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LT3080-1 1 30801fa + C LT3080-1 in v in 4.8v to 28v v control out* 25m 10f v out 3.3v 2.2a *outputs can be directly mounted to power plane 30801 ta01 165k set 1f + C LT3080-1 in v control out* 25m set typical application 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 applications n internal ballast resistor permits direct connection to power plane for higher current and heat spreading n output current: 1.1a n single resistor programs output voltage n 1% initial accuracy of set pin current n output adjustable to 0v n low output noise: 40v rms (10hz to 100khz) n wide input voltage range: 1.2v to 36v n low dropout voltage: 350mv n <0.001%/ v line regulation n minimum load current: 0.5ma n stable with 2.2f minimum ceramic output capacitor n current limit with foldback and overtemperature protected n available in 8-lead msop and 3mm 3mm dfn features description parallelable 1.1a adjustable single resistor low dropout regulator the lt ? 3080-1 is a 1.1a low dropout linear regulator that incorporates an internal ballast resistor to allow direct paralleling of devices without the need for pc board trace resistors. the internal ballast resistor allows multiple devices to be paralleled directly on a surface mount board for higher output current and power dissipation while keeping board layout simple and easy. the device brings out the collector of the pass transistor to allow low dropout operationdown to 350mv when used with multiple input supplies. the LT3080-1 is capable of supplying a wide output volt- age range. a reference current through a single resistor programs the output voltage to any level between zero and 36v. the LT3080-1 is stable with 2.2f of ceramic capacitance on the output, not requiring additional esr as is common with other regulators. internal protection includes current limiting and thermal limiting. the LT3080-1 regulator is offered in the 8- lead msop (with an exposed pad for better thermal characteristics) and 3mm 3mm dfn packages. paralleling regulators , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the p ro p ert y of their res p ective owners. offset voltage distribution v os distribution (mv) 2 30801 ta01b C1 0 1 C2 n = 13250
LT3080-1 2 30801fa v control pin voltage .....................................40v, ?0.3v in pin voltage ................................................40v, ?0.3v set pin current (note 7) .....................................10ma set pin voltage (relative to out) .........................0.3v output short-circuit duration .......................... inde? nite (note 1) all voltages relative to v out top view 9 dd package 8-lead ( 3mm 3mm ) plastic dfn 5 6 7 8 4 3 2 1out out out set in in nc v control t jmax = 125c, 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/ f
LT3080-1 3 30801fa the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. parameter conditions min typ max units set pin current i set v in = 1v, v control = 2.0v, i load = 1ma, t j = 25c v in 1v, v control 2.0v, 1ma i load 1.1a (note 9) 9.90 9.80 10 10 10.10 10.20 a a output offset voltage (v out C v set )v os v in = 1v, v control = 2v, i out = 1ma C2 C3.5 2 3.5 mv mv load regulation i set v os v os i load = 1ma to 1.1a i load = 1ma to 1.1a (note 8) i load = 1ma to 1.1a (note 8) C0.1 27.5 34 48 na mv mv line regulation (note 9) i set v os v in = 1v to 22v, v control =1v to 22v, i load =1ma v in = 1v to 22v, v control =1v to 22v, 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 = 22v 300 500 1 a ma v control dropout voltage (note 4) i load = 100ma i load = 1.1a 1.2 1.35 1.6 v v v in dropout voltage (note 4) i load = 100ma i load = 1.1a 100 350 200 500 mv mv control pin current (note 5) i load = 100ma i load = 1.1a 4 17 6 30 ma ma current limit (note 9) v in = 5v, v control = 5v, v set = 0v, v out = C0.1v 1.1 1.4 a error ampli? er rms output noise (note 6) i load = 1.1a, 10hz f 100khz, c out = 10f, c set = 0.1f 40 v rms reference current rms output noise (note 6) 10hz f 100khz 1 na rms ripple rejection f = 120hz, v ripple = 0.5v p-p , i load = 0.2a, c set = 0.1f, c out = 2.2f f = 10khz f = 1mhz 75 55 20 db db db thermal regulation, i set 10ms pulse 0.003 %/w 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 LT3080-1 is tested and speci? ed under pulse load conditions such that t j t a . the LT3080-1 is 100% tested at t a = 25c. performance at C 40c and 125c is assured by design, characterization and correlation with statistical process controls. 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 LT3080-1, 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. note 5: the 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 the applications information section). note 7: set pin is clamped to the output with diodes. these diodes only carry current under transient overloads. note 8: load regulation is kelvin sensed at the package. note 9: current limit may decrease to zero at input-to-output differential voltages (v in C v out ) greater than 22v. operation at voltages for both in and v control is allowed up to a maximum of 36v as long as the difference between input and output voltage is below the speci? ed differential (v in C v out ) voltage. line and load regulation speci? cations are not applicable when the device is in current limit. 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. electrical characteristics
LT3080-1 4 30801fa input-to-output voltage (v) 0 offset voltage (mv) C 0.25 0 0.25 18 30 30801 g05 C 0.50 C 0.75 C1.00 612 24 0.50 0.75 1.00 36* i load = 1ma *see note 9 in electrical characteristics table set pin current set pin current distribution offset voltage (v out C v set ) offset voltage dropout voltage (minimum in voltage) temperature (c) C50 set pin current (a) 10.00 10.10 150 30801 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 30801 g02 9.90 10.00 10.10 9.80 n = 13792 temperature (c) C50 offset voltage (mv) 0 1.0 150 30801 g03 C1.0 C2.0 0 50 100 C25 25 75 125 2.0 C 0.5 0.5 C1.5 1.5 i l = 1ma v os distribution (mv) 2 30801 g04 C1 0 1 C2 n = 13250 temperature (c) C50 minimum load current (ma) 0.4 0.6 150 30801 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 *see note 9 in electrical characteristics table output current (a) 0 minimum in voltage (v in C v out ) (mv) 150 200 250 0.6 1.0 30801 g09 100 50 0 0.2 0.4 0.8 300 350 400 1.2 t j = 25c t j = 125c offset voltage offset voltage distribution minimum load current load regulation typical performance characteristics load current (a) 0 offset voltage (mv) C30 C25 C20 0.6 1.0 30801 g06 C35 C40 C45 0.2 0.4 0.8 C10 0 C15 C5 5 1.2 t j = 25c t j = 125c temperature (c) C50 change in offset voltage with load (mv) change in reference current with load (na) C20 C10 150 30801 g07 C30 C50 0 50 100 C25 25 75 125 0 C25 C15 C35 C40 C45 C5 40 60 20 C20 C10 0 80 30 50 10 70 i load = 1ma to 1.1a v in C v out = 2v change in reference current change in offset voltage (v out C v set )
LT3080-1 5 30801fa time (s) 0 output voltage (v) input voltage (v) 1 3 5 8 30801 g18 2.0 1.0 0 2 4 1.5 0.5 0 2 1 4 3 67 9 5 10 r set = 100k c set = 0 r load = 1 c out = 2.2f ceramic dropout voltage (minimum in voltage) dropout voltage (minimum v control pin voltage) dropout voltage (minimum v control pin voltage) current limit load transient response load transient response line transient response temperature (c) C50 minimum in voltage (v in C v out ) (mv) 200 300 150 30801 g10 100 0 0 50 100 C25 25 75 125 400 150 250 50 350 i load = 1.1a i load = 500ma i load = 100ma output current (a) 0 minimum control voltage (v control C v out ) (v) 0.6 0.8 1.0 0.6 1.0 30801 g11 0.4 0.2 0 0.2 0.4 0.8 1.2 1.4 1.6 1.2 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 30801 g12 0.4 0 0 50 100 C25 25 75 125 1.6 0.6 1.0 0.2 1.4 i load = 1.1a i load = 1ma current limit time (s) 0 in/control voltage (v) output voltage deviation (mv) C25 25 75 80 30801 g17 6 4 C50 0 50 5 3 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 turn-on response temperature (c) C50 current limit (a) 0.8 1.2 150 30801 g13 0.4 0 0 50 100 C25 25 75 125 1.6 0.6 1.0 0.2 1.4 v in = 7v v out = 0v input-to-output differential (v) 0 current limit (a) 0.6 0.8 1.0 18 30 30801 g14 0.4 0.2 0 612 24 1.2 1.4 1.6 36* t j = 25c *see note 9 in electrical characteristics table typical performance characteristics time (s) 0 output voltage deviation (mv) load current (ma) C20 20 60 40 30801 g15 400 200 C40 0 40 300 100 0 10 5 20 15 30 35 45 25 50 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 output voltage deviation (mv) load current (a) C50 50 150 40 30801 g16 1.2 0.6 C100 0 100 0.9 0.3 0 10 5 20 15 30 35 45 25 50 v in = v control = 3v v out = 1.5v c out = 10f ceramic c set = 0.1f
LT3080-1 6 30801fa frequency (hz) 1 error amplifier noise spectral density (nv/ hz ) reference current noise spectral density ( p a/ hz ) 10k 10k 100k 100 10 1k 30801 g26 100 10 1k 0.1 1k 10 1.0 100 v control pin current residual output voltage with less than minimum load ripple rejection - single supply ripple rejection - dual supply - in pin ripple rejection (120hz) noise spectral density ripple rejection - dual supply - v control pin load current (a) 0 0 control pin current (ma) 5 10 15 20 30 0.2 0.4 0.6 0.8 30801 g20 1.0 1.2 25 v control C v out = 2v v in C v out = 1v t j = C50c t j = 125c t j = 25c r test () 0 output voltage (v) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 30801 g21 2k 1k v in = 20v v in = 5v v in = 10v set pin = 0v v in v out r test frequency (hz) 0 ripple rejection (db) 40 100 10k 100k 100 10 1k 1m 30801 g22 20 60 80 30 90 10 50 70 v in = v control = v out (nominal) + 2v c out = 2.2f ceramic ripple = 50mv pCp i load = 100ma i load = 1.1a frequency (hz) 0 ripple rejection (db) 40 100 10k 100k 100 10 1k 1m 30801 g23 20 60 80 30 90 10 50 70 v in = v out (nominal) + 1v v control = v out (nominal) +2v c out = 2.2f ceramic ripple = 50mv pCp i load = 100ma i load = 1.1a frequency (hz) 0 ripple rejection (db) 40 100 10k 100k 100 10 1k 1m 30801 g24 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 i load = 1.1a v control pin current input-to-output differential (v) 0 0 control pin current (ma) 5 10 15 20 25 6 12 18 24 30801 g19 30 36* i load = 1.1a i load = 1ma device in current limit *see note 9 in electrical characteristics table temperature ( o c) C50 70 ripple rejection (db) 71 73 74 75 80 77 0 50 75 30801 g25 72 78 79 76 C25 25 100 125 150 single supply operation v in = v out(nominal) + 2v ripple = 500mv p-p , f=120hz i load = 1.1a c set = 0.1f, c out = 2.2f typical performance characteristics
LT3080-1 7 30801fa output voltage noise error ampli? er gain and phase frequency (hz) C30 gain (db) phase (degrees) C10 20 10k 100k 100 10 1k 1m 30801 g28 C20 0 10 C15 15 C25 C5 5 C200 0 300 C100 100 200 C50 250 C150 50 150 i l = 1.1a i l = 100ma i l = 100ma i l = 1.1a v control (pin 5/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 dropout speci? cations). in (pins 7, 8/pins 7, 8): this is the collector to the power device of the LT3080-1. 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 dropout speci? cations). nc (pin 6/pin 6): no connection. no connect pins have no connection to internal circuitry and may be tied to v in , v control , v out , gnd, or ? oated. out (pins 1-3/pins 1-3): this is the power output of the device. there must be a minimum load current of 1ma or the output may not regulate. set (pin 4/pin 4): this pin is the 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 by adding a small capacitor from the set pin to ground. exposed pad (pin 9/pin 9): out on ms8e and dfn packages. (dd/ms8e) v out 100v/div time 1ms/div 30801 g27 v out = 1v r set = 100k c set = o.1f c out = 10f i load = 1.1a typical performance characteristics pin functions
LT3080-1 8 30801fa applications information the LT3080-1 regulator is easy to use and has all the protection features expected in high performance regulators. included are short-circuit protection and safe operating area protection, as well as thermal shutdown. the LT3080-1 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-regulatedsuch as a 5v or 3.3v input supplyexternal 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 bene? 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 LT3080-1, 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 LT3080-1 also incorporates an internal ballast resistor to allow for direct paralleling of devices without the need for pc board trace resistors or sense resistors. this internal ballast resistor allows multiple devices to be paralleled directly on a surface mount board for higher output current and higher power dissipation while keeping board layout simple and easy. it is not dif? cult to add more regulators for higher output current; inputs of devices are all tied together, outputs of all devices are tied directly together, and set pins of all devices are tied directly together. because of the internal ballast resistor, devices automatically share the load and the power dissipation. the LT3080-1 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 300mv, two supplies can be used to power the LT3080-1 to reduce C + v control in 10a 25m 30801 bd out set block diagram
LT3080-1 9 30801fa 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. the LT3080-1 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 300mv dropout on the in pin and minimizing the power dissipation. this allows for a 1.1a supply regulating from 2.5v in to 1.8v out or 1.8v in to 1.2v out with low dissipation. output voltage the LT3080-1 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. 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. 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 residues will probably be required. surface coating may be necessary to provide a moisture barrier in high humidity environments. board leakage can be minimized by encircling the set pin and circuitry with a guard ring operated at a potential close to itself; the guard ring 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 the possible operating 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. stability and output capacitance the LT3080-1 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 LT3080-1, increase the effective output capacitor value. for improvement in transient performance, place a capacitor across the voltage setting resistor. capacitors up to 1f can be used. this bypass capacitor reduces system noise as well, but start-up time is proportional to the time constant of the voltage setting resistor (r set in figure 1) and set pin bypass capacitor. figure 1. basic adjustable regulator + C LT3080-1 in v control v control out 30801 f01 set c out r set v out c set + v in + 25m applications information
LT3080-1 10 30801fa 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 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, similar to the way a piezoelectric microphone works. for a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. paralleling devices LT3080-1s may be directly paralleled 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; the internal ballast resistor equalizes the currents. the worst-case offset between the set pin and the output of only 2 millivolts allows very small ballast resistors to be used. as shown in figure 4, the two devices have internal ballast resistors, which at full output current gives dc bias voltage (v) change in value (%) 30801 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 3080 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 figure 4. parallel devices applications information + C LT3080-1 v in v control out set 25m + C LT3080-1 v in v in 4.8v to 28v v out 3.3v 2.2a v control out 10f 1f set 165k 30801 f04 25m
LT3080-1 11 30801fa better than 90 percent equalized sharing of the current. the internal resistance of 25 milliohms (per device) only adds about 25 millivolts of output regulation drop at an output of 2a. at low output voltage, 1v, this adds 2.5% regulation. the output can be set 19mv high for lower absolute error 1.3%. of course, more than two LT3080-1s 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 LT3080-1 3mm 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 ? rst test was done with approximately 0.7v input- to-output and 1a per device. this gave a 700 milliwatt dissipation in each device and a 2a 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 excellent. the thermograph in figure 5 shows the temperature distribution between these devices and the pc board reaches ambient temperature within about a half an inch from the devices. the power is then increased with 1.7v 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 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 temperature from exceeding 125c. a three meter per second air? ow across the devices will decrease the device temperature about 20c providing a margin for higher operating ambient temperatures. both at low power and relatively high power levels devices can be paralleled for higher output current. current sharing and thermal sharing is excellent, showing that acceptable operation can be had while keeping the peak temperatures below excessive operating temperatures on a board. this technique allows higher operating current linear regulation to be used in systems where it could never be used before. figure 6. temperature rise at 1.7w dissipation figure 5. temperature rise at 700mw dissipation applications information
LT3080-1 12 30801fa quieting the noise the LT3080-1 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 reference out to an external pin (usually through a large value resistor) to allow for bypassing and noise reduction of reference noise. the LT3080-1 does not use a traditional voltage reference like other linear regulators, but instead uses a reference current. that current operates with typical noise current levels of 3.2pa/ hz (1na 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 setting resistor may be bypassed with a capacitor, though this causes start-up time to increase as a factor of the rc time constant. the LT3080-1 uses a unity-gain follower from the set pin to drive the output, and there is no requirement to use a resistor to set the output voltage. use a high accuracy voltage reference placed at the set pin to remove the errors in output voltage due to reference current tolerance and resistor tolerance. active driving of the set pin is acceptable; the limitations are the creativity and ingenuity of the circuit designer. one problem that a normal linear regulator sees with reference voltage noise is that noise is gained up along with the output when using a resistor divider to operate at levels higher than the normal reference voltage. with the LT3080-1, 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 125nv/ hz (40v 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 characteristics for both the reference current and error ampli? er over the 10hz to 100khz bandwidth. overload recovery like many ic power regulators, the LT3080-1 has safe operating area (soa) protection. the soa protection decreases current limit as the input-to-output voltage increases and keeps the power dissipation at safe levels for all values of input-to-output voltage. the LT3080-1 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 section. 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 voltage to recover. other regulators, such as the lt1085 and lt1764a, also exhibit this phenomenon so it is not unique to the LT3080-1. the problem occurs with a heavy output load when the input voltage is high and the output voltage is low. common situations are immediately after the removal of a short circuit. the load line for such a load may intersect the output current curve at two points. if this happens, there are two stable operating points for the regulator. with this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. applications information
LT3080-1 13 30801fa function of output load current. output voltage is set based on the midpoint of the output load current range: 1 2 ? () ( ) ii out min out max + () as output current decreases below the midpoint, output voltage increases above the nominal set-point. corre- spondingly, as output current increases above the midpoint, output voltage decreases below the nominal set-point. during a large output load transient, output voltage perturbation is contained within a window that is tighter than what would result if active voltage positioning is not employed. choose the set pin resistor value by using the formula below: r vir i set out mid ballast set = + (?) where i mid = 1/2 (i out(min) + i out(max) ) r ballast = 25m i set = 10a thermal considerations the LT3080-1 has internal power and thermal limiting circuitry designed to protect it under overload conditions. for continuous normal load conditions, maximum junction temperature must not be exceeded. it is important to figure 7. connections for best load regulation + C LT3080-1 in v control out 30801 f07 set r set r p 25m parasitic resistance r p r p load load regulation because the LT3080-1 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 LT3080-1 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. the internal 25m ballast resistor is outside of the LT3080-1s feedback loop. therefore, the voltage drop across the ballast resistor appears as additional dc load regulation. however, this additional load regulation can actually improve transient response performance by decreasing peak-to-peak output voltage deviation and even save on total output capacitance. this technique is called active voltage positioning and is especially useful for applications that must withstand large output load current transients. for more information, see design note 224, active voltage positioning reduces output capacitors. the basic principle uses the fact that output voltage is a applications information
LT3080-1 14 30801fa 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. 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 measurements were taken in still air on two-sided 1/16" fr-4 board with one ounce copper. table 1. 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 2. dd package, 8-lead dfn copper area thermal resistance (junction-to-ambient) topside* backside board area 2500mm 2 2500mm 2 2500mm 2 60c/w 1000mm 2 2500mm 2 2500mm 2 62c/w 225mm 2 2500mm 2 2500mm 2 65c/w 100mm 2 2500mm 2 2500mm 2 68c/w *device is mounted on topside pcb layers, copper weight, board layout and thermal vias affect the resultant thermal resistance. although tables 1 and 2 provide thermal resistance numbers for a 2-layer board with 1 ounce copper, modern multilayer pcbs provide better performance than found in these tables. for example, a 4-layer, 1 ounce copper pcb board with ? ve thermal vias from the dfn or msop exposed backside pad to inner layers (connected to v out ) achieves 40c/w thermal resistance. demo circuit 995as board layout achieves this 40c/w performance. this is approximately a 33% improvement over the numbers shown in tables 1 and 2. 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 1a and a maximum ambient 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. 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 = 1a, t a = 50c applications information
LT3080-1 15 30801fa power dissipation under these conditions is equal to: pdrive = (v control C v out )(i control ) i i a ma control out === 60 1 60 17 p drive = (3.630v C 0.9v)(17ma) = 46mw p output = (v in C v out )(i out ) p output = (1.575v C 0.9v)(1a) = 675mw total power dissipation = 721mw junction temperature will be equal to: t j = t a + p total ? e ja (approximated using tables) t j = 50c + 721mw ? 64c/w = 96c 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 LT3080-1 package without sacri? cing output current capability. two techniques are available. the ? rst technique, illustrated in figure 8, employs a resistor in series with the regulators input. the voltage drop across r s decreases the LT3080-1s in-to- figure 8. reducing power dissipation using a series resistor + C LT3080-1 in v control out v out v in a v in c2 30801 f08 set r set 25m r s c1 applications information out differential voltage and correspondingly decreases the LT3080-1s power dissipation. as an example, assume: v in = v control = 5v, v out = 3.3v and i out(max) = 1a. use the formulas from the calculating junction temperature section previously discussed. without series resistor r s , power dissipation in the LT3080-1 equals: pvv a vva total = () 2 | + () = 533 1 60 533 11 C. ? C. ? .7 73 w if the voltage differential (v diff ) across the npn pass transistor is chosen as 0.5v, then r s equals: r vvv a s = < = 53305 1 12 C. . . 1 power dissipation in the LT3080-1 now equals: pvv a va w total = () 2 | + () = 533 1 60 05 1 053 C. ? . ? . the LT3080-1s power dissipation is now only 30% compared to no series resistor. r s dissipates 1.2w of power. choose appropriate wattage resistors to handle and dissipate the power properly.
LT3080-1 16 30801fa the second technique for reducing power dissipation, shown in figure 9, uses a resistor in parallel with the LT3080-1. this resistor provides a parallel path for current ? ow, reducing the current ? owing through the LT3080-1. 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) = 1a and i out(min) = 0.7a. also, assuming that r p carries no more than 90% of i out(min) = 630ma. calculating r p yields: r vv a p == 55 32 063 365 .C. . . 1 (5% standard value = 3.6) the maximum total power dissipation is (5.5v C 3.2v) ? 1a = 2.3w. however, the LT3080-1 supplies only: 1 55 32 36 036 a vv a C .C. . . 1 = therefore, the LT3080-1s power dissipation is only: p dis = (5.5v C 3.2v) ? 0.36a = 0.83w r p dissipates 1.47w of power. as with the ? rst technique, choose appropriate wattage resistors to handle and dissipate the power properly. with this con? guration, the LT3080-1 supplies only 0.36a. therefore, load current can increase by 0.64a to 1.64a while keeping the LT3080-1 in its normal operating range. figure 9. reducing power dissipation using a parallel resistor + C in v control out v out v in c2 30801 f09 set r set r p c1 LT3080-1 25m applications information
LT3080-1 17 30801fa adding shutdown current source typical applications + C LT3080-1 in v in v control out v out 30801 ta02 set r1 on off shutdown q1 vn2222ll q2* vn2222ll *q2 insures zero output in the absence of any output load 25m + C LT3080-1 in v control out set 25m LT3080-1 25m + C in v control out 1 100k 30801 ta03 set i out 0a to 2a 10f v in 10v + C LT3080-1 in v control out set 25m 2.2f
LT3080-1 18 30801fa using a lower value set resistor adding soft-start typical applications 2ma v out 0.5v to 10v 30801 ta04 set r1 24.9k 1% r set 4.99k 1% v out = 0.5v + 2ma ? r set v in 10v + C LT3080-1 in v control out set 25m + C LT3080-1 in v control out 25m c1 2.2f r2 249 1% c out 10f 30801 ta05 set r1 165k v in 4.8v to 28v + C LT3080-1 in v control out set 25m + C LT3080-1 in v control out 25m c1 2.2f c out 10f v out 3.3v 2.2a d1 in4148 c2 0.01f
LT3080-1 19 30801fa typical applications lab supply 3080 ta06 set v in 13v to 18v + C LT3080-1 in v control out set 25m 0.5 + C LT3080-1 in v control out 25m 15f 10f 50k 0a to 2a current limit + 15f 100f + v out 0v to 10v set + C LT3080-1 in v control out set 25m + C LT3080-1 in v control out 25m + r4 500k 30801 ta07 20m 42* 47f 3.3v out 2.6a 33k *4mv drop ensures LT3080-1 is off with no-load multiple LT3080-1s can be used in parallel + C 10f 5v out set lt1963-3.3 LT3080-1 25m boosting fixed output regulators
LT3080-1 20 30801fa low voltage, high current adjustable high ef? ciency regulator* LT3080-1 25m 2.7v to 5.5v ? 2 100f 2.2meg 100k 470pf 10k 1000pf 2 100f 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 in v control out set + C in v control out 0v to 4v ? 4a set + C in v control out set 30801 ta08 + C in v control out 100f set + + + * differential voltage on LT3080-1 is 0.6v set by the v be of the 2n3906 pnp ? maximum output voltage is 1.5v below input voltage LT3080-1 25m LT3080-1 25m LT3080-1 25m typical applications
LT3080-1 21 30801fa adjustable high ef? ciency regulator* 2 terminal current source typical applications 30801 ta09 4.5v to 25v ? 10f 68f 0.1f 10h mbrm140 10k 10k 1f v in boost sw fb shdn gnd lt3493 cmdsh-4e 0.1f tp0610l + C in v control out set 4.7f 0v to 10v ? 1a * differential voltage on LT3080-1 1.4v set by the tpo610l p-channel threshold. 1meg ? maximum output voltage is 2v below input voltage LT3080-1 25m 100k 30801 ta10 r1 out 100k current set + C c comp * in v control set *c comp r1 10 10f r1 10 2.2f i out = 1v r1 LT3080-1 25m
LT3080-1 22 30801fa dd package 8-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1698) package description 3.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (weed-1) 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 top and bottom of package 0.38 0.10 bottom view?xposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.115 typ 2.38 0.10 (2 sides) 1 4 8 5 pin 1 top mark (note 6) 0.200 ref 0.00 ?0.05 (dd) dfn 1203 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50 bsc 0.675 0.05 3.5 0.05 package outline 0.25 0.05 0.50 bsc
LT3080-1 23 30801fa information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ms8e package 8-lead plastic msop (reference ltc dwg # 05-08-1662) package description msop (ms8e) 0307 rev d 0.53 0.152 (.021 .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 0.18 (.007) 0.254 (.010) 1.10 (.043) max 0.22 ?0.38 (.009 ?.015) typ 0.86 (.034) ref 0.65 (.0256) bsc 0 ?6 typ detail ? detail ? gauge plane 12 3 4 4.90 0.152 (.193 .006) 8 8 1 bottom view of exposed pad option 7 6 5 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) (note 4) 0.52 (.0205) ref 1.83 0.102 (.072 .004) 2.06 0.102 (.081 .004) 5.23 (.206) min 3.20 ?3.45 (.126 ?.136) 2.083 0.102 (.082 .004) 2.794 0.102 (.110 .004) 0.889 0.127 (.035 .005) recommended solder pad layout 0.42 0.038 (.0165 .0015) typ 0.65 (.0256) bsc 0.1016 0.0508 (.004 .002)
LT3080-1 24 30801fa 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 1008 rev a ? printed in usa part number description comments ldos lt1086 1.5a low dropout regulator fixed 2.85v, 3.3v, 3.6v, 5v and 12v output lt1117 800ma low dropout regulator 1v dropout, adjustable or fixed output, dd-pak, sot-223 packages lt1118 800ma low dropout regulator okay for sinking and sourcing, s0-8 and sot-223 packages 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 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. switching regulators 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/ltc3406b 600ma (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 vldo and thinsot are trademarks of linear technology corporation. paralleling regulators + C LT3080-1 in v in 4.8v to 28v v control out 25m 10f v out 3.3v 2.2a 30801 ta11 165k set 1f + C LT3080-1 in v control out 25m set typical application related parts

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