LT3089 800mA 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: 800mA 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: 1A/C Output Adjustable to 0V 50A SET Pin Current: 1% Initial Accuracy Output Voltage Noise: 27VRMS 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 x 4mm DFN, 16-Lead TSSOP, and 7-Lead DD-Pak n n n n The LT3089's precision 50A reference current source allows a single resistor to program output voltage to any level between zero and 34.5V. The current reference architecture enables load regulation to be independent of output voltage. The LT3089 is stable with or without input and output capacitors. The output current monitor (IOUT/5000) and die junction temperature output (1A/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 LT3089 is offered in the 12-lead 4mm x 4mm DFN and 16-lead TSSOP (both with exposed pad for improved thermal performance), and 7-lead DD-Pak power package. APPLICATIONS n The LT(R)3089 is an 800mA 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 LT3089 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. 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 1A/C 50A + - IMON TEMP SET 1k 1k 30.1k OUT ILIM 10F* 4.12k 499* IOUT 1.5V 0.75A 3089 TA01a *OPTIONAL SET PIN CURRENT (A) ILOAD/5000 50.3 IN LT3089 ILOAD = 3mA 50.2 50.1 50.0 49.9 49.8 49.7 49.6 49.5 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 3089 TA01b 3089f For more information www.linear.com/LT3089 1 LT3089 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........................................ -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) FE, R Packages Only.......................................... 300C PIN CONFIGURATION TOP VIEW TOP VIEW OUT 1 16 OUT OUT 2 15 IN 3 14 IN OUT 1 12 IN OUT 2 11 IN OUT OUT 3 10 IN OUT 4 OUT 4 9 IN OUT 5 ILIM 6 11 TEMP SET 7 10 IMON OUT 8 9 13 OUT ILIM 5 8 TEMP SET 6 7 IMON DF PACKAGE 12-LEAD (4mm x 4mm) PLASTIC DFN TJMAX = 125C, JA = 41C/W, JC = 1.6C/W EXPOSED PAD (PIN 13) IS OUT, MUST BE SOLDERED TO PCB 17 OUT 13 IN 12 IN FRONT VIEW TAB IS OUT NC IN TEMP OUT IMON SET ILIM R PACKAGE 7-LEAD PLASTIC DD OUT FE PACKAGE 16-LEAD PLASTIC TSSOP TJMAX = 125C, JA = 35C/W, JC = 2.3C/W EXPOSED PAD (PIN 17) IS OUT, MUST BE SOLDERED TO PCB 7 6 5 4 3 2 1 TJMAX = 125C, JA = 34C/W, JC = 3C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3089EDF#PBF LT3089EDF#TRPBF 3089 12-Lead (4mm x 4mm) Plastic DFN -40C to 125C LT3089IDF#PBF LT3089IDF#TRPBF 3089 12-Lead (4mm x 4mm) Plastic DFN -40C to 125C LT3089EFE#PBF LT3089EFE#TRPBF 3089FE 16-Lead Plastic TSSOP -40C to 125C LT3089IFE#PBF LT3089IFE#TRPBF 3089FE 16-Lead Plastic TSSOP -40C to 125C LT3089ER#PBF LT3089ER#TRPBF LT3089R 7-Lead Plastic DD-Pak -40C to 125C LT3089IR#PBF LT3089IR#TRPBF LT3089R 7-Lead Plastic DD-Pak -40C to 125C 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/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 2 3089f For more information www.linear.com/LT3089 LT3089 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C. (Note 2) PARAMETER CONDITIONS ISET SET Pin Current VOS Offset Voltage (VOUT - VSET) ISET Load Regulation VOS Load Regulation (Note 7) MIN TYP MAX UNITS VIN = 2V, ILOAD = 3mA 2V VIN 36V, 3mA ILOAD 800mA l 49.5 48.75 50 50 50.5 51.25 A A VIN = 2V, ILOAD = 3mA VIN = 2V, ILOAD = 3mA l -1.5 -3.5 0 0 1.5 3.5 mV mV ILOAD = 3mA to 800mA ILOAD = 3mA to 800mA Line Regulation ISET VOS -0.1 nA DF, FE Packages l -0.5 -3 mV R Package l -1.5 -4 mV VIN = 2V to 36V, ILOAD = 3mA VIN = 2V to 36V, ILOAD = 3mA 1.5 0.001 nA/V mV/V Minimum Load Current (Note 3) 2V VIN 36V l 1.1 3 Dropout Voltage (Note 4) ILOAD = 100mA ILOAD = 800mA l 1.21 1.47 1.65 VIN = 5V, VSET = 0V, VOUT = -0.1V l 0.8 1 l 155 175 l 130 160 Internal Current Limit ILIM Programming Ratio ILIM Minimum Output Current Resistance mA V V A 210 mA/k 190 A 300 IMON Full-Scale Output Current ILOAD = 800mA IMON Scale Factor 100mA ILOAD 800mA 200 IMON Operating Range l VOUT - 40V A/A VOUT + 0.4V TJ > 5C TEMP Output Current Absolute Error (Note 9) 0C <TJ 125C 125C <TJ 150C Reference Current RMS Output Noise (Note 5) 10Hz f 100kHz 5.7 nARMS Error Amplifier RMS Output Noise (Note 5) ILOAD = 800mA, 10Hz f 100kHz, COUT =10F, CSET = 0.1F 27 VRMS Ripple Rejection VRIPPLE = 0.5VP-P, ILOAD = 0.1A, CSET = 0.1F, COUT=10F, 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 LT3089 is tested and specified under pulse load conditions such that TJ TA. The LT3089E is tested at TA = 25C and performance is guaranteed from 0C to 125C. Performance of the LT3089E over the full -40C and 125C operating temperature range is assured by design, characterization, and correlation with statistical process controls. The LT3089I is guaranteed over the full -40C to 125C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is degraded at junction temperatures greater than 125C. 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. 1 V TEMP Output Current (Note 9) -10 -15 75 A/C 10 15 0.003 A A %/W Note 4: For the LT3089, dropout is specified as the minimum input-tooutput voltage differential required supplying a given output current. 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 400 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. 3089f For more information www.linear.com/LT3089 3 LT3089 TYPICAL PERFORMANCE CHARACTERISTICS SET Pin Current SET Pin Current 50.5 2.0 N = 1297 ILOAD = 3mA 50.4 TJ = 25C unless otherwise specified. ILOAD = 3mA 1.5 OFFSET VOLTAGE (mV) 50.3 SET PIN CURRENT (A) Offset Voltage (VOUT - VSET) 50.2 50.1 50.0 49.9 49.8 49.7 1.0 0.5 0 -0.5 -1.0 -1.5 49.6 49.5 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 49 49.5 50 50.5 SET PIN CURRENT DISTRIBUTION (A) -2.0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 51 3089 G02 3089 G01 Offset Voltage 1.0 N = 1297 3089 G03 Offset Voltage (VOUT OUT - VSET SET) 0.4 ILOAD = 3mA 0.8 0.0 OFFSET VOLTAGE (mV) 0.6 OFFSET VOLTAGE (mV) Offset Voltage (VOUT OUT - VSET SET) 0.4 0.2 0.0 -0.2 -0.4 -0.4 TJ = 125C -0.8 TJ = 25C -1.2 -0.6 -0.8 -1 0 1 VOS DISTRIBUTION (mV) -1.0 2 0 6 12 18 24 30 INPUT-TO-OUTPUT DIFFERENTIAL (V) 3089 G04 0 0.1 0.2 0.3 0.4 0.5 0.6 LOAD CURRENT (A) -25 -1.0 -50 -1.5 -75 -2.0 -100 -2.5 -125 ILOAD = 3mA to 800mA -150 -3.0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) MINIMUM LOAD CURRENT (mA) -0.5 1.7 1.25 1.6 1.00 0.50 VIN - VOUT = 36V VIN - VOUT = 2V 0.25 1.5 1.4 1.3 1.2 TJ = -50C TJ = 25C TJ = 125C 1.1 0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 3089 G08 3089 G07 0.8 Dropout Voltage 1.50 0.75 0.7 3089 G06 Minimum Load Current 0 SET PIN CURRENT LOAD REGULATION (nA) OFFSET VOLTAGE LOAD REGULATION (mV) -1.6 3089 G05 Load Regulation 0 4 36 DROPOUT VOLTAGE (V) -2 1.0 0 0.1 0.2 0.3 0.4 0.5 0.6 LOAD CURRENT (A) 0.7 0.8 3089 G09 3089f For more information www.linear.com/LT3089 LT3089 TYPICAL PERFORMANCE CHARACTERISTICS Internal Current Limit 1.50 1.6 1.25 1.5 ILOAD = 800mA 1.4 1.3 1.2 ILOAD = 3mA 1.0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 1.00 0.75 0.50 Programmable Programmable Current Current Limit Limit 0.6 0.4 0.2 0 RILIM = 3.01k 0.4 RILIM = 1.50k 0.2 VIN = 7V VOUT = 0V 6 12 18 24 30 INPUT-TO-OUTPUT DIFFERENTIAL (V) 0.6 0.4 RILIM 1.50k 0.95 RILIM 3.01k RILIM 4.53k 0.4 0.2 0.2 0 1 2 3 4 RILIM (k) 3089 G13 TEMP TEMP Pin Pin Current Current 200 160 RSET = 20k TJ = 25C 1.00 0.8 0 0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) TJ = 25C VIN = 7V VOUT = 0V 1.0 36 Programmable ProgrammableCurrent CurrentLimit Limit 1.05 OUTPUT VOLTAGE (V) RILIM = 4.53k 0 3089 G12 Programmable Current Limit 1.2 PROGRAMMED CURRENT LIMIT (A) PROGRAMMED CURRENT LIMIT (A) 0.8 3089 G11 1.0 5 0 6 0 0.25 0.50 0.75 OUTPUT CURRENT (A) 1 3089 G15 3089 G14 IMON MON Pin Current 25 Pin Line Line Regulation Regulation IIMON MON Pin 180 140 160 100 80 60 40 20 IMON PIN CURRENT (A) 120 IMON PIN CURRENT (A) TEMP PIN CURRENT (A) 1.0 0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 3089 G10 0.6 VIN = 7V VOUT = 0V 0.25 1.1 0.8 Internal Current Limit 1.2 CURRENT LIMIT (A) 1.7 CURRENT LIMIT (A) DROPOUT VOLTAGE (V) Dropout Voltage TJ = 25C unless otherwise specified. 140 120 100 80 60 40 20 15 10 5 20 0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 3089 G16 0 0 0.1 0.2 0.3 0.4 0.5 0.6 LOAD CURRENT (A) 0.7 0.8 3089 G17 0 ILOAD = 100mA 0 6 12 18 24 30 36 INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V) 3089 G18 3089f For more information www.linear.com/LT3089 5 LT3089 TYPICAL PERFORMANCE CHARACTERISTICS Linear Regulator Linear Regulator Load Transient Response OUTPUT VOLTAGE DEVIATION (mV) -50 100 0 VIN = 3V VOUT = 1V COUT = 2.2F CSET = 0.1F 0 ILOAD = 5mA TO 100mA -100 0 -200 ILOAD = 100mA TO 800mA 1.0 0.5 0 20 40 60 80 100 120 140 160 180 200 TIME (s) 0 20 40 60 80 100 120 140 160 180 200 TIME (s) Linear Regulator Load LoadTransient TransientResponse Response 0 10 20 30 40 50 60 70 80 90 100 TIME (s) Current Source Line Line Transient Transient Response Response INPUT VOLTAGE (V) 6 RSET = 20k RLOAD = 1.25 COUT = 2.2F CSET = 0.1F 5 4 3 RSET = 6.04k ROUT = 3.01 COUT = 0 CSET = 30pF 5 4 3 tr = tf = 1s 0.5 0 0 -20 -40 10 20 30 40 50 60 70 80 90 100 TIME (s) 0 5 3 INPUT VOLTAGE (V) RSET = 6.04k ROUT = 0.6 COUT = 0 CSET = 30pF 500mA CURRENT SOURCE CONFIGURATION 520 95 90 10 15 20 25 30 35 40 45 50 TIME (s) 4 3 3 2 RSET = 20k RLOAD = 1.25 COUT = 2.2F CERAMIC CSET = 0 1 10 20 30 40 50 60 70 80 90 100 TIME (s) 3089 G25 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 0 0.5 0 -0.5 0 5 10 15 20 25 30 35 40 45 50 TIME (s) 3089 G26 2 RSET = 20k RLOAD = 1.25 COUT = 2.2F CERAMIC CSET = 0.1F 1 0 1.0 490 10 20 30 40 50 60 70 80 90 100 TIME (s) Linear Regulator Turn-On Turn-OnResponse Response 4 0 510 500 0 3089 G24 Linear Regulator Turn-On Turn-OnResponse Response 6 4 100 3089 G23 Current Source Line Transient Response 5 105 OUTPUT CURRENT (mA) 1.0 20 3089 G22 INPUT VOLTAGE (V) ILOAD = 5mA TO 100mA 3089 G21 INPUT VOLTAGE (V) LOAD CURRENT (mA) -400 OUTPUT CURRENT (mA) -100 100mA CURRENT SOURCE CONFIGURATION ILOAD = 100mA TO 800mA OUTPUT VOLTAGE DEVIATION (mV) OUTPUT VOLTAGE DEVIATION (mV) 0 -200 6 tr = tf = 1s 0 6 600 200 100 Linear Regulator LineTransient TransientResponse Response Line VIN = 3V VOUT = 1V COUT = 0 CSET = 30pF VIN = 3V VOUT = 1V COUT = 0 CSET = 30pF -100 3089 G20 3089 G19 400 0 INPUT VOLTAGE (V) 100 100 -200 LOAD CURRENT (mA) -100 -100 LOAD CURRENT (mA) 200 LOAD CURRENT (mA) OUTPUT VOLTAGE DEVIATION (mV) 0 200 VIN = 3V VOUT = 1V COUT = 2.2F CSET = 0.1F OUTPUT VOLTAGE DEVIATION (mV) 300 50 480 Linear Regulator Load Transient Transient Response Response Load Load Transient Response 100 0 TJ = 25C unless otherwise specified. 1.0 0.5 0 -0.5 0 2 4 6 8 10 12 14 16 18 20 TIME (ms) 3089 G27 3089f For more information www.linear.com/LT3089 LT3089 TYPICAL PERFORMANCE CHARACTERISTICS Current Source Turn-On Turn-OnResponse Response 4 3 3 RSET = 6.04k ROUT = 3.01 COUT = 0 CSET = 30pF 1 100 50 0 0 1000 RSET = 6.04k ROUT = 0.6 COUT = 0 CSET = 30pF 2 1 500mA CURRENT SOURCE CONFIGURATION 600 400 10 20 30 40 50 60 70 80 90 100 TIME (s) 0 30 ILOAD = 100mA ILOAD = 500mA ILOAD = 800mA 10 0 10 100 1k 10k 100k FREQUENCY (Hz) 80 60 40 VIN = VOUT + 5V VIN = VOUT + 2V VIN = VOUT + 1.5V 20 1M 10M 0 10 100 VOUT RTEST 0 0.5 1 1.5 2 2.5 3 3.5 RTEST (k) 4 4.5 5 3089 G30 Output Impedance CURRENT SOURCE CONFIGURATION 1M 100k 10k 1k 100 ISOURCE = 10mA ISOURCE = 100mA ISOURCE = 500mA 10 1k 10k 100k FREQUENCY (Hz) 1M 3089 G31 10M 1 10 100 1k 10k 100k FREQUENCY (Hz) 3089 G32 1M 10M 3089 G33 Ripple Rejection (10kHz) Ripple Rejection (120Hz) 95 70 90 RIPPLE REJECTION (dB) 20 VIN 10M OUTPUT IMPEDANCE () 40 SET PIN = 0V 300 0 COUT = 2.2F CERAMIC CSET = 0.1F ILOAD = 100mA 100 RIPPLE REJECTION (dB) 50 RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) 60 400 10 20 30 40 50 60 70 80 90 100 TIME (s) Ripple Ripple Rejection Rejection 70 500 100 120 COUT = 2.2F CERAMIC CSET = 0.1F VIN = VOUT(NOMINAL) + 2V 80 600 3089 G29 Ripple Rejection 90 700 200 3089 G28 100 800 200 0 VIN = 5V VIN = 36V 900 0 100mA CURRENT SOURCE CONFIGURATION OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 0 Residual Output Voltage with Less Less Than Than Minimum Minimum Load Load OUTPUT VOLTAGE (mV) 4 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Current Source Turn-On Turn-On Response Response 2 TJ = 25C unless otherwise specified. 85 80 75 70 VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 120Hz ILOAD = 100mA COUT = 2.2F CSET = 0.1F 65 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 65 60 55 VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 10kHz ILOAD = 100mA COUT = 2.2F CSET = 0.1F 50 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 3089 G34 3089 G35 3089f For more information www.linear.com/LT3089 7 LT3089 TYPICAL PERFORMANCE CHARACTERISTICS Ripple Rejection Ripple Rejection Rejection (1MHz) (1MHz) Ripple 45 90 80 RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) 43 41 39 VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 1MHz ILOAD = 100mA COUT = 2.2F CSET = 0.1F 37 TJ = 25C unless otherwise specified. ILOAD = 800mA CLOAD = 2.2F 70 60 50 40 30 10kHz 100kHz 1MHz 20 35 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C) 10 1 1.5 2 2.5 3 3.5 4 4.5 5 INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V) 3089 G36 3089 G37 10Hz to 100kHz Output Voltage Noise Noise Spectral Density 1000 10 100 REFERENCE CURRENT NOISE SPECTRAL DENSITY (pA/Hz) ERROR AMPLIFIER NOISE SPECTRAL DENSITY (nV/Hz) 100 CSET = 0.1F COUT = 4.7F ILOAD = 800mA VOUT 100V/DIV NOISE INDEPENDENT OF OUTPUT VOLTAGE 1ms/DIV 10 10 100 1k 10k FREQUENCY (Hz) 3089 G39 1 100k 3089 G38 8 3089f For more information www.linear.com/LT3089 LT3089 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 LT3089 requires a 3mA 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 1A/C for temperatures above 5C. The TEMP pin output current typically equals 25A at 25C. 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 175mA/k with a 300 offset. If programmable current limit is not used, leave this pin open; the internal current limit of the LT3089 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 200A per amp of output current. Terminating this pin with a resistor to GND produces a voltage proportional to ILOAD. For example, at ILOAD = 800mA, IMON typically sources 160A. With a 1k resistor to GND, this produces 160mV. 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 50A 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 package are tied internally to OUT. As such, tie them directly to OUT (Pins 1-4/Pins 1-5, 8, 9, 16/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. BLOCK DIAGRAM IN 50A + CURRENT MONITOR IMON = ILOAD/5000 IMON TEMPERATURE DEPENDENT CURRENT SOURCE 1A/C TEMP - PROGRAMMABLE CURRENT LIMIT SET ILIM OUT 3089 BD 3089f For more information www.linear.com/LT3089 9 LT3089 APPLICATIONS INFORMATION Introduction The LT3089 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 LT3089 is extended, allowing for use in harsh industrial and automotive environments where sudden spikes in input voltage lead to high power dissipation. The LT3089 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 50A 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 0, 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 LT3089, 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. 10 The LT3089 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 100mA of load current, the IMON pin sources 20A 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 0C, the TEMP pin sources a current equal to 1A/C. This pin operates normally during output short-circuit conditions. Programming Linear Regulator Output Voltage The LT3089 generates a 50A 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 50A multiplied by the value of the SET pin resistor. Any voltage can be generated and there is no minimum output voltage for the regulator. LT3089 IN CIN 50A + - SET OUT VOUT = 50A * RSET CSET RSET COUT RLOAD 3089 F01 Figure 1. Basic Adjustable Regulator 3089f For more information www.linear.com/LT3089 LT3089 APPLICATIONS INFORMATION 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 3mA. For true zero voltage output operation, return this 3mA load current to a negative output voltage. Table 1. 1% Resistors for Common Output Voltages VOUT (V) RSET (k) 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 50A 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. 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. 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. Configuring the LT3089 as a Current Source Setting the LT3089 to operate as a 2-terminal current source is a simple matter. The 50A 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. IN LT3089 OUT IOUT 3mA 50A VSET = 50A * RSET + - SET OUT + VSET SET PIN ROUT IOUT 3089 F02 Figure 2. Guard Ring Layout Example of DF Package VSET 50A * RSET = ROUT ROUT 3089 F03 RSET - GND IOUT = Figure 3. Using the LT3089 as a Current Source 3089f For more information www.linear.com/LT3089 11 LT3089 APPLICATIONS INFORMATION Again, the lower current levels used in the LT3089 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 LT3089 is determined by the ratio of RSET to ROUT, those resistors should have matching temperature characteristics. Less expensive resistors made from the same material provide matching temperature coefficients. See resistor manufacturers' data sheets for more details. 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. 12 Programming Current Limit Externally A resistor placed between ILIM and OUT on the LT3089 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/175mA/k + 300 The resistor for a 0.5A current limit is: RILIM = 0.5A/175mA/ k + 300 = 3.16k. Tolerance over temperature is 15%, so current limit is normally set 20% above maximum load current. The 300 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 LT3089'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 1A 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 LT3089 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 LT3089. 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 LT3089 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 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 LT3089 instability, but is a common ceramic input bypass capacitor application issue. 3089f For more information www.linear.com/LT3089 LT3089 APPLICATIONS INFORMATION 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 LT3089 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 LT3089 also stabilizes the application. As little as 0.1 to 0.5, 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 LT3089 does not require an output capacitor for stability. LTC recommends an output capacitor of 10F with an ESR of 0.5 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 LT3089, increase the effective output capacitor value. For improvement in transient performance, place a capacitor across the voltage setting resistor. Capacitors up to 1F 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 LT3089 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 LT3089 without requiring capacitors to frequency compensate the circuit. Figure 3 highlights the simplicity of using the LT3089 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 LT3089, 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. Although the LT3089'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 LT3089 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 LT3089 application. 3089f For more information www.linear.com/LT3089 13 LT3089 APPLICATIONS INFORMATION In LT3089 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 LT3089 are complex enough such that series damping resistors are 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 100 to 5k. Once again, Linear Technology strongly recommends testing stability in situ for any LT3089 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 LT3089 current source to GND, it may be necessary to bypass the top of the current source with a capacitor to GND. In some cases, this capacitor may already exist and no additional capacitance is required. For example, if the LT3089 was used as a variable current source on the output of a power supply, the output bypass capacitance would suffice to provide LT3089 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. LONG LINE REACTANCE/INDUCTANCE IN LT3089 RCOMP RSERIES 50A IN LT3089 CCOMP OR + - 50A + - SET RSET SET OUT RSET CCOMP OUT ROUT 3089 F05 ROUT Figure 5. Compensation from Input to Output of Current Source Provides Stability 3089 F04 RSERIES LONG LINE REACTANCE/INDUCTANCE Figure 4. Adding Series Resistance Decouples and Dampens Long Line Reactances 14 3089f For more information www.linear.com/LT3089 LT3089 APPLICATIONS INFORMATION In some extreme cases, capacitors or series RC networks may be required on both the LT3089'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 0.1F to 1F 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 IN LT3089 CIN 50A + - SET RSET OUT ROUT IOUT COUT OR ROUT COUT 3089 F06 Figure 6. Input and/or Output Capacitors May Be Used for Compensation Using Ceramic Capacitors 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 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 10F Y5V capacitor can exhibit an effective value as low as 1F to 2F 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. 40 20 X5R 0 -20 -40 Y5V -60 -80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F 0 CHANGE IN VALUE (%) CHANGE IN VALUE (%) 20 50 25 75 0 TEMPERATURE (C) -40 -60 Y5V -80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F -100 -50 -25 X5R -20 100 125 -100 0 3089 F07 Figure 7. Ceramic Capacitor Temperature Characteristics 2 4 8 6 10 12 DC BIAS VOLTAGE (V) 14 16 3089 F08 Figure 8. Ceramic Capacitor DC Bias Characteristics 3089f For more information www.linear.com/LT3089 15 LT3089 APPLICATIONS INFORMATION 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. LT3089 IN 50A + - OUT SET Paralleling Devices Higher output current is obtained by paralleling multiple LT3089s 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. LT3089 IN VIN 4.8V TO 40V 50A + - 1F SET 33k Table 2. PC Board Trace Resistance WEIGHT (oz) 10mil WIDTH 1 54.3 2 27.1 Trace resistance is measured in m/in. OUT 20m 10F VOUT 3.3V 1.6A 3089 F09 20mil WIDTH 27.1 13.6 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 LT3089 has a small 20m ballast resistor, which at full output current gives better than 80% equalized sharing of the current. The external resistance of 20m (10m for the two devices in parallel) only adds about 16mV of output regulation drop at an output of 1.6A. Even with an output voltage as low as 1V, this only adds 1.6% to the regulation. Of course, paralleling more than two LT3089s 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. 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 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). 16 20m Figure 9. Parallel Devices Quieting the Noise The LT3089 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. 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 LT3089 does not use a traditional voltage reference like other linear regulators. Instead, it uses a 50A reference current. The 50A 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. 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 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. 3089f For more information www.linear.com/LT3089 LT3089 APPLICATIONS INFORMATION The LT3089 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 LT3089'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(27VRMS 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 LT3089 IN 50A + - PARASITIC RESISTANCE SET OUT RSET RP RP LOAD RP 3089 F10 Figure 10. Connections for Best Load Regulation TEMP Pin Operation (Die Temperature Monitor) The TEMP pin of the LT3089 outputs a current proportional to average die temperature. At 25C, the current from the TEMP pin is 25A, with a slope of 1A/C. The current out of the TEMP pin is valid for junction temperatures above 0C (absent initial offset considerations). Below 0C, 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 0C to 150C. The LT3089 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). 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. Connected as shown, system load regulation is the sum of the LT3089'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. The LT3089'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 short-circuit conditions. IMON Pin Operation (Current Monitor) 3089f For more information www.linear.com/LT3089 17 LT3089 APPLICATIONS INFORMATION 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 160mV indicates 0A to 800mA of load current. Compensating for Cable Drops with IMON The IMON pin can compensate for resistive drops in wires or cables between the LT3089 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. OUT IN RCABLE2 0.02 LT3089 SET CIN 1F IMON RSET 29.8k RCOMP 200 COUT 10F RCABLE 0.02 LOAD 3089 F11 RCOMP = 5000 * RCABLE(TOTAL) VOUT(LOAD) = 50A (RSET + RCOMP) 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. 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 package 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 TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 21C/W 1000mm2 2500mm2 2500mm2 24C/W 225mm2 2500mm2 2500mm2 30C/W 100mm2 2500mm2 2500mm2 35C/W *Device is mounted on topside Figure 11. Using IMON to Compensate for Cable Drops Table 4. FE Package, 16-Lead TSSOP COPPER AREA Thermal Considerations The LT3089's internal power and thermal limiting circuitry protects itself under overload conditions. For continuous normal load conditions, do not exceed the 125C (E- and I-grades) maximum junction temperature. Carefully consider all sources of thermal resistance from junctionto-ambient. This includes (but is not limited to) junctionto-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. Surface mount packages provide the necessary heat sinking by using the heat spreading capabilities of the 18 TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 18C/W 1000mm2 2500mm2 2500mm2 22C/W 225mm2 2500mm2 2500mm2 27C/W 100mm2 2500mm2 2500mm2 32C/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 13C/W 1000mm2 2500mm2 2500mm2 14C/W 225mm2 2500mm2 2500mm2 16C/W *Device is mounted on topside 3089f For more information www.linear.com/LT3089 LT3089 APPLICATIONS INFORMATION 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 2318A's board layout using multiple inner VOUT planes and multiple thermal vias achieves 17C/W performance for the DF package. Calculating Junction Temperature Example: Given an output voltage of 0.9V, an IN voltage of 2.5V 5%, output current range from 10mA to 0.8A and a maximum ambient temperature of 50C, what is the maximum junction temperature for the DD-Pak on a 2500mm2 board with topside copper of 1000mm2? Reducing Power Dissipation In some applications it may be necessary to reduce the power dissipation in the LT3089 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 LT3089's IN-to-OUT differential voltage and correspondingly decreases the LT3089's power dissipation. As an example, assume: VIN = 7V, VOUT = 3.3V and IOUT(MAX) = 0.8A. Use the formulas from the Calculating Junction Temperature section previously discussed. Without series resistor RS, power dissipation in the LT3089 equals: PTOTAL = (7V - 3.3V) * 0.8A = 2.96W If the voltage differential (VDIFF) across the LT3089 is chosen as 1.5V, then RS equals: RS = The power in the circuit equals: 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 = 0.8A, TA = 50C Power dissipation under these conditions equals: 7V - 3.3V - 1.5V = 2.8 0.8A Power dissipation in the LT3089 now equals: PTOTAL = 1.5V * 0.8A = 1.2W The LT3089's power dissipation is now only 40% compared to no series resistor. RS dissipates 1.8W of power. Choose appropriate wattage resistors or use multiple resistors in parallel to handle and dissipate the power properly. PTOTAL = (VIN - VOUT)(IOUT) VIN RS PTOTAL = (2.625V - 0.9V)(0.8A) = 1.38W VIN Junction Temperature equals: TJ = TA + PTOTAL * JA (using tables) C1 IN LT3089 50A + - TJ = 50C + 1.38W * 14C/W = 69.3C In this case, the junction temperature is below the maximum rating, ensuring reliable operation. SET RSET OUT C2 VOUT 3089 F12 Figure 12. Reducing Power Dissipation Using a Series Resistor 3089f For more information www.linear.com/LT3089 19 LT3089 APPLICATIONS INFORMATION The second technique for reducing power dissipation, shown in Figure 13, uses a resistor in parallel with the LT3089. This resistor provides a parallel path for current flow, reducing the current flowing through the LT3089. 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. VIN C1 IN LT3089 50A RP + - SET OUT RSET VOUT C2 3089 F13 Figure 13. Reducing Power Dissipation Using a Parallel Resistor RP dissipates 0.85W of power. As with the first technique, choose appropriate wattage resistors to handle and dissipate the power properly. With this configuration, the LT3089 supplies only 0.43A. Therefore, load current can increase by 0.37A to a total output current of 1.17A while keeping the LT3089 in its normal operating range. Protection Features The LT3089 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 LT3089 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 165C and incorporates about 5C of hysteresis. As an example, assume: VIN = 5V, VIN(MAX) = 5.5V, VOUT = 3.3V, VOUT(MIN) = 3.2V, IOUT(MAX) = 0.8A and IOUT(MIN) = 0.4A. Also, assuming that RP carries no more than 90% of IOUT(MIN) = 360mA. The LT3089'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 100A), protecting the LT3089 and sensitive loads. Calculating RP yields: Clamping diodes and 400 limiting resistors protect the LT3089'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. RP = 5.5V - 3.2V = 6.39 0.36A (5% Standard value = 6.2) The maximum total power dissipation is: (5.5V - 3.2V) * 0.8A = 1.84W However, the LT3089 supplies only: 0.8A - 5.5V - 3.2V = 0.43A 6.2 Therefore, the LT3089's power dissipation is only: PDISS = (5.5V - 3.2V) * 0.43A = 0.99W 20 3089f For more information www.linear.com/LT3089 LT3089 TYPICAL APPLICATIONS Paralleling Regulators VIN IN LT3089 ISET 50A + - IMON OUT 20m OUT 20m VOUT 3V 1.6A ILIM SET TEMP 1k IN LT3089 ISET 50A + - IMON SET TEMP 3.01k 1k RSET 30.1k 1k 3089 TA02 ILIM Using IMON Cancels Ballast Resistor Drop VIN IN LT3089 ISET 50A + - IMON SET TEMP OUT RBALLAST 20m OUT RBALLAST 20m ILIM VOUT 1.5V 1.6A 1k IN LT3089 ISET 50A + - IMON SET TEMP RSET 15k ILIM 3089 TA03 1k RCOMP 50 3089f For more information www.linear.com/LT3089 21 LT3089 TYPICAL APPLICATIONS Load Sharing Without Ballast Resistors VIN 3V TO 18V 22F IN OUT IN 22F LT3089 SET 0.1F 20k OUT OUT LT3089 IMON 5.1k 20k 0.1F LT3089 IMON SET 1k IN SET 1k 0.1F 100k 20k VOUT 1V 2.4A IMON 1k 100k + + 1/2 LT1638 1/2 LT1638 5.1k - - 0.47F 0.47F 5.1k 5.1k 3089 TA04 Load Current Sharing Without Ballasting VOUT 1V 1.6A VIN 3V TO 36V 4.7F IN OUT LT3089 100 IMON SET 0.1F ILIM OUT 2.2F 20k ILIM IMON IN LT3089 SET 20k = 2N3904 1k 0.1F 1k 3089 TA05 22 3089f For more information www.linear.com/LT3089 LT3089 TYPICAL APPLICATIONS Boosting Fixed Output Regulators IN LT3089 ISET 50A + - IMON 5V OUT 20m ILIM SET TEMP 20m LT1963-3.3 3.3VOUT 2.3A 8.2* 10F 47F 3089 TA06 6.2k *4mV DROP ENSURES LT3089 IS OFF WITH NO LOAD MULTIPLE LT3089s CAN BE USED Reference Buffer VIN IN LT3089 ISET 50A + - IMON SET TEMP 1k INPUT LT1019 OUT VOUT ILIM 1k 1k* 47F OUTPUT 1F GND *MIN LOAD 3mA 3089 TA07 Adding Soft-Start VIN 4.8V TO 36V IN LT3089 10F ISET 50A + - 1N4148 IMON OUT SET TEMP 1k ILIM 1k VOUT 3.3V 0.8A 10F 3089 TA08 0.1F 66.5k 3089f For more information www.linear.com/LT3089 23 LT3089 TYPICAL APPLICATIONS Using a Lower Value Set Resistor VIN 12V 4.7F IN LT3089 ISET 50A + - IMON OUT SET TEMP 1k 4.02k VOUT 0.2V TO 10V ILIM 1k 40.2 4.7F 3089 TA09 RSET 2k VOUT = 0.2V + 5mA * RSET Using an External Reference Current VIN 1F LT3092 IN 10A ISET 50A + - SET 20k IN LT3089 + - OUT OUT 215 IMON SET TEMP 1k 1k ILIM VOUT 0V TO 20V 1F 3089 TA10 20k 24 1mA 3089f For more information www.linear.com/LT3089 LT3089 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3089#packaging for the most recent package drawings. DF Package 12-Lead Plastic DFN (4mm x 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 x 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 3089f For more information www.linear.com/LT3089 25 LT3089 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3089#packaging for the most recent package drawings. FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev K) 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 FRAME FEATURE FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 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 26 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 K 0913 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 3089f For more information www.linear.com/LT3089 LT3089 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3089#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 3089f 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/LT3089 27 LT3089 TYPICAL APPLICATION High Efficiency Adjustable Supply VIN 6.3V TO 36V VIN BD RUN/SS BOOST 15k 63.4k 1000pF VC RT PG LT3680 SYNC GND 0.47F SW IN 6.8H 47F MBRA340T3 590k OUT 6.04k 6V MTD2955 FB LT3089 1k IMON TEMP 1k 15k 22F SET ILIM 500k VOUT 0V TO 25V, 0.8A 0.1F 10k 1F 1k 1F 2N3904 3089 TA11 CMDSH-4E RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1764/ LT1764A 3A, Fast Transient Response, Low Noise LDO 340mV Dropout Voltage, Low Noise: 40VRMS, VIN = 2.7V to 20V, TO-220, TSSOP and DD-Pak, LT1764A Version Stable Also with Ceramic Capacitors LT1963/ LT1963A 1.5A Low Noise, Fast Transient Response LDO 340mV Dropout Voltage, Low Noise: 40VRMS, 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: 40VRMS, VIN: 1.8V to 20V, VOUT: 1.2V to 19.5V, Stable with Ceramic Capacitors, TO-220, DD-Pak, MSOP and 3mm x 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 x 3mm) and 16-Lead MSOP Packages LT3070/ LT3071 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: 25VRMS (10Hz to 100kHz), Parallelable: Use Two for a 10A Output, Stable with Low ESR Ceramic Output Capacitors (15F Minimum), 28-Lead 4mm x 5mm QFN Package. LT3071Has Analog Margining. LT3080/ LT3080-1 1.1A, Parallelable, Low Noise, Low Dropout Linear Regulator 300mV Dropout Voltage (2-Supply Operation), Low Noise: 40VRMS, 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 x 3mm DFN-8 Packages; LT3080-1 Version Has Integrated Internal Ballast Resistor LT3081 1.5A Single Resistor Rugged Linear Regulator with Monitors Extended Safe Operating Area (SOA). Output Current: 1.5A Stable with/without Input/Output Capacitors. VIN Range: 1.2V to 36V. 50A Set Pin Current: TSSOP-16, TO-220, DD-Pak, 4mm x 4mm DFN-12 Packages. 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: 2.2F, Single Resistor Sets Output Voltage 8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm x 3mm DFN Packages LT3085 500mA, Parallelable, Low Noise, Low Dropout Linear Regulator 275mV Dropout Voltage (2-Supply Operation), Low Noise: 40VRMS, 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 LT3092 200mA 2-Terminal Programmable Programmable 2-Terminal Current Source, Maximum Output Current = 200mA, Wide Input Voltage Current Source Range: 1.2V to 40V, Resistor Ratio Sets Output Current, Initial Set Pin Current Accuracy = 1%, Current Limit and Thermal Shutdown Protection, Reverse-Voltage Protection, Reverse-Current Protection, 8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm x 3mm DFN Packages. LT3083 Adjustable 3A Single Resistor Low Dropout Regulator 28 Low Noise: 40VRMS, 50A 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) 3089f Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT3089 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT3089 LT 0116 * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2016