET pin and circuitry with a guard ring operated at a potential close to itself. Tie the guard ring to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. 50nA of leakage into or out of the SET pin and its associated circuitry creates a 0.1% reference voltage error. Leakages of this magnitude, coupled with other sources of leakage, can cause significant offset voltage and reference drift, especially over the possible operating temperature range. Figure 2 depicts an example guard ring layout. RSET COUT RLOAD 3081 F01 Figure 1. Basic Adjustable Regulator Setting the LT3081 to operate as a 2-terminal current source is a simple matter. The 50µA reference current from the SET pin is used with one resistor to generate a small voltage, usually in the range of 100mV to 1V (200mV is a level that rejects offset voltage, line regulation, and other errors without being excessively large). This voltage is then applied across a second resistor that connect from OUT to the first resistor. Figure 3 shows connections and formulas to calculate a basic current source configuration. 3081f For more information www.linear.com/LT3081 11 LT3081 APPLICATIONS INFORMATION provide matching temperature coefficients. See resistor manufacturers’ data sheets for more details. IN LT3081 IOUT ≥ 5mA 50µA VSET = 50µA •RSET + – IOUT = SET OUT + VSET VSET 50µA •RSET = ROUT ROUT 3081 F03 RSET ROUT – IOUT Programming Current Limit Externally Figure 3. Using the LT3081 as a Current Source Again, the lower current levels used in the LT3081 necessitate attention to board leakages as error sources (see the Programming Linear Regulator Output Voltage section). In a current source configuration, programmable current limit and current monitoring functions are often unused. When not used, tie IMON to OUT and leave ILIM open. The TEMP pin is still available for use, if unused tie TEMP to OUT. Selecting RSET and ROUT in Current Source Applications In Figure 3, both resistors RSET and ROUT program the value of the output current. The question now arises: the ratio of these resistors is known, but what value should each resistor be? The first resistor to select is RSET. The value selected should generate enough voltage to minimize the error caused by the offset between the SET and OUT pins. A reasonable starting level is ~200mV of voltage across RSET (RSET equal to 4.02k). Resultant errors due to offset voltage are a few percent. The lower the voltage across RSET becomes, the higher the error term due to the offset. From this point, selecting ROUT is easy, as it is a straightforward calculation from RSET. Take note, however, resistor errors must be accounted for as well. While larger voltage drops across RSET minimize the error due to offset, they also increase the required operating headroom. Obtaining the best temperature coefficient does not require the use of expensive resistors with low ppm temperature coefficients. Instead, since the output current of the LT3081 is determined by the ratio of RSET to ROUT, those resistors should have matching temperature characteristics. Less expensive resistors made from the same material 12 Higher output currents necessitate the use of higher wattage resistors for ROUT. There may be a difference between the resistors used for ROUT and RSET. A better method to maintain consistency in resistors is to use multiple resistors in parallel to create ROUT, allowing the same wattage and type of resistor as RSET. A resistor placed between ILIM and OUT on the LT3081 externally sets current limit to a level lower than the internal current limit. Connect this resistor directly at the OUT pins for best accuracy. The value of this resistor calculates as: RILIM = ILIMIT/400mA/kΩ + 400Ω The resistor for a 1.3A current limit is: RILIM = 1.3A/400mA/ kΩ + 400Ω = 3.65k. Tolerance over temperature is ±15%, so current limit is normally set 20% above maximum load current. The 400Ω offset resistance built in to the programmable current limit allows for lowering the maximum output current to only bias currents (see curve of Minimum Load Current in Typical Performance Characteristics) using external switches. The LT3081’s internal current limit overrides the programmed current limit if the input-to-output voltage differential in the power transistor is excessive. The internal current limit is ≈2A with a foldback characteristic dependent on input-to-output differential voltage, not output voltage per se (see Typical Performance Characteristics). Stability and Input Capacitance The LT3081 does not require an input capacitor to maintain stability. Input capacitors are recommended in linear regulator configurations to provide a low impedance input source to the LT3081. If using an input capacitor, low ESR, ceramic input bypass capacitors are acceptable for applications without long input leads. However, applications connecting a power supply to an LT3081 circuit’s IN and GND pins with long input wires combined with low ESR, ceramic input capacitors are prone to voltage spikes, reliability concerns and application-specific board oscillations. The input wire inductance found in many battery-powered For more information www.linear.com/LT3081 3081f LT3081 APPLICATIONS INFORMATION applications, combined with the low ESR ceramic input capacitor, forms a high Q LC resonant tank circuit. In some instances this resonant frequency beats against the output current dependent LDO bandwidth and interferes with proper operation. Simple circuit modifications/solutions are then required. This behavior is not indicative of LT3081 instability, but is a common ceramic input bypass capacitor application issue. The self-inductance, or isolated inductance, of a wire is directly proportional to its length. Wire diameter is not a major factor on its self-inductance. For example, the selfinductance of a 2-AWG isolated wire (diameter = 0.26") is about half the self-inductance of a 30-AWG wire (diameter = 0.01"). One foot of 30-AWG wire has about 465nH of self inductance. One of two ways reduces a wire’s self-inductance. One method divides the current flowing towards the LT3081 between two parallel conductors. In this case, the farther apart the wires are from each other, the more the selfinductance 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 input and GND wires) in very close proximity. Two 30-AWG wires separated by only 0.02", used as forward and return current conductors, reduce the overall self-inductance to approximately one-fifth that of a single isolated wire. If wiring modifications are not permissible for the applications, including series resistance between the power supply and the input of the LT3081 also stabilizes the application. As little as 0.1Ω to 0.5Ω, often less, is effective in damping the LC resonance. If the added impedance between the power supply and the input is unacceptable, adding ESR to the input capacitor also provides the necessary damping of the LC resonance. However, the required ESR is generally higher than the series impedance required. Stability and Frequency Compensation for Linear Regulator Configurations The LT3081 does not require an output capacitor for stability. LTC recommends an output capacitor of 10μF with an ESR of 0.5Ω or less to provide good transient performance in linear regulator configurations. 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 LT3081, 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. Stability and Frequency Compensation for Current Source Configurations The LT3081 does not require input or output capacitors for stability in many current-source applications. Clean, tight PCB layouts provide a low reactance, well controlled operating environment for the LT3081 without requiring capacitors to frequency compensate the circuit. Figure 3 highlights the simplicity of using the LT3081 as a current source. Some current source applications use a capacitor connected in parallel with the SET pin resistor to lower the current source’s noise. This capacitor also provides a soft-start function for the current source. See Quieting the Noise section for further details. When operating without output capacitors, the high impedance nature of the SET pin as the input of the error amplifier allows signal from the output to couple in, showing as high frequency ringing during transients. Bypassing the SET resistor with a capacitor in the range of 20pF to 30pF dampens the ringing. Depending on the pole introduced by a capacitor or other complex impedances presented to the LT3081, external compensation may be required for stability. Techniques are discussed to achieve this in the following paragraphs. Linear Technology strongly recommends testing stability in situ with final components before beginning production. 3081f For more information www.linear.com/LT3081 13 LT3081 APPLICATIONS INFORMATION Although the LT3081’s design strives to be stable without capacitors over a wide variety of operating conditions, it is not possible to test for all possible combinations of input and output impedances that the LT3081 will encounter. These impedances may include resistive, capacitive, and inductive components and may be complex distributed networks. In addition, the current source’s value will differ between applications and its connection may be GND referenced, power supply referenced, or floating in a signal line path. Linear Technology strongly recommends that stability be tested in situ for any LT3081 application. In LT3081 applications with long wires or PCB traces, the inductive reactance may cause instability. In some cases, adding series resistance to the input and output lines (as shown in Figure 4) may sufficiently dampen these possible high-Q lines and provide stability. The user must evaluate the required resistor values against the design’s headroom constraints. In general, operation at low output current levels (<20mA) automatically requires higher values of programming resistors and may provide the necessary damping without additional series impedance. If the line impedances in series with the LT3081 are complex enough such that series damping resistors are LONG LINE REACTANCE/INDUCTANCE RSERIES not sufficient, a frequency compensation network may be necessary. Several options may be considered. Figure 5 depicts the simplest frequency compensation networks as a single capacitor across the two terminals of the current source. Some applications may use the capacitance to stand off DC voltage but allow the transfer of data down a signal line. For some applications, pure capacitance may be unacceptable or present a design constraint. One circuit example typifying this is an “intrinsically-safe” circuit in which an overload or fault condition potentially allows the capacitor’s stored energy to create a spark or arc. For applications where a single capacitor is unacceptable, Figure 5 alternately shows a series RC network connected across the two terminals of the current source. This network has the added benefit of limiting the discharge current of the capacitor under a fault condition, preventing sparks or arcs. In many instances, a series RC network is the best solution for stabilizing the application circuit. Typical resistor values will range from 100Ω to 5k. Once again, Linear Technology strongly recommends testing stability in situ for any LT3081 application across all operating conditions, especially ones that present complex impedance networks at the input and output of the current source. If an application refers the bottom of the LT3081 current source to GND, it may be necessary to bypass the top of the current source with a capacitor to GND. In some IN LT3081 50µA IN LT3081 + – RCOMP 50µA SET + – OUT RSET CCOMP OR ROUT SET CCOMP OUT 3081 F04 RSET RSERIES ROUT 3081 F05 LONG LINE REACTANCE/INDUCTANCE Figure 4. Adding Series Resistance Decouples and Dampens Long Line Reactances Figure 5. Compensation from Input to Output of Current Source Provides Stability 3081f 14 For more information www.linear.com/LT3081 LT3081 APPLICATIONS INFORMATION In some extreme cases, capacitors or series RC networks may be required on both the LT3081’s input and output to stabilize the circuit. Figure 6 depicts a general application using input and output capacitor networks rather than an input-to-output capacitor. As the input of the current source tends to be high impedance, placing a capacitor on the input does not have the same effect as placing a capacitor on the lower impedance output. Capacitors in the range of 0.1µF to 1µF usually provide sufficient bypassing on the input, and the value of input capacitance may be increased without limit. Pay careful attention to using low ESR input capacitors with long input lines (see the Stability and Input Capacitance section for more information). VIN RIN are specified with EIA temperature characteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but they tend to have strong voltage and temperature coefficients as shown in Figures 7 and 8. 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 40 20 CHANGE IN VALUE (%) cases, this capacitor may already exist and no additional capacitance is required. For example, if the LT3081 was used as a variable current source on the output of a power supply, the output bypass capacitance would suffice to provide LT3081 stability. Other applications may require the addition of a bypass capacitor. A series RC network may also be used as necessary, and depends on the application requirements. X5R 0 –20 –40 Y5V –60 IN LT3081 –80 50µA SET BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF –100 –50 –25 + – 50 25 75 0 TEMPERATURE (°C) 100 125 3081 F07 Figure 7. Ceramic Capacitor Temperature Characteristics OUT RSET ROUT IOUT 20 COUT OR ROUT COUT 3081 F06 Figure 6. Input and/or Output Capacitors May Be Used for Compensation Using Ceramic Capacitors BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF 0 CHANGE IN VALUE (%) CIN X5R –20 –40 –60 Y5V –80 Give extra consideration 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 –100 0 2 4 8 6 10 12 DC BIAS VOLTAGE (V) 14 16 3081 F08 Figure 8. Ceramic Capacitor DC Bias Characteristics 3081f For more information www.linear.com/LT3081 15 LT3081 APPLICATIONS INFORMATION 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. In a ceramic capacitor, the stress can be induced by vibrations in the system or thermal transients. LT3081 IN 50µA + – 50µA + – 1µF SET Higher output current is obtained by paralleling multiple LT3081s together. Tie the individual SET pins together and tie the individual IN pins together. Connect the outputs in common using small pieces of PC trace as ballast resistors to promote equal current sharing. PC trace resistance in milliohms/inch is shown in Table 2. Ballasting requires only a tiny area on the PCB. 33k WEIGHT (oz) 10mil WIDTH 1 54.3 2 27.1 Trace resistance is measured in mΩ/in. 20mil WIDTH 27.1 13.6 10mΩ LT3081 IN VIN 4.8V TO 40V Paralleling Devices Table 2. PC Board Trace Resistance OUT SET OUT 10mΩ 10µF VOUT 3.3V 3A 3081 F09 Figure 9. Parallel Devices Ballast Resistor Drop in the Typical Applications section). Regulator paralleling without the use of ballast resistors is accomplished by comparing the IMON outputs of regulators (see Load Current Sharing Without Ballasting in the Typical Applications section). Quieting the Noise The worst-case room temperature offset, only ±1.5mV between the SET pin and the OUT pin, allows the use of very small ballast resistors. As shown in Figure 9, each LT3081 has a small 10mΩ ballast resistor, which at full output current gives better than 80% equalized sharing of the current. The external resistance of 10mΩ (5mΩ for the two devices in parallel) only adds about 15mV of output regulation drop at an output of 3A. Even with an output voltage as low as 1V, this only adds 1.5% to the regulation. Of course, paralleling more than two LT3081s yields even higher output current. Spreading the devices on the PC board also spreads the heat. Series input resistors can further spread the heat if the input-to-output difference is high. The LT3081 offers numerous noise performance advantages. Every linear regulator has its sources of noise. In general, a linear regulator’s critical noise source is the reference. In addition, consider the error amplifier’s noise contribution along with the resistor divider’s noise gain. If the increase in load regulation from the ballast resistors is unacceptable, the IMON output can be used to compensate for these drops (see Using IMON Cancels The SET pin resistor generates spot noise equal to √4kTR (k = Boltzmann’s constant, 1.38 • 10–23J/°K, and T is absolute temperature) which is RMS summed with the voltage 16 Many traditional low noise regulators bond out the voltage reference to an external pin (usually through a large value resistor) to allow for bypassing and noise reduction. The LT3081 does not use a traditional voltage reference like other linear regulators. Instead, it uses a 50µA reference current. The 50µA current source generates noise current levels of 18pA/√Hz (5.7nARMS over a 10Hz to 100kHz bandwidth). The equivalent voltage noise equals the RMS noise current multiplied by the resistor value. For more information www.linear.com/LT3081 3081f LT3081 APPLICATIONS INFORMATION noise. If the application requires lower noise performance, bypass the voltage setting resistor with a capacitor to GND. Note that this noise-reduction capacitor increases start-up time as a factor of the RC time constant. 50µA + – The LT3081 uses a unity-gain follower from the SET pin to the OUT pin. Therefore, multiple possibilities exist (besides a SET pin resistor) to set output voltage. For example, using a high accuracy voltage reference from SET to GND removes the errors in output voltage due to reference current tolerance and resistor tolerance. Active driving of the SET pin is acceptable. The typical noise scenario for a linear regulator is that the output voltage setting resistor divider gains up the reference noise, especially if VOUT is much greater than VREF. The LT3081’s noise advantage is that the unity-gain follower presents no noise gain whatsoever from the SET pin to the output. Thus, noise figures do not increase accordingly. Error amplifier noise is typical 85nV/√Hz(27µVRMS over a 10Hz to 100kHz bandwidth). The error amplifier’s noise is RMS summed with the other noise terms to give a final noise figure for the regulator. Paralleling of regulators adds the benefit that output noise is reduced. For n regulators in parallel, the output noise drops by a factor of √n. Curves in the Typical Performance Characteristics section show noise spectral density and peak-to-peak noise characteristics for both the reference current and error amplifier over a 10Hz to 100kHz bandwidth. Load Voltage Regulation The LT3081 is a floating device. No ground pin exists on the packages. Thus, the IC delivers all quiescent current and drive current to the load. Therefore, it is not possible to provide true remote load sensing. The connection resistance between the regulator and the load determines load regulation performance. The data sheet’s load regulation specification is Kelvin sensed at the package’s pins. Negative-side sensing is a true Kelvin connection by returning the bottom of the voltage setting resistor to the negative side of the load (see Figure 10). LT3081 IN PARASITIC RESISTANCE SET OUT RSET RP RP LOAD RP 3081 F10 Figure 10. Connections for Best Load Regulation Connected as shown, system load regulation is the sum of the LT3081’s load regulation and the parasitic line resistance multiplied by the output current. To minimize load regulation, keep the positive connection between the regulator and load as short as possible. If possible, use large diameter wire or wide PC board traces. TEMP Pin Operation (Die Temperature Monitor) The TEMP pin of the LT3081 outputs a current proportional to average die temperature. At 25°C, the current from the TEMP pin is 25µA, with a slope of 1µA/°C. The current out of the TEMP pin is valid for junction temperatures above 0°C (absent initial offset considerations). Below 0°C, the TEMP pin will not sink current to indicate die temperature. The TEMP pin output current is valid for voltages up to 40V below and 0.4V above the OUT pin allowing operation even during short-circuit conditions. Connecting a resistor from TEMP to ground converts the TEMP pin current into a voltage to allow for monitoring by an ADC. With a 1k resistor, 0mV to 150mV indicates 0°C to 150°C. It should be noted that the TEMP pin current represents an average temperature and should not be used to guarantee that maximum junction temperature is not exceeded. Instantaneous power along with thermal gradients and time constants may cause portions of the die to exceed maximum ratings and thermal shutdown thresholds. Be sure to calculate die temperature rise for steady state (>1 minute) as well as impulse conditions. 3081f For more information www.linear.com/LT3081 17 LT3081 APPLICATIONS INFORMATION IMON Pin Operation (Current Monitor) The LT3081’s IMON pin outputs a current proportional to the load current supplied at a ratio of 1:5000. The IMON pin current is valid for voltages up to 40V below and 0.4V above the OUT pin, allowing operation even during shortcircuit conditions. Connecting a resistor from IMON to ground converts the IMON pin current into a voltage to allow for monitoring by an ADC. With a 1k resistor, 0mV to 300mV indicates 0A to 1.5A of load current. Compensating for Cable Drops with IMON The IMON pin can compensate for resistive drops in wires or cables between the LT3081 and the load. Breaking the SET resistor into two pieces adjusts the output voltage as a function of load current. The ratio of the output wire/cable impedance to the bottom resistor should be 1:5000. The sum total of the two SET resistor values determines the initial output voltage. Figure 11 shows a typical application and formulas for calculating resistor values. IN OUT RCABLE2 0.02Ω SET IMON RSET 29.8k RCOMP 200Ω COUT 10µF RCABLE 0.02Ω Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly, or the bottom of the pin most directly in the heat path. This is the lowest thermal resistance path for heat flow. Only proper device mounting ensures the best possible thermal flow from this area of the packages to the heat sinking material. Note that the exposed pad of the DFN and TSSOP packages and the tab of the DD-Pak and TO-220 packages are electrically connected to the output (VOUT). Tables 3 through 5 list thermal resistance as a function of copper areas on a fixed board size. All measurements were taken in still air on a 4-layer FR-4 board with 1oz solid internal planes and 2oz external trace planes with a total finished board thickness of 1.6mm. Table 3. DF Package, 12-Lead DFN COPPER AREA LT3081 CIN 1µF Surface mount packages provide the necessary heat sinking by using the heat spreading capabilities of the PC board, copper traces and planes. Surface mount heat sinks, plated through-holes and solder-filled vias can also spread the heat generated by power devices. LOAD TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 18°C/W 1000mm2 2500mm2 2500mm2 22°C/W 225mm2 2500mm2 2500mm2 29°C/W 100mm2 2500mm2 2500mm2 35°C/W *Device is mounted on topside 3081 F11 RCOMP = 5000 • RCABLE(TOTAL) VOUT(LOAD) = 50µA (RSET + RCOMP) Table 4. FE Package, 16-Lead TSSOP COPPER AREA Figure 11. Using IMON to Compensate for Cable Drops Thermal Considerations The LT3081’s internal power and thermal limiting circuitry protects itself under overload conditions. For continuous normal load conditions, do not exceed the 125°C maximum junction temperature. Carefully consider all sources of thermal resistance from junction-to-ambient. This includes (but is not limited to) junction-to-case, case-to-heat sink interface, heat sink resistance or circuit board-to-ambient as the application dictates. Consider all additional, adjacent heat generating sources in proximity on the PCB. TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 16°C/W 1000mm2 2500mm2 2500mm2 20°C/W 225mm2 2500mm2 2500mm2 26°C/W 100mm2 2500mm2 2500mm2 32°C/W *Device is mounted on topside Table 5. R Package, 7-Lead DD-Pak COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 13°C/W 1000mm2 2500mm2 2500mm2 14°C/W 225mm2 2500mm2 2500mm2 16°C/W *Device is mounted on topside 3081f 18 For more information www.linear.com/LT3081 LT3081 APPLICATIONS INFORMATION T7 Package, 7-Lead TO-220 Reducing Power Dissipation Thermal Resistance (Junction-to-Case) = 3°C/W In some applications it may be necessary to reduce the power dissipation in the LT3081 package without sacrificing output current capability. Two techniques are available. The first technique, illustrated in Figure 12, employs a resistor in series with the regulator’s input. The voltage drop across RS decreases the LT3081’s IN-to-OUT differential voltage and correspondingly decreases the LT3081’s power dissipation. For further information on thermal resistance and using thermal information, refer to JEDEC standard JESD51, notably JESD51-12. PCB layers, copper weight, board layout and thermal vias affect the resultant thermal resistance. Tables 3 through 5 provide thermal resistance numbers for best-case 4-layer boards with 1oz internal and 2oz external copper. Modern, multilayer PCBs may not be able to achieve quite the same level performance as found in these tables. Demo circuit 1870A’s board layout using multiple inner VOUT planes and multiple thermal vias achieves 16°C/W performance for the FE package. As an example, assume: VIN = 7V, VOUT = 3.3V and IOUT(MAX) = 1.5A. Use the formulas from the Calculating Junction Temperature section previously discussed. Without series resistor RS, power dissipation in the LT3081 equals: PTOTAL = (7V – 3.3V) • 1.5A = 5.55W Calculating Junction Temperature Example: Given an output voltage of 0.9V, an IN voltage of 2.5V ±5%, output current range from 10mA to 1A and a maximum ambient temperature of 50°C, what is the maximum junction temperature for the DD-Pak on a 2500mm2 board with topside copper of 1000mm2? The power in the circuit equals: If the voltage differential (VDIFF) across the LT3081 is chosen as 1.5V, then RS equals: RS = 7V – 3.3V – 1.5V = 1.5Ω 1.5A Power dissipation in the LT3081 now equals: PTOTAL = 1.5V • 1.5A = 2.25W PTOTAL = (VIN – VOUT)(IOUT) The current delivered to the SET pin is negligible and can be ignored. VIN(MAX_CONTINUOUS) = 2.625V (2.5V + 5%) VOUT = 0.9V, IOUT = 1A, TA = 50°C Power dissipation under these conditions equals: PTOTAL = (VIN – VOUT)(IOUT) PTOTAL = (2.625V – 0.9V)(1A) = 1.73W Junction Temperature equals: TJ = TA + PTOTAL • θJA (using tables) TJ = 50°C + 1.73W • 14°C/W = 74.2°C In this case, the junction temperature is below the maximum rating, ensuring reliable operation. The LT3081’s power dissipation is now only 40% compared to no series resistor. RS dissipates 3.3W of power. Choose appropriate wattage resistors or use multiple resistors in parallel to handle and dissipate the power properly. The second technique for reducing power dissipation, shown in Figure 13, uses a resistor in parallel with the LT3081. This resistor provides a parallel path for current flow, reducing the current flowing through the LT3081. 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 = 5V, VIN(MAX) = 5.5V, VOUT = 3.3V, VOUT(MIN) = 3.2V, IOUT(MAX) = 1.5A and IOUT(MIN) = 0.7A. Also, assuming that RP carries no more than 90% of IOUT(MIN) = 630mA. 3081f For more information www.linear.com/LT3081 19 LT3081 APPLICATIONS INFORMATION Calculating RP yields: LT3081 supplies only 0.86A. Therefore, load current can increase by 0.64A to a total output current of 2.14A while keeping the LT3081 in its normal operating range. 5.5V – 3.2V = 3.65Ω 0.63A (5% Standard value = 3.6Ω) RP = Protection Features The maximum total power dissipation is: (5.5V – 3.2V) • 1.5A = 3.5W However, the LT3081 supplies only: 1.5A – 5.5V – 3.2V = 0.86A 3.6Ω Therefore, the LT3081’s power dissipation is only: PDISS = (5.5V – 3.2V) • 0.86A = 1.98W RP dissipates 1.52W of power. As with the first technique, choose appropriate wattage resistors to handle and dissipate the power properly. With this configuration, the VIN RS VIN′ C1 IN LT3081 50µA + – SET OUT RSET C2 VOUT 3081 F12 Figure 12. Reducing Power Dissipation Using a Series Resistor VIN C1 IN LT3081 The LT3081 incorporates several protection features ideal for harsh industrial and automotive environments, among other applications. In addition to normal monolithic regulator protection features such as current limiting and thermal limiting, the LT3081 protects itself against reverse-input voltages, reverse-output voltages, and large OUT-to-SET pin voltages. Current limit protection and thermal overload protection protect the IC against output current overload conditions. For normal operation, do not exceed the rated absolute maximum junction temperature. The thermal shutdown circuit’s temperature threshold is typically 165°C and incorporates about 5°C of hysteresis. The LT3081’s IN pin withstands ±40V voltages with respect to the OUT and SET pins. Reverse current flow, if OUT is greater than IN, is less than 1mA (typically under 100µA), protecting the LT3081 and sensitive loads. Clamping diodes and 400Ω limiting resistors protect the LT3081’s SET pin relative to the OUT pin voltage. These protection components typically only carry current under transient overload conditions. These devices are sized to handle ±10V differential voltages and ±25mA crosspin current flow without concern. Relative to these application concerns, note the following two scenarios. The first scenario employs a noise-reducing SET pin bypass capacitor while OUT is instantaneously shorted to GND. The second scenario follows improper shutdown techniques in which the SET pin is reset to GND quickly while OUT is held up by a large output capacitance with light load. 50µA RP + – SET RSET OUT VOUT C2 3081 F13 Figure 13. Reducing Power Dissipation Using a Parallel Resistor 3081f 20 For more information www.linear.com/LT3081 LT3081 TYPICAL APPLICATIONS Paralleling Regulators VIN IN LT3081 ISET 50µA + – IMON SET TEMP OUT 10mΩ OUT 10mΩ VOUT 3V 3A ILIM 1k IN LT3081 ISET 50µA + – IMON 1k SET TEMP 1k RSET 30.1k 3081 TA03 ILIM 3.01k Using IMON Cancels Ballast Resistor Drop VIN IN LT3081 ISET 50µA + – IMON SET TEMP OUT RBALLAST 10mΩ OUT RBALLAST 10mΩ ILIM VOUT 1.5V 3A 1k IN LT3081 ISET 50µA + – IMON SET TEMP RSET 15k ILIM 3081 TA04 1k RCOMP 25Ω 3081f For more information www.linear.com/LT3081 21 LT3081 TYPICAL APPLICATIONS Load Sharing Without Ballast Resistors VIN 3V TO 18V 22µF IN OUT IN 22µF LT3081 SET 0.1µF 20k OUT OUT LT3081 IMON 5.1k 20k 0.1µF LT3081 IMON SET 1k IN SET 1k 0.1µF 100k 20k VOUT 1V 4.5A IMON 1k 100k + + 1/2 LT1638 1/2 LT1638 5.1k – – 0.47µF 0.47µF 5.1k 5.1k 3081 TA06 Load Current Sharing Without Ballasting VOUT 1V 3A VIN 3V TO 36V 4.7µF IN OUT LT3081 100Ω IMON SET 0.1µF ILIM OUT 2.2µF 20k ILIM IMON IN LT3081 SET 20k = 2N3904 1k 0.1µF 1k 3081 TA05 3081f 22 For more information www.linear.com/LT3081 LT3081 Arduino Monitored Supply TYPICAL APPLICATIONS 3081f For more information www.linear.com/LT3081 23 LT3081 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DF Package 12-Lead Plastic DFN (4mm × 4mm) (Reference LTC DWG # 05-08-1733 Rev A) 2.50 REF 0.70 ±0.05 3.38 ±0.05 4.50 ±0.05 3.10 ±0.05 2.65 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (4 SIDES) 2.50 REF 7 12 0.40 ±0.10 3.38 ±0.10 2.65 ±0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (NOTE 6) 0.200 REF 6 R = 0.115 TYP 0.75 ±0.05 1 (DF12) DFN 1112 REV A 0.25 ±0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD 0.00 – 0.05 NOTE: 1. PACKAGE OUTLINE DOES NOT CONFORM TO JEDEC MO-229 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 3081f 24 For more information www.linear.com/LT3081 LT3081 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev J) Exposed Pad Variation BB 4.70 (.185) 3.58 (.141) DETAIL A 4.90 – 5.10* (.193 – .201) 0.56 (.022) REF 3.58 (.141) NOTE 5 16 1514 13 12 1110 9 NOTE 5 6.60 ±0.10 2.94 3.05 (.116) (.120) 4.50 ±0.10 DETAIL A SEE NOTE 4 2.94 6.40 (.116) (.252) BSC 0.53 (.021) REF DETAIL A IS THE PART OF THE LEAD FRAM FEATURE FOR REFERENCE ONLY NO MEASUREMENT PUROSE 1.05 ±0.10 0.65 BSC 0.45 ±0.05 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.25 REF 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT 1.10 (.0433) MAX 0° – 8° 0.65 (.0256) BSC 0.195 – 0.30 (.0077 – .0118) TYP 0.05 – 0.15 (.002 – .006) FE16 (BB) TSSOP REV J 1012 5. BOTTOM EXPOSED PADDLE MAY HAVE METAL PROTRUSION IN THIS AREA. THIS REGION MUST BE FREE OF ANY EXPOSED TRACES OR VIAS ON PBC LAYOUT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 3081f For more information www.linear.com/LT3081 25 LT3081 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. T7 Package 7-Lead Plastic TO-220 (Straight Lead) (Nonstandard Flow 06) (Reference LTC DWG # 05-08-1422) .390 – .415 (9.906 – 10.541) .147 – .155 (3.734 – 3.937) DIA .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) .230 – .270 (5.842 – 6.858) .460 – .500 (11.684 – 12.700) .570 – .620 (14.478 – 15.748) .330 – .370 (8.382 – 9.398) .980 – 1.070 (24.892 – 27.178) .520 – .570 (13.208 – 14.478) .050 (1.27) BSC .026 – .036 (0.660 – 0.914) .013 – .023 (0.330 – 0.584) .095 – .115 (2.41 – 2.92) T7 (STRAIGT) 0801 3081f 26 For more information www.linear.com/LT3081 LT3081 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. R Package 7-Lead Plastic DD Pak (Reference LTC DWG # 05-08-1462 Rev F) .256 (6.502) .060 (1.524) TYP .060 (1.524) .390 – .415 (9.906 – 10.541) .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) 15° TYP .060 (1.524) .183 (4.648) +.008 .004 –.004 +0.203 0.102 –0.102 .059 (1.499) TYP .330 – .370 (8.382 – 9.398) ( ) .095 – .115 (2.413 – 2.921) .075 (1.905) DETAIL A .300 (7.620) +.012 .143 –.020 +0.305 3.632 –0.508 ( BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK ) .026 – .035 (0.660 – 0.889) TYP .050 (1.27) BSC .013 – .023 (0.330 – 0.584) .050 ±.012 (1.270 ±0.305) DETAIL A 0° – 7° TYP .420 .080 .420 0° – 7° TYP .276 .350 .325 .205 .585 .585 .320 .090 .050 .035 RECOMMENDED SOLDER PAD LAYOUT NOTE: 1. DIMENSIONS IN INCH/(MILLIMETER) 2. DRAWING NOT TO SCALE .090 .050 .035 RECOMMENDED SOLDER PAD LAYOUT FOR THICKER SOLDER PASTE APPLICATIONS R (DD7) 0212 REV F 3081f 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. For more information www.linear.com/LT3081 27 LT3081 TYPICAL APPLICATION High Efficiency Adjustable Supply VIN 6.3V TO 36V IN 15k 10µF 1000pF 63.4k RUN/SS BOOST VC LT3680 RT PG SYNC GND SW FB OUT LT3081 BD VIN 0.47µF 6.8µH 1k IMON TEMP 1k 590k 1µF 100k MTD2955 = MBRA340T3 6.04k 22µF ILIM SET 100k 1k 2N3904 1µF 10k 3081 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1185 3A Negative Low Dropout Regulator VIN: –4.5V to –35V, 0.8V Dropout Voltage, DD-Pak and TO-220 Packages LT1764/LT1764A 3A, Fast Transient Response, Low Noise LDO 340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.7V to 20V, TO-220, TSSOP and DD Packages, LT1764A Version Stable Also with Ceramic Capacitors LT1963/LT1963A 1.5A Low Noise, Fast Transient Response LDO 340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.5V to 20V, LT1963A Version Stable with Ceramic Capacitors, TO-220, DD, TSSOP, SOT-223 and SO-8 Packages LT1965 1.1A, Low Noise, Low Dropout Linear Regulator 290mV Dropout Voltage, Low Noise: 40µVRMS, VIN: 1.8V to 20V, VOUT: 1.2V to 19.5V, Stable with Ceramic Capacitors, TO-220, DDPak, MSOP and 3mm × 3mm DFN Packages LT3022 1A, Low Voltage, VLDO Linear Regulator VIN: 0.9V to 10V, Dropout Voltage: 145mV Typical, Adjustable Output (VREF = VOUT(MIN) = 200mV), Stable with Low ESR, Ceramic Output Capacitors, 16-Pin DFN (5mm × 3mm) and 16-Lead MSOP Packages LT3070 5A, Low Noise, Programmable VOUT, 85mV Dropout Linear Regulator with Digital Margining Dropout Voltage: 85mV, Digitally Programmable VOUT: 0.8V to 1.8V, Digital Output Margining: ±1%, ±3% or ±5%, Low Output Noise: 25µVRMS (10Hz to 100kHz), Parallelable: Use Two for a 10A Output, Stable with Low ESR Ceramic Output Capacitors (15µF Minimum), 28-Lead 4mm × 5mm QFN Package LT3071 5A, Low Noise, Programmable VOUT, 85mV Dropout Linear Regulator with Analog Margining Dropout Voltage: 85mV, Digitally Programmable VOUT: 0.8V to 1.8V, Analog Margining: ±10%, Low Output Noise: 25µVRMS (10Hz to 100kHz), Parallelable: Use Two for a 10A Output, IMON Output Current Monitor, Stable with Low ESR Ceramic Output Capacitors (15µF Minimum) 28-Lead 4mm × 5mm QFN Package LT3080/LT3080-1 1.1A, Parallelable, Low Noise, Low Dropout Linear Regulator 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, DD-Pak, SOT-223, MS8E and 3mm × 3mm DFN-8 Packages; LT3080-1 Version Has Integrated Internal Ballast Resistor LT3082 200mA, Parallelable, Single Resistor, Low Dropout Linear Regulator Outputs May Be Paralleled for Higher Output, Current or Heat Spreading, Wide Input Voltage Range: 1.2V to 40V Low Value Input/Output Capacitors Required: 2.2µF, Single Resistor Sets Output Voltage 8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm × 3mm DFN Packages LT3085 500mA, Parallelable, Low Noise, Low Dropout Linear Regulator 275mV 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, MS8E and 2mm x 3mm DFN-6 packages LTC3026 1.5A, Low Input Voltage VLDO Linear Regulator 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-E and DFN-10 Packages LT3083 Adjustable 3A Single Resistor Low Dropout Regulator Low Noise: 40µVRMS, 50µA Set Pin Current, Output Adjustable to 0V, Wide input Voltage Range: 1.2V to 23V (DD-Pak and TO-220), Low Dropout Operation: 310mV (2 Supplies) 3081f 28 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT3081 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3081 LT 0513 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2013