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ltc3400/ltc3400b 1 3400fa n pagers n mp3 players n digital cameras n lcd bias supplies n handheld instruments n wireless handsets n gps receivers n up to 92% efficiency n generates 3.3v at 100ma from a single aa cell n low start-up voltage: 0.85v n 1.2mhz fixed frequency switching n internal synchronous rectifier n 2.5v to 5v output range n automatic burst mode ? operation (ltc3400) n continuous switching at light loads (ltc3400b) n logic controlled shutdown (< 1 m a) n antiringing control minimizes emi n tiny external components n low profile (1mm) sot-23 package 600ma, 1.2mhz micropower synchronous boost converter in thinsot figure 1. single cell to 3.3v synchronous boost converter the ltc ? 3400/ltc3400b are synchronous, fixed fre- quency, step-up dc/dc converters delivering high effi- ciency in a 6-lead thinsot? package. capable of supplying 3.3v at 100ma from a single aa cell input, the devices contain an internal nmos switch and pmos synchronous rectifier. a switching frequency of 1.2mhz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. the current mode pwm design is internally compensated, reducing external parts count. the ltc3400 features automatic shifting to power saving burst mode operation at light loads, while the ltc3400b features continuous switching at light loads. antiringing control circuitry reduces emi concerns by damping the inductor in discontinuous mode, and the devices feature low shutdown current of under 1 m a. both devices are available in the low profile (1mm) sot-23 package. thinsot is a trademark of linear technology corporation. sw l1 4.7 h v out ltc3400 fb v in shdn 2 1 3 3400 f01 r1 1.02m 1% c1, c2: taiyo-yuden x5r emk316bj475ml l1: coilcraft do160c-472 r2 604k 1% c2 4.7 f c1 4.7 f single aa cell v out 3.3v 100ma 5 4 6 gnd + off on load current (ma) 60 efficiency (%) 80 100 50 70 90 0.1 10 100 1000 3400 f01a 40 1 v in = 2.4v v in = 1.5v figure 1 circuit with optional schottky diode (see applications information) efficiency features descriptio u applicatio s u typical applicatio u , ltc, lt and burst mode are registered trademarks of linear technology corporation.
ltc3400/ltc3400b 2 3400fa v in voltage ................................................. C 0.3v to 6v sw voltage ................................................. C 0.3v to 6v shdn, fb voltage ....................................... C 0.3v to 6v v out ........................................................... C 0.3v to 6v operating temperature range (note 2) .. C 30 c to 85 c storage temperature range ................... C 65 c to 125 lead temperature (soldering, 10 sec).................. 300 c order part number s6 part marking t jmax = 125 c, q jc = 102 c/w ltwk ltun ltc3400es6 ltc3400bes6 (note 1) note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the ltc3400e/ltc3400be are guaranteed to meet performance specifications from 0 c to 70 c. specifications over the C 30 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 1.2v, v out = 3.3v, unless otherwise specified. parameter conditions min typ max units minimum start-up voltage i load = 1ma 0.85 1 v minimum operating voltage shdn = v in (note 4) 0.5 0.65 v output voltage adjust range 2.5 5 v feedback voltage l 1.192 1.23 1.268 v feedback input current v fb = 1.25v (note 3) 1 na quiescent current (burst mode operation) v fb = 1.4v (note 5), ltc3400 only 19 30 m a quiescent current (shutdown) v shdn = 0v, not including switch leakage 0.01 1 m a quiescent current (active) measured on v out 300 500 m a nmos switch leakage v sw = 5v 0.1 5 m a pmos switch leakage v sw = 0v 0.1 5 m a nmos switch on resistance v out = 3.3v 0.35 w v out = 5v 0.20 w pmos switch on resistance v out = 3.3v 0.45 w v out = 5v 0.30 w nmos current limit 600 850 ma burst mode operation current threshold ltc3400 only (note 3) 3 ma current limit delay to output (note 3) 40 ns max duty cycle v fb = 1.15v l 80 87 % switching frequency 0.95 1.2 1.5 mhz l 0.85 1.2 1.5 mhz shdn input high 1v shdn input low 0.35 v shdn input current v shdn = 5.5v 0.01 1 m a absolute axi u rati gs w ww u package/order i for atio uu w electrical characteristics note 3: specification is guaranteed by design and not 100% tested in production. note 4: minimum v in operation after start-up is only limited by the batterys ability to provide the necessary power as it enters a deeply discharged state. note 5: burst mode operation i q is measured at v out . multiply this value by v out /v in to get the equivalent input (battery) current. sw 1 gnd 2 fb 3 6 v in 5 v out 4 shdn top view s6 package 6-lead plastic sot-23 consult ltc marketing for parts specified with wider operating temperature ranges.
ltc3400/ltc3400b 3 3400fa typical perfor a ce characteristics uw output load burst mode threshold vs v in v in (v) 0.9 0 output current (ma) 1.5 2.1 2.7 3.3 3400 g01 3.9 4.5 20 10 v out = 3.3v v out = 5v l = 4.7 h t a = 25 c temperature ( c) ?0 3.24 v out (v) 3.26 3.28 3.30 3.32 3.36 ?0 03060 3400 g02 90 120 3.34 figure 1 circuit i o = 10ma i out (ma) current source load 0.1 0.8 start-up voltage (v) 1.2 1.3 1.4 1 10 100 3400 g03 1.1 1.0 0.9 t a = 25 c v out vs temperature minimum start-up voltage vs load current no load battery current vs v batt battery voltage (v) 1.2 10 100 1000 1.8 3400 g04 battery current ( a) 0.9 3.0 1.5 2.1 2.4 2.7 v out = 3.3v t a = 25 c sw pin fixed frequency, continuous inductor current operation temperature ( c) ?0 normalized frequency 0.99 1.00 1.01 10 50 3400 g05 0.98 0.97 ?0 ?0 30 70 90 0.96 0.95 sw pin antiringing operation fixed frequency and burst mode operation v out transient response normalized oscillator frequency vs temperature v sw 1v/div 0v v in = 1.3v 100ns/div 3400 g06 v out = 3.3v i out = 10ma l = 6.8 m h c out = 4.7 m f v sw 1v/div 0v v in = 1.3v 100ns/div 3400 g07 v out = 3.3v i out = 50ma l = 6.8 m h c out = 4.7 m f v out(ac) 100mv/div 60ma v in = 1.3v 10ms/div 3400 g08 v out = 3.3v i out = 60ma to 10 m a l = 6.8 m h c out = 4.7 m f 10 m a i out v out(ac) 100mv/div 100ma v in = 1.3v 100 m s/div 3400 g09 v out = 3.3v i out = 40ma to 100ma l = 6.8 m h c out = 4.7 m f 40ma i out
ltc3400/ltc3400b 4 3400fa uu u pi fu ctio s sw (pin 1): switch pin. connect inductor between sw and v in . optional schottky diode is connected between sw and v out . keep these pcb trace lengths as short and wide as possible to reduce emi and voltage overshoot. if the inductor current falls to zero, or shdn is low, an internal 100 w antiringing switch is connected from sw to v in to minimize emi. gnd (pin 2): signal and power ground. provide a short direct pcb path between gnd and the (C) side of the output capacitor(s). fb (pin 3): feedback input to the g m error amplifier. connect resistor divider tap to this pin. the output voltage can be adjusted from 2.5v to 5v by: v out = 1.23v ? [1 + (r1/r2)] shdn (pin 4): logic controlled shutdown input. shdn = high: normal free running operation, 1.2mhz typical operating frequency. shdn = low: shutdown, quiescent current < 1 m a. 100 w connected between sw and v in . typically, shdn should be connected to v in through a 1m pull-up resistor. v out (pin 5): output voltage sense input and drain of the internal synchronous rectifier mosfet. bias is derived from v out . pcb trace length from v out to the output filter capacitor(s) should be as short and wide as possible. v out is held at v in C 0.6v in shutdown due to the body diode of the internal pmos. v in (pin 6): battery input voltage. the device gets its start-up bias from v in . once v out exceeds v in , bias comes from v out . thus, once started, operation is com- pletely independent from v in . operation is only limited by the output power level and the batterys internal series resistance. 1.23v ref burst mode operation control shutdown control slope comp pwm control start-up osc mux a b a/b ramp gen 1.2mhz fb 3400 bd 3 v out optional schottky l1 4.7 h 5 sw 1 v in single cell input 6 shdn 4 gnd 2 + g m error amp + v out good + pwm comparator r c 80k shutdown c c 150pf c p2 2.5pf r2 604k 1% (external) r1 1.02m 1% (external) sleep s sync drive control 0.35 0.45 2.3v c out 4.7 f 3.3v output c in 1 f + current sense c ff (optional) block diagra w
ltc3400/ltc3400b 5 3400fa operatio u the ltc3400/ltc3400b are 1.2mhz, synchronous boost converters housed in a 6-lead thinsot package. able to operate from an input voltage below 1v, the devices feature fixed frequency, current mode pwm control for exceptional line and load regulation. with its low r ds(on) and gate charge internal mosfet switches, the devices maintain high efficiency over a wide range of load current. detailed descriptions of the three distinct operating modes follow. operation can be best understood by referring to the block diagram. low voltage start-up the ltc3400/ltc3400b will start up at a typical v in volt- age of 0.85v or higher. the low voltage start-up circuitry controls the internal nmos switch up to a maximum peak inductor current of 850ma (typ), with an approximate 1.5 m s off-time during start-up, allowing the devices to start up into an output load. once v out exceeds 2.3v, the start-up circuitry is disabled and normal fixed frequency pwm operation is initiated. in this mode, the ltc3400/ ltc3400b operate independent of v in , allowing extended operating time as the battery can droop to several tenths of a volt without affecting output voltage regulation. the limiting factor for the application becomes the ability of the battery to supply sufficient energy to the output. low noise fixed frequency operation oscillator: the frequency of operation is internally set to 1.2mhz. error amp: the error amplifier is an internally compensated transconductance type (current output) with a transconduc- tance (g m ) = 33 microsiemens. the internal 1.23v reference voltage is compared to the voltage at the fb pin to generate an error signal at the output of the error amplifier. a volt- age divider from v out to ground programs the output voltage via fb from 2.5v to 5v using the equation: v out = 1.23v ? [1 + (r1/r2)] current sensing: a signal representing nmos switch current is summed with the slope compensator. the summed signal is compared to the error amplifier output to provide a peak current control command for the pwm. peak switch current is limited to approximately 850ma independent of input or output voltage. the current signal is blanked for 40ns to enhance noise rejection. zero current comparator: the zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier once this current reduces to ap- proximately 20ma. this prevents the inductor current from reversing in polarity improving efficiency at light loads. antiringing control: the antiringing control circuitry pre- vents high frequency ringing of the sw pin as the inductor current goes to zero by damping the resonant circuit formed by l and c sw (capacitance on sw pin). burst mode operation portable devices frequently spend extended time in low power or standby mode, only switching to high power drain when specific functions are enabled. in order to improve battery life in these types of products, high power converter efficiency needs to be maintained over a wide output power range. in addition to its high efficiency at moderate and heavy loads, the ltc3400 includes auto- matic burst mode operation that improves efficiency of the power converter at light loads. burst mode operation is initiated if the output load current falls below an internally programmed threshold (see typical perfor- mance graph, output load burst mode threshold vs v in ). once initiated, the burst mode operation circuitry shuts down most of the device, only keeping alive the circuitry required to monitor the output voltage. this is referred to as the sleep state. in sleep, the ltc3400 draws only 19 m a from the output capacitor, greatly en hancing efficiency. when the output voltage has drooped approximately 1% from nominal, the ltc3400 wakes up and commences normal pwm operation. the output capacitor recharges and causes the ltc3400 to reenter sleep if the output load remains less than the sleep threshold. the frequency of this intermittent pwm or burst operation is proportional to load current; that is, as the load current drops further below the burst threshold, the ltc3400 turns on less frequently. when the load current increases above the
ltc3400/ltc3400b 6 3400fa pcb layout guidelines the high speed operation of the ltc3400/ltc3400b demands careful attention to board layout. you will not get advertised performance with careless layout. figure 2 shows the recommended component placement. a large ground pin copper area will help to lower the chip tempera- ture. a multilayer board with a separate ground plane is ideal, but not absolutely necessary. applicatio s i for atio wu uu ii vd fl d out max p in () = ? ? ? ? () h 2 1 where: h = estimated efficiency i p = peak current limit value (0.6a) v in = input (battery) voltage d = steady-state duty ratio = (v out C v in )/v out f = switching frequency (1.2mhz typical) l = inductance value sw gnd fb 1 2 3 6 5 4 v in v out shdn shdn (optional) 3400 f02 v out v in recommended component placement. traces carrying high current are direct. trace area at fb pin is small. lead length to battery is short figure 2. recommended component placement for single layer board component selection inductor selection the ltc3400/ltc3400b can utilize small surface mount and chip inductors due to their fast 1.2mhz switching frequency. a minimum inductance value of 3.3 m h is necessary for 3.6v and lower voltage applications and 4.7 m h for output voltages greater than 3.6v. larger values inductance ( h) 3 60 output current (ma) 80 110 120 160 7 11 13 21 180 140 59 15 17 19 23 3400 f03 v in =1.2v v out = 3v v out = 3.3v v out = 3.6v v out = 5v figure 3. maximum output current vs inductance based on 90% efficiency of inductance will allow greater output current capability by reducing the inductor ripple current. increasing the inductance above 10 m h will increase size while providing little improvement in output current capability. the approximate output current capability of the ltc3400/ ltc3400b versus inductance value is given in the equa- tion below and illustrated graphically in figure 3. burst threshold, the ltc3400 will resume continuous pwm operation seamlessly. referring to the block dia- gram, an optional capacitor (c ff ) between v out and fb in some circumstances can reduce the peak-to-peak v out ripple and input quiescent current during burst mode operation. typical values for c ff range from 15pf to 220pf. the ltc3400b does not use burst mode operation and features continous operation at light loads, eliminat- ing low frequency output voltage ripple at the expense of light load efficiency. operatio u
ltc3400/ltc3400b 7 3400fa the inductor current ripple is typically set for 20% to 40% of the maximum inductor current (i p ). high frequency ferrite core inductor materials reduce frequency depen- dent power losses compared to cheaper powdered iron types, improving efficiency. the inductor should have low esr (series resistance of the windings) to reduce the i 2 r power losses, and must be able to handle the peak inductor current without saturating. molded chokes and some chip inductors usually do not have enough core to support the peak inductor currents of 850ma seen on the ltc3400/ltc3400b. to minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. see table 1 for some suggested components and suppliers. table 1. recommended inductors max l dcr height part ( m h) m w (mm) vendor cdrh5d18-4r1 4.1 57 2.0 sumida cdrh5d18-100 10 124 2.0 (847) 956-0666 cdrh3d16-4r7 4.7 105 1.8 www.sumida.com cdrh3d16-6r8 170 1.8 cr43-4r7 4.7 109 3.5 cr43-100 10 182 3.5 cmd4d06-4r7mc 4.7 216 0.8 cmd4d06-3r3mc 3.3 174 0.8 ds1608-472 4.7 60 2.9 coilcraft ds1608-103 10 75 2.9 (847) 639-6400 do1608c-472 4.7 90 2.9 www.coilcraft.com d52lc-4r7m 4.7 84 2.0 toko d52lc-100m 10 137 2.0 (408) 432-8282 www.tokoam.com lqh3c4r7m24 4.7 195 2.2 murata www.murata.com output and input capacitor selection low esr (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. multilayer ceramic capacitors are an excellent choice as they have applicatio s i for atio wu uu extremely low esr and are available in small footprints. a 2.2 m f to 10 m f output capacitor is sufficient for most applications. larger values up to 22 m f may be used to obtain extremely low output voltage ripple and improve transient response. an additional phase lead capacitor may be required with output capacitors larger than 10 m f to maintain acceptable phase margin. x5r and x7r dielectric materials are preferred for their ability to main- tain capacitance over wide voltage and temperature ranges. low esr input capacitors reduce input switching noise and reduce the peak current drawn from the battery. it follows that ceramic capacitors are also a good choice for input decoupling and should be located as close as pos- sible to the device. a 4.7 m f input capacitor is sufficient for virtually any application. larger values may be used with- out limitations. table 2 shows a list of several ceramic capacitor manufacturers. consult the manufacturers di- rectly for detailed information on their entire selection of ceramic parts. table 2. capacitor vendor information supplier phone website avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com taiyo yuden (408) 573-4150 www.t-yuden.com output diode use a schottky diode such as an mbr0520l, pmeg2010ea, 1n5817 or equivalent if the converter output voltage is 4.5v or greater. the schottky diode carries the output current for the time it takes for the synchronous rectifier to turn on. do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. a schottky diode is optional for output voltages below 4.5v, but will increase converter efficiency by 2% to 3%.
ltc3400/ltc3400b 8 3400fa typical applicatio s u sw l1 4.7 h v out ltc3400 fb v in shdn 2 1 3 3400 ta01a r1 1.02m 1% r2 604k 1% q1 2n3904 d1: central semi cmdsh2-3 l1: coilcraft ds1608-472 c1 4.7 f single aa cell v out 3.3v 100ma 5 4 6 gnd + off on c2 4.7 f r3 510k r3 510k m1 si2305ds d1 single cell to 3.3v synchronous boost converter with load disconnect in shutdown
ltc3400/ltc3400b 9 3400fa typical applicatio s u d1 1nf optional snubber sw l1 4.7 h 2 v out ltc3400 fb v in shdn 2 3400 ta02a 1 3 c2 4.7 f c3 100pf r1 1.02m 1% d1: philips pmeg2010ea l1: sumida cmd4d06-4r7 c1, c2: taiyo yuden jmk212bj475mg c1 4.7 f lithium cell 5 4 6 gnd + off on r2 332k 1% single lithium cell to 5v, 250ma 3.6v to 5v efficiency load current (ma) 60 efficiency (%) 70 80 90 100 0.1 10 100 1000 3400 ta02b 50 1 ltc3400 c o = 4.7 f l = 4.7 h
ltc3400/ltc3400b 10 3400fa typical applicatio s u sw l1 4.7 h c3 1 f v out ltc3400 fb v in shdn 2 1 3 3400 ta03a r1 1.02m 1% r2 750k 1% c1 4.7 f single aa cell v out1 3v 90ma v out2 ?v 10ma 5 d1 d2 4 6 gnd + off on c2 4.7 f d1, d2: zetex fmnd7000 dual diode l1: coilcraft ds1608-472 c4 10 f single cell aa cell to 3v synchronous boost converter
ltc3400/ltc3400b 11 3400fa s6 package 6-lead plastic tsot-23 (reference ltc dwg # 05-08-1636) u package descriptio 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1.50 ?1.75 (note 4) 2.80 bsc 0.30 ?0.45 6 plcs (note 3) datum ? 0.09 ?0.20 (note 3)
ltc3400/ltc3400b 12 3400fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com ? linear technology corporation 2001 lt/tp 0903 1k rev a ? printed in usa part number description comments lt1308a/lt1308b high current, micropower, single cell 600khz dc/dc converter 5v at 1a with single li-ion cell, v out to 34v lt1613 1.4mhz, single cell dc/dc converter in thinsot v in as low as 1.1v, 3v at 30ma from single cell lt1615 micropower step-up dc/dc converter in thinsot i q = 20 m a, 1 m a shutdown current, v in as low as 1v lt ? 1618 1.4mhz step-up dc/dc converter with current limit 1.5a switch, 1.6v to 18v input range, input or output current limiting lt1619 high efficiency boost dc/dc controller 1a gate drive, 1.1v to 20v input, separate v cc for gate drive ltc1872 thinsot boost dc/dc controller 50khz, 2.5v to 9.8v input lt1930/lt1930a 1.2mhz/2.2mhz dc/dc converters in thinsot v in = 2.6v to 16v, 5v at 450ma from 3.3v input lt1932 constant current step-up led driver drives up to eight white leds, thinsot package lt1946/lt1946a 1.2mhz/2.7mhz boost dc/dc converters 1.5a, 36v internal switch, 8-pin msop package lt1949 600khz, 1a switch pwm dc/dc converter 1a, 0.5 w , 30v internal switch, v in as low as 1.5v, low-battery detect active in shutdown ltc3401 1a, 3mhz micropower synchronous boost converter 1a switch, programmable frequency, 10-pin msop package ltc3402 2a, 3mhz micropower synchronous boost converter 2a switch, programmable frequency, 10-pin msop package ltc3423 1a, 3mhz micropower synchronous boost converter 1a switch, separate bias pin for low output voltages ltc3424 2a, 3mhz micropower synchronous boost converter 2a switch, separate bias pin for low output voltages ltc3425 5a, 8mhz, 4-phase micropower synchronous boost converter up to 95% efficiency, 5a switch, v in : 0.5v to 4.5v, v out (min): 2.4v to 5.25v, i q = 12 m a, qfn related parts single aa cell to 2.5v synchronous boost converter sw l1 3.3 h v out ltc3400 fb v in shdn 2 1 d1 3 3400 ta04a r1 1.02m 1% r2 1.02m 1% c2 4.7 f d1: philips pmeg2010ea l1: sumida cmd4d06-3r3mc c1 4.7 f single aa cell v out 2.5v 130ma 5 4 6 gnd + off on u typical applicatio

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