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LT3081 1 3081f for more information www.linear.com/LT3081 typical application features description 1.5a single resistor rugged linear regulator with monitors the lt ? 3081 is a 1.5a low dropout linear regulator de- signed 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 LT3081s 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 makes load regulation independent of output voltage. the LT3081 is stable with or without input and output capacitors. the output current monitor (i out /5000) and die junction temperature output (1a/c) provide system monitoring and debug capability. in addition, a single resistor pro- grams 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. wide safe operating area supply applications n extended safe operating area n maximum output current: 1.5a n stable with or without input/output capacitors n wide input voltage range: 1.2v to 36v n single resistor sets output voltage n output current monitor: i mon = i out /5000 n junction temperature monitor: 1a/c n output adjustable to 0v n 50a set pin current: 1% initial accuracy n output voltage noise: 27v rms n parallel multiple devices for higher current or heat spreading n programmable current limit n reverse-battery and reverse-current protection n <1mv load regulation typical independent of v out n <0.001%/v line regulation typical n available in thermally-enhanced 12-lead 4mm 4mm dfn and 16-lead tssop, 7-lead dd-pak and 7-lead to-220 n all surface mount power supply n rugged industrial power supply n post regulator for switching supplies n low output voltage supply n 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. 3081 ta01a in set r set 30.1k r ilim 6.04k c out * 10f *optional temp r temp 1k r imon 1k i mon i lim out + ? LT3081 i set 50a i out 1.5v 1.5a v in r load * 5ma min temperature (c) ?50 49.5 set pin current (a) 49.6 49.8 49.9 50.0 50.5 50.2 0 50 75 3081 ta01b 49.7 50.3 50.4 50.1 ?25 25 100 125 150 i l = 5ma set pin current
LT3081 2 3081f for more information www.linear.com/LT3081 absolute maximum ratings 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, C 40v i lim pin voltage (relative to out) ......................... 0.2v i mon pin voltage (relative to out) ................... 1v, C 40v (note 1) all voltages relative to v out . top view 13 out df package 12-lead (4mm 4mm) plastic dfn 12 11 8 9 10 4 5 3 2 1 in in in in temp i mon out out out out i lim set 6 7 t jmax = 125c, v ja = 32c/w, v jc = 4c/w exposed pad (pin 13) is out, must be soldered to pcb fe package 16-lead plastic tssop 1 2 3 4 5 6 7 8 top view 16 15 14 13 12 11 10 9 out out out out out i lim set out out in in in in temp i mon out 17 out t jmax = 125c, v ja = 29c/w, v jc = 8c/w exposed pad (pin 17) is out, must be soldered to pcb r package 7-lead plastic dd front view tab is out nc in temp out i mon set i lim 7 6 5 4 3 2 1 t jmax = 125c, v ja = 15c/w, v jc = 3c/w t7 package 7-lead plastic to-220 tab is out nc in temp out i mon set i lim front view 7 6 5 4 3 2 1 t jmax = 125c, v ja = 40c/w, v jc = 3c/w pin configuration output short-circuit duration .......................... indefinite operating junction temperature range (note 2) e-, i-grades ....................................... C40c to 125c storage temperature range .................. C65c to 150c lead temperature (soldering, 10 sec) fe, r, t7 packages only ................................... 300c
LT3081 3 3081f for more information www.linear.com/LT3081 the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t j = 25c. (note 2) electrical characteristics 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 C40c to 125c LT3081idf#pbf LT3081idf#trpbf 3081 12-lead (4mm 4mm) plastic dfn C40c to 125c LT3081efe#pbf LT3081efe#trpbf 3081fe 16-lead plastic tssop C40c to 125c LT3081ife#pbf LT3081ife#trpbf 3081fe 16-lead plastic tssop C40c to 125c LT3081er#pbf LT3081er#trpbf LT3081r 7-lead plastic dd-pak C40c to 125c LT3081ir#pbf LT3081ir#trpbf LT3081r 7-lead plastic dd-pak C40c to 125c LT3081et7#pbf na LT3081t7 7-lead plastic to-220 C40c to 125c LT3081it7#pbf na LT3081t7 7-lead plastic to-220 C40c 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. 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/ parameter conditions min typ max units set pin current i set v in = 2v, i load = 5ma 2v v in 36v, 5ma i load 1.5a l 49.5 48.75 50 50 50.5 51.25 a a offset voltage v os (v out C v set ) v in = 2v, i load = 5ma v in = 2v, i load = 5ma l C1.5 C3.5 0 0 1.5 3.5 mv mv i set load regulation ?i load = 5ma to 1.5a C0.1 na v os load regulation ?i load = 5ma to 1.5a (note 7) df, fe packages l C0.5 C3 mv r, t7 packages l C1.5 C4 mv line regulation ?i set ?v os ?v in = 2v to 36v, i load = 5ma ?v in = 2v to 36v, i load = 5ma 1.5 0.001 na/v mv/v minimum load current (note 3) 2v v in 36v l 1.1 5 ma dropout voltage (note 4) i load = 100ma i load = 1.5a l 1.21 1.23 1.5 v v internal current limit v in = 5v, v set = 0v, v out = C0.1v l 1.5 2 a i lim programming ratio l 300 400 500 ma/k i lim minimum output current resistance 400 i mon full-scale output current i load = 1.5a 290 300 330 a i mon scale factor 100ma i load 1.5a 200 a/a i mon operating range l v out C 40v v out + 0.4v v
LT3081 4 3081f for more information www.linear.com/LT3081 electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t j = 25c. (note 2) 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 v out . the LT3081 is tested and specified under pulse load conditions such that t j t a . the LT3081e is tested at t a = 25c and performance is guaranteed from 0c to 125c. performance of the LT3081e over the full C40c and 125c operating temperature range is assured by design, characterization, and correlation with statistical process controls. the LT3081i is guaranteed over the full C40c to 125c 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-to- output 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. parameter conditions min typ max units temp output current (note 9) t j > 5c 1 a/c temp output current absolute error (note 9) 0c LT3081 5 3081f for more information www.linear.com/LT3081 typical performance characteristics offset voltage offset voltage (v out C v set ) offset voltage (v out C v set ) load regulation minimum load current dropout voltage set pin current set pin current t j = 25c unless otherwise specified. offset voltage (v out C v set ) temperature (c) ?50 49.5 set pin current (a) 49.6 49.8 49.9 50.0 50.5 50.2 0 50 75 3081 g01 49.7 50.3 50.4 50.1 ?25 25 100 125 150 i load = 5ma set pin current distribution (a) 49 n = 3195 49.5 50 3081 g02 50.5 51 temperature (c) ?50 offset voltage (mv) 0 1.0 150 3081 g03 ?1.0 ?2.0 0 50 100 ?25 25 75 125 2.0 ?0.5 0.5 ?1.5 1.5 i load = 5ma v os distribution (mv) ?2 n = 3195 ?1 0 3081 g04 1 2 input-to-output differential (v) 0 ?1.0 offset voltage (mv) ?0.6 ?0.2 0.2 6 12 18 24 3081 g05 30 0.6 1.0 ?0.8 ?0.4 0 0.4 0.8 36 i load = 5ma load current (a) 0 offset voltage (mv) ?0.6 3081 g06 ?1.0 ?1.4 0.5 1 0.25 0.75 1.25 ?0.2 0.2 ?0.8 ?1.2 ?0.4 0 1.5 t j = 25c t j = 125c temperature (c) ?50 0 set pin current load regulation (na) offset voltage load regulation (mv) 50 100 150 200 0 50 100 150 3081 g07 250 300 ?3.0 ?2.5 ?2.0 ?1.5 ?1.0 ?0.5 0 ?25 25 75 125 ?i load = 5ma to 1.5a temperature (c) ?50 0 minimum load current (ma) 0.5 1.0 1.5 2.0 0 50 100 150 3081 g08 2.5 3.0 ?25 25 75 125 v in ? v out = 36v v in ? v out = 2v load current (a) 0 1.0 dropout voltage (v) 1.1 1.2 1.3 1.4 1.5 0.25 0.5 0.75 1 3081 g09 1.25 1.5 t j = ?50c t j = 25c t j = 125c
LT3081 6 3081f for more information www.linear.com/LT3081 to-220 package maximum power dissipation programmable current limit programmable current limit programmable current limit temp pin current i mon pin current dropout voltage internal current limit internal current limit temperature (c) ?50 dropout voltage (v) 1.3 1.4 1.5 25 75 150 3081 g10 1.2 1.1 1.0 ?25 0 50 100 i load = 1.5a i load = 5ma 125 temperature (c) ?50 0 current limit (a) 0.5 1.0 1.5 2.0 0 50 100 150 3081 g11 2.5 3.0 ?25 25 75 125 v in = 7v v out = 0v input-to-output differential voltage (v) 0 0 current limit (a) 0.4 0.8 1.2 6 12 18 24 3081 g12 30 1.6 2.0 0.2 0.6 1.0 1.4 1.8 36 to-220 and dd-pak tssop and dfn case temperature (c) 50 power (w) 10 20 150 3081 g13 0 70 90 110 60 80 100 120 130 140 30 5 15 25 v in ? v out = 20v limited by foldback current limit v in ? v out = 10v v in ? v out = 5v jc = 3c/w r ilim (k) 0 0 programmed current limit (a) 0.5 1.0 1.5 2.0 1 2 3 4 3081 g14 5 6 t j = 25c v in = 7v v out = 0v output current (a) 0 0 output voltage (v) 0.2 0.4 0.6 0.95 1.00 1.05 0.5 1 1.5 2 3081 g15 r ilim 1.5k r ilim 3.01k r ilim 4.53k r set = 20k temperature (c) ?50 temp pin current (a) 80 120 150 3081 g16 40 0 0 50 100 ?25 25 75 125 160 60 100 20 140 load current (a) 0 250 300 350 1.2 3081 g17 200 150 0.3 0.6 0.9 1.5 100 50 0 i mon pin current (a) temperature (c) ?50 programmed current limit (a) 0.8 1.2 150 3081 g39 0.4 0 0 50 100 ?25 25 75 125 1.6 0.6 1.0 0.2 1.4 r ilim = 4.53k r ilim = 3.01k r ilim = 1.50k v in = 7v v out = 0v typical performance characteristics t j = 25c unless otherwise specified.
LT3081 7 3081f for more information www.linear.com/LT3081 linear regulator load transient response linear regulator line transient response current source line transient response current source line transient response linear regulator turn-on response i mon pin line regulation linear regulator load transient response linear regulator load transient response linear regulator load transient response input-to-output differential voltage (v) 0 0 i mon pin current (a) 10 20 30 6 12 18 24 3791 ta02b 30 40 50 5 15 25 35 45 36 i load = 200ma time (s) 0 output voltage deviation (mv) load current (ma) ?50 0 50 160 180 8081 g19 ?100 400 0 40 80 120 20 200 60 100 140 200 150 100 v in = 3v v out = 1v c set = 0.1f c out = 2.2f ?i load = 100ma to 500ma time (s) 0 output voltage deviation (mv) load current (ma) ?100 0 100 160 180 3081 g20 ?200 2.0 0 40 80 120 20 200 60 100 140 1.0 300 200 v in = 3v v out = 1v c set = 0.1f c out = 2.2f ?i load = 500ma to 1.5a time (s) 0 output voltage deviation (mv) load current (ma) ?200 ?100 0 40 45 3081 g21 600 400 0 10 20 30 5 50 15 25 35 200 200 100 v in = 3v v out = 1v c set = 30pf c out = 0 ?i load = 100ma to 500ma t r = t f = 1s time (s) 0 output voltage deviation (mv) load current (ma) ?400 ?200 0 40 45 3081 g22 1.5 1.0 0 10 20 30 5 50 15 25 35 0.5 400 200 v in = 3v v out = 1v c set = 30pf c out = 0 ?i load = 500ma to 1.5a t r = t f = 1s time (s) 0 output voltage deviation (mv) input voltage (v) 3 4 5 40 45 3081 g23 0.1 0 ?0.2 10 20 30 5 50 15 25 35 ?0.1 7 6 r set = 20k r load = 0.67 c out = 2.2f c set = 0.1f time (s) 0 output current (ma) input voltage (v) 2 3 4 40 45 3081 g24 150 100 0 10 20 30 5 50 15 25 35 50 6 5 r set = 6.04k r out = 3.01 c out = 0 c set = 30pf 100ma current source configuration time (s) 0 output current (a) input voltage (v) 2 3 4 40 45 3081 g25 1.2 1.0 0.6 10 20 30 5 50 15 25 35 0.8 6 5 r set = 6.04k r out = 0.3 c out = 0 c set = 30pf 1a current source configuration time (s) 0 output voltage (v) input voltage (v) 0 1 2 40 45 3081 g26 1.0 0.5 ?0.5 10 20 30 5 50 15 25 35 0 4 3 r set = 20k r load = 0.67 c out = 2.2f ceramic c set = 0 typical performance characteristics t j = 25c unless otherwise specified.
LT3081 8 3081f for more information www.linear.com/LT3081 ripple rejection ripple rejection output impedance ripple rejection (120hz) ripple rejection (10khz) residual output voltage with less than minimum load current source turn-on response current source turn-on response time (s) 0 output current (ma) input voltage (v) 0 1 2 160 180 3081 g28 150 100 0 40 80 120 20 200 60 100 140 50 4 3 r set = 6.04k r out = 3.01 c out = 0 c set = 20pf 100ma current source configuration time (s) 0 output current (a) input voltage (v) 0 1 2 160 180 3081 g29 1.5 1.0 0 40 80 120 20 200 60 100 140 0.5 4 3 r set = 6.04k r out = 0.3 c out = 0 c set = 20pf 1a current source configuration r test () 0 output voltage (mv) 400 500 600 2000 3081 g30 300 200 0 500 1000 1500 100 800 700 v in = 36v v in = 5v v out set pin = 0v r test v in frequency (hz) 10 100 40 ripple rejection (db) 50 60 70 80 1k 10k 100k 1m 10m 3081 g31 30 20 10 0 90 100 i load = 100ma i load = 500ma i load = 1.5a c out = 2.2f ceramic c set = 0.1f v in = v out(nominal) + 2v frequency (hz) 10 100 40 ripple rejection (db) 50 60 70 80 1k 10k 100k 1m 10m 3081 g32 30 20 10 0 90 100 v in = v out + 5v v in = v out + 2v v in = v out + 1.5v c out = 2.2f ceramic c set = 0.1f i load = 100ma frequency (hz) 10 1 output impedance () 10 100 1k 10k 100k 1m 10m 100 1k 10k 100k 1m 10m 3081 g33 i source = 10ma i source = 100ma i source = 1a current source configuration temperature (c) ?50 70 ripple rejection (db) 72 76 78 80 90 84 0 50 75 3081 g34 74 86 88 82 ?25 25 100 125 150 v in = v out(nominal) + 2v ripple = 500mv p-p f = 120hz i load = 0.1a c out = 2.2f c set = 0.1f temperature (c) ?50 45 ripple rejection (db) 47 51 53 55 65 59 0 50 75 3081 g34 49 61 63 57 ?25 25 100 125 150 v in = v out(nominal) + 2v ripple = 500mv p-p f = 10khz i load = 0.1a c out = 2.2f c set = 0.1f linear regulator turn-on response time (ms) 0 output voltage (v) input voltage (v) 0 1 2 16 18 3081 g27 1.0 0.5 ?0.5 4 8 12 2 20 6 10 14 0 4 3 r set = 20k r load = 0.67 c out = 2.2f ceramic c set = 0.1f typical performance characteristics t j = 25c unless otherwise specified.
LT3081 9 3081f for more information www.linear.com/LT3081 pin functions noise spectral density 10hz to 100khz output voltage noise 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 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 v out + 0.4v to v out C 40v. if unused, connect this pin to out. i lim : 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/k. 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 v out will affect the current limit. keep drops below 1mv. i mon : output current monitor. the i mon pin sources a current typically equal to i load /5000 or 200a per amp of output current. terminating this pin with a resistor to gnd produces a voltage proportional to i load . for example, at i load = 1.5a, i mon typically sources 300a. with a 1k resistor to gnd, this produces 300mv. the output of the i mon pin is valid for voltages from v out + 0.4v to v out C 40v. if unused, connect this pin to out. set: set. this pin is the error amplifiers 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 v out . 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. ripple rejection (1mhz) temperature (c) ?50 ripple rejection (db) 18 22 150 3081 g36 14 10 0 50 100 ?25 25 75 125 26 16 20 12 24 v in = v out(nominal) + 2v ripple = 200mv p-p f = 1mhz i load = 0.1a c out = 2.2f ceramic c set = 0.1f frequency (hz) 10 10 error amplifier noise spectral density (nv/hz) reference current noise spectral density (pa/hz) 100 1000 1 10 100 1k 100 10k 100k 3981 g37 time 1ms/div v out 50v/div 3081 g38 c set = 0.1f c out = 4.7f i load = 1.5a noise independent of output voltage typical performance characteristics t j = 25c unless otherwise specified.
LT3081 10 3081f for more information www.linear.com/LT3081 block diagram ? + 50a in temp temperature dependent current source 1a/c set i lim i mon out 3081 bd programmable current limit current monitor i mon = i load /5000 applications information introduction the LT3081 regulator is easy to use and has all the pro - tection features expected in high performance regulators. included are short-circuit protection, reverse-input protec - tion 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 manage - ment 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 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 pro - grammable via a single resistor between the i lim pin and out. shorting this resistor out disables all output current to the load, only bias currents remain. the i mon pin produces a current output proportional to load current. for every 1a of load current, the i mon pin sources 200a of current. this can be sensed using an external resistor to monitor load requirements and detect potential faults. the i mon 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 cur - rent 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.
LT3081 11 3081f for more information www.linear.com/LT3081 applications information programming linear regulator output voltage the LT3081 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. 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 v out (v) r set (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 reduc - tion 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 magni - tude, 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. 3081 f01 in set out + ? LT3081 50a r load c set r set c in v out = 50a ? r set c out figure 1. basic adjustable regulator 3081 f02 set pin gnd out figure 2. guard ring layout example of df package configuring the LT3081 as a current source setting the LT3081 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.
LT3081 12 3081f for more information www.linear.com/LT3081 applications information again, the lower current levels used in the LT3081 neces - sitate 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 i mon to out and leave i lim open. the temp pin is still available for use, if unused tie temp to out. selecting r set and r out in current source applications in figure 3, both resistors r set and r out 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 r set . 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 r set (r set equal to 4.02k). resultant errors due to offset voltage are a few percent. the lower the voltage across r set becomes, the higher the error term due to the offset. from this point, selecting r out is easy, as it is a straight - forward calculation from r set . take note, however, resistor errors must be accounted for as well. while larger voltage drops across r set 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 r set to r out , those resis - tors 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 watt - age resistors for r out . there may be a difference between the resistors used for r out and r set . a better method to maintain consistency in resistors is to use multiple resis - tors in parallel to create r out , allowing the same wattage and type of resistor as r set . programming current limit externally a resistor placed between i lim 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: r ilim = i limit /400ma/k + 400 the resistor for a 1.3a current limit is: r ilim = 1.3a/400ma/ k + 400 = 3.65k. tolerance over temperature is 15%, so current limit is normally set 20% above maximum load current. the 400 offset resistance built in to the pro - grammable current limit allows for lowering the maximum output current to only bias currents (see curve of minimum load current in typical performance characteristics) us - ing external switches. the LT3081s internal current limit overrides the pro - grammed current limit if the input-to-output voltage dif - ferential 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 main - tain 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 ap- plications without long input leads. however, applications connecting a power supply to an LT3081 circuits in and gnd pins with long input wires combined with low esr, ceramic input capacitors are prone to voltage spikes, reli - ability concerns and application-specific board oscillations. the input wire inductance found in many battery-powered figure 3. using the LT3081 as a current source in set out + ? LT3081 50a i out v set r set 3081 f03 + ? r out i out 5ma v set = 50a ? r set i out = v set r out = 50a ? r set r out
LT3081 13 3081f for more information www.linear.com/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/solu - tions 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 self- inductance 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 wires 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 self- inductance is reduced; up to a 50% reduction when placed a few inches apart. splitting the wires basically connects two equal inductors in parallel, but placing them in close proximity gives the wires mutual inductance adding to the self-inductance. the second and most effective way to reduce overall inductance is to place both forward and return current conductors (the input and gnd wires) in very close proximity. two 30-awg wires separated by only 0.02", used as forward and return current conduc - tors, reduce the overall self-inductance to approximately one-fifth that of a single isolated wire. if wiring modifications are not permissible for the applica - tions, including series resistance between the power supply and the input of the LT3081 also stabilizes the application. as little as 0.1 to 0.5, often less, is effective in damp- ing 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 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 LT3081, increase the effec - tive 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 (r set 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 con - nected in parallel with the set pin resistor to lower the current sources 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 ring - ing 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.
LT3081 14 3081f for more information www.linear.com/LT3081 applications information although the LT3081s 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 sources value will dif - fer 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 designs 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 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 unaccept - able 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 capaci - tors stored energy to create a spark or arc. for applica - tions 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 resis - tor values will range from 100 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 set out + ? LT3081 50a r set r out r series r series long line reactance/inductance 3081 f04 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 3081 f05 in set out + ? LT3081 50a c comp or r set r out r comp c comp
LT3081 15 3081f for more information www.linear.com/LT3081 applications information 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 ap - plication requirements. in some extreme cases, capacitors or series rc networks may be required on both the LT3081s 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 stabil - ity and input capacitance section for more information). 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 figure 8. ceramic capacitor dc bias characteristics figure 7. ceramic capacitor temperature characteristics figure 6. input and/or output capacitors may be used for compensation 3081 f06 in set out + ? LT3081 50a i out r set r out c out or v in c out r out c in r in using ceramic capacitors give extra consideration to the use of ceramic capacitors. ceramic capacitors are manufactured with a variety of di - electrics, each with different behavior across temperature and applied voltage. the most common dielectrics used temperature (c) ?50 40 20 0 ?20 ?40 ?60 ?80 ?100 25 75 3081 f07 ?25 0 50 100 125 y5v change in value (%) x5r both capacitors are 16v, 1210 case size, 10f dc bias voltage (v) change in value (%) 3081 f08 20 0 ?20 ?40 ?60 ?80 ?100 0 4 8 10 2 6 12 14 x5r y5v 16 both capacitors are 16v, 1210 case size, 10f
LT3081 16 3081f for more information www.linear.com/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. paralleling devices 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. table 2. pc board trace resistance weight (oz) 10mil width 20mil width 1 54.3 27.1 2 27.1 13.6 trace resistance is measured in m/in. 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 10m ballast resistor, which at full output current gives better than 80% equalized sharing of the current. the external resistance of 10m (5m 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. if the increase in load regulation from the ballast resis - tors is unacceptable, the i mon output can be used to compensate for these drops (see using i mon cancels ballast resistor drop in the typical applications section). regulator paralleling without the use of ballast resistors is accomplished by comparing the i mon outputs of regula - tors (see load current sharing without ballasting in the typical applications section). quieting the noise the LT3081 offers numerous noise performance advan - tages. every linear regulator has its sources of noise. in general, a linear regulators critical noise source is the reference. in addition, consider the error amplifiers noise contribution along with the resistor dividers 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 LT3081 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 (5.7na rms 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 = boltzmanns constant, 1.38 ? 10 C23 j/k, and t is abso- lute temperature) which is rms summed with the voltage set + ? LT3081 50a 10m 10m in v in 4.8v to 40v v out 3.3v 3a out 10f 1f 33k 3081 f09 set + ? LT3081 50a in out figure 9. parallel devices
LT3081 17 3081f for more information www.linear.com/LT3081 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. 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 v out is much greater than v ref . the LT3081s 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 (27v rms over a 10hz to 100khz bandwidth). the error amplifiers 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 sec - tion 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 re - sistance between the regulator and the load determines load regulation performance. the data sheets load regulation specification is kelvin sensed at the packages 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). connected as shown, system load regulation is the sum of the LT3081s 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 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. 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. applications information figure 10. connections for best load regulation in set + ? LT3081 50a 3081 f10 out r set r p parasitic resistance r p r p load
LT3081 18 3081f for more information www.linear.com/LT3081 i mon pin operation (current monitor) the LT3081s i mon pin outputs a current proportional to the load current supplied at a ratio of 1:5000. the i mon pin 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 i mon to ground converts the i mon 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 i mon the i mon 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. 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. junction-to-case thermal resistance is specified from the ic junction to the bottom of the case directly, or the bot - tom 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 pack - ages and the tab of the dd-pak and to-220 packages are electrically connected to the output (v out ). 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 board area thermal resistance (junction-to-ambient) topside* backside 2500mm 2 2500mm 2 2500mm 2 18c/w 1000mm 2 2500mm 2 2500mm 2 22c/w 225mm 2 2500mm 2 2500mm 2 29c/w 100mm 2 2500mm 2 2500mm 2 35c/w *device is mounted on topside table 4. fe package, 16-lead tssop copper area board area thermal resistance (junction-to-ambient) topside* backside 2500mm 2 2500mm 2 2500mm 2 16c/w 1000mm 2 2500mm 2 2500mm 2 20c/w 225mm 2 2500mm 2 2500mm 2 26c/w 100mm 2 2500mm 2 2500mm 2 32c/w *device is mounted on topside table 5. r package, 7-lead dd-pak copper area board area thermal resistance (junction-to-ambient) topside* backside 2500mm2 2500mm2 2500mm2 13c/w 1000mm2 2500mm2 2500mm2 14c/w 225mm2 2500mm2 2500mm2 16c/w *device is mounted on topside applications information LT3081 in c in 1f c out 10f 3081 f11 out set r set 29.8k r comp = 5000 ? r cable(total) v out(load) = 50a (r set + r comp ) r cable2 0.02 r cable 0.02 r comp 200 i mon load figure 11. using i mon to compensate for cable drops thermal considerations the LT3081s internal power and thermal limiting circuitry protects itself under overload conditions. for continuous normal load conditions, do not exceed the 125c 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.
LT3081 19 3081f for more information www.linear.com/LT3081 applications information t7 package, 7-lead to-220 thermal resistance (junction-to-case) = 3c/w 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 1870as board layout using multiple inner v out planes and multiple thermal vias achieves 16c/w performance for the fe 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 1a and a maximum ambient temperature of 50c, what is the maxi - mum junction temperature for the dd-pak on a 2500mm2 board with topside copper of 1000mm 2 ? the power in the circuit equals: p total = (v in C v out )(i out ) the current delivered to the set pin is negligible and can be ignored. v in(max_continuous) = 2.625v (2.5v + 5%) v out = 0.9v, i out = 1a, t a = 50c power dissipation under these conditions equals: p total = (v in C v out )(i out ) p total = (2.625v C 0.9v)(1a) = 1.73w junction temperature equals: t j = t a + p total ? ja (using tables) t j = 50c + 1.73w ? 14c/w = 74.2c in this case, the junction temperature is below the maxi - mum rating, ensuring reliable operation. reducing power dissipation 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 resis - tor in series with the regulators input. the voltage drop across r s decreases the LT3081s in-to-out differential voltage and correspondingly decreases the LT3081s power dissipation. as an example, assume: v in = 7v, v out = 3.3v and i out(max) = 1.5a. use the formulas from the calculating junction temperature section previously discussed. without series resistor r s , power dissipation in the LT3081 equals: p total = (7v C 3.3v) ? 1.5a = 5.55w if the voltage differential (v diff ) across the LT3081 is chosen as 1.5v, then r s equals: r s = 7v ? 3.3v ? 1.5v 1.5a = 1.5 ? power dissipation in the LT3081 now equals: p total = 1.5v ? 1.5a = 2.25w the LT3081s power dissipation is now only 40% compared to no series resistor. r s 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: v in = 5v, v in(max) = 5.5v, v out = 3.3v, v out(min) = 3.2v, i out(max) = 1.5a and i out(min) = 0.7a. also, assuming that r p carries no more than 90% of i out(min) = 630ma.
LT3081 20 3081f for more information www.linear.com/LT3081 3081 f12 in v in set out + ? LT3081 50a r set r s v out v in c2 c1 figure 12. reducing power dissipation using a series resistor applications information calculating r p yields: r p " 5.5v ? 3.2v 0.63a " 3.65 < (5% standard value = 3.6) the maximum total power dissipation is: (5.5v C 3.2v) ? 1.5a = 3.5w however, the LT3081 supplies only: 1.5a ? 5.5v ? 3.2v 3.6 < " 0.86a therefore, the LT3081s power dissipation is only: p diss = (5.5v C 3.2v) ? 0.86a = 1.98w r p dissipates 1.52w of power. as with the first technique, choose appropriate wattage resistors to handle and dis - sipate the power properly. with this configuration, the 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. protection features the LT3081 incorporates several protection features ideal for harsh industrial and automotive environments, among other applications. in addition to normal monolithic regula- tor 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 circuits temperature threshold is typically 165c and incorporates about 5c of hysteresis. the LT3081s 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 LT3081 and sensitive loads. clamping diodes and 400 limiting resistors protect the LT3081s 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 applica - tion concerns, note the following two scenarios. the first scenario employs a noise-reducing set pin bypass ca - pacitor 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. 3081 f13 in set out + ? LT3081 50a r set v out v in c2 c1 r p figure 13. reducing power dissipation using a parallel resistor
LT3081 21 3081f for more information www.linear.com/LT3081 typical applications paralleling regulators using i mon cancels ballast resistor drop in set r set 30.1k 1k temp i mon i lim 10m out + ? LT3081 i set 50a v out 3v 3a v in in set 1k temp i mon i lim 10m out + ? LT3081 i set 50a 3.01k 3081 ta03 1k in set r set 15k 1k temp i mon i lim out + ? LT3081 i set 50a v out 1.5v 3a v in in set 1k temp i mon i lim r ballast 10m out + ? LT3081 i set 50a 3081 ta04 r comp 25 r ballast 10m
LT3081 22 3081f for more information www.linear.com/LT3081 typical applications load sharing without ballast resistors load current sharing without ballasting in 22f 20k out v in 3v to 18v i mon set LT3081 0.1f 22f 1k 5.1k in 20k out i mon set LT3081 100k 0.47f 5.1k 5.1k 0.1f 1k in out i mon set LT3081 ? + 20k v out 1v 4.5a 100k 0.47f 5.1k 0.1f 1k 3081 ta06 ? + 1/2 lt1638 1/2 lt1638 in 4.7f 20k out v in 3v to 36v i mon set i lim LT3081 0.1f 2.2f v out 1v 3a 0.1f 3081 ta05 100 1k 1k 20k = 2n3904 out in i mon set i lim LT3081
LT3081 23 3081f for more information www.linear.com/LT3081 typical applications arduino monitored supply
LT3081 24 3081f for more information www.linear.com/LT3081 package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 4.00 0.10 (4 sides) 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 pin 1 top mark (note 6) 0.40 0.10 1 6 12 7 bottom view?exposed pad 2.65 0.10 0.75 0.05 r = 0.115 typ 0.25 0.05 0.50 bsc 2.50 ref 3.38 0.10 0.200 ref 0.00 ? 0.05 (df12) dfn 1112 rev a recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 3.10 0.05 4.50 0.05 package outline pin 1 notch r = 0.20 typ or 0.35 45 chamfer 2.65 0.05 3.38 0.05 2.50 ref df package 12-lead plastic dfn (4mm 4mm) (reference ltc dwg # 05-08-1733 rev a)
LT3081 25 3081f for more information www.linear.com/LT3081 package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. fe16 (bb) tssop rev j 1012 0.09 ? 0.20 (.0035 ? .0079) 0 ? 8 0.25 ref 0.50 ? 0.75 (.020 ? .030) 4.30 ? 4.50* (.169 ? .177) 1 3 4 5 6 7 8 10 9 4.90 ? 5.10* (.193 ? .201) 16 1514 13 12 11 1.10 (.0433) max 0.05 ? 0.15 (.002 ? .006) 0.65 (.0256) bsc 2.94 (.116) 0.195 ? 0.30 (.0077 ? .0118) typ 2 recommended solder pad layout 0.45 0.05 0.65 bsc 4.50 0.10 6.60 0.10 1.05 0.10 2.94 (.116) 3.05 (.120) 3.58 (.141) 3.58 (.141) 4.70 (.185) millimeters (inches) note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale 4. recommended minimum pcb metal size for exposed pad attachment see note 4 note 5 note 5 6.40 (.252) bsc fe package 16-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663 rev j) exposed pad variation bb 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 detail a detail a is the part of the lead fram feature for reference only no measurement purose 0.56 (.022) ref 0.53 (.021) ref detail a
LT3081 26 3081f for more information www.linear.com/LT3081 package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. .050 (1.27) bsc .520 ? .570 (13.208 ? 14.478) .026 ? .036 (0.660 ? 0.914) t7 (straigt) 0801 .045 ? .055 (1.143 ? 1.397) .095 ? .115 (2.41 ? 2.92) .013 ? .023 (0.330 ? 0.584) .980 ? 1.070 (24.892 ? 27.178) .165 ? .180 (4.191 ? 4.572) .147 ? .155 (3.734 ? 3.937) dia .390 ? .415 (9.906 ? 10.541) .330 ? .370 (8.382 ? 9.398) .460 ? .500 (11.684 ? 12.700) .570 ? .620 (14.478 ? 15.748) .230 ? .270 (5.842 ? 6.858) t7 package 7-lead plastic to-220 (straight lead) (nonstandard flow 06) (reference ltc dwg # 05-08-1422)
LT3081 27 3081f for more information www.linear.com/LT3081 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 representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. r (dd7) 0212 rev f .026 ? .035 (0.660 ? 0.889) typ .143 +.012 ?.020 ( ) 3.632 +0.305 ?0.508 .050 (1.27) bsc .013 ? .023 (0.330 ? 0.584) .095 ? .115 (2.413 ? 2.921) .004 +.008 ?.004 ( ) 0.102 +0.203 ?0.102 .050 .012 (1.270 0.305) .059 (1.499) typ .045 ? .055 (1.143 ? 1.397) .165 ? .180 (4.191 ? 4.572) .330 ? .370 (8.382 ? 9.398) .060 (1.524) typ .390 ? .415 (9.906 ? 10.541) 15 typ .420 .350 .585 .090 .035 .050 .325 .205 .080 .585 recommended solder pad layout for thicker solder paste applications recommended solder pad layout .090 .035 .050 .420 .276 .320 note: 1. dimensions in inch/(millimeter) 2. drawing not to scale .300 (7.620) .075 (1.905) .183 (4.648) .060 (1.524) .060 (1.524) .256 (6.502) bottom view of dd pak hatched area is solder plated copper heat sink r package 7-lead plastic dd pak (reference ltc dwg # 05-08-1462 rev f) detail a detail a 0 ? 7 typ 0 ? 7 typ
LT3081 28 3081f for more information www.linear.com/LT3081 ? linear technology corporation 2013 lt 0513 ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/LT3081 related parts typical application run/ss 0.47f 1f 1f 1000pf 10f v in 6.3v to 36v 6.8h temp set v in bd lt3680 15k 590k 1k 10k 3081 ta02 2n3904 mtd2955 gnd boost in out i mon i lim 1k 1k v c sw fb 63.4k rt pg sync 100k = mbra340t3 6.04k LT3081 100k 22f high efficiency adjustable supply part number description comments lt1185 3a negative low dropout regulator v in : C4.5v to C35v, 0.8v dropout voltage, dd-pak and to-220 packages lt1764/lt1764a 3a, fast transient response, low noise ldo 340mv dropout voltage, low noise: 40v rms , v in = 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: 40v rms , v in = 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: 40v rms , v in : 1.8v to 20v, v out : 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 v in : 0.9v to 10v, dropout voltage: 145mv typical, adjustable output (v ref = v out(min) = 200mv), stable with low esr, ceramic output capacitors, 16-pin dfn (5mm 3mm) and 16-lead msop packages lt3070 5a, low noise, programmable v out , 85mv dropout linear regulator with digital margining dropout voltage: 85mv, digitally programmable v out : 0.8v to 1.8v, digital output margining: 1%, 3% or 5%, low output noise: 25v rms (10hz to 100khz), parallelable: use two for a 10a output, stable with low esr ceramic output capacitors (15f minimum), 28-lead 4mm 5mm qfn package lt3071 5a, low noise, programmable v out , 85mv dropout linear regulator with analog margining dropout voltage: 85mv, digitally programmable v out : 0.8v to 1.8v, analog margining: 10%, low output noise: 25v rms (10hz to 100khz), parallelable: use two for a 10a output, i mon output current monitor, stable with low esr ceramic output capacitors (15f 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: 40v rms , v in : 1.2v to 36v, v out : 0v to 35.7v, current-based reference with 1-resistor v out 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: 2.2f, 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: 40v rms , v in : 1.2v to 36v, v out : 0v to 35.7v, current-based reference with 1-resistor v out 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 v in : 1.14v to 3.5v (boost enabled), 1.14v to 5.5v (with external 5v), v do = 0.1v, i q = 950a, stable with 10f ceramic capacitors, 10-lead msop-e and dfn-10 packages lt3083 adjustable 3a single resistor low dropout regulator 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)

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