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ltc3428 1 3428f the ltc ? 3428 is a 2-phase, current mode boost con- verter, capable of supplying 2a at 5v from a 3.3v input. two 93m ? , 2a n-channel mosfet switches allow the ltc3428 to deliver high efficiency from input voltages as low as 1.6v. external parts count and size are minimized by a 1mhz switching frequency and a 2-phase design. two phase operation significantly reduces peak inductor currents and capacitor ripple current, doubling the effective switch- ing frequency and minimizing inductor and capacitor size. external compensation allows the feedback loop response to be optimized for a particular application. other features include: an active low shutdown pin re- duces supply current to below 1 a, internal soft-start, antiringing control and thermal shutdown. the ltc3428 is available in a low profile (0.75mm) 10-lead (3mm 3mm) dfn package. features descriptio u applicatio s u typical applicatio u networking equipment handheld instruments digital cameras distributed power local 3.3v to 5v conversion , ltc and lt are registered trademarks of linear technology corporation. v out swa swb fb pgndb v in shdn v c agnd pgnda ltc3428 383k 121k 22 f**** 22pf 10k 1000pf 4.7 f*** v in 3.3v v out 5v/2a 3428 ta01 2.2 h* 2.2 h* off on toko fdv06302r2 philips pmeg1020 taiyo yuden x5r jmk212bj475md taiyo yuden x5r jmk316bj226ml * ** *** **** ** ** efficiency vs load current 3.3v to 5v at 2a converter high efficiency: up to 92% 2-phase control reduces output voltage ripple 5v at 2a from 3.3v input 3.3v at 1.5a from 1.8v input 1.6v to 5.25v adjustable output voltage 1.6v to 4.5v input range internal soft-start operation low shutdown current: <1 a uses small surface mount components 10-pin 3mm 3mm dfn package 4a, 2mhz dual phase step-up dc/dc converter in 3mm 3mm dfn load current (a) 0.1 efficiency (%) 95 90 85 80 75 70 65 60 55 50 45 12 3428 ta02 v in = 3.3v v out = 5v l = 2.2 h
ltc3428 2 3428f v in , v out , swa, swb voltage ....................... C 0.3 to 6v swa, swb voltage, pulsed, <100ns ......................... 7v shdn, vc voltage ......................................... C 0.3 to 6v fb voltage ................................... C 0.3 to (v out + 0.3v) operating temperature range (note 2) .. C 40 c to 85 c storage temperature range ..................C65 c to 125 c order part number dd part marking t jmax = 125 c, ja = 45 c/w, jc = 3 c/w consult ltc marketing for parts specified with wider operating temperature ranges. lbbg absolute axi u rati gs w ww u package/order i for atio uu w (note 1) electrical characteristics note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the ltc3428e is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the C40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3.3v, v out = 5v unless otherwise noted. parameter conditions min typ max units minimum startup voltage 1.5 1.6 v quiescent current, v out shdn = v in 100 200 a quiescent current, v in shdn = v in 1.3 2.0 ma shutdown current shdn = 0v 1 a switching frequency per phase 0.8 1.0 1.2 mhz fb regulated voltage 1.219 1.243 1.268 v fb input current v fb = 1.24v 1 50 na error amp transconductance 170 s output adjust voltage 1.6 5.25 v nmos switch leakage v swa , v swb = 5.5v, per phase 0.1 2.5 a nmos switch on resistance v out = 5v, per phase 0.093 ? nmos current limit per phase 2 2.5 a shdn input threshold 0.4 0.8 1.5 v shdn input current 0.01 1 a maximum duty cycle 80 87 % minimum duty cycle 0% current limit delay to output (note 3) 40 ns note 3: specification is guaranteed by design and not 100% tested in production. note 4: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed 125 c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may impair device reliability. top view dd package 10-lead (3mm 3mm) plastic dfn exposed pad must be soldered to ground plane on pcb 10 9 6 7 8 4 5 3 2 1 pgndb swb v in agnd fb pgnda swa v out shdn v c 11 ltc3428edd
ltc3428 3 3428f typical perfor a ce characteristics uw 3428 g09 load current (a) 0.05 efficiency (%) 95 90 85 80 75 70 65 60 55 0.1 1 2 3428 g05 3428 g04 3.3v to 5v 2.5v to 3.3v 2.5v to 5v output voltage (v) 2.5 r ds(on) (m ? ) 108 106 104 102 100 98 96 94 92 90 88 4.5 3428 g06 3428 g02 3428 g01 3428 g03 3.0 3.5 4.0 5.0 r ds(on) (m ? ) 120 110 100 90 80 70 60 fb voltage (v) 1.27 1.26 1.25 1.24 1.23 1.22 3428 g08 temperature ( c) 3428 g07 10ns/div C45 15 55 115 C25 C5 35 75 95 temperature ( c) C45 15 55 115 C25 C5 35 75 95 500ns/div 500ns/div 500ns/div 100 s/div 5v/div 50mv/div 1v/div 2v/div 500ma/div 100mv/div 500ma/div swa swb swa, swb switching waveforms swa, swb rise time, i = 2a switch r ds(on) vs v out converter efficiency output voltage ripple with 22 f ceramic capacitor transient response, 0.5a to 1.5a sw pin and inductor current in discontinuous mode, demonstrating anti-ring circuit operation switch r ds(on) vs temperature feedback voltage vs temperature all characteristic curves at t a = 25 c unless otherwise noted.
ltc3428 4 3428f pi fu ctio s uuu pgnda, pgndb (pins 1, 10, 11 (exposed pad)): power ground for the ic. tie directly to local ground plane. swb (pin 2), swa (pin 9): phase b and phase a switch pins. the inductor and schottky diodes for each phase are connected to these pins. minimize trace length to reduce emi. v out (pin 3): power supply output and bootstrapped power source for the ic. connect low esr output filter capacitors from this pin to the ground plane. shdn (pin 4): shutdown pin. grounding this pin shuts down the ic. connect to a voltage greater than 1.5v to enable. typical perfor a ce characteristics uw peak current limit (a) 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 3428 g10 temperature ( c) C45 15 55 C25 C5 35 75 95 peak current limit vs temperature v c (pin 5): error amp output. a frequency compensation network is connected to this pin to compensate the boost converter loop. fb (pin 6): feedback pin. a resistor divider from v out is connected here to set the output voltage according to v out = 1.243 ? (1 + r1 / r2) agnd (pin 7): signal ground for the ic. connect to ground plane near feedback resistor divider. v in (pin 8): input supply pin. bypass v in with a low esr ceramic capacitor of at least 4.7 f. x5r and x7r dielec- trics are preferred for their superior voltage and tempera- ture characteristics.
ltc3428 5 3428f block diagra w C + C + C pwm comp + C C pwm comp pwm logic pwm logic tsd current limit current limit 1.243v v c error amplifier/soft-start ramp/ slope comp oscillator clk b clk a channel b channel a ramp/ slope comp i sena i senb fb driver driver i sena i senb swb v out pgndb swa pgnda v c shdn shutdown agnd 3428 bd v in fb 5pf
ltc3428 6 3428f detailed description the ltc3428 provides high efficiency, low noise power for high current boost applications. a current mode archi- tecture with adaptive slope compensation provides both simple loop compensation as well as excellent transient response. the low r ds(on) switches provide the pulse width modulation control at high efficiency. oscillator: the per phase switching frequency is internally set to a nominal value of 1mhz. current sensing: lossless current sensing converts the peak current signal to a voltage which is summed with the internal slope compensation. this summed signal is then compared with the error amplifier output to provide a peak current command for the pwm. slope compensation is internal to the ic and adapts to changes to the input voltage, allowing the converter to provide the necessary degree of slope compensation without causing a loss in phase margin in the loop characteristic. error amplifier: the error amplifier is a transconductance amplifier with a transconductance (g m ) = 1/7.5k ? . a simple compensation network is placed from v c to ground. the internal 5pf capacitor between v c and ground will often simplify the external network to a simple r-c com- bination. the internal 1.243v reference voltage is com- pared to the voltage on fb to generate an error signal at the output of the error amplifier (v c ). a voltage divider from v out to ground programs the output voltage from 1.6v to 5.25v using the equation: v out = 1.243v ? ( 1+ r1/r2) soft-start: an internal soft-start of approximately 1.5ms is provided. this is a ramp signal that limits the peak current until the internal soft-start voltage is greater than the internal current limit voltage. the internal soft-start capacitor is automatically discharged when the part is in shutdown mode. current limit: the current limit comparator in each phase will shut off the n-channel mosfet switches once the current exceeds the current limit threshold, nominally 2.5a. the current limit delay to output is typically 50ns. the current signal leading edge is blanked for 50ns to enhance noise rejection. anti-ringing control: the antiringing control places an impedance across the inductor of each phase to damp the high frequency ringing on the swa, swb pins during discontinuous mode operation. the lc ringing on the switch pin due to the inductor and switch pin capacitance is low energy, but can cause emi radiation. 2-phase operation the ltc3428 uses a two-phase architecture, rather than the conventional single phase architecture used in most other boost converters. the two phases are spaced 180 apart. two phase operation doubles the output ripple frequency and provides a significant reduction in output ripple current, minimizing the stress on the output capaci- tor. inductor (input) peak and ripple currents are also reduced, allowing for the use of smaller, lower cost inductors. the greatly reduced output ripple current also minimizes the output capacitance requirement. the higher frequency output ripple is easier to filter for lower noise applications. input and output current comparisons for single and 2-phase converters are illustrated in figures 1 and 2. for the example illustrated in figure 2, peak-to-peak output ripple current was reduced by 85%, from 4.34a, to 0.64a, and peak inductor current was reduced by 53%, from 4.34a to 2.02a. these reductions enable the use of low profile, smaller valued inductors and output capaci- tors as compared to a single-phase design. applicatio s i for atio wu u u figure 1. input ripple current comparison between single phase and two-phase boost converters with a 2a load and 50% duty cycle time ( s) 0 input current (a) 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 1.6 3428 f01 0.4 0.2 0.6 1.0 1.4 1.8 0.8 1.2 2.0 1 phase converter 2 phase converter
ltc3428 7 3428f component selection inductor selection the high frequency operation of the ltc3428 allows for the use of small surface mount inductors. the inductor ripple current is typically set to between 20% and 40% of the maximum inductor current. for a given set of condi- tions, the inductance is given as follows: l vvv rv lh in min out in min out > () () ?( C ) ? ,2 where: r = allowable inductor current ripple (amps p-p) v in(min) = minimum input voltage (v) v out = output voltage (v) for high efficiency, the inductor should have a high frequency core material, such as ferrite, to reduce core losses. the inductor should have a low esr (equivalent series resistance) to reduce i 2 r losses and must be able to handle the peak inductor current without saturating. use of a toroid, pot core, or shielded bobbin inductor will minimize radiated noise. see table 1 for a list of inductor manufacturers. some example inductor part types are: coilcraft 1608 and 3316 series, murata lqh55d series, applicatio s i for atio wu uu sumida cdrh4d22c/ld or cdrh5d28 series, toko fdv0630 or d62cb series. table 1. inductor vendor information supplier phone fax website coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com murata usa: usa: www.murata.com (814) 238-1431 (814) 238-0490 sumida usa: usa: www.sumida.com (847) 956-6666 (847) 956-0702 japan: japan: 81-3-3607-5111 81-3-3607-5144 tdk (847) 803-6100 (847) 803-6296 www.component.tdk.com toko (847) 299-0070 (847) 699-7864 www.toko.com wurth (201)785-8800 (201)785-8810 www.we-online.com output capacitor selection the minimum value of the capacitor is set to reduce the output ripple voltage due to charging and discharging the capacitor each cycle. the steady state ripple due to this charging is given by: v ivv cvf ripple c peak out in min out out () () ? ?( C ) ?? = 1 2 where: i peak = peak inductor current (a) the equivalent series resistance (esr) of the output capacitor will contribute another term to output voltage ripple. ripple voltage due to capacitor esr is: vir ripple esr peak esr c () () ? = where: r esr(c) = capacitor esr the esl (equivalent series inductance) is another capacitor characteristic that needs to be minimized. esl will be minimized by using small surface mount ceramic capacitors, placed as close to the v out pin as possible. input capacitor selection since the v in pin directly powers most of the internal circuitry, it is recommended to place at least a 4.7 f, low esr bypass capacitor between v in and agnd, as close to the ic as possible. see table 2 for a list of capacitor manufacturers. figure 2. output ripple current comparison between single phase and two phase boost converters with a 2a load and 50% duty cycle time ( s) 0 1.6 3428 f02 0.4 0.2 0.6 1.0 1.4 1.8 0.8 1.2 2.0 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 output (diode) current (a) 1 phase converter 2 phase converter
ltc3428 8 3428f table 2. capacitor vendor information supplier phone fax website avx (803) 448-9411 (803) 448-1943 www.avxcorp.com sanyo (619) 661-9322 (619) 661-1055 www.sanyovideo.com tdk (847) 803-6100 (847) 803-6296 www.component.tdk.com murata (814) 237-1431 (814) 238-0490 www.murata.com taiyo yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com output diode selection for high efficiency, a fast switching diode with low reverse leakage and a low forward drop is required. schottky diodes are recommended for their low forward drop and fast switching times. when selecting a diode, it is important to remember that the average diode current in a boost converter is equal to the average load current: i d = i load when selecting a diode, make sure that the peak forward current and average power dissipation ratings meet the application requirements. see table 3 for a list of schottky diode manufacturers. example diodes are philips pmeg1020, pmeg2010, on-semi mbra210, ir 10bq015, microsemi ups120e, ups315. table 3. diode vendor information supplier phone fax website philips +31 40 27 24825 www.philips.com microsemi (949) 221-7100 (949)756-0308 www.microsemi.com on-semi (602) 244-6600 www.onsemi.com international (310) 469-2161 (310) 322-3332 www.irf.com rectifier thermal considerations to deliver maximum power, it is necessary to provide a good thermal path to dissipate the heat generated within the ltc3428s package. the large thermal pad on the ic underside can accomplish this requirement. use multiple pc board vias to conduct heat from the ic and to a copper plane that has as much area as possible. applicatio s i for atio wu uu if the junction temperature gets too high, the ltc3428 will stop all switching until the junction temperature drops to safe levels. the typical over temperature threshold is 150 c. closing the feedback loop the ltc3428 uses current mode control with internal, adaptive slope compensation. current mode control elimi- nates the 2nd order pole in the loop response of voltage mode converters due to the inductor and output capacitor, simplifying it to a single pole response. the product of the modulator control to output dc gain and the error amp open-loop gain equals the dc gain of the system. gg g v v g v i g dc control ea ref out control in out ea = = ?? ? 2 100 the output filter pole is given by: f i vc hz pole out out out = ?? where c out is the output filter capacitor value. the output filter zero is given by: f rc hz zero esr out = 1 2? ? ? where r esr is the output capacitor equivalent series resistance. a complication of the boost converter topology is the right half plane (rhp) zero and is given by: f vr lv hz rhp in o o = 2 2 2 ? ???
ltc3428 9 3428f figure 3. C + 1.243v fb r1 r2 v c v out r z c c1 c c2 3428 f03 5pf this zero causes a gain increase with phase lag. with heavy loads, this can occur at a relatively low frequency. for this reason, loop gain is typically rolled off below the rhp zero frequency. a typical error amp compensation is shown in figure 3 and in the typical application section. the equations for the loop dynamics are as follow: f ec f rc f rc pf pole c zero zc zero zc 1 1 1 1 2 2 1 2 400 6 1 2 1 25 + ?? ? ?? ? ?? ?( ) applicatio s i for atio wu uu
ltc3428 10 3428f v in shdn v c agnd pgnda v out swa swb fb pgndb 8 4 5 7 1 3 2 9 6 10 22pf 4.7 f 10k 1000pf 4.7 f*** 4 2.5v in shutdown 4.7 h* 4.7 h* ** ** v out 3.3v, 2.5a 205k 121k toko dc53lc microsemi ups120e taiyo yuden x5r jmk212bj475md * ** *** 3428 ta03 ltc3428 2.5v to 3.3v at 2.5a converter typical applicatio s u
ltc3428 11 3428f u package descriptio dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699) 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. 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 0.38 0.10 bottom viewexposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.115 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 C 0.05 (dd10) dfn 1103 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50 bsc 0.675 0.05 3.50 0.05 package outline 0.25 0.05 0.50 bsc
ltc3428 12 3428f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2004 lt/tp 0804 1k ? printed in usa related parts part number description comments lt1613 550ma (i sw ), 1.4mhz, high efficiency step-up 90% efficiency, v in : 0.9v to 10v, v out(max) = 34v, i q = 3ma, dc/dc converter i sd <1 a, thinsot package lt1615/lt1615-1 300ma/80ma (i sw ), high efficiency step-up v in : 1v to 15v, v out(max) = 34v, i q = 20 a, dc/dc converters i sd <1 a, thinsot package lt1618 1.5a (i sw ), 1.25mhz, high efficiency step-up 90% efficiency, v in : 1.6v to 18v, v out(max) = 35v, i q = 1.8ma, dc/dc converter i sd <1 a, ms package lt1930/lt1930a 1a (i sw ), 1.2mhz/2.2mhz, high efficiency step-up high efficiency, v in : 2.6v to 16v, v out(max) = 34v, dc/dc converters i q = 4.2ma/5.5ma, i sd <1 a, thinsot package lt1946/lt1946a 1.5a (i sw ), 1.2mhz/2.7mhz, high efficiency step-up high efficiency, v in : 2.45v to 16v, v out(max) = 34v, i q = 3.2ma, dc/dc converters i sd <1 a, ms8 package lt1961 1.5a (i sw ), 1.25mhz, high efficiency step-up 90% efficiency, v in : 3v to 25v, v out(max) = 35v, i q = 0.9ma, dc/dc converter i sd 6 a, ms8e package ltc3400/ltc3400b 600ma (i sw ), 1.2mhz, synchronous step-up 92% efficiency, v in : 0.85v to 5v, v out(max) = 5v, i q = 19 a/300 a, dc/dc converter i sd <1 a, thinsot package ltc3401 1a (i sw ), 3mhz, synchronous step-up dc/dc converter 97% efficiency, v in : 0.5v to 5v, v out(max) = 5.5v, i q = 38 a, i sd <1 a, ms package ltc3402 2a (i sw ), 3mhz, synchronous step-up dc/dc converter 97% efficiency, v in : 0.5v to 5v, v out(max) = 5.5v, i q = 38 a, i sd <1 a, ms package ltc3421 3a, 3mhz synchronous boost converter 96% efficiency, v in : 0.5v to 4.5v, v out(max) = 5.5v, i q = 12 a, with output disconnect i sd <1 a, qfn-24 package ltc3425 5a (i sw ), 8mhz, 4-phase synchronous step-up 95% efficiency, v in : 0.5v to 4.5v, v out(max) = 5.25v, i q = 12 a, dc/dc converter i sd <1 a, qfn-32 package ltc3429 600ma, 500khz synchronous boost converter 96% efficiency, v in : 0.5v to 4.4v, v out(max) = 5.5v, i q = 20 a, with output disconnect i sd <1 a, thinsot package ltc3436 3a (i sw ), 1mhz, 34v step-up dc/dc converter v in : 3v to 25v, v out(max) = 34v, i q = 0.9ma, i sd <6 a, tssop-16e package ltc3459 10v micropower synchronous boost converter 85% efficiency, v in : 1.5v to 5.5v, v out(max) = 10v, i q = 10 a, i sd <1 a, thinsot package lt3464 85ma (i sw ), high efficiency step-up dc/dc converter v in : 2.3v to 10v, v out(max) = 34v, i q = 25 a, with integrated schottky and pnp disconnect i sd <1 a, thinsot package no r sense is a registered trademark of linear technology corporation.

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