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1 for more information www.linear.com/LT3980 58v, 2a, 2.4mhz step-down switching regulator with 85a quiescent current the lt ? 3980 is an adjustable frequency (100khz to 2.4mhz) monolithic buck switching regulator that accepts input voltages up to 58v (80v transient). a high effciency 200m switch is included on the die along with a boost schottky diode and the necessary oscillator, control, and logic circuitry. current mode topology is used for fast transient response and good loop stability. catch diode current sense (da pin) protects the circuit during input voltage transients even when a high switching frequency is used. low ripple burst mode operation maintains high effciency at low output currents while keeping output ripple below 15mv in a typical application. in addition, the LT3980 can further enhance low output current effciency by drawing bias current from the output when v out is above 3v. shutdown reduces input supply current to less than 1a while a resistor and capacitor on the run/ss pin provide a controlled output voltage ramp (soft-start). a power good fag signals when v out reaches 91% of the programmed output voltage. the LT3980 is available in 16-pin msop and 3mm 4mm dfn packages with exposed pads for low thermal resistance. automotive battery regulation distributed supply regulation industrial supplies wall transformer regulation wide input range: operation from 3.6v to 58v overvoltage lockout protects circuits through 80v transients 2a maximum output current low ripple (<15mv p-p ) burst mode ? operation: i q = 85a at 12v in to 3.3v out adjustable switching frequency: 100khz to 2.4mhz low shutdown current: i q < 1a catch diode current sense protects circuit through short-circuit and input overvoltage synchronizable between 250khz to 2mhz power good flag saturating switch design: 200m on-resistance thermal protection soft-start capability small 16-pin thermally enhanced msop and 3mm 4mm dfn packages 5v step-down converter effciency, v out = 5v typical a pplica t ion descrip t ion fea t ures a pplica t ions sw fb v c pg rt v in bd v in 6.5v to 58v transient to 80v v out 5v 2a 10f 0.47f 1nf 47f 100k 4.75k 97.6k 10h 22pf 536k gnd da off on LT3980 3980 ta01 run/ss boost sync l , lt, ltc, ltm, linear technology, burst mode and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. i load (a) 0 0.5 efficiency (%) 1 2 3980 ta01b 1.5 v in = 12v v in = 48v f = 400khz d = diodes, inc. sbr3u100lp v in = 24v 85 70 60 55 50 95 90 80 75 65 3980fa LT3980
2 for more information www.linear.com/LT3980 the denotes the specifcations which apply over the full operating temper- ature range, otherwise specifcations are at t a = 25c. v in = 10v, v run/ss = 10v, v boost = 15v, v bd = 3.3v unless otherwise noted. (note 2) e lec t rical c harac t eris t ics v in , run/ss voltage (note 5) ................................... 80v boost pin voltage ................................................... 75v boost pin above sw pin ......................................... 30v fb, rt, v c voltage ....................................................... 5v pg, bd, sync voltage .............................................. 25v (note 1) parameter conditions min typ max units minimum input voltage 3 3.6 v v in overvoltage lockout 58 61.5 64 v quiescent current from v in v run/ss = 0.2v v bd = 3v, not switching v bd = 0, not switching 20 70 0.01 35 120 0.5 60 160 a a a operating junction temperature range (note 2) LT3980e ............................................. C 40c to 125c LT3980i .............................................. C 40c to 125c LT3980h ............................................ C 40c to 150c storage temperature range ................... C 65c to 150c lead temperature (soldering, 10 sec) (mse only) ....................................................... 300c 1 2 3 4 5 6 7 14 13 12 11 10 9 8 da nc v in sw boost bd run/ss sync nc pg fb v c rt gnd top view de14 package 14-lead (4mm 3mm) plastic dfn 15 gnd ja = 45c/w, jc = 10c/w exposed pad (pin 15) is gnd, must be soldered to pcb 1 2 3 4 5 6 7 8 sync pg nc fb nc v c rt gnd 16 15 14 13 12 11 10 9 nc da v in nc sw boost bd run/ss top view mse package 16-lead plastic msop 17 gnd ja = 45c/w, jc = 10c/w exposed pad (pin 17) is gnd, must be soldered to pcb p in con f i g ura t ion or d er in f orma t ion lead free finish tape and reel part marking* package description temperature range LT3980ede#pbf LT3980ede#trpbf 3980 14-lead (3mm 4mm) plastic dfn C 40c to 125c LT3980ide#pbf LT3980ide#trpbf 3980 14-lead (3mm 4mm) plastic dfn C 40c to 125c LT3980emse#pbf LT3980emse#trpbf 3980 16-lead plastic msop C 40c to 125c LT3980imse#pbf LT3980imse#trpbf 3980 16-lead plastic msop C 40c to 125c LT3980hmse#pbf LT3980hmse#trpbf 3980 16-lead plastic msop C 40c to 150c consult ltc marketing for parts specifed with wider operating temperature ranges. *the temperature grade is identifed by a label on the shipping container. consult ltc marketing for information on non-standard lead based fnish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifcations, go to: http://www.linear.com/tapeandreel/ a bsolu t e m aximum r a t in g s 3980fa LT3980
3 for more information www.linear.com/LT3980 parameter conditions min typ max units quiescent current from bd v run/ss = 0.2v v bd = 3v, not switching v bd = 0, not switching 55 0.01 82 1 0.5 115 5 a a a feedback voltage 782 770 790 790 798 805 mv mv fb pin bias current (note 3) v fb = 0.8v, v c = 1.2v 10 40 na fb voltage line regulation 4v < v in < 56v 0.002 0.01 %/v error amp g m 500 mho error amp gain 1800 v c source current 60 a v c sink current 60 a v c pin to switch current gain 3.87 a/v v c clamp voltage 2 v switching frequency r t = 8.66k r t = 29.4k r t = 187k 1.95 0.86 195 2.25 1.07 225 2.55 1.27 255 mhz mhz khz minimum switch off-time 140 230 ns switch current limit duty cycle = 5% 3.3 4 4.9 a switch v cesat i sw = 2a 540 mv da pin current to pause osc 1.9 2.4 3 a boost schottky reverse leakage v bd = 0v 0.02 2 a minimum boost voltage (note 4) 1.7 2.2 v boost pin current i sw = 2a 40 55 ma run/ss pin current v run/ss = 2.5v 6 10 a run/ss input voltage high 2.5 v run/ss input voltage low 0.4 v pg threshold offset from feedback voltage v fb rising 50 65 80 mv pg hysteresis 14 mv pg leakage v pg = 5v 0.1 1 a pg sink current v pg = 0.4v 200 700 a sync threshold 0.575 0.675 0.775 v sync pin bias current v sync = 0v 0.1 a 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: the LT3980e is guaranteed to meet performance specifcations from 0c to 125c. specifcations over the C40c to 125c operating temperature range are assured by design, characterization and correlation with statistical process controls. the LT3980i specifcations are guaranteed over the C40c to 125c temperature range. the LT3980h specifcations are guaranteed over the C40c to 150c operating temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. note 3: bias current fows out of the fb pin. note 4: this is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch. note 5: absolute maximum at v in and run/ss pins is 80v for non- repetitive 1 minute transients, and 60v for continuous operation. the denotes the specifcations which apply over the full operating temperature range, otherwise specifcations are at t a = 25c. v in = 10v, v run/ss = 10v, v boost = 15v, v bd = 3.3v unless otherwise noted. (note 2) e lec t rical c harac t eris t ics 3980fa LT3980
4 for more information www.linear.com/LT3980 input voltage (v) 0 supply current (a) 3980 g04 50 30 10 20 10 130 110 90 70 30 40 50 60 v out = 3.3v duty cycle (%) 0 switch current limit (a) 40 3980 g08 3.5 20 60 2.5 2.0 5.0 4.5 4.0 3.0 80 100 typical minimum temperature (c) ?50 supply current (a) 350 25 3980 g05 200 100 ?25 0 50 50 0 400 300 250 150 75 100 150125 v in = 12v v out = 3.3v catch diode: diodes, inc. pds360 increased supply current due to catch diode leakage at high temperature i load (a) 0 0.5 efficiency (%) 1 2 3980 g02 1.5 v in = 12v v in = 48v f = 400khz d = diodes, inc. sbr3u100lp v in = 24v 85 70 60 55 50 95 90 80 75 65 input voltage (v) load current (a) 3980 g07 2.0 3.5 3.0 2.5 typical minimum 5 10 20 30 40 50 15 25 35 45 6055 input voltage (v) load current (a) 3980 g06 2.0 3.5 3.0 2.5 typical minimum 5 10 20 30 40 50 15 25 35 45 6055 temperature (c) switch current limit (a) 4.0 4.5 5.5 5.0 3980 g09 3.5 3.0 2.0 2.5 6.5 6.0 duty cycle = 10% ?50 25 ?25 0 50 75 100 150125 efciency, v out = 5v no-load supply current maximum load current, v out = 3.3v switch current limit switch current limit maximum load current, v out = 5v no-load supply current t a = 25c unless otherwise noted. switching frequency (mhz) 0.20 efficiency (%) power loss (w) 84 86 1.60 82 80 0.60 1.00 0.40 0.80 1.20 1.80 1.40 2.00 74 72 78 88 76 3.0 3.5 2.5 2.0 0.5 0 1.5 4.0 1.0 3980 g03 v in = 12v v out = 5v i out = 2a typical p er f ormance c harac t eris t ics efciency, v out = 3.3v efciency vs switching frequency i load (a) 0 0.5 efficiency (%) 1 2 3980 g01 1.5 v in = 12v v in = 48v f = 400khz d = diodes, inc. sbr3u100lp v in = 24v 85 70 60 55 50 90 80 75 65 3980fa LT3980
5 for more information www.linear.com/LT3980 run/ss pin voltage (v) 0 switch current limit (a) 1.5 3980 g17 4 2 0.5 1 2 1 0 7 6 5 3 2.5 3 3.5 fb pin voltage (mv) 0 switching frequency (khz) 800 1000 1200 600 3980 g14 600 400 200 400 800 500 100 300 700 900 200 0 temperature (c) minimum switch on-time (ns) 180 200 220 3980 g16 160 140 120 100 240 ?50 25 ?25 0 50 75 100 150125 i load = 1a run/ss pin voltage (v) run/ss pin current (a) 16 20 24 3980 g18 12 8 4 0 0 10 20 30 40 50 60 switch current (a) 0 boost pin current (ma) 15 45 60 75 120 3980 g11 30 90 105 0 3 1 2 temperature (c) feedback voltage (mv) 800 3980 g12 760 840 780 820 ?50 25 ?25 0 50 75 100 150125 temperature (c) frequency (mhz) 1.00 1.10 3880 g13 0.90 0.80 1.20 0.95 1.05 0.85 1.15 ?50 25 ?25 0 50 75 100 150125 rf = 32.4k switch current (a) 0 400 500 700 3 3980 g10 300 200 1 2 100 0 600 voltage drop (mv) boost pin current vs switch current feedback voltage switching frequency frequency foldback minimum switch on-time soft-start run/ss pin current switch voltage drop t a = 25c unless otherwise noted. typical p er f ormance c harac t eris t ics r t vs frequency resistance (k) 1 2000 switching frequency (khz) 2500 3000 10 100 1000 1500 1000 500 0 3500 3980 g15 3980fa LT3980
6 for more information www.linear.com/LT3980 fb pin error voltage (mv) ?200 ?50 v c pin current (a) ?20 0 20 0 200 50 3980 g20 ?40 ?100 100 40 10 ?10 30 ?30 error amp output current temperature (c) v c voltage (v) 1.50 2.00 2.50 3980 g23 1.00 0.50 0 current limit clamp switching threshold ?50 25 ?25 0 50 75 100 150125 3980 g25 i l 0.2a/div v sw 5v/div v out 10mv/div 5s/div v in = 12v v out = 3.3v i load = 10ma temperature (c) threshold voltage (%) 85 90 95 3980 g24 80 75 ?50 25 ?25 0 50 75 100 150125 3980 g26 i l 0.2a/div v sw 5v/div v out 10mv/div v in = 12v v out = 3.3v i load = 110ma 1s/div 3980 g27 i l 0.5a/div v sw 5v/div v out 10mv/div v in = 12v v out = 3.3v i load = 1a 1s/div minimum input voltage, v out = 3.3v minimum input voltage, v out = 5v v c voltages power good threshold switching waveforms: transition from burst mode operation to full frequency switching waveforms: full frequency continuous operation switching waveforms: burst mode operation t a = 25c, unless otherwise noted. typical p er f ormance c harac t eris t ics boost diode current (a) 0 boost diode v f (v) 0.8 1.0 1.2 2.0 3980 g19 0.6 0.4 0 0.5 1.0 1.5 0.2 1.4 boost diode 1 10 100 1000 2000 f = 400khz i load (ma) input voltage (v) 4 5 3980 g21 3 2 6 to start to run i load (ma) input voltage (v) 6 7 3980 g22 5 4 8 1 10 100 1000 2000 to start to run f = 400khz 3980fa LT3980
7 for more information www.linear.com/LT3980 sync (pin 1/pin 1): this is the external clock synchro - nization input. ground this pin for low ripple burst mode operation at low output loads. tie to a voltage above 0.8v to select pulse-skipping mode. tie to a clock source for synchronization. clock edges should have rise and fall times faster than 1s. tie pin to gnd if not used. see the synchronization section in applications information. nc (pins 2, 13/pins 3, 5, 13, 16): no connect. these pins are not connected to internal circuitry. pg (pin 3/pin 2): the pg pin is the open collector output of an internal comparator. pg remains low until the fb pin is within 9% of the fnal regulation voltage. pg output is valid when v in is above 3.6v and run/ss is high. fb (pin 4/pin 4): the LT3980 regulates the fb pin to 0.790v. connect the feedback resistor divider tap to this pin. v c (pin 5/pin 6): the v c pin is the output of the internal error amplifer. the voltage on this pin controls the peak switch current. tie an rc network from this pin to ground to compensate the control loop. rt (pin 6/pin 7): oscillator resistor input. connecting a resistor to ground from this pin sets the switching frequency. gnd (pin 7, 15/pin 8, 17): ground. the exposed pads must be soldered to the pcb. run/ss (pin 8/pin 9): the run/ss pin is used to put the LT3980 in shutdown mode. tie to ground to shut down the LT3980. tie to 2.5v or more for normal operation. if the shutdown feature is not used, tie this pin to the v in pin. run/ss also provides a soft-start function; see the applications information section. bd (pin 9/pin 10): this pin connects to the anode of the boost schottky diode. bd also supplies current to the internal regulator. boost (pin 10/pin 11): this pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar npn power switch. sw (pin 11/pin 12): the sw pin is the output of the internal power switch. connect this pin to the inductor, catch diode and boost capacitor. v in (pin 12/pin 14): the v in pin supplies current to the LT3980s internal regulator and to the internal power switch. this pin must be locally bypassed. da (pin 14/pin 15): this pin measures catch diode current and pauses the oscillator during overcurrent conditions. + ? + ? + ? oscillator 100khzto2.4mhz burstmode detect v c clamp soft-start slope comp r v in v in run/ss boost sw switch latch v c v out c2 c3 c f l1 d1 disable c c r c bd rt r2 gnd error amp r1 fb r t c1 pg 0.725v s q da 3680 bd internal 0.79v ref sync b lock dia g ram p in func t ions (dfn, msop) 3980fa LT3980
8 for more information www.linear.com/LT3980 the LT3980 is a constant frequency, current mode step- down regulator. an oscillator, with frequency set by rt, enables an rs fip-fop, turning on the internal power switch. an amplifer and comparator monitor the current fowing between the v in and sw pins, turning the switch off when this current reaches a level determined by the voltage at v c . an error amplifer measures the output voltage through an external resistor divider tied to the fb pin and servos the v c pin. if the error amplifers output increases, more current is delivered to the output; if it decreases, less current is delivered. an active clamp on the v c pin provides current limit. the v c pin is also clamped to the voltage on the run/ss pin; soft-start is implemented by generating a voltage ramp at the run/ss pin using an external resistor and capacitor. an internal regulator provides power to the control circuitry. the bias regulator normally draws power from the v in pin, but if the bd pin is connected to an external voltage higher than 3v bias power will be drawn from the external source (typically the regulated output voltage). this improves effciency. the run/ss pin is used to place the LT3980 in shutdown, disconnecting the output and reducing the input current to less than 0.5a. the switch driver operates from either the input or from the boost pin. an external capacitor and diode are used to generate a voltage at the boost pin that is higher than the input supply. this allows the driver to fully saturate the internal bipolar npn power switch for effcient operation. to further optimize effciency, the LT3980 automatically switches to burst mode operation in light load situations. between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 75a in a typical application. the oscillator reduces the LT3980s operating frequency when the voltage at the fb pin is low. this frequency foldback helps to control the output current during startup and overload. in addition, the LT3980 monitors the catch diode current fowing through the da pin and pauses the oscillator during overcurrent conditions to keep inductor current at safe levels. the LT3980 contains a power good comparator which trips when the fb pin is at 91% of its regulated value. the pg output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the pg pin high. power good is valid when the LT3980 is enabled and v in is above 3.6v. the LT3980 has an overvoltage protection feature which disables switching action when the v in goes above 61.5v typical (58v minimum). when switching is disabled, the LT3980 can safely sustain input voltages up to 62v. o pera t ion 3980fa LT3980
9 for more information www.linear.com/LT3980 fb resistor network the output voltage is programmed with a resistor divider between the output and the fb pin. choose the 1% resis - tors according to: rr v v out 12 07 9 1 = ? ? ? ? ? ? . ? reference designators refer to the block diagram. setting the switching frequency the LT3980 uses a constant frequency pwm architecture that can be programmed to switch from 100khz to 2.4mhz by using a resistor tied from the rt pin to ground. a table showing the necessary rt value for a desired switching frequency is in figure 1. switching frequency (mhz) r t value (k?) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 432 215 137 97.6 76.8 60.4 51.1 43.2 35.7 32.4 24.9 20 16.2 14 11 figure 1. switching frequency vs r t value operating frequency trade-offs selection of the operating frequency is a trade-off between effciency, component size, minimum dropout voltage, and maximum input voltage. the advantage of high frequency operation is that smaller inductor and capacitor values may be used. the disadvantages are lower effciency , lower maximum input voltage, and higher dropout voltage. the highest acceptable switching frequency (f sw(max) ) for a given application can be calculated as follows: f vv tv vv sw ma x d out on mi n di ns w () () = + + () ? where v in is the typical input voltage, v out is the output voltage, v d is the catch diode drop (~0.5v) and v sw is the internal switch drop (~0.5v at max load). this equation shows that slower switching frequency is necessary to safely accommodate high v in /v out ratio. also, as shown in the next section, lower frequency allows a lower dropout voltage. the reason input voltage range depends on the switching frequency is because the LT3980 switch has fnite minimum on and off times. the switch can turn on for a minimum of ~200ns and turn off for a minimum of ~200ns. this means that the minimum and maximum duty cycles are: dc ft dc ft mins w on mi n ma xs w of fm in = = () () 1? where f sw is the switching frequency, the t on(min) is the minimum switch on time (~200ns), and the t off(min) is the minimum switch off time (~200ns). these equations show that duty cycle range increases when switching frequency is decreased. a good choice of switching frequency should allow ade - quate input voltage range (see next section) and keep the inductor and capacitor values small. input v oltage range the maximum input voltage for LT3980 applications de - pends on switching frequency, absolute maximum ratings of the v in and boost pins, and the operating mode. the LT3980 can operate from input voltages of up to 58v, and withstand voltages up to 80v. note that while v in is above 61v typical (58v minimum and 64v maximum) the part will keep the switch off and the output will not be in regulation. t he switching frequency should be chosen according to the following equation: v vv ft vv in ma x out d sw on mi n ds w () () = + + ? where v in(max) is the maximum typical operating input voltage, v out is the output voltage, v d is the catch diode a pplica t ions i n f orma t ion 3980fa LT3980
10 for more information www.linear.com/LT3980 drop (~0.5v), v sw is the internal switch drop (~0.5v at max load), f sw is the switching frequency (set by r t ), and t on(min) is the minimum switch on time (~200ns). note that a higher switching frequency will depress the maximum operating input voltage. conversely, a lower switching frequency will be necessary to achieve safe operation at high input voltages. input voltages up to 58v are acceptable regardless of the switching frequency. in this mode, the LT3980 may enter pulse-skipping operation where some switching pulses are skipped to maintain safe inductor current. the minimum input voltage is determined by either the LT3980s minimum operating voltage of ~3.6v or by its maximum duty cycle (see equation in previous section). the minimum input voltage due to duty cycle is: v vv ft vv in mi n out d sw of fm in ds w () () = + + 1? ? where v in(min) is the minimum input voltage, and t off(min) is the minimum switch off time (200ns). note that higher switching frequency will increase the minimum input voltage. if a lower dropout voltage is desired, a lower switching frequency should be used. inductor selection for a given input and output voltage, the inductor value and switching frequency will determine the ripple current. the ripple current i l increases with higher v in or v out and decreases with higher inductance and faster switching frequency. a reasonable starting point for selecting the ripple current is: i l = 0.4(i out(max) ) where i out(max) is the maximum output load current. to guarantee suffcient output current, peak inductor current must be lower than the LT3980s switch current limit (i lim ). the peak inductor current is: i l(peak) = i out(max) + i l /2 where i l(peak) is the peak inductor current, i out(max) is the maximum output load current, and i l is the inductor ripple current. the LT3980s switch current limit (i lim ) is 4a at low duty cycles and decreases linearly to 3a at dc = 0.8. the maximum output current is a function of the inductor ripple current: i out(max) = i lim C i l /2 be sure to pick an inductor ripple current that provides suffcient maximum output current (i out(max) ). the largest inductor ripple current occurs at the highest v in . to guarantee that the ripple current stays below the specifed maximum, the inductor value should be chosen according to the following equation: l vv fi vv v out d sw l out d in ma x = + ? ? ? ? ? ? + ? ? ? ? ? ? 1? () ?? ? ? where v d is the voltage drop of the catch diode (~0.4v), v in(max) is the maximum input voltage, v out is the output voltage, f sw is the switching frequency (set by rt), and l is in the inductor value. the inductors rms and saturation current rating must be greater than the maximum load current. for robust operation in fault conditions (start-up or short circuit) and high input voltage (>40v), the saturation current should be above 3.5a. to keep the effciency high, the series resistance (dcr) should be less than 0.1, and the core material should be intended for high frequency applications. table 1 lists several vendors and suitable types. table 1. inductor vendors vendor url part series type murata www.murata.com lqh55d open tdk www.component.tdk.com slf10145 shielded toko www.toko.com d75c d75f shielded open sumida www.sumida.com cdrh74 cr75 cdrh8d43 shielded open shielded nec www .nec-tokin.com mplc073 mpbi0755 shielded shielded vishay www .vishay.com ihlp2525ce01 shielded a pplica t ions i n f orma t ion 3980fa LT3980
11 for more information www.linear.com/LT3980 of course, such a simple design guide will not always re - sult in the optimum inductor for your application. a larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. if your load is lower than 2a , then you can decrease the value of the inductor and operate with higher ripple current. this allows you to use a physically smaller inductor , or one with a lower dcr resulting in higher effciency. there are several graphs in the typical performance characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. low inductance may result in discontinuous mode operation, which is okay but further reduces maximum load current. for details of maximum output current and discontinuous mode oper - ation, see linear technology application note 44. finally, for duty cycles greater than 50% (v out /v in > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. see an19. input capacitor bypass the input of the LT3980 circuit with a ceramic capacitor of x7r or x5r type. y5v types have poor performance over temperature and applied voltage, and should not be used. a 10f to 22f ceramic capacitor is adequate to bypass the LT3980 and will easily handle the ripple current. note that larger input capacitance is required when a lower switching frequency is used. if the input power source has high impedance, or there is signifcant inductance due to long wires or cables, additional bulk capacitance may be necessary. this can be provided with a lower performance electrolytic capacitor. step-down regulators draw current from the input sup - ply in pulses with very fast rise and fall times. the input capacitor is required to reduce the resulting voltage rip - ple at the LT3980 and to force this very high frequency switching current into a tight local loop, minimizing emi. a 10f capacitor is capable of this task, but only if it is placed close to the l t3980 and the catch diode (see the pcb layout section). a second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3980. a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. if the l t3980 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3980s voltage rating. this situation is easily avoided (see the hot plugging safety section). for space sensitive applications, a 4.7f ceramic ca - pacitor can be used for local bypassing of the LT3980 input. however , the lower input capacitance will result in increased input current ripple and input voltage ripple, and may couple noise into other circuitr y . also, the increased voltage ripple will raise the minimum operating voltage of the LT3980 to ~3.7v. output capacitor and output ripple the output capacitor has two essential functions. along with the inductor, it flters the square wave generated by the LT3980 to produce the dc output. in this role it determines the output ripple, and low impedance at the switching frequency is important. the second function is to store energy in order to satisfy transient loads and stabilize the LT3980s control loop. ceramic capacitors have very low equivalent series resistance (esr) and provide the best ripple performance. a good starting value is: c vf out out sw = 100 where f sw is in mhz, and c out is the recommended output capacitance in f. use x5r or x7r types. this choice will provide low output ripple and good transient response. transient performance can be improved with a higher value capacitor if the compensation network is also adjusted to maintain the loop bandwidth. a lower value of output capacitor can be used to save space and cost but transient performance will suffer. see the frequency compensation section to choose an appropriate compensation network. when choosing a capacitor, look carefully through the data sheet to fnd out what the actual capacitance is under operating conditions (applied voltage and temperature). a physically larger capacitor, or one with a higher voltage rating, may be required. high performance tantalum or electrolytic capacitors can be used for the output capacitor. low esr is important, so choose one that is intended for a pplica t ions i n f orma t ion 3980fa LT3980
12 for more information www.linear.com/LT3980 use in switching regulators. the esr should be specifed by the supplier, and should be 0.05 or less. such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the capacitor must be large to achieve low esr. table 2 lists several capacitor vendors. table 2. capacitor vendors vendor url part series commands panasonic www.panasonic.com ceramic, polymer, tantalum eef series kemet www.kemet.com ceramic, tantalum t494, t495 sanyo www.sanyovideo.com ceramic, polymer, tantalum poscap murata www.murata.com ceramic sot-23 avx www.avxcorp.com ceramic, tantalum sot-23 taiyo yuden www.taiyo-yuden.com ceramic tps series catch diode the catch diode conducts current only during switch off time. average forward current in normal operation can be calculated from: i d(avg) = i out (v in C v out )/v in where i out is the output load current. the only reason to consider a diode with a larger current rating than necessary for nominal operation is for the worst-case condition of shorted output. the diode current will then increase to the typical peak switch current. peak reverse voltage is equal to the regulator input voltage. use a schottky diode with a reverse voltage rating greater than the input voltage. the overvoltage protection feature in the LT3980 will keep the switch off when v in > 64v which allows the use of 64v rated schottky even when v in ranges up to 80v. ceramic capacitors ceramic capacitors are small, robust and have very low esr. however, ceramic capacitors can cause problems when used with the LT3980 due to their piezoelectric nature. when in burst mode operation, the LT3980s switching frequency depends on the load current, and at very light loads the LT3980 can excite the ceramic capacitor at audio frequencies, generating audible noise. since the LT3980 operates at a lower current limit during burst mode operation, the noise is nearly silent to a casual ear. if this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. frequency compensation the LT3980 uses current mode control to regulate the output. this simplifes loop compensation. in particular, the LT3980 does not require the esr of the output capacitor for stability, so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. frequen - cy compensation is provided by the components tied to the v c pin, as shown in figure 2. generally a capacitor (c c ) and a resistor (r c ) in series to ground are used. in addition, there may be lower value capacitor in parallel. this capacitor (c f ) is not part of the loop compensation but is used to flter noise at the switching frequency, and is required only if a phase-lead capacitor is used or if the output capacitor has high esr. ? + 0.79v sw v c g m = 500mho gnd 3m LT3980 3980 f02 r1 output esr c f c c r c error amplifier fb r2 c1 c1 current mode power stage g m = 5.3mho + polymer or tantalum ceramic c pl figure 2. model for loop response a pplica t ions i n f orma t ion 3980fa LT3980
13 for more information www.linear.com/LT3980 loop compensation determines the stability and transient perfor mance. designing the compensation network is a bit complicated and the best values depend on the application and in particular the type of output capacitor. a practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the com - pensation network to optimize the performance. stability should then be checked across all operating conditions, including load current, input voltage and temperature. the lt1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the sta - bility using a transient load. figure 2 shows an equivalent cir cuit for the LT3980 control loop. the error amplifer is a transconductance amplifer with fnite output impedance. the power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifer generating an output current proportional to the voltage at the v c pin. note that the output capacitor integrates this current, and that the capacitor on the v c pin (c c ) integrates the error amplifer output current, resulting in two poles in the loop. in most cases a zero is required and comes from either the output capacitor esr or from a resistor r c in series with c c . this simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. a phase lead capacitor (c pl ) across the feedback divider may improve the transient response. figure 3 shows the transient response when the load current is stepped from 0.5a to 1.5a and back to 0.5a. low ripple burst mode operation and pulse-skipping mode the LT3980 is capable of operating in either low ripple burst mode operation or pulse-skipping mode which are selected using the sync pin. see the synchronization section for details. to enhance effciency at light loads, the LT3980 can be operated in low ripple burst mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. during burst mode operation, the LT3980 delivers single cycle bursts of current to the output capacitor followed by sleep periods where the output power is delivered to the load by the output capacitor. because the LT3980 delivers power to the output with single, low current pulses, the output ripple is kept below 15mv for a typical application. in addition, v in and bd quiescent currents are reduced to typically 35a and 82a respectively during the sleep time. as the load current decreases towards a no-load condition, the percentage of time that the LT3980 operates in sleep mode increases and the average input current is greatly reduced resulting in high effciency even at very low loads. see figure 4. at higher output loads (above 140ma for the front page application) the LT3980 will be running at the frequency programmed by the r t resistor, and will be operating in standard pwm mode. the transition between pwm and low ripple burst mode operation is seamless, and will not disturb the output voltage. figure 3. transient load response of the LT3980 front page application as the load current is stepped from 0.5a to 1.5a 3980 f03 i l 0.5a/div v out 100mv/div 50s/div v in = 12v v out = 5v a pplica t ions i n f orma t ion figure 4. burst mode operation 3980 f04 i l 0.2a/div v sw 5v/div v out 10mv/div 5s/div v in = 12v v out = 3.3v i load = 10ma 3980fa LT3980
14 for more information www.linear.com/LT3980 if low quiescent current is not required the LT3980 can operate in pulse-skipping mode. the beneft of this mode is that the LT3980 will enter full frequency standard pwm operation at a lower output load current than when in burst mode operation. the front page application circuit will switch at full frequency at output loads higher than about 60ma. boost and bias pin considerations capacitor c3 and the internal boost schottky diode (see the block diagram) are used to generate a boost voltage that is higher than the input voltage. in most cases a 0.22f capacitor will work well. figure 2 shows three ways to arrange the boost circuit. the boost pin must be more than 2.3v above the sw pin for best effciency. for outputs of 3v and above, the standard circuit (figure 5a) is best. for outputs between 2.8v and 3v, use a 1f boost capacitor. a 2.5v output presents a special case because it is marginally adequate to support the boosted drive stage while using the internal boost diode. for reliable boost pin operation with 2.5v outputs use a good external schottky diode (such as the on semi mbr0540), and a 1f boost capacitor (see figure 5b). for lower output voltages the boost diode can be tied to the input (figure 5c), or to an - other supply greater than 2.8v. tying bd to v in reduces the maximum input voltage to 28v. the circuit in figure 5a is more effcient because the boost pin current and bd pin quiescent current comes from a lower voltage source. you must also be sure that the maximum voltage ratings of the boost and bd pins are not exceeded. a pplica t ions i n f orma t ion figure 5. three circuits for generating the boost voltage v in boost sw bd v in v out 4.7f c3 gnd LT3980 v in boost sw bd v in v out 4.7f c3 d2 gnd LT3980 v in boost sw bd v in v out 4.7f c3 gnd LT3980 3980 fo5 (5a) for v out > 2.8v (5b) for 2.5v < v out < 2.8v (5c) for v out < 2.5v; v in(max) = 30v 3980fa LT3980
15 for more information www.linear.com/LT3980 on input and output voltages, and on the arrangement of th e boost circuit. the minimum load generally goes to zero once the circuit has started. figure 6 shows a plot of minimum load to start and to run as a function of input voltage. in many cases the discharged output capacitor will present a load to the switcher, which will allow it to start. the plots show the worst-case situation where v in is ramping very slowly. for lower start-up voltage, the boost diode can be tied to v in ; however, this restricts the input range to one-half of the absolute maximum rating of the boost pin. at light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. this reduces the minimum input voltage to approximately 300mv above v out . at higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3980, requiring a higher input voltage to maintain regulation. soft-start the run/ss pin can be used to soft-start the LT3980, reducing the maximum input current during start-up. the run/ss pin is driven through an external rc flter to while operating with high boost voltages (>10v), it is important to ensure that the power dissipation from the boost circuit is not too high. see the typical performance characteristics section for the plot, boost pin current vs switch current. boost circuit power dissipation is calculated as follows: p boost = i boost v boost C sw dc where dc is the switch duty cycle, i boost is the boost pin current, and v boost C v sw is the voltage between the boost pin and switch pin. if the p boost > 0.5w, a zener can be put between the boost pin and the boost capacitor such that the power is dissipated in the zener instead of the LT3980. the minimum operating voltage of an LT3980 application is limited by the minimum input voltage (3.6v) and by the maximum duty cycle as outlined in a previous section. for proper startup, the minimum input voltage is also limited by the boost circuit. if the input voltage is ramped slowly, or the LT3980 is turned on with its run/ss pin when the output is already in regulation, then the boost capacitor may not be fully charged. because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. this minimum load will depend figure 6. the minimum input voltage depends on output voltage, load current and boost circuit a pplica t ions i n f orma t ion 1 10 100 1000 2000 f = 400khz i load (ma) input voltage (v) 4 5 3980 f06a 3 2 6 to start to run i load (ma) input voltage (v) 6 7 3980 f06b 5 4 8 1 10 100 1000 2000 to start to run f = 400khz 3980fa LT3980
16 for more information www.linear.com/LT3980 create a voltage ramp at this pin. figure 7 shows the start- up and shutdown waveforms with the soft-start circuit. by choosing a large rc time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. choose the value of the resistor so that it can supply 20a when the run/ ss pin reaches 2.5v. synchronization to select low ripple burst mode operation, tie the sync pin below 0.5v (this can be ground or a logic output). tie to a voltage above 0.8v to select pulse-skipping mode. synchronizing the LT3980 oscillator to an external fre - quency can be done by connecting a square wave (with 20% to 80% duty cycle) to the sync pin. the square wave amplitude should have valleys that are below 0.3v and peaks that are above 0.8v (up to 6v). the LT3980 will not enter burst mode operation at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. the LT3980 may be synchronized over a 150khz to 2mhz range. the r t resistor should be chosen to set the LT3980 switching frequency 25% below the lowest synchronization input. for example, if the synchronization signal will be 250khz and higher, the r t should be chosen for 200khz. to assure reliable and safe operation the LT3980 will only synchronize when the output voltage is near regulation as indicated by the pg fag. it is therefore necessary to choose a large enough inductor value to supply the required output current at the frequency set by the r t resistor. see the inductor selection section. it is also important to note that slope compensation is set by the r t value: when the sync frequency is much higher than the one set by r t , the slope compensation will be signifcantly reduced which may require a larger inductor value to prevent subharmonic oscillation. shorted and reversed input protection if an inductor is chosen that will not saturate excessively, an LT3980 buck regulator will tolerate a shorted output. there is another situation to consider in systems where the output will be held high when the input to the LT3980 is absent. this may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ored with the LT3980s output. if the v in pin is allowed to foat and the run/ss pin is held high (either by a logic signal or because it is tied to v in ), then the LT3980s internal circuitry will pull its quiescent current through its sw pin. this is fne if your system can tolerate a few ma in this state. if you ground the run/ ss pin, the sw pin current will drop to essentially zero. however, if the v in pin is grounded while the output is held high, then parasitic diodes inside the LT3980 can pull large currents from the output through the sw pin and the a pplica t ions i n f orma t ion figure 7. to soft-start the LT3980, add a resistor and capacitor to the run/ss pin 3680 f07 i l 1a/div v run/ss 2v/div v out 2v/div run/ss gnd run 15k 2ms/div 0.22f 3980fa LT3980
17 for more information www.linear.com/LT3980 figure 8. diode d4 prevents a shorted input from discharging a backup battery tied to the output. it also protects the circuit from a reversed input. the LT3980 runs only when the input is present v in boost gnd fb run/ss v c sw d4 mbrs360 v in LT3980 3980 f08 v out backup figure 9. a good pcb layout ensures proper, low emi operation pacitors can cause problems if the LT3980 is plugged into a live supply (see linear technology application note 88 for a complete discussion). the low loss ceramic capacitor, combined with stray inductance in series with the power source, forms an under damped tank circuit, and the voltage at the v in pin of the LT3980 can ring to twice the nominal input voltage, possibly exceeding the LT3980s rating and damaging the part. if the input supply is poorly controlled or the user will be plugging the LT3980 into an energized supply, the input network should be designed to prevent this overshoot. figure 10 shows the waveforms that result when an LT3980 circuit is connected to a 24v supply through six feet of 24-gauge twisted pair. the frst plot is the response with a 4.7f ceramic capacitor at the input. the input voltage rings as high as 50v and the input current peaks at 26a. a good solution is shown in figure 10b. a 0.7 resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). a 0.1f capacitor improves high frequency fltering. for high input voltages its impact on effciency is minor, reducing effciency by 1.5 percent for a 5v output at full load operating from 24v. a pplica t ions i n f orma t ion v in pin. figure 8 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. r pg vias to local ground plane vias to v out vias to run/ss vias to pg vias to v in outline of local ground plane 3980 f09 l1 c2 r rt r c r2 r1 c c v out d1 c1 gnd vias to sync pcb layout for proper operation and minimum emi, care must be taken during printed circuit board layout. figure 9 shows the recommended component placement with trace, ground plane and via locations. note that large, switched currents fow in the LT3980s v in and sw pins, the catch diode (d1) and the input capacitor (c1). the loop formed by these components should be as small as possible. these components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. place a local, unbroken ground plane below these components. the sw and boost nodes should be as small as possible. finally, keep the fb and v c nodes small so that the ground traces will shield them from the sw and boost nodes. the exposed pad on the bottom of the package must be soldered to ground so that the pad acts as a heat sink. to keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT3980 to additional ground planes within the circuit board and on the bottom side. hot plugging safely the small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3980 circuits. however, these ca - 3980fa LT3980
18 for more information www.linear.com/LT3980 high temperature considerations the pcb must provide heat sinking to keep the LT3980 cool. the exposed pad on the bottom of the package must be soldered to a ground plane. this ground should be tied to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LT3980. place additional vias can reduce thermal resistance further. with these steps, the thermal resistance from die (or junction) to ambient can be reduced to ja = 35c/w or less. with 100 lfpm airfow, this resistance can fall by another 25%. further increases in airfow will lead to lower thermal re - sistance. because of the large output current capability of the LT3980, it is possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125c. when operating at high ambient temperatures, the maximum load current should be derated as the ambient temperature approaches 125c. power dissipation within the LT3980 can be estimated by calculating the total power loss from an effciency mea - surement and subtracting the catch diode loss and inductor loss. the die temperature is calculated by multiplying the LT3980 power dissipation by the thermal resistance from junction to ambient. other linear technology publications application notes 19, 35 and 44 contain more detailed descriptions and design information for buck regulators and other switching regulators. the lt1376 data sheet has a more extensive discussion of output ripple, loop compensation and stability testing. design note 100 shows how to generate a bipolar output supply using a buck regulator. a pplica t ions i n f orma t ion figure 10. a well chosen input network prevents input voltage overshoot and ensures reliable operation when the LT3980 is connected to a live supply + LT3980 4.7f v in 20v/div i in 10a/div 20s/div v in closing switch simulates hot plug i in (10a) (10b) low impedance energized 24v supply stray inductance due to 6 feet (2 meters) of twisted pair + LT3980 4.7f 0.1f 0.7 v in 20v/div i in 10a/div 20s/div danger ringing v in may exceed absolute maximum rating (10c) + LT3980 4.7f 22f ai.ei. 3980 f10 v in 20v/div i in 10a/div 20s/div + 3980fa LT3980
19 for more information www.linear.com/LT3980 typical a pplica t ions 5v step-down converter 3.3v step-down converter sw fb v c pg rt v in bd v in 6.5v to 58v transient to 80v v out 5v 2a 4.7f 0.47f 47f f = 400khz d 4.75k 97.6k l 8.2h 536k gnd 1nf on off LT3980 3980 ta02 run/ss boost sync da 100k 22pf sw fb v c pg rt v in bd v in 4.3v to 58v transient to 80v v out 3.3v 2a 4.7f 0.47f 47f f = 400khz d 4.75k 97.6k l 6.8h gnd 2.2nf on off LT3980 3980 ta03 run/ss boost sync 316k da 100k 22pf 2.5v step-down converter sw fb v c pg rt v in bd v in 4v to 58v transient to 80v v out 2.5v 2a 4.7f 1f 47f f = 300khz d1 8.45k 137k l 4.7h 215k gnd 2.2nf on off LT3980 d2 3980 ta04 run/ss boost sync da 100k 22pf 3980fa LT3980
20 for more information www.linear.com/LT3980 typical a pplica t ions 1.8v step-down converter 12v step-down converter sw fb v c pg rt v in bd v in 15v to 58v transient to 80v v out 12v 2a 10f 0.47f 22f 50k f = 600khz d 12k 60.4k l 15h gnd 1nf on off LT3980 3980 ta06 run/ss boost sync 715k da sw fb v c pg rt v in bd v in 3.5v to 32v v out 1.8v 2a 4.7f 0.47f 100f f = 400khz d 2.49k 97.6k l 3.3h 127k gnd 680pf on off LT3980 3980 ta08 run/ss boost sync da 100k 22pf 5v, 1.2mhz step-down converter sw fb v c pg rt v in bd v in 8.6v to 40v transient to 80v v out 5v 2a 4.7f 0.47f 22f f = 1.2mhz d 4.75k 24.9k l 4.7h gnd 1nf on off LT3980 3980 ta05 run/ss boost sync 536k da 100k 22pf 3980fa LT3980
21 for more information www.linear.com/LT3980 3.00 0.10 (2 sides) 4.00 0.10 (2 sides) note: 1. drawing proposed to be made variation of version (wged-3) in jedec package outline mo-229 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom view?exposed pad 1.70 0.10 0.75 0.05 r = 0.115 typ r = 0.05 typ 3.00 ref 1.70 0.05 1 7 14 8 pin 1 top mark (see note 6) 0.200 ref 0.00 ? 0.05 (de14) dfn 0806 rev b pin 1 notch r = 0.20 or 0.35 45 chamfer 3.00 ref recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 2.20 0.05 0.70 0.05 3.60 0.05 package outline 0.25 0.05 0.25 0.05 0.50 bsc 3.30 0.05 3.30 0.10 0.50 bsc de package 14-lead plastic dfn (4mm 3mm) (reference ltc dwg # 05-08-1708 rev b) p acka g e descrip t ion please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 3980fa LT3980
22 for more information www.linear.com/LT3980 msop (mse16) 0213 rev f 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 ?0.27 (.007 ? .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 16 16151413121110 1 2 3 4 5 6 7 8 9 9 1 8 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 include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.305 0.038 (.0120 .0015) typ 0.50 (.0197) bsc bottom view of exposed pad option 2.845 0.102 (.112 .004) 2.845 0.102 (.112 .004) 4.039 0.102 (.159 .004) (note 3) 1.651 0.102 (.065 .004) 1.651 0.102 (.065 .004) 0.1016 0.0508 (.004 .002) 3.00 0.102 (.118 .004) (note 4) 0.280 0.076 (.011 .003) ref 4.90 0.152 (.193 .006) detail ?b? detail ?b? corner tail is part of the leadframe feature. for reference only no measurement purpose 0.12 ref 0.35 ref mse package 16-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1667 rev f) p acka g e descrip t ion please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 3980fa LT3980
23 for more information www.linear.com/LT3980 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. r evision h is t ory rev date description page number a 10/13 clarifed effciency graph clarifed graphs clarifed sync pin description clarifed graph clarifed graph clarifed synchronization description 1 6 7 15 16 16 3980fa LT3980
24 for more information www.linear.com/LT3980 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 ? linear technology corporation 2009 lt 1013 rev a ? printed in usa (408) 432-1900 o fax : (408) 434-0507 o www.linear.com/LT3980 part number description comments lt3689 36v, 60v transient protection, 800ma, 2.2mhz high effciency micropower step-down dc/dc converter with por reset and watchdog timer v in : 3.6v to 36 v (transient to 60v), v out(min) = 0.8v, i q = 75a, i sd < 1 a, 3mm 3mm qfn-16 package lt3682 36v, 60v max , 1a, 2.2mhz high effciency micropower step-down dc/dc converter v in : 3.6v to 36v, v out(min) = 0.8v, i q = 75a, i sd < 1 a, 3mm 3mm dfn-12 lt3970 40v, 350ma (i out ), 2.2mhz high effciency step-down dc/dc converter with only 2.5a of quiescent current v in : 4.2v to 40v, v out(min) = 1.21v, i q = 2.5a, i sd < 1 a, 3mm 3mm dfn-10 and msop-10 packages lt3480 36v with transient protection to 60v, 2a (i out ), 2.4mhz, high effciency step-down dc/dc converter with burst mode operation v in : 3.6v to 38v, v out(min) = 0.78v, i q = 70a, i sd < 1 a, 3mm 3mm dfn-10 and msop-10e packages lt3685 36v with transient protection to 60v, dual 2a (i out ), 2.4mhz, high effciency step-down dc/dc converter v in : 3.6v to 38v, v out(min) = 0.78v, i q = 70a, i sd < 1 a, 3mm 3mm dfn-10 and msop-10e packages lt3481 34v with transient protection to 36v, 2a (i out ), 2.8mhz, high effciency step-down dc/dc converter with burst mode operation v in : 3.6v to 34v, v out(min) = 1.26v, i q = 50a, i sd < 1 a, 3mm 3mm dfn-10 and msop-10e packages lt3684 34v with transient protection to 36v, 2a (i out ), 2.8mhz, high effciency step-down dc/dc converter v in : 3.6v to 34v, v out(min) = 1.26v, i q = 850a, i sd < 1 a, 3mm 3mm dfn-10 and msop-10e packages lt3508 36v with transient protection to 40v, dual 1.4a (i out ), 3mhz, high effciency step-down dc/dc converter v in : 3.7v to 37v, v out(min) = 0.8v, i q = 4.6ma, i sd = 1 a, 4mm 4mm qfn-24 and tssop-16e packages lt3505 36v with transient protection to 40v, 1.4a (i out ), 3mhz, high effciency step-down dc/dc converter v in : 3.6v to 34v, v out(min) = 0.78v, i q = 2ma, i sd = 2a, 3mm 3mm dfn-8 and msop-8e packages lt3500 36v, 40v max , 2.5mhz high effciency step-down dc/dc converter and ldo controller v in : 3.6v to 36v, v out(min) = 0.8v, i q = 2.5ma, i sd = 10a, 3mm 3mm dfn-10 package lt3507 36v, 2.5mhz, triple (2.4a + 1.5a + 1.5a (i out )) with ldo controller high effciency step-down dc/dc converter v in : 4v to 36v, v out(min) = 0.8v, i q = 7ma, i sd < 1 a, 5mm 7mm qfn-38 package lt3437 60v, 400ma (i out ), micropower step-down dc/dc converter with burst mode operation v in : 3.3v to 60v, v out(min) = 1.25v, i q = 100a, i sd < 1 a, 3mm 3mm dfn-10 and tssop-16e packages lt1976/lt1977 60v, 1.2a (i out ), 200khz/500khz, high effciency step-down dc/dc converters with burst mode operation v in : 3.3v to 60v, v out(min) = 1.20v, i q = 100a, i sd < 1 a, tssop-16e package lt3434/lt3435 60v , 2.4a (i out ), 200khz/500khz, high effciency step-down dc/dc converters with burst mode operation v in : 3.3v to 60v, v out(min) = 1.2v, i q = 100a, i sd < 1 a, tssop-16e package lt1936 36v, 1.4a (i out ), 500khz, high effciency step-down dc/dc converter v in : 3.6v to 36v, v out(min) = 1.2v, i q = 1.9ma, i sd < 1a, ms8e package lt3493 36v, 1.4a (i out ), 750khz high effciency step-down dc/dc converter v in : 3.6v to 36v, v out(min) = 0.8v, i q = 1.9ma, i sd < 1 a, 2mm 3mm dfn-6 package lt1766 60v, 1.2a (i out ), 200khz, high effciency step-down dc/dc converter v in : 5.5v to 60v, v out(min) = 1.20v, i q = 2.5ma, i sd < 25a, tssop-16 and tssop-16e packages sw fb v c pg rt v in bd v in 3.6v to 32v v out 1.2v 2a 4.7f 0.47f 100f f = 400khz d 14k 97.6k l 3.3h gnd 1nf on off LT3980 3980 ta09 run/ss boost sync 100k 52.3k da 1.2v step-down converter r ela t e d p ar t s typical a pplica t ion 3980fa LT3980

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