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1 typical application features applications description 36v, 2a, 2.4mhz step-down switching regulator with 70a quiescent current the lt ? 3480 is an adjustable frequency (200khz to 2.4mhz) monolithic buck switching regulator that ac - cepts input voltages up to 36v (60v maximum). a high effciency 0.25 switch is included on the die along with a boost schottky diode and the necessary oscillator, con - trol, and logic circuitry. current mode topology is used for fast transient response and good loop stability. 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 lt3480 can further enhance low output current effciency by draw - ing 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 86% of the programmed output voltage. the lt3480 is available in 10-lead msop and 3mm 3mm dfn packages with exposed pads for low thermal resistance. n wide input range: operation from 3.6v to 36v over-voltage lockout protects circuits through 60v transients n 2a maximum output current n low ripple burst mode ? operation 70a i q at 12v in to 3.3v out output ripple < 15mv n adjustable switching frequency: 200khz to 2.4mhz n low shutdown current: i q < 1a n integrated boost diode n synchronizable between 250khz to 2mhz n power good flag n saturating switch design: 0.25 on-resistance n 0.790v feedback reference voltage n output voltage: 0.79v to 20v n soft-start capability n small 10-lead thermally enhanced msop and (3mm 3mm) dfn packages n automotive battery regulation n power for portable products n distributed supply regulation n industrial supplies , lt, ltc and ltm are registered trademarks of linear technology corporation. burst mode is a registered trademark of linear technology corporation. all other trademarks are the property of their respective owners. 3.3v step-down converter sw fb v c pg rt v in bd v in 4.5v to 36v transient to 60v v out 3.3v 2a 4.7f 0.47f 470pf 22f 100k 14k 40.2k 4.7h 316k gnd off on lt3480 3480 ta01 run/ss boost sync effciency load current (a) 0 efficiency (%) 50 0.5 1.0 1.5 2 3480 ta01b 60 100 90 80 70 v in = 12v l = 5.6h f = 800 khz v out = 3.3v v out = 5v lt3480 3480fe for more information www.linear.com/lt3480
2 absolute maximum ratings v in , run/ss voltage (note 5) ................................... 60v boost pin voltage ................................................... 56v boost pin above sw pin ......................................... 30v fb, rt, v c voltage ....................................................... 5v pg, bd, sync voltage .............................................. 30v operating junction temperature range (note 2) lt3480e ............................................. C40c to 125c lt3480i .............................................. C40c to 125c lt3480h ............................................ C40c to 150c lt3480mp .......................................... C55c to 150c (note 1) top view dd package 10-lead (3mm 3mm) plastic dfn 10 9 6 7 8 4 5 3 11 2 1 rt v c fb pg sync bd boost sw v in run/ss ja = 45c/w, jc = 10c/w exposed pad (pin 11) is gnd, must be soldered to pcb 1 2 3 4 5 bd boost sw v in run/ss 10 9 8 7 6 rt v c fb pg sync top view mse package 10-lead plastic msop 11 ja = 45c/w, jc = 10c/w exposed pad (pin 11) is gnd, must be soldered to pcb pin configuration order information lead free finish tape and reel part marking* package description temperature range lt3480edd#pbf lt3480edd #trpbf lctp 10-lead (3mm 3mm) plastic dfn C40c to 125c lt3480idd #pbf lt3480idd #trpbf lctp 10-lead (3mm 3mm) plastic dfn C40c to 125c lt3480emse#pbf lt3480emse #trpbf ltctm 10-lead plastic msop C40c to 125c lt3480imse#pbf lt3480imse #trpbf ltctm 10-lead plastic msop C40c to 125c lt3480hmse#pbf lt3480hmse #trpbf ltctm 10-lead plastic msop C40c to 150c lt3480mpmse#pbf lt3480mpmse #trpbf ltctm 10-lead plastic msop C55c to 150c lead based finish tape and reel part marking* package description temperature range lt3480edd l t3480edd#tr lctp 10-lead (3mm 3mm) plastic dfn C40c to 125c lt3480idd lt3480idd #tr lctp 10-lead (3mm 3mm) plastic dfn C40c to 125c lt3480emse lt3480emse #tr ltctm 10-lead plastic msop C40c to 125c lt3480imse lt3480imse #tr ltctm 10-lead plastic msop C40c to 125c lt3480hmse lt3480hmse #tr ltctm 10-lead plastic msop C40c to 150c lt3480mpmse lt3480mpmse #tr ltctm 10-lead plastic msop C55c 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. 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/ storage temperature range ................... C65c to 150c lead temperature (soldering, 10 sec) (mse only) ....................................................... 300c lt3480 3480fe for more information www.linear.com/lt3480
3 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. the l 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) note 2: the lt3480e 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 lt3480i specifcations are parameter conditions min typ max units minimum input voltage l 3 3.6 v v in overvoltage lockout l 36 38 40 v quiescent current from v in v run/ss = 0.2v v bd = 3v, not switching v bd = 0, not switching l 0.01 30 105 0.5 100 160 a a a quiescent current from bd v run/ss = 0.2v v bd = 3v, not switching v bd = 0, not switching l 0.01 80 1 0.5 120 5 a a a minimum bias voltage (bd pin) 2.7 3 v feedback voltage l 780 775 790 790 800 805 mv mv fb pin bias current (note 3) v fb = 0.8v, v c = 0.4v l 7 30 na fb voltage line regulation 4v < v in < 36v 0.002 0.01 %/v error amp g m 400 mho error amp gain 1000 v c source current 45 a v c sink current 45 a v c pin to switch current gain 3.5 a/v v c clamp voltage 2 v switching frequency r t = 8.66k r t = 29.4k r t = 187k 2.1 0.9 160 2.4 1 200 2.7 1.15 240 mhz mhz khz minimum switch off-time l 60 150 ns switch current limit duty cycle = 5% 3 3.5 4 a switch v cesat i sw = 2a 500 mv boost schottky reverse leakage v bd = 0v 0.02 2 a minimum boost voltage (note 4) l 1.5 2.1 v boost pin current i sw = 1a 22 35 ma run/ss pin current v run/ss = 2.5v 5 10 a run/ss input voltage high 2.5 v run/ss input voltage low 0.2 v pg threshold offset from feedback voltage v fb rising 100 mv pg hysteresis 12 mv pg leakage v pg = 5v 0.1 1 a pg sink current v pg = 0.4v l 100 600 a sync low threshold 0.5 v sync high threshold 0.7 v sync pin bias current v sync = 0v 0.1 a electrical characteristics lt3480 3480fe for more information www.linear.com/lt3480
4 typical performance characteristics load current (a) 0 50 efficiency (%) 100 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 2.0 1.0 3480 g01 60 90 80 70 v in = 24v v in = 34v v in = 12v l: nec plc-0745-5r6 f: 800khz v out = 5v 0 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 2.0 1.0 load current (a) 50 efficiency (%) 90 3480 g02 60 65 55 85 80 70 75 v in = 12v v in = 7v l: nec plc-0745-5r6 f: 800khz v in = 24v v in = 34v v out = 3.3v load current (a) 0 efficiency (%) power loss (w) 40 30 0.5 1.0 1.5 2 3480 g27 60 50 90 80 70 0.01 0.1 10 1 v in = 12v v out = 3.3v l = 5.6h f = 800 khz input voltage (v) 0 supply current (a) 15 3480 g04 40 20 5 10 20 0 120 100 80 60 25 30 35 v out = 3.3v temperature (c) ?50 supply current (a) 350 25 3480 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 input voltage (v) 5 load current (a) 15 3480 g06 2.5 10 20 1.5 1.0 4.0 3.5 3.0 2.0 25 30 typical minimum v out = 3.3v t a = 25 c l = 4.7h f = 800 khz effciency effciency effciency no load supply current no load supply current maximum load current electrical characteristics c c t lth c c t ltmp c c note 3: bias current ows 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: for operation at t 125c, the absolute maximum voltage at v in and run/ss pins is 40v for continuous operation and 60v for up to 1 second nonrepetitive transients. for operation at t 125c, the absolute maximum voltage at v in and run/ss pins is 36v. lt3480 3480fe for more information www.linear.com/lt3480
5 input voltage (v) 5 load current (a) 15 3480 g07 2.5 10 20 1.5 1.0 3.5 3.0 2.0 25 30 typical minimum v out = 5v t a = 25 c l = 4.7h f = 800khz duty cycle (%) 0 switch current limit(a) 40 3480 g08 2.5 20 60 1.5 1.0 4.0 3.5 3.0 2.0 80 100 temperature (c) switch current limit (a) 2.0 2.5 3.5 3.0 3480 g09 1.5 1.0 0 0.5 4.5 4.0 duty cycle = 10 % duty cycle = 90 % ?50 25 ?25 0 50 75 100 150125 maximum load current switch current limit switch current limit typical performance characteristics switch current (ma) 0 400 500 700 1500 3480 g10 300 200 500 1000 2000 2500 100 0 600 voltage drop (mv) switch current (ma) 0 boost pin current (ma) 10 30 40 50 80 3480 g11 20 60 70 0 1500 500 1000 2000 2500 temperature (c) feedback voltage (mv) 800 4380 g12 760 840 780 820 ?50 25 ?25 0 50 75 100 150125 temperature (c) frequency (mhz) 1.00 1.10 4380 g13 0.90 0.80 1.20 0.95 1.05 0.85 1.15 ?50 25 ?25 0 50 75 100 150125 fb pin voltage (mv) 0 switching frequency (khz) 800 1000 1200 600 3480 g14 600 400 200 400 800 500 100 300 700 900 200 0 temperature (?c) minimum switch on time (ns) 80 100 120 3480 g15 60 40 20 0 140 ?50 25 ?25 0 50 75 100 150125 switch voltage drop boost pin current feedback voltage switching frequency frequency foldback minimum switch on-time lt3480 3480fe for more information www.linear.com/lt3480
6 fb pin error voltage (v) ?200 ?50 v c pin current (a) ?20 0 20 0 200 50 3480 g19 ?40 ?100 100 40 10 ?10 30 ?30 load current (a) 1 input voltage (v) 3.0 3.5 10000 3480 g20 2.5 2.0 10 100 1000 5.0 4.5 4.0 v out = 3.3v t a = 25c l = 4.7h f = 800khz 1 10000 10 100 1000 load current (a) input voltage (v) 5.0 5.5 3480 g21 4.5 4.0 6.5 6.0 v out = 5v t a = 25 c l = 4.7h f = 800khz temperature (c) v c voltage (v) 1.50 2.00 2.50 3480 g22 1.00 0.50 0 current limit clamp switching threshold ?50 25 ?25 0 50 75 100 150125 temperature (c) threshold voltage (%) 85 90 95 3480 g23 80 75 ?50 25 ?25 0 50 75 100 150125 3480 g24 i l 0.2a/div v sw 5v/div v out 10mv/div 5s/div v in = 12v; front page application i load = 10ma error amp output current minimum input voltage minimum input voltage v c voltages power good threshold switching waveforms; burst mode typical performance characteristics run/ss pin voltage (v) 0 switch current limit (a) 3.5 1.5 3480 g16 2.0 1.0 0.5 1 2 0.5 0 4.0 3.0 2.5 1.5 2.5 3 3.5 run/ss pin voltage (v) 0 run/ss pin current (a) 8 10 12 15 25 3480 g17 6 4 5 10 20 30 35 2 0 boost diode current (a) 0 boost diode v f (v) 0.8 1.0 1.2 2.0 3480 g18 0.6 0.4 0 0.5 1.0 1.5 0.2 1.4 soft-start run/ss pin current boost diode lt3480 3480fe for more information www.linear.com/lt3480
7 pin functions bd (pin 1): this pin connects to the anode of the boost schottky diode. bd also supplies current to the internal regulator. bd must be locally bypassed when not tied to v out with a low esr capacitor (1f). boost (pin 2): this pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar npn power switch. sw (pin 3): 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 4): the v in pin supplies current to the lt3480s internal regulator and to the internal power switch. this pin must be locally bypassed. run/ss (pin 5): the run/ss pin is used to put the lt3480 in shutdown mode. tie to ground to shut down the lt3480. 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. sync (pin 6): this is the external clock synchronization input. ground this pin for low ripple burst mode operation at low output loads. tie to a clock source for synchronization. clock edges should have rise and fall times faster than 1s. see synchronizing section in applications information. pg (pin 7): the pg pin is the open collector output of an internal comparator. pg remains low until the fb pin is within 14% of the fnal regulation voltage. pg output is valid when v in is above 3.6v and run/ss is high. fb (pin 8): the lt3480 regulates the fb pin to 0.790v. connect the feedback resistor divider tap to this pin. v c (pin 9): 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 10): oscillator resistor input. connecting a resistor to ground from this pin sets the switching frequency. exposed pad (pin 11): ground. the exposed pad must be soldered to pcb. 3480 g25 i l 0.2a/div v sw 5v/div v out 10mv/div v in = 12v; front page application i load = 110ma 1s/div 3480 g26 i l 0.5a/div v sw 5v/div v out 10mv/div v in = 12v; front page application i load = 1a 1s/div switching waveforms; transition from burst mode to full frequency switching waveforms; full frequency continuous operation typical performance characteristics lt3480 3480fe for more information www.linear.com/lt3480
8 operation the lt3480 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 lt3480 in shutdown, disconnecting the output and reducing the input current to less than 1a. 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 lt3480 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 70a in a typical application. the oscillator reduces the lt3480s operating frequency when the voltage at the fb pin is low. this frequency foldback helps to control the output current during startup and overload. block diagram + ? + ? + ? oscillator 200khz?2.4mhz burst mode 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 0.7v s q 3480 bd 4 5 10 7 1 2 3 9 11 8 6 internal 0.79v ref sync lt3480 3480fe for more information www.linear.com/lt3480
9 applications information operation 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: r1 = r2 v out 0.79v ? 1 ? ? ? ? ? ? reference designators refer to the block diagram. setting the switching frequency the lt3480 uses a constant frequency pwm architecture that can be programmed to switch from 200khz to 2.4mhz by using a resistor tied from the rt pin to ground. a table showing the necessary r t value for a desired switching frequency is in figure 1. switching frequency (mhz) r t value (k ?) 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 2.2 2.4 187 121 88.7 68.1 56.2 46.4 40.2 34 29.4 23.7 19.1 16.2 13.3 11.5 9.76 8.66 figure 1. switching frequency vs. r t value operating frequency tradeoffs selection of the operating frequency is a tradeoff 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 sw(max) = v d + v out t on(min) v d + v in ? v sw ( ) 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 lt3480 switch has fnite minimum on and off times. the switch can turn on for a minimum of ~150ns and turn off for a minimum of ~150ns. typical minimum on time at 25c is 80ns. this means that the minimum and maximum duty cycles are: dc min = f sw t on(min) dc max = 1? f sw t off(min ) where f sw is the switching frequency, the t on(min) is the minimum switch on time (~150ns), and the t off(min) is the minimum switch off time (~150ns). these equations show that duty cycle range increases when switching frequency is decreased. the lt3480 contains a power good comparator which trips when the fb pin is at 86% 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 lt3480 is enabled and v in is above 3.6v. the lt3480 has an overvoltage protection feature which disables switching action when the v in goes above 38v typical (36v minimum). when switching is disabled, the lt3480 can safely sustain input voltages up to 60v. lt3480 3480fe for more information www.linear.com/lt3480
10 applications information a good choice of switching frequency should allow ad - equate input voltage range (see next section) and keep the inductor and capacitor values small. input voltage range the maximum input voltage for lt3480 applications depends on switching frequency, the absolute maximum ratings of the v in and boost pins, and the operating mode. the lt3480 can operate from input voltages up to 38v, and safely withstand input voltages up 60v. note that while v in >38v (typical), the lt3480 will stop switching, allowing the output to fall out of regulation. while the output is in start-up, short-circuit, or other overload conditions, the switching frequency should be chosen according to the following discussion. for safe operation at inputs up to 60v the switching fre- quency must be set low enough to satisfy v in(max) 40v according to the following equation. if lower v in(max) is desired, this equation can be used directly. v in(max) = v out + v d f sw t on(min) ? v d + v sw where v in(max) is the maximum operating input voltage, v out is the output voltage, v d is the catch diode 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 (~150ns). 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. if the output is in regulation and no short-circuit, start- up, or overload events are expected, then input voltage transients of up to 60v are acceptable regardless of the switching frequency. in this mode, the lt3480 may enter pulse skipping operation where some switching pulses are skipped to maintain output regulation. in this mode the output voltage ripple and inductor current ripple will be higher than in normal operation. above 38v switching will stop. the minimum input voltage is determined by either the lt3480s 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 in(min) = v out + v d 1? f sw t off(min) ? v d + v sw where v in(min) is the minimum input voltage, and t off(min) is the minimum switch off time (150ns). 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 lt3480s 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 lt3480s switch current limit (i lim ) is at least 3.5a at low duty cycles and decreases linearly to 2.5a at dc = 0.8. the maximum output current is a func - tion 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 = v out + v d f sw ? i l ? ? ? ? ? ? 1? v out + v d v in(max) ? ? ? ? ? ? lt3480 3480fe for more information www.linear.com/lt3480
11 applications information 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 current rating must be greater than the maximum load current and its saturation current should be about 30% higher. for robust operation in fault conditions (start-up or short circuit) and high input voltage (>30v), 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.componenttdk.com slf7045 slf10145 shielded shielded toko www.toko.com d62cb d63cb d75c d75f shielded shielded shielded open sumida www.sumida.com cr54 cdrh74 cdrh6d38 cr75 open shielded shielded open 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 opera - tion, 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 lt3480 circuit with a ceramic capaci - tor of x7r or x5r type. y5v types have poor performance over temperature and applied voltage, and should not be used. a 4.7f to 10f ceramic capacitor is adequate to bypass the lt3480 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 ripple at the lt3480 and to force this very high frequency switching current into a tight local loop, minimizing emi. a 4.7f capacitor is capable of this task, but only if it is placed close to the lt3480 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 lt3480. a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. if the lt3480 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the lt3480s voltage rating. this situation is easily avoided (see the hot plugging safely section). for space sensitive applications, a 2.2f ceramic capaci - tor can be used for local bypassing of the lt3480 input. however, the lower input capacitance will result in in - creased input current ripple and input voltage ripple, and may couple noise into other circuitry. also, the increased voltage ripple will raise the minimum operating voltage of the lt3480 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 lt3480 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 lt3480 3480fe for more information www.linear.com/lt3480
12 applications information table 2. capacitor vendors vendor phone url part series commands panasonic (714) 373-7366 www.panasonic.com ceramic, polymer, tantalum eef series kemet (864) 963-6300 www.kemet.com ceramic, tantalum t494, t495 sanyo (408) 749-9714 www.sanyovideo.com ceramic, polymer, tantalum poscap murata (408) 436-1300 www.murata.com ceramic avx www.avxcorp.com ceramic, tantalum tps series taiyo yuden (864) 963-6300 www.taiyo-yuden.com ceramic energy in order to satisfy transient loads and stabilize the lt3480s control loop. ceramic capacitors have very low equivalent series resistance (esr) and provide the best ripple performance. a good starting value is: c out = 100 v out f sw 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 use in switching regulators. the esr should be specifed by the supplier, and should be 0.05 or less. such a capaci - tor 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. 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 lt3480 will keep the switch off when v in > 38v which allows the use of 40v rated schottky even when v in ranges up to 60v. table 3 lists several schottky diodes and their manufacturers. table 3. diode vendors part number v r (v) i ave (a) v f at 1a (mv) v f at 2a (mv) on semiconductor mbrm120e mbrm140 20 40 1 1 530 550 595 diodes inc. b120 b130 b220 b230 dfls240l 20 30 20 30 40 1 1 2 2 2 500 500 500 500 500 international rectifer 10bq030 20bq030 30 30 1 2 420 470 470 lt3480 3480fe for more information www.linear.com/lt3480
13 applications information ? + 0.8v sw v c g m = 420mho gnd 3m lt3480 3480 f02 r1 output esr c f c c r c error amplifier fb r2 c1 c1 current mode power stage g m = 3.5mho + polymer or tantalum ceramic c pl figure 2. model for loop response ceramic capacitors ceramic capacitors are small, robust and have very low esr. however, ceramic capacitors can cause problems when used with the lt3480 due to their piezoelectric nature. when in burst mode operation, the lt3480s switching frequency depends on the load current, and at very light loads the lt3480 can excite the ceramic capacitor at audio frequencies, generating audible noise. since the lt3480 operates at a lower current limit during burst mode operation, the noise is typically very quiet to a casual ear. if this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. a fnal precaution regarding ceramic capacitors concerns the maximum input voltage rating of the lt3480. a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. if the lt3480 circuit is plugged into a live supply, the input volt - age can ring to twice its nominal value, possibly exceeding the lt3480s rating. this situation is easily avoided (see the hot plugging safely section). frequency compensation the lt3480 uses current mode control to regulate the output. this simplifes loop compensation. in particular, the lt3480 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. frequency 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 addi - tion, 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. loop compensation determines the stability and transient performance. 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 compensation 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 stability using a transient load. figure 2 shows an equivalent circuit for the lt3480 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 500ma to 1500ma and back to 500ma. lt3480 3480fe for more information www.linear.com/lt3480
14 applications information figure 4. burst mode operation 3480 f04 i l 0.2a/div v sw 5v/div v out 10mv/div 5s/div v in = 12v; front page application i load = 10ma figure 3. transient load response of the lt3480 front page application as the load current is stepped from 500ma to 1500ma. v out = 3.3v 3480 f03 i l 0.5a/div v out 100mv/div 10s/div v in = 12v; front page application low-ripple burst mode and pulse-skip mode the lt3480 is capable of operating in either low-ripple burst mode or pulse-skip mode which are selected using the sync pin. see the synchronization section for details. to enhance effciency at light loads, the lt3480 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 lt3480 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 lt3480 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 30a and 80a respectively during the sleep time. as the load cur - rent decreases towards a no load condition, the percentage of time that the lt3480 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 lt3480 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 is seamless, and will not disturb the output voltage. if low quiescent current is not required the lt3480 can operate in pulse-skip mode. the beneft of this mode is that the lt3480 will enter full frequency standard pwm operation at a lower output load current than when in burst mode. 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 volt - age 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 another supply greater than 2.8v. tying bd to v in reduces the maximum input voltage to 30v. 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. the minimum operating voltage of an lt3480 application is limited by the minimum input voltage (3.6v) and by the lt3480 3480fe for more information www.linear.com/lt3480
15 applications information v in boost sw bd v in v out 4.7f c3 gnd lt3480 v in boost sw bd v in v out 4.7f c3 d2 gnd lt3480 v in boost sw bd v in v out 4.7f c3 gnd lt3480 3480 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 figure 6. the minimum input voltage depends on output voltage, load current and boost circuit 3480 f06 load current (a) 1 input voltage (v) 4.0 4.5 5.0 10000 3.5 3.0 2.0 10 100 1000 1 10000 10 100 1000 2.5 6.0 5.5 to start (worst case) to run load current (a) input voltage (v) 5.0 6.0 7.0 4.0 2.0 3.0 8.0 to run v out = 3.3v t a = 25c l = 8.2h f = 700khz v out = 5v t a = 25c l = 8.2h f = 700khz to start (worst case) figure 5. three circuits for generating the boost voltage 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 lt3480 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 on input and output voltages, and on the arrangement of the 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 discontinu - ous 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 lt3480, requiring a higher input voltage to maintain regulation. lt3480 3480fe for more information www.linear.com/lt3480
16 applications information figure 7. to soft-start the lt3480, add a resisitor and capacitor to the run/ss pin 3480 f07 i l 1a/div v run/ss 2v/div v out 2v/div run/ss gnd run 15k 2ms/div 0.22f 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 lt3480 runs only when the input is present v in boost gnd fb run/ss v c sw d4 mbrs140 v in lt3480 3480 f08 v out backup soft-start the run/ss pin can be used to soft-start the lt3480, reducing the maximum input current during start-up. the run/ss pin is driven through an external rc flter to create a voltage ramp at this pin. figure 7 shows the start- up and shut-down 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 0.3v (this can be ground or a logic output). synchronizing the lt3480 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 lt3480 will not enter burst mode at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. the lt3480 may be synchronized over a 250khz to 2mhz range. the r t resistor should be chosen to set the lt3480 switching frequency 20% 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 lt3480 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 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 the inductor is chosen so that it wont saturate excessively, an lt3480 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 lt3480 is absent. this may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode or-ed with the lt3480s 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 lt3480s 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 lt3480 can pull large currents from the output through the sw pin and the 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. lt3480 3480fe for more information www.linear.com/lt3480
17 applications information 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 3480 f09 l1 c2 r rt r pg r c r2 r1 c c v out d1 c1 gnd vias to sync figure 9. a good pcb layout ensures proper, low emi operation 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 lt3480s 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 lt3480 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 lt3480 circuits. however, these capaci - tors can cause problems if the lt3480 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 lt3480 can ring to twice the nominal input voltage, possibly exceeding the lt3480s rating and damaging the part. if the input supply is poorly controlled or the user will be plugging the lt3480 into an energized supply, the input network should be designed to prevent this overshoot. figure 10 shows the waveforms that result when an lt3480 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. high temperature considerations the pcb must provide heat sinking to keep the lt3480 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 lay - ers will spread the heat dissipated by the lt3480. 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 lt3480 3480fe for more information www.linear.com/lt3480
18 applications information figure 10. a well chosen input network prevents input voltage overshoot and ensures reliable operation when the lt3480 is connected to a live supply + lt3480 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 + lt3480 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) + lt3480 4.7f 22f 35v ai.ei. 3480 f10 v in 20v/div i in 10a/div 20s/div + the lt3480, 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 lt3480 can be estimated by calculating the total power loss from an effciency measure - ment and subtracting the catch diode loss and inductor loss. the die temperature is calculated by multiplying the lt3480 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. lt3480 3480fe for more information www.linear.com/lt3480
19 typical applications sw fb v c pg rt v in bd v in 6.8v to 36v transient to 60v* v out 5v 2a 4.7f 0.47f 22f 100k f = 800khz d: diodes inc. dfls240l l: taiyo yuden np06dzb6r8m d 16.2k 40.2k l 6.8h 536k gnd 470pf on off lt3480 3480 ta02 run/ss boost sync 5v step-down converter 3.3v step-down converter sw fb v c pg rt v in bd v in 4.4v to 36v transient to 60v* v out 3.3v 2a 4.7f 0.47f 22f 100k f = 800khz d: diodes inc. dfls240l l: taiyo yuden np06dzb4r7m d 14k 40.2k l 4.7h 316k gnd 470pf on off lt3480 3480 ta03 run/ss boost sync 2.5v step-down converter sw fb v c pg rt v in bd v in 4v to 36v transient to 60v* v out 2.5v 2a 4.7f 1f 47f 100k f = 600khz d1: diodes inc. dfls240l d2: mbr0540 l: taiyo yuden np06dzb4r7m d1 20k 56.2k l 4.7h 215k gnd 330pf on off lt3480 d2 3480 ta04 run/ss boost sync lt3480 3480fe for more information www.linear.com/lt3480
20 typical applications 1.8v step-down converter 12v step-down converter sw fb v c pg rt v in bd v in 15v to 36v transient to 60v* v out 12v 2a 10f 0.47f 22f 50k f = 800khz d: diodes inc. dfls240l l: nec/tokin plc-0755-100 d 26.1k 40.2k l 10h 715k gnd 330pf on off lt3480 3480 ta06 run/ss boost sync sw fb v c pg rt v in bd v in 3.5v to 27v v out 1.8v 2a 4.7f 0.47f 47f 100k f = 500khz d: diodes inc. dfls240l l: taiyo yuden np06dzb3r3m d 18.2k 68.1k l 3.3h 127k gnd 330pf on off lt3480 3480 ta08 run/ss boost sync 5v, 2mhz step-down converter sw fb v c pg rt v in bd v in 8.6v to 22v transient to 38v v out 5v 2a 2.2f 0.47f 22f 100k f = 2mhz d: diodes inc. dfls240l l: sumida cdrh4d22/hp-2r2 d 14k 11.5k l 2.2h 536k gnd 470pf on off lt3480 3480 ta05 run/ss boost sync lt3480 3480fe for more information www.linear.com/lt3480
21 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description 3.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (weed-2). check the ltc website data sheet for current status of variation assignment 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 1.65 0.10 (2 sides) 0.75 0.05 r = 0.125 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 ? 0.05 (dd) dfn rev c 0310 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 0.70 0.05 3.55 0.05 package outline 0.25 0.05 0.50 bsc dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699 rev c) pin 1 notch r = 0.20 or 0.35 45 chamfer please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. lt3480 3480fe for more information www.linear.com/lt3480
22 package description msop (mse) 0910 rev g 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 1 2 3 4 5 4.90 0.152 (.193 .006) 0.497 0.076 (.0196 .003) ref 8910 10 1 7 6 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) (note 4) note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does not include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.23 (.206) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 1.68 0.102 (.066 .004) 1.88 0.102 (.074 .004) 0.50 (.0197) bsc 0.305 0.038 (.0120 .0015) typ bottom view of exposed pad option 1.68 (.066) 1.88 (.074) 0.1016 0.0508 (.004 .002) detail ?b? detail ?b? corner tail is part of the leadframe feature. for reference only no measurement purpose 0.05 ref 0.29 ref mse package 10-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1664 rev g) please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. lt3480 3480fe for more information www.linear.com/lt3480
23 revision history rev date description page number d 10/11 added h- and mp-grades for the mse package revised bd pin description revised figure 5 to add capacitors 2, 3 7 15 e 8/13 clarifed maximum temperature range of lt3480e 2, 3 (revision history begins at rev d) lt3480 3480fe for more information www.linear.com/lt3480
24 ? linear technology corporation 2008 lt 0813 rev e ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/lt3480 related parts typical application part number description comments lt1933 500ma (i out ), 500khz step-down switching regulator in sot-23 v in : 3.6v to 36v, v out(min) = 1.2v, i q = 1.6ma, i sd <1a, thinsot package lt3437 60v, 400ma (i out ), micropower step-down dc/dc converter with burst mode v in : 3.3v to 80v, v out(min) = 1.25v, i q = 100a, i sd <1a, 10-pin 3mm x 3mm dfn and 16-pin tssop packages 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, 1.2a (i out ), 750khz high effciency step-down dc/dc converter v in : 3.6v to 40v, v out(min) = 0.8v, i q = 1.9ma, i sd <1a, 6-pin 2mm x 3mm dfn package lt1976 / lt1977 60v, 1.2a (i out ), 200khz/500khz, high effciency step-down dc/dc converter with burst mode v in : 3.3v to 60v, v out(min) = 1.2v, i q = 100a, i sd <1a, 16-pin tssop package lt1767 25v, 1.2a (i out ), 1.1mhz, high effciency step-down dc/dc converter v in : 3v to 25v, v out(min) = 1.2v, i q = 1ma, i sd <6a, ms8e package lt1940 dual 25v, 1.4a (i out ), 1.1mhz, high effciency step-down dc/dc converter v in : 3.6v to 25v, v out(min) = 1.2v, i q = 3.8ma, i sd <30a, 16-pin tssop package lt1766 60v, 1.2a (i out ), 200khz, high effciency step-down dc/dc converter v in : 5.5v to 60v, v out(min) = 1.2v, i q = 2.5ma, i sd = 25a, 16-pin tssop package lt3434 / lt3435 60v, 2.4a (i out ), 200/500khz, high effciency step-down dc/dc converter with burst mode v in : 3.3v to 60v, v out(min) = 1.2v, i q = 100a, i sd <1a, 16-pin tssop package lt3481 36v, 2a (i out ), 2.8mhz, high effciency step-down dc/dc converter with burst mode v in : 3.6v to 34v, v out(min) = 1.26v, i q = 50a, i sd <1a, 10-pin 3mm x 3mm dfn and 10-pin msop packages lt3684 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 = 1.5ma, i sd <1a, 10-pin 3mm x 3mm dfn and 10-pin msop packages sw fb v c pg rt v in bd v in 3.6v to 27v v out 1.2v 2a 4.7f 0.47f 47f f = 500khz d: diodes inc. dfls240l l: taiyo yuden np06dzb3r3m d 16.2k 68.1k l 3.3h gnd 330pf on off lt3480 3480 ta09 run/ss boost sync 100k 52.3k 1.2v step-down converter lt3480 3480fe for more information www.linear.com/lt3480

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