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lt3085 1 3085fb typical application features applications description adjustable 500ma single resistor low dropout regulator the lt ? 3085 is a 500ma low dropout linear regulator that can be paralleled to increase output current or spread heat on surface mounted boards. designed as a precision current source and voltage follower, this new regulator ? nds use in many applications requiring high current, adjustability to zero, and no heat sink. the device also brings out the collector of the pass transistor to allow low dropout operationdown to 275mvwhen used with a second supply. a key feature of the lt3085 is the capability to supply a wide output voltage range. by using a reference current through a single resistor, the output voltage is programmed to any level between zero and 36v. the lt3085 is stable with 2.2f of capacitance on the output, and the ic uses small ceramic capacitors that do not require additional esr as is common with other regulators. internal protection circuitry includes current limiting and thermal limiting. the lt3085 is offered in the 8-lead msop and a low pro? le (0.75mm) 6-lead 2mm 3mm dfn package (both with an exposed pad for better thermal characteristics). variable output voltage 500ma supply n outputs may be paralleled for higher current and heat spreading n output current: 500ma n single resistor programs output voltage n 1% initial accuracy of set pin current n output adjustable to 0v n current limit constant with temperature n low output noise: 40v rms (10hz to 100khz) n wide input voltage range: 1.2v to 36v n low dropout voltage: 275mv n < 1mv load regulation n < 0.001%/ v line regulation n minimum load current: 0.5ma n stable with minimum 2.2f ceramic capacitor n current limit with foldback and overtemperature protected n 8-lead msop, and 6-lead 2mm 3mm dfn packages n high current all surface mount supply n high ef? ciency linear regulator n post regulator for switching supplies n low parts count variable voltage supply n low output voltage power supplies + C lt3085 in v in 1.2v to 36v v control out 3085 ta01a set 1f 2.2f r set v out = r set ? 10a v out set pin current distribution (a) 10.20 3085 ta01b 9.90 10.00 10.10 9.80 n = 1676 l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks and vldo and thinsot are trademarks of linear technology corporation. all other trademarks are the property of their respective owners.
lt3085 2 3085fb absolute maximum ratings v control pin voltage ..................................... 40v, C0.3v in pin voltage ................................................ 40v, C0.3v set pin current (note 7) .................................... 15ma set pin voltage (relative to out) .......................... 10v output short-circuit duration .......................... inde? nite (note 1) all voltages relative to v out top view in in v control out out set dcb package 6-lead (2mm s 3mm) plastic dfn 4 5 7 6 3 2 1 t jmax = 125c, ja = 73c/w, jc = 10.6c/w exposed pad (pin 7) is out, must be soldered to v out on pcb see the applications information section 1 2 3 4 out out out set 8 7 6 5 in in nc v control top view ms8e package 8-lead plastic msop 9 t jmax = 125c, ja = 60c/w, jc = 10c/w exposed pad (pin 9) is out, must be soldered to v out on pcb see the applications information section pin configuration order information lead free finish tape and reel part marking* package description temperature range lt3085edcb#pbf lt3085edcb#trpbf ldqq 6-lead (2mm 3mm) plastic dfn C40c to 125c lt3085ems8e#pbf lt3085ems8e#trpbf ltdqp 8-lead plastic msop C40c to 125c lt3085idcb#pbf lt3085idcb#trpbf ldqq 6-lead (2mm 3mm) plastic dfn C40c to 125c lt3085ims8e#pbf lt3085ims8e#trpbf ltdqp 8-lead plastic msop C40c to 125c lt3085mpms8e#pbf lt3085mpms8e#trpbf ltdwq 8-lead plastic msop C55c to 125c lead based finish tape and reel part marking* package description temperature range lt3085edcb lt3085edcb#tr ldqq 6-lead (2mm 3mm) plastic dfn C40c to 125c lt3085ems8e lt3085ems8e#tr ltdqp 8-lead plastic msop C40c to 125c lt3085idcb lt3085idcb#tr ldqq 6-lead (2mm 3mm) plastic dfn C40c to 125c lt3085ims8e lt3085ims8e#tr ltdqp 8-lead plastic msop C40c to 125c lt3085mpms8e lt3085mpms8e#tr lt d w q 8-lead plastic msop C55c to 125c consult ltc marketing for parts speci? ed with wider operating temperature ranges. *the temperature grade is identi? ed 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 speci? cations, go to: http://www.linear.com/tapeandreel/ operating junction temperature range (notes 2, 10) e, i grade ........................................... C40c to 125c mp grade ........................................... C55c to 125c storage temperature range ................... C65c to 150c lead temperature (soldering, 10 sec) ms8e package only .......................................... 300c
lt3085 3 3085fb electrical characteristics 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 speci? ed, all voltages are with respect to v out . the lt3085 is tested and speci? ed under pulse load conditions such that t j ? t a . the lt3085e is 100% tested at t a = 25c. performance of the lt3085e over the full C40c to 125c operating junction temperature range is assured by design, characterization, and correlation with statistical process controls. the lt3085i regulators are guaranteed over the full C40c to 125c operating junction temperature range. the lt3085 (mp grade) is 100% tested and guaranteed over the C55c 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 lt3085, dropout is caused by either minimum control voltage (v control ) or minimum input voltage (v in ). both parameters are speci? ed with respect to the output voltage. the speci? cations represent the minimum input-to-output differential voltage required to maintain regulation. parameter conditions min typ max units set pin current i set v in = 1v, v control = 2v, i load = 1ma, t j = 25c v in 1v, v control 2v, 1ma i load 500ma (note 9) l 9.9 9.8 10 10 10.1 10.2 a a output offset voltage (v out C v set ) v os v in = 1v, v control = 2v, i load = 1ma, t j = 25c v in = 1v, v control = 2v, i load = 1ma l C1.5 C3 1.5 3 mv mv load regulation i set v os i load = 1ma to 500ma i load = 1ma to 500ma (note 8) l C0.1 C0.6 C1 na mv line regulation i set v os v in = 1v to 36v, v control = 2v to 36v, i load = 1ma v in = 1v to 36v, v control = 2v to 36v, i load = 1ma 0.1 0.003 0.5 na/v mv/v minimum load current (notes 3, 9) v in = v control = 10v v in = v control = 36v l l 300 500 1 a ma v control dropout voltage (note 4) i load = 100ma i load = 500ma l 1.2 1.35 1.6 v v v in dropout voltage (note 4) i load = 100ma i load = 500ma l l 85 275 150 450 mv mv v control pin current (note 5) i load = 100ma i load = 500ma l l 3 8 6 15 ma ma current limit (note 9) v in = 5v, v control = 5v, v set = 0v, v out = C0.1v l 500 650 ma error ampli? er rms output noise (note 6) i load = 500ma, 10hz f 100khz, c out = 10f, c set = 0.1f 33 v rms reference current rms output noise (note 6) 10hz f 100khz 0.7 na rms ripple rejection f = 120hz, v ripple = 0.5v p-p , i load = 0.1a, c set = 0.1f, c out = 2.2f f=10khz f=1mhz 90 75 20 db db db thermal regulation, i set 10ms pulse 0.003 %/w the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c (note 2). note 5. the v control pin current is the drive current required for the output transistor. this current will track output current with roughly a 1:60 ratio. the minimum value is equal to the quiescent current of the device. note 6. output noise is lowered by adding a small capacitor across the voltage setting resistor. adding this capacitor bypasses the voltage setting resistor shot noise and reference current noise; output noise is then equal to error ampli? er noise (see applications information section). note 7. the set pin is clamped to the output with diodes through 1k resistors. these resistors and diodes will only carry current under transient overloads. note 8. load regulation is kelvin sensed at the package. note 9. current limit includes foldback protection circuitry. current limit decreases at higher input-to-output differential voltages. see the typical performance characteristics graphs for more information. note 10. this ic includes over-temperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed the maximum operating junction temperature when over-temperature protection is active. continuous operation above the speci? ed maximum operating junction temperature may impair device reliability.
lt3085 4 3085fb typical performance characteristics temperature (c) C50 set pin current (a) 10.00 10.10 150 3085 g01 9.90 9.80 0 50 100 C25 25 75 125 10.20 9.95 10.05 9.85 10.15 set pin current distribution (a) 10.20 3085 g02 9.90 10.00 10.10 9.80 n = 1676 temperature (c) C50 offset voltage (mv) 0 1.0 150 3085 g03 C1.0 C2.0 0 50 100 C25 25 75 125 2.0 C0.5 0.5 C1.5 1.5 v os distribution (mv) 2 3085 g04 C1 0 1 C2 n = 1676 input-to-output voltage (v) 0 offset voltage (mv) C0.25 0 0.25 18 30 3085 g05 C0.50 C0.75 C1.00 612 24 0.50 0.75 1.00 36 i load = 1ma load current (ma) 0 offset voltage (mv) C1.00 C0.75 C0.50 250 300 450 3085 g06 C1.25 C1.50 C1.75 50 100 150 200 350 400 C0.25 0 0.25 500 t j = 25c t j = 125c temperature (c) C50 change in offset voltage with load (mv) change in reference current with load (na) 150 3085 g07 0 50 100 C25 25 75 125 020 change in reference current change in offset voltage (v out C v set ) C0.4 C0.2 C0.6 C0.8 C0.5 C0.3 C0.7 C0.1 C20 0 C40 C60 C30 C10 C50 10 i load = 1ma to 500ma v in C v out = 2v temperature (c) C50 minimum load current (ma) 0.4 0.6 150 3085 g08 0.2 0 0 50 100 C25 25 75 125 0.8 0.3 0.5 0.1 0.7 v in, control C v out = 36v v in, control C v out = 1.5v load current (ma) 0 minimum in voltage (v in C v out ) (mv) 150 200 250 3085 g09 100 50 0 300 350 400 0 250 300 450 50 100 150 200 350 400 500 t j = 125c t j = 25c set pin current set pin current distribution offset voltage (v out C v set ) offset voltage distribution offset voltage offset voltage load regulation minimum load current dropout voltage (minimum in voltage)
lt3085 5 3085fb typical performance characteristics temperature (c) C50 minimum in voltage (v in C v out ) (mv) 200 300 150 3085 g10 100 0 0 50 100 C25 25 75 125 400 150 250 50 350 i load = 500ma i load = 100ma load current (ma) 0 minimum control voltage (v control C v out ) (v) 0.6 0.8 1.0 3085 g11 0.4 0.2 0 1.2 1.4 1.6 250 300 450 50 100 150 200 350 400 500 t j = 125c t j = 25c t j = C50c temperature (c) C50 minimum control voltage (v control C v out ) (v) 0.8 1.2 150 3085 g12 0.4 0 0 50 100 C25 25 75 125 1.6 0.6 1.0 0.2 1.4 i load = 500ma i load = 100ma temperature (c) C50 current limit (ma) 300 500 150 3085 g13 0 0 50 100 C25 25 75 125 700 200 400 100 600 v in = 7v v out = 0v input-to-output differential (v) 0 current limit (ma) 300 400 500 20 30 3085 g14 200 100 0 51015 25 600 700 35 40 t j = 25c time (s) 0 output voltage deviation (mv) load current (ma) C20 60 160 3085 g15 200 C40 0 40 20 100 0 40 20 80 60 120 140 180 100 200 v out = 1.5v c set = 0.1f v in = v control = 3v c out = 10f ceramic c out = 2.2f ceramic time (s) 0 C50 50 150 80 3085 g16 C100 0 100 500 250 0 20 10 40 30 60 70 90 50 100 v in = v control = 3v v out = 1.5v c set = 0.1f output voltage deviation (mv) load current (ma) c out = 10f ceramic c out = 2.2f ceramic time (s) 0 in/control voltage (v) output voltage deviation (mv) C50 100 80 3085 g17 6 4 C100 0 50 0 2 20 10 40 30 60 70 90 50 100 v out = 1.5v i load = 10ma c out = 2.2f ceramic c set = 0.1f ceramic time (s) 0 in/control voltage (v) output voltage (v) 0 1.5 16 3085 g18 6 4 8 0.5 1 0 2 4 2 8 6 12 14 18 10 20 c out = 2.2f ceramic r set = 100k c set = 0 r load = 2 dropout voltage (minimum in voltage) dropout voltage (minimum v control pin voltage) dropout voltage (minimum v control pin voltage) current limit current limit load transient response load transient response line transient response turn-on response
lt3085 6 3085fb typical performance characteristics input-to-output differential (v) 0 0 control pin current (ma) 2 4 6 8 16 14 12 10 20 6 12 18 24 3085 g19 30 36 18 i load = 1ma i load = 500ma device in current limit load current (a) 0 0.1 0.2 control pin current (ma) 8 7 6 5 4 3 2 1 0 3085 g20 0.5 0.3 0.4 t j = C50c t j = 25c t j = 125c v in = v control = 2v v in = v out = 1v r test () 0 output voltage (mv) 800 700 600 500 400 300 200 100 0 3085 g21 2k 1k v in = 10v set pin = 0v v in v out r test v in = 20v v in = 5v frequency (hz) 0 ripple rejection (db) 40 100 10k 100k 100 10 1k 1m 3085 g22 20 60 80 30 90 10 50 70 v in = v control = v out (nominal) +2v ripple = 50mv pCp c out = 2.2f ceramic c set = 0.1f ceramic i load = 100ma i load = 500ma frequency (hz) 0 ripple reje c ti o n (db) 40 100 10k 100k 100 10 1k 1 m 3085 g 23 20 60 80 30 90 10 50 70 v in = v out (nominal) + 1v v control = v out (nominal) +2v ripple = 50mv pCp c out = 2.2f ceramic c set = 0.1f ceramic i load = 100ma i load = 500ma frequency (hz) 10 0 ripple rejection (db) 10 30 40 50 100 70 100 10k 3085 g24 20 80 90 60 1k 100k 1m v in = v control +2v v control = v out (nominal) +2v ripple = 50mv pCp c out = 2.2f ceramic c set = 0.1f ceramic i load = 100ma i load = 500ma v control pin current v control pin current residual output voltage with less than minimum load ripple rejection - single supply ripple rejection - dual supply - v control pin ripple rejection - dual supply - in pin frequency (hz) 1 error amplifier noise spectral density (nv/hz) reference current noise spectral density ( p a/ hz) 10k 10k 100k 100 10 1k 3085 g26 100 10 1k 0.1 1k 10 1.0 100 noise spectral density v out 100v/div time 1ms/div 3085 g27 v out = 1v r set = 100k c set = o.1f c out = 10f i load = 0.5a output voltage noise frequency (hz) 77 78 ripple rejection (db) 85 84 100 125 150 0 C50 C25 25 50 75 3085 g25 81 82 80 79 83 single supply operation v in = v out (nominal) +2v ripple = 50mv pCp , f = 120hz i load = 0.1a c out = 2.2f, c set = 0.1f ripple rejection (120hz)
lt3085 7 3085fb typical performance characteristics error ampli? er gain and phase frequency (hz) 10 gain (db) phase (deg) 9 15 21 100k 3085 g28 3 C3 6 12 18 0 C6 C9 C72 72 216 C216 C360 C144 0 144 C288 C432 C504 100 1k 10k 1m i load = 500ma i load = 100ma i load = 100ma i load = 500ma ripple rejection - set pin current frequency (hz) 0 ripple rejection (db) 60 150 10k 100k 100 10 1k 1m 3085 g29 30 90 120 45 135 15 75 105 c set = 0.1f c set = 0 r set = 100k v in = v control = v out (nominal) +2v ripple = 50mv pCp pin functions v control (pin 4/pin 5): this pin is the supply pin for the control circuitry of the device. the current ? ow into this pin is about 1.7% of the output current. for the device to regulate, this voltage must be more than 1.2v to 1.35v greater than the output voltage (see v control dropout voltage in the electrical characteristics table and graphs in the typical performance characteristics). the lt3085 requires a bypass capacitor at v control if more than six inches away from the main input ? lter capacitor. the output impedance of a battery rises with frequency, so include a bypass capacitor in battery-powered circuits. a bypass capacitor in the range of 1f to 10f suf? ces. in (pins 5, 6/pins 7, 8): this is the collector to the power device of the lt3085. the output load current is supplied through this pin. for the device to regulate, the voltage at this pin must be more than 0.1v to 0.5v greater than the output voltage (see v in dropout voltage in the electrical characteristics table and graphs in the typical perfor- mance characteristics). the lt3085 requires a bypass capacitor at in if more than six inches away from the main input ? lter capacitor. the output impedance of a battery rises with frequency, so include a bypass capacitor in battery-powered circuits. a bypass capacitor in the range of 1f to 10f suf? ces. nc (na/pin 6): no connection. the no connect pin has no connection to internal circuitry and may be tied to v in , v control , v out , gnd, or ? oated. out (pins 1, 2/pins 1, 2, 3): this is the power output of the device. there must be a minimum load current of 1ma or the output may not regulate. a minimum 2.2f output capacitor is required for stability. set (pin 3/pin 4): this pin is the non-inverting input to the error ampli? er and the regulation set point for the device. a ? xed current of 10a ? ows out of this pin through a single external resistor, which programs the output voltage of the device. output voltage range is zero to the absolute maximum rated output voltage. transient performance can be improved and output noise can be decreased by adding a small capacitor from the set pin to ground. exposed pad (pin 7/pin 9): out. tie directly to pins 1, 2/ pins 2, 3 directly at the pcb. (dcb/ms8e)
lt3085 8 3085fb block diagram C + v control in 10a 3085 bd out set applications information the lt3085 regulator is easy to use and has all the pro- tection features expected in high performance regulators. included are short-circuit protection and safe operating area protection, as well as thermal shutdown. the lt3085 is especially well suited to applications needing multiple rails. the new architecture adjusts down to zero with a single resistor, handling modern low voltage digital ics as well as allowing easy parallel operation and thermal management without heat sinks. adjusting to zero output allows shutting off the powered circuitry and when the input is pre-regulated C such as a 5v or 3.3v input supply C external resistors can help spread the heat. a precision 0 tc 10a internal current source is connected to the non-inverting input of a power operational ampli? er. the power operational ampli? er provides a low impedance buffered output to the voltage on the non-inverting input. a single resistor from the non-inverting input to ground sets the output voltage and if this resistor is set to zero, zero output results. as can be seen, any output voltage can be obtained from zero up to the maximum de? ned by the input power supply. what is not so obvious from this architecture are the ben- e? ts of using a true internal current source as the reference as opposed to a bootstrapped reference in older regulators. a true current source allows the regulator to have gain and frequency response independent of the impedance on the positive input. older adjustable regulators, such as the lt1086, have a change in loop gain with output voltage as well as bandwidth changes when the adjustment pin is bypassed to ground. for the lt3085, the loop gain is unchanged by changing the output voltage or bypassing. output regulation is not ? xed at a percentage of the output voltage but is a ? xed fraction of millivolts. use of a true current source allows all the gain in the buffer ampli? er to provide regulation and none of that gain is needed to amplify up the reference to a higher output voltage. the lt3085 has the collector of the output transistor connected to a separate pin from the control input. since the dropout on the collector (in pin) is only 275mv, two supplies can be used to power the lt3085 to reduce dissipation: a higher voltage supply for the control circuitry and a lower voltage supply for the collector. this increases ef? ciency and reduces dissipation. to further spread the heat, a resistor can be inserted in series with the collector to move some of the heat out of the ic and spread it on the pc board.
lt3085 9 3085fb the lt3085 can be operated in two modes. three terminal mode has the control pin connected to the power input pin which gives a limitation of 1.35v dropout. alternatively, the control pin can be tied to a higher voltage and the power in pin to a lower voltage giving 275mv dropout on the in pin and minimizing the power dissipation. this allows for a 500ma supply regulating from 2.5v in to 1.8v out or 1.8v in to 1.2v out with low dissipation. setting output voltage the lt3085 generates a 10a reference current that ? ows out of the set pin. connecting a resistor from set to ground generates a voltage that becomes the reference point for the error ampli? er (see figure 1). the reference voltage is a straight multiplication of the set pin current and the value of the resistor. any voltage can be generated and there is no minimum output voltage for the regulator. table 1 lists many common output voltages and standard 1% resistor values used to generate that output voltage. a minimum load current of 1ma is required to maintain regulation regardless of output voltage. for true zero voltage output operation, this 1ma load current must be returned to a negative supply voltage. applications information with the low level current used to generate the reference voltage, leakage paths to or from the set pin can create errors in the reference and output voltages. high quality insulation should be used (e.g., te? on, kel-f); cleaning of all insulating surfaces to remove ? uxes and other resi- dues will probably be required. surface coating may be necessary to provide a moisture barrier in high humidity environments. table 1. 1% resistors for common output voltages v out r set 1v 100k 1.2v 121k 1.5v 150k 1.8v 182k 2.5v 249k 3.3v 332k 5v 499k board leakage can be minimized by encircling the set pin and circuitry with a guardring operated at a potential close to itself; the guardring should be tied to the out pin. guarding both sides of the circuit board is required. bulk leakage reduction depends on the guard ring width. ten nanoamperes of leakage into or out of the set pin and associated circuitry creates a 0.1% error in the reference voltage. leakages of this magnitude, coupled with other sources of leakage, can cause signi? cant offset voltage and reference drift, especially over a wide temperature range. if guardring techniques are used, this bootstraps any stray capacitance at the set pin. since the set pin is a high impedance node, unwanted signals may couple into the set pin and cause erratic behavior. this will be most noticeable when operating with minimum output capacitors at full load current. the easiest way to remedy this is to bypass the set pin with a small amount of capacitance from set to ground, 10pf to 20pf is suf? cient. figure 1. basic adjustable regulator + C lt3085 10a in v control v control out 3085 f01 set c out r set v out c set + v in + v out = r set ? 10a
lt3085 10 3085fb applications information input capacitance and stability the lt3085 is designed to be stable with a minimum capacitance of 1f at each input pin. ceramic capacitors with low esr are available for use to bypass these pins, but in cases where long wires connect the lt3085 inputs to a power supply (and also from ground of the lt3085 circuitry back to power supply ground), this causes insta- bilities. this happens due to the wire inductance forming an lc tank circuit with the input capacitor and not as a result of instability on the lt3085. the self-inductance, or isolated inductance, of a wire is directly proportional to its length. the diameter does not have a major in? uence on its self-inductance. as an ex- ample, the self-inductance of a 2-awg isolated wire with a diameter of 0.26in. is approximately half the self-inductance of a 30-awg wire with a diameter of 0.01in. one foot of 30-awg wire has 465nh of self-inductance. the overall self-inductance of a wire is reduced in one of two ways. one is to divide the current ? owing towards the lt3085 between two parallel conductors. in this case, the farther apart the wires are from each other, the more the self-inductance is reduced, up to a 50% reduc- tion when placed a few inches apart. splitting the wires basically connects two equal inductors in parallel, but placing them in close proximity gives the wires mutual inductance adding to the self-inductance. the second and most effective way to reduce overall inductance is to place both forward- and return-current conductors (the wire for the input and the wire for ground) in very close proximity. two 30-awg wires separated by only 0.02in. used as forward- and return-current conductors reduce the overall self-inductance to approximately one-? fth that of a single isolated wire. if the lt3085 is powered by a battery mounted in close proximity on the same circuit board, a 2.2f input capaci- tor is suf? cient for stability. when powering from distant supplies, use a larger input capacitor based on a guide- line of 1f plus another 1f per 8 inches of wire length. as power supply impedance does vary, the amount of capacitance needed to stabilize your application will also vary. extra capacitance placed directly on the output of the power supply requires an order of magnitude more capacitance as opposed to placing extra capacitance close to the lt3085. using series resistance between the power supply and the input of the lt3085 also stabilizes the application. as little as 0.1 to 0.5, often less, is all that is needed to provide damping in the circuit. if the extra impedance between the power supply and the input is unacceptable, placing the resistors in series with the capacitors will pro- vide damping to prevent the lc resonance from causing full-blown oscillation. stability and output capacitance the lt3085 requires an output capacitor for stability. it is designed to be stable with most low esr capacitors (typically ceramic, tantalum or low esr electrolytic). a minimum output capacitor of 2.2f with an esr of 0.5 or less is recommended to prevent oscillations. larger values of output capacitance decrease peak deviations and provide improved transient response for larger load current changes. bypass capacitors, used to decouple individual components powered by the lt3085, increase the effective output capacitor value. for improvement in transient performance, place a capaci- tor 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. extra consideration must be given to the use of ceramic capacitors. ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. the most common dielectrics used are speci? ed with eia temperature characteristic codes of z5u, y5v, x5r and x7r. the z5u and y5v dielectrics are good for providing high capacitances
lt3085 11 3085fb applications information dc bias voltage (v) change in value (%) 3085 f02 20 0 C20 C40 C60 C80 C100 0 4 8 10 26 12 14 x5r y5v 16 both capacitors are 16v, 1210 case size, 10f figure 2. ceramic capacitor dc bias characteristics temperature (c) C50 40 20 0 C20 C40 C60 C80 C100 25 75 3085 f03 C25 0 50 100 125 y5v change in value (%) x5r both capacitors are 16v, 1210 case size, 10f figure 3. ceramic capacitor temperature characteristics in a small package, but they tend to have strong voltage and temperature coef? cients as shown in figures 2 and 3. 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 signi? cant 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 veri? ed. voltage and temperature coef? cients are not the only sources of problems. some ceramic capacitors have a piezoelectric response. a piezoelectric device generates voltage across its terminals due to mechanical stress, ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. paralleling devices lt3085s may be paralleled with other lt308x devices to obtain higher output current. the set pins are tied together and the in pins are tied together. this is the same whether its in three terminal mode or has separate input supplies. the outputs are connected in common using a small piece of pc trace as a ballast resistor to equalize the currents. pc trace resistance in milliohms/inch is shown in table 1. only a tiny area is needed for ballasting. table 1. pc board trace resistance weight (oz) 10 mil width 20 mil width 1 54.3 27.1 2 27.1 13.6 trace resistance is measured in m/in
lt3085 12 3085fb + C lt3080 v in v control out set 10m + C lt3085 v in v in 4.8v to 28v v out 3.3v 1.5a v control out 10f 1f set 165k 3085 f04 20m figure 4. parallel devices applications information the worst-case offset between the set pin and the output of only 1.5mv allows very small ballast resistors to be used. as shown in figure 4, the two devices have a small 10m and 20m ballast resistors, which at full output current gives better than 80% equalized sharing of the current. the external resistance of 20m (6.6m for the two devices in parallel) only adds about 10mv of output regulation drop at an output of 1.5a. even with an output voltage as low as 1v, this only adds 1% to the regulation. of course, more than two lt308xs can be paralleled for even higher output current. they are spread out on the pc board, spreading the heat. input resistors can further spread the heat if the input-to-output difference is high. thermal performance in this example, two lt3085 2mm 3mm dfn devices are mounted on a 1oz copper 4-layer pc board. they are placed approximately 1.5 inches apart and the board is mounted vertically for convection cooling. two tests were set up to measure the cooling performance and current sharing of these devices. the first test was done with approximately 1.6v input- to-output and 0.5a per device. this gave a 800mw dissipation in each device and a 1a output current. the temperature rise above ambient is approximately 28c and both devices were within plus or minus 1c. both the thermal and electrical sharing of these devices is excel- lent. the thermograph in figure 5 shows the temperature distribution between these devices and the pc board reaches ambient temperature within about a half an inch from the devices. the power is then increased with 3.4v across each device. this gives 1.7 watts dissipation in each device and a device temperature of about 90c, about 65c above ambient as shown in figure 6. again, the temperature matching figure 6. temperature rise at 1.7w dissipation figure 5. temperature rise at 800mw dissipation
lt3085 13 3085fb applications information the lt3085 uses a unity-gain follower from the set pin to drive the output, and there is no requirement to use a resistor to set the output voltage. use a high accuracy voltage reference placed at the set pin to remove the er- rors in output voltage due to reference current tolerance and resistor tolerance. active driving of the set pin is acceptable; the limitations are the creativity and ingenuity of the circuit designer. one problem that a normal linear regulator sees with refer- ence voltage noise is that noise is gained up along with the output when using a resistor divider to operate at levels higher than the normal reference voltage. with the lt3085, the unity-gain follower presents no gain whatsoever from the set pin to the output, so noise ? gures do not increase accordingly. error ampli? er noise is typically 100nv/ hz (33v rms over the 10hz to 100khz bandwidth); this is another factor that is rms summed in to give a ? nal noise ? gure for the regulator. curves in the typical performance characteristics show noise spectral density and peak-to-peak noise character- istics for both the reference current and error ampli? er over the 10hz to 100khz bandwidth. overload recovery like many ic power regulators, the lt3085 has safe operat- ing area (soa) protection. the soa protection decreases current limit as the input-to-output voltage increases and keeps the power dissipation at safe levels for all values of input-to-output voltage. the lt3085 provides some output current at all values of input-to-output voltage up to the device breakdown. see the current limit curve in the typical performance characteristics. when power is ? rst turned on, the input voltage rises and the output follows the input, allowing the regulator to start into very heavy loads. during start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output currents. with a high input voltage, a problem can occur wherein removal of an output short will not allow the output volt- age to recover. other regulators, such as the lt1085 and lt1764a, also exhibit this phenomenon so it is not unique to the lt3085. between the devices is within 2c, showing excellent tracking between the devices. the board temperature has reached approximately 40c within about 0.75 inches of each device. while 90c is an acceptable operating temperature for these devices, this is in 25c ambient. for higher ambients, the temperature must be controlled to prevent device tempera- ture from exceeding 125c. a 3-meter-per-second air? ow across the devices will decrease the device temperature about 20c providing a margin for higher operating ambi- ent temperatures. both at low power and relatively high power levels de- vices can be paralleled for higher output current. current sharing and thermal sharing is excellent, showing that acceptable operation can be had while keeping the peak temperatures below excessive operating temperatures on a board. this technique allows higher operating current linear regulation to be used in systems where it could never be used before. quieting the noise the lt3085 offers numerous advantages when it comes to dealing with noise. there are several sources of noise in a linear regulator. the most critical noise source for any ldo is the reference; from there, the noise contribution from the error ampli? er must be considered, and the gain created by using a resistor divider cannot be forgotten. traditional low noise regulators bring the voltage refer- ence out to an external pin (usually through a large value resistor) to allow for bypassing and noise reduction of reference noise. the lt3085 does not use a traditional voltage reference like other linear regulators, but instead uses a reference current. that current operates with typi- cal noise current levels of 2.3pa/ hz (0.7na rms over the 10hz to 100khz bandwidth). the voltage noise of this is equal to the noise current multiplied by the resistor value. the resistor generates spot noise equal to 4ktr (k = boltzmanns constant, 1.38 ? 10 -23 j/k, and t is absolute temperature) which is rms summed with the reference current noise. to lower reference noise, the voltage set- ting resistor may be bypassed with a capacitor, though this causes start-up time to increase as a factor of the rc time constant.
lt3085 14 3085fb applications information the problem occurs with a heavy output load when the input voltage is high and the output voltage is low. com- mon situations are immediately after the removal of a short circuit. the load line for such a load may intersect the output current curve at two points. if this happens, there are two stable operating points for the regulator. with this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. load regulation because the lt3085 is a ? oating device (there is no ground pin on the part, all quiescent and drive current is delivered to the load), it is not possible to provide true remote load sensing. load regulation will be limited by the resistance of the connections between the regulator and the load. the data sheet speci? cation for load regulation is kelvin sensed at the pins of the package. negative side sensing is a true kelvin connection, with the bottom of the voltage setting resistor returned to the negative side of the load (see figure 7). connected as shown, system load regulation will be the sum of the lt3085 load regulation and the parasitic line resistance multiplied by the output current. it is important to keep the positive connection between the regulator and load as short as possible and use large wire or pc board traces. internal parasitic diodes and protection diodes in normal operation, the lt3085 does not require protection diodes. older three-terminal regulators require protection diodes between the vout pin and the input pin or between the adj pin and the vout pin to prevent die overstress. figure 7. connections for best load regulation + C lt3085 in v control out 3085 f07 set r set r p parasitic resistance r p r p load on the lt3085, internal resistors and diodes limit current paths on the set pin. even with bypass capacitors on the set pin, no protection diode is needed to ensure device safety under short-circuit conditions. the set pin handles 10v (either transient or dc) with respect to out without any device degradation. internal parasitic diodes exist between out and the two inputs. negative input voltages are transferred to the output and may damage sensitive loads. reverse-biasing either input to out will turn on these parasitic diodes and allow current ? ow. this current ? ow will bias internal nodes of the lt3085 to levels that possibly cause errors when suddenly returning to normal operating conditions and expecting the device to start and operate. prediction of results of a bias fault is impossible, immediate return to normal operating conditions can be just as dif? cult after a bias fault. suf? ce it to say that extra wait time, power cycling, or protection diodes may be needed to allow the lt3085 to return to a normal operating mode as quickly as possible. protection diodes are not otherwise needed between the out pin and in pin. the internal diodes can handle microsecond surge currents of up to 50a. even with large output capacitors, obtaining surge currents of those magnitudes is dif? cult in normal operation. only with large output capacitors, such as 1000f to 5000f, and with in instantaneously shorted to ground will damage occur. a crowbar circuit at in is capable of generating those levels of currents, and then protection diodes from out to in are recommended. normal power supply cycling or system hot plugging and unplugging does not do any damage. a protection diode between out and v control is usually not needed. the internal parasitic diode on v control of the lt3085 handles microsecond surge currents of 1a to 10a. again, this only occurs when using crowbar circuits with large value output capacitors. since the v control pin is usually a low current supply, this is unlikely. still, a protection diode is recommended if v control can be instantaneously shorted to ground. normal power supply cycling or system hot plugging and unplugging does not do any damage.
lt3085 15 3085fb if the lt3085 is con? gured as a three-terminal (single supply) regulator with in and v control shorted together, the internal diode of the in pin will protect the v control pin. like any other regulator, exceeding the maximum input- to-output differential causes internal transistors to break down and then none of the internal protection circuitry is functional. thermal considerations the lt3085 has internal power and thermal limiting cir- cuitry designed to protect it under overload conditions. for continuous normal load conditions, maximum junc- tion temperature must not be exceeded. it is important to give consideration to all sources of thermal resistance from junction to ambient. this includes junction-to-case, case-to-heat sink interface, heat sink resistance or circuit board-to-ambient as the application dictates. additional heat sources nearby must also be considered. for surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the pc board and its copper traces. surface mount heat sinks and plated through-holes can also be used to spread the heat generated by power devices. boards speci? ed in thermal resistance tables have no vias on plated through-holes from topside to backside. junction-to-case thermal resistance is speci? ed from the ic junction to the bottom of the case directly below the die. this is the lowest resistance path for heat ? ow. proper mounting is required to ensure the best possible thermal ? ow from this area of the package to the heat sinking material. note that the exposed pad is electrically connected to the output. the following tables list thermal resistance for several different copper areas given a ? xed board size. all mea- surements were taken in still air on two-sided 1/16 fr-4 board with one ounce copper. pcb layers, copper weight, board layout and thermal vias affect the resultant thermal resistance. although tables 2 and 3 provide thermal resistance numbers for 2-layer board with 1 ounce copper, modern multi-layer pcbs applications information provide better performance than found in these tables. for example, a 4-layer, 1 ounce copper pcb board with 5 thermal vias from the dfn or msop exposed backside pad to inner layers (connected to v out ) achieves 40 c/w thermal resistance. demo circuit 1401as board layout achieves this 40 c/w performance. this is approximately a 45% improvement over the numbers shown in tables 2 and 3. table 2. mse package, 8-lead msop copper area thermal resistance (junction-to-ambient) topside* backside board area 2500mm 2 2500mm 2 2500mm 2 55c/w 1000mm 2 2500mm 2 2500mm 2 57c/w 225mm 2 2500mm 2 2500mm 2 60c/w 100mm 2 2500mm 2 2500mm 2 65c/w *device is mounted on topside table 3. dcb package, 6-lead dfn copper area thermal resistance (junction-to-ambient) topside* backside board area 2500mm 2 2500mm 2 2500mm 2 68c/w 1000mm 2 2500mm 2 2500mm 2 70c/w 225mm 2 2500mm 2 2500mm 2 73c/w 100mm 2 2500mm 2 2500mm 2 78c/w *device is mounted on topside for future information on the thermal resistance and using thermal information, refer to jedec standard jesd51, notably jesd51-12. calculating junction temperature example: given an output voltage of 0.9v, a v control voltage of 3.3v 10%, an in voltage of 1.5v 5%, output current range from 1ma to 0.5a and a maximum ambi- ent temperature of 50c, what will the maximum junction temperature be for the dfn package on a 2500mm 2 board with topside copper area of 500mm 2 ? the power in the drive circuit equals: p drive = (v control C v out )(i control ) where i control is equal to i out /60. i control is a function of output current. a curve of i control vs i out can be found in the typical performance characteristics curves.
lt3085 16 3085fb applications information figure 8. reducing power dissipation using a series resistor + C lt3085 in v control out v out v in a v in c2 3085 f08 set r set r s c1 the power in the output transistor equals: p output = (v in C v out )(i out ) the total power equals: p total = p drive + p output the current delivered to the set pin is negligible and can be ignored. v control(max continuous) = 3.630v (3.3v + 10%) v in(max continuous) = 1.575v (1.5v + 5%) v out = 0.9v, i out = 0.5a, t a = 50c power dissipation under these conditions is equal to: p drive = (v control C v out )(i control ) i control = i out 60 = 0.5a 60 = 8.3ma p drive = (3.630v C 0.9v)(8.3ma) = 23mw p output = (v in C v out )(i out ) p output = (1.575v C 0.9v)(0.5a) = 337mw total power dissipation = 360mw junction temperature will be equal to: t j = t a + p total ? ja (approximated using tables) t j = 50c + 360mw ? 73c/w = 76c in this case, the junction temperature is below the maximum rating, ensuring reliable operation. reducing power dissipation in some applications it may be necessary to reduce the power dissipation in the lt3085 package without sacri? cing output current capability. two techniques are available. the ? rst technique, illustrated in figure 8, em- ploys a resistor in series with the regulators input. the voltage drop across r s decreases the lt3085s in-to-out differential voltage and correspondingly decreases the lt3085s power dissipation. as an example, assume: v in = v control = 5v, v out = 3.3v and i out(max) = 0.5a. use the formulas from the calculating junction temperature section previously discussed.
lt3085 17 3085fb without series resistor r s , power dissipation in the lt3085 equals: p total = 5v C 3.3v () ? 0.5a 60 + 5v C 3.3v () ? 0.5a = 0.86w if the voltage differential (v diff ) across the npn pass transistor is chosen as 0.5v, then r s equals: r s = 5v ? 3.3v ? 0.5v 0.5a = 2.4 power dissipation in the lt3085 now equals: p total = 5v C 3.3v () ? 0.5a 60 + 0.5v () ? 0.5a = 0.26w the lt3085s power dissipation is now only 30% compared to no series resistor. r s dissipates 0.6w of power. choose appropriate wattage resistors to handle and dissipate the power properly. the second technique for reducing power dissipation, shown in figure 9, uses a resistor in parallel with the lt3085. this resistor provides a parallel path for current ? ow, reducing the current ? owing through the lt3085. this technique works well if input voltage is reasonably constant and output load current changes are small. this technique also increases the maximum available output current at the expense of minimum load requirements. as an example, assume: v in = v control = 5v, v in(max) = 5.5v, v out = 3.3v, v out(min) = 3.2v, i out(max) = 0.5a and i out(min) = 0.35a. also, assuming that r p carries no more than 90% of i out(min) = 630ma. calculating r p yields: r p = 5.5v ? 3.2v 315ma = 7.30 (5% standard value = 7.) the maximum total power dissipation is (5.5v C 3.2v) ? 0.5a = 1.2w. however the lt3085 supplies only: 0.5a ? 5.5v ? 3.2v 7.5 = 0.193a therefore, the lt3085s power dissipation is only: p dis = (5.5v C 3.2v) ? 0.193a = 0.44w r p dissipates 0.71w of power. as with the ? rst technique, choose appropriate wattage resistors to handle and dis- sipate the power properly. with this con? guration, the lt3085 supplies only 0.36a. therefore, load current can increase by 0.3a to 0.143a while keeping the lt3085 in its normal operating range. figure 9. reducing power dissipation using a parallel resistor + C lt3085 in v control out v out v in c2 3085 f09 set r set r p c1 applications information
lt3085 18 3085fb typical applications higher output current + C lt3085 in 50 mj4502 v control out 3085 ta02 set 4.7f 332k v out 3.3v 5a + 1f 100f + 100f v in 6v current source + C lt3085 in v control out 2 0.5w 100k 3085 ta03 set i out 0a to 0.5a 4.7f v in 10v 1f power oscillator + C lt3085 in v in v control out v out 400hz 4vac p-p 3085 ta22 10f set 499k 8.45k 8.45k 47nf 4.7f 2.21k 47nf 220n 121 6.3v, 150ma light bulb #47 20
lt3085 19 3085fb typical applications adding shutdown low dropout voltage led driver + C lt3085 in 100ma d1 v control out v in 3085 ta05 set r1 24.9k r2 2.49 c1 + C lt3085 in v in v control out v out 3085 ta04 set r1 on off shutdown q1 vn2222ll q2* vn2222ll q2 insures zero output in the absence of any output load. * using a lower value set resistor + C lt3085 in 1ma v in 12v v control out c out 4.7f v out 0.5v to 10v 3085 ta06 set r1 49.9k 1% r set 10k r2 499 1% c1 1f v out = 0.5v + 1ma ? r set
lt3085 20 3085fb typical applications adding soft-start coincident tracking + C lt3085 in v control out 4.7f v out3 5v 0.5a set c3 4.7f + C lt3085 in v control out v out2 3.3v 0.5a 3085 ta08 set r2 80.6k 169k c2 4.7f c1 1.5f + C lt3085 in v control v in 7v to 28v out set r1 249k v out1 2.5v 0.5a + C lt3085 in v in 4.8v to 28v v control out v out 3.3v 0.5a c out 4.7f 3085 ta07 set r1 332k c2 0.01f c1 1f d1 1n4148
lt3085 21 3085fb typical applications high voltage regulator ramp generator + C lt3085 6.1v in 1n4148 v in 50v v control out v out 0.5a v out = 20v v out = 10a ? r set 3085 ta10 set r set 2m 4.7f 15f 10f buz11 10k + + + C lt3085 in v in 5v v control out v out 3085 ta12 set vn2222ll vn2222ll 4.7f 1f 1f + C lt3085 + C lt3085 in in v in 12v to 18v v control v control out out 4.7f 100f v out 0v to 10v 3085 ta09 set set + 15f r4 1m 1 0.25w 50k 0a to 0.5a + 15f + lab supply
lt3085 22 3085fb typical applications ground clamp reference buffer + C lt3085 in v in v control out 4.7f v out v ext 3085 ta13 1n4148 set 5k 20 1f + C lt3085 in v in v control out v out * 3085 ta11 set output input c1 1f gnd c2 4.7f lt1019 *min load 0.5ma 3085 ta20 20m 20m 42* 47f 3.3v out 2a 33k *4mv drop ensures lt3085 is off with no load multiple lt3085s can be used + C lt3085 10f 5v out set lt1963-3.3 in v control boosting fixed output regulators
lt3085 23 3085fb typical applications low voltage, high current adjustable high ef? ciency regulator* 2.7v to 5.5v ? 100f 2 2.2meg 100k 470pf 10k 1000pf 100f 2 294k 12.1k 0.47h 78.7k 100k 124k pv in sw 2n3906 sv in i th r t v fb sync/mode pgood run/ss sgnd pgnd ltc3414 + C lt3085 in v control out set + C lt3085 in v control out 0v to 4v ? 2a set + C lt3085 in v control out set 3085 ta18 + C lt3085 in v control out 100f set + + + *differential voltage on lt3085 is 0.6v set by the v be of the 2n3906 pnp . 20m 20m 20m 20m ? maximum output voltage is 1.5v below input voltage
lt3085 24 3085fb typical applications adjustable high ef? ciency regulator* 3085 ta19 4.5v to 25v ? 10f 100k 0.1f 68f 10h mbrm140 10k 10k 1f v in boost sw fb shdn gnd lt3493 cmdsh-4e 0.1f tp0610l + C lt3085 in v control out set 4.7f 0v to 10v ? 0.5a *differential voltage on lt3085 1.4v set by the tpo610l p-channel threshold. 1meg ? maximum output voltage is 2v below input voltage 200k 3085 ta21 r1 100k + C lt3085 c comp * in v control set out *c comp r1 10 10f r1 10 2.2f i out = 1v r1 2 terminal current source
lt3085 25 3085fb package description 3.00 p 0.10 (2 sides) 2.00 p 0.10 (2 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (tbd) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 p 0.10 bottom viewexposed pad 1.65 p 0.10 (2 sides) 0.75 p 0.05 r = 0.115 typ r = 0.05 typ 1.35 p 0.10 (2 sides) 1 3 6 4 pin 1 bar top mark (see note 6) 0.200 ref 0.00 C 0.05 (dcb6) dfn 0405 0.25 p 0.05 0.50 bsc pin 1 notch r0.20 or 0.25 s 45 chamfer 0.25 p 0.05 1.35 p 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 p 0.05 (2 sides) 2.15 p 0.05 0.70 p 0.05 3.55 p 0.05 package outline 0.50 bsc dcb package 6-lead plastic dfn (2mm 3mm) (reference ltc dwg # 05-08-1715 rev a)
lt3085 26 3085fb package description msop (ms8e) 0210 rev f 0.53 p 0.152 (.021 p .006) seating plane note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does not include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.18 (.007) 0.254 (.010) 1.10 (.043) max 0.22 C 0.38 (.009 C .015) typ 0.86 (.034) ref 0.65 (.0256) bsc 0 o C 6 o typ detail a detail a gauge plane 12 3 4 4.90 p 0.152 (.193 p .006) 8 8 1 bottom view of exposed pad option 7 6 5 3.00 p 0.102 (.118 p .004) (note 3) 3.00 p 0.102 (.118 p .004) (note 4) 0.52 (.0205) ref 1.68 (.066) 1.88 (.074) 5.23 (.206) min 3.20 C 3.45 (.126 C .136) 1.68 p 0.102 (.066 p .004) 1.88 p 0.102 (.074 p .004) 0.889 p 0.127 (.035 p .005) recommended solder pad layout 0.42 p 0.038 (.0165 p .0015) typ 0.65 (.0256) bsc 0.1016 p 0.0508 (.004 p .002) detail b detail b corner tail is part of the leadframe feature. for reference only no measurement purpose 0.05 ref 0.29 ref ms8e package 8-lead plastic msop , exposed die pad (reference ltc dwg # 05-08-1662 rev f)
lt3085 27 3085fb information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. revision history rev date description page number b 6/10 updated trademarks revised conditions in electrical characteristics table changed i load value on curve g27 in typical performance characteristics section revised figure 1 added 200k resistor to drawing 3085 ta19 in typical applications section updated package description drawings 1 3 6 9 24 25, 26 (revision history begins at rev b)
lt3085 28 3085fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2008 lt 0610 rev b ? printed in usa related parts typical application part number description comments ldos lt1086 1.5a low dropout regulator fixed 2.85v, 3.3v, 3.6v, 5v and 12v output lt1763 500ma, low noise ldo 300mv dropout voltage, low noise = 20v rms , v in : 1.8v to 20v, so-8 package lt3021 500ma vldo regulator v in : 0.9v to 10v, dropout voltage = 190mv, v adj = 200mv, 5mm 5mm dfn-16, so-8 packages lt3080 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, sot-223, msop and 3mm 3mm dfn packages lt3080-1 parallelable 1.1a adjustable single resistor low dropout regulator (with internal ballast r) 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, sot-223, msop and 3mm 3mm dfn packages. lt3080-1 version has integrated ballast resistor lt1963a 1.5a low noise, fast transient response ldo 340mv dropout voltage, low noise = 40v rms , v in : 2.5v to 20v, to-220, dd, sot-223 and so-8 packages lt1965 1.1a low noise ldo 290mv dropout voltage, low noise = 40v rms , v in : 1.8v to 20v, v out : 1.2v to 19.5v, stable with ceramic caps to-220, ddpak, msop and 3mm 3mm dfn packages lt c ? 3026 1.5a low input voltage vldo tm 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 and dfn packages switching regulators lt1976 high voltage, 1.5a step-down switching regulator f = 200khz, i q = 100a, tssop-16e package ltc3414 4a (i out ), 4mhz synchronous step-down dc/dc converter 95% ef? ciency, v in : 2.25v to 5.5v, v out(min) = 0.8v, tssop package ltc3406/ltc 3406b 600 ma (i out ), 1.5mhz synchronous step-down dc/dc converter 95% ef? ciency, v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 20a, i sd < 1a, thinsot tm package ltc3411 1.25a (i out ), 4mhz synchronous step-down dc/dc converter 95% ef? ciency, v in : 2.5v to 5.5v, v out(min) = 0.8v, i q = 60a, i sd < 1a, 10-lead ms or dfn packages paralleling regulators + C lt3085 in v in 4.8v to 36v v control out 20m 10f v out 3.3v 1.5a 3085 ta14 165k set 1f + C lt3080 in v control out 10m set

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