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ltc 3442 1 3442fb for more information www.linear.com/ltc3442 typical application features description micropower synchronous buck-boost dc/dc converter with automatic burst mode operation the lt c ? 3442 is a highly efficient, fixed frequency, buck- boost dc/dc converter, which operates from input volt- ages above, below, and equal to the output voltage. the topology incorporated in the ic provides a continuous transfer function through all operating modes, making the product ideal for a single lithium-ion or multicell alkaline applications where the output voltage is within the battery voltage range. the device includes two 0.10 n - channel mosfet switches and two 0.10 p-channel switches. operating frequency and average input current limit can each be programmed with an external resistor. quiescent current is only 35a in burst mode operation, maximizing battery life in portable applications. automatic burst mode opera- tion allows the user to program the load current for burst mode operation, or to control it manually. other features include 1a shutdown current, program- mable soft-start, peak current limit and thermal shutdown. the ltc3442 is available in a low profile, thermally en- hanced 12-lead (4mm 3mm 0.75mm) dfn package. applications n regulated output with input voltages above, below, or equal to the output n single inductor, no schottky diodes required n manual or programmable automatic burst mode ? operation n programmable average input current limit n up to 1.2a continuous output current from a single lithium-ion cell n high efficiency: up to 95% n output disconnect in shutdown n 2.4 v to 5.5v input range n 2.4 v to 5.25v output range n 35 a quiescent current in burst mode operation n programmable frequency from 300khz to 2mhz n <1 a shutdown current n small, thermally enhanced 12-lead (4mm 3mm) dfn package n pda/ smart phones n handheld computers n mp3 players n handheld instruments n digital cameras n wireless handsets n usb peripherals l, lt , lt c , lt m , linear technology , the linear logo and burst mode are registered trademarks and thinsot is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 6404251, 6166527. sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd ltc3442 10f 0.01f v in 2.5v to 4.2v li-ion 340k 2.2k 22f 220pf v out 3.3v 1.2a 200k 0.01f 15k 470pf 3442 ta01a 4.7h 1m 71.5k 200k v in (v) 2.5 efficiency (%) 100 90 80 70 60 50 3.0 3.5 4.0 4.5 3442 ? ta01b 5.0 5.5 1a load 300ma load v out = 3.3v l = 4.7h f = 600khz efficiency vs v in
ltc 3442 2 3442fb for more information www.linear.com/ltc3442 pin configuration absolute maximum ratings v in , v out voltage ............................................ C 0.3 to 6 v sw 1, sw 2 voltage dc ............................................................... C0.3 to 6 v pulsed <100 ns ................................................. C0.3 to 7 v shdn / ss , burst voltage ............................... C0.3 to 6 v r lim ........................................................................... v in operating temperature ( note 2) ................ C40 c to 85 c maximum junction temperature ( note 4) .............. 125 c storage temperature range .................... C65 c to 125 c (notes 1, 4) 12 11 10 9 8 7 1 2 3 4 5 6 fb v c r lim v in v out burst shdn/ss r t sgnd sw1 pgnd sw2 top view 13 pgnd de12 package 12-lead (4mm 3mm) plastic dfn t jmax = 125c, v ja = 53c/w 1- layer board v ja = 43c/w 4- layer board, v jc = 4.3c/w exposed pad (pin 13) is pgnd, must be soldered to pcb order information lead free finish tape and reel part marking package description temperature range ltc3442ede#pbf ltc3442ede#trpbf 3442 12-lead (4mm w 3mm) plastic dfn C40c to 85c consult lt c marketing for parts specified with wider operating temperature ranges. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v in = v out = 3.6v, r t = 64.9k, unless otherwise noted (note 2). parameter conditions min typ max units input start-up voltage l 2.3 2.4 v output voltage adjust range l 2.4 5.25 v feedback voltage l 1.19 1.22 1.25 v feedback input current v fb = 1.22v 1 50 na quiescent current C burst mode operation v fb = 1.22v, burst = 0v (note 3) 35 60 a quiescent current C shutdown shdn = 0v, v out = 0v, not including switch leakage 0.1 1 a quiescent current C active burst = v in (note 3) 600 1100 a nmos switch leakage switches b and c 0.1 2 a pmos switch leakage switches a and d 0.1 3 a nmos switch on resistance switches b and c 0.10 pmos switch on resistance switches a and d 0.10 input current limit l 2 3 a reverse current limit 0.5 a burst mode operation current limit 0.9 a max duty cycle boost (% switch c on) buck (% switch a in) l l 70 100 88 % % min duty cycle l 0 % frequency accuracy l 570 670 770 khz error amp a vol 90 db error amp source current burst > 1.25v 11 a
ltc 3442 3 3442fb for more information www.linear.com/ltc3442 electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v in = v out = 3.6v, r t = 64.9k, unless otherwise noted (note 2). parameter conditions min typ max units error amp sink current burst > 1.25v 300 a burst threshold (falling) 0.88 v burst threshold (rising) 1.12 v burst current ratio ratio of i out to i burst 20,000 input current ratio ratio of i in to i rlim , i in = 0.5a 70,000 r lim threshold 0.95 v shdn/ss threshold when ic is enabled when ea is at max boost duty cycle l 0.4 0.7 2.2 1.4 2.4 v v shdn/ss input current v shdn = 5.5v 0.01 1 a note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc3442e is guaranteed to meet performance specifications from 0c to 85c. specifications over the C40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 3: current measurements are performed when the outputs are not switching. note 4: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed 125c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. typical performance characteristics efficiency vs load efficiency and power loss vs load efficiency vs frequency 3442 g01 load (ma) 0.1 efficiency (%) 1 10 100 1000 10000 90 60 100 80 70 50 40 30 20 burst mode operation fixed frequency v in = 5v v in = 3.3v v in = 2.5v v in = 5v v in = 3.3v v in = 2.5v v out = 3.3v 600khz load current (ma) 0.1 efficiency (%) 1 10 100 1000 10000 3442 g02 90 60 40 30 20 100 80 70 50 10 1 0.1 1000 100 power loss (mw) burst mode operation fixed frequency power loss v in = 3.6v v out = 3.3v frequency (khz) 400 efficiency (%) 2000 3442 g03 800 1200 1600 600 1000 1400 1800 96 94 92 90 88 86 84 82 80 without schottky diodes with schottky diodes v in = 3.6v v out = 3.3v ( t a = 25c unless otherwise specified).
ltc 3442 4 3442fb for more information www.linear.com/ltc3442 typical performance characteristics quiescent current vs v in (fixed frequency mode) burst mode quiescent current vs v in peak current clamp vs v in automatic burst mode threshold vs r burst minimum start voltage vs temperature average input current limit vs temperature (normalized) input current mirror linearity average input current limit vs v in (normalized) average input current limit vs frequency (normalized) input current (a) 0 1.00 0.90 0.80 0.60 0.70 0.50 0.40 0.30 0.20 0.10 0.00 .40 3442 g04 .10.05 .15 .25 .35 .45 .20 .30 .50 r lim voltage (v) v in = 3.6v v out = 3.3v r lim = 133k v in (v) 2.5 % change (normalized) 4.0 5.0 3442 g05 3.0 3.5 4.5 8 6 4 2 0 ?2 ?4 ?6 ?8 v out = 3.3v 1mhz frequency (mhz) 0.50 % change (normalized) 0.75 1.00 1.25 1.50 3442 ta01b 1.75 15 10 5 0 ?5 ?10 2.00 v in = 5v v out shorted v out drops 10% ( t a = 25c unless otherwise specified). v in (v) 2.5 v in quiescent current (ma) 4.0 5.0 3442 g07 3.0 3.5 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 5.5 2.0 mhz 1.5 mhz 1.0 mhz 0.5 mhz no switching v in (v) 2.5 v in quiescent current (a) 3.0 3.5 4.0 4.5 3442 g08 5.0 50 45 40 35 30 25 20 15 10 5 0 5.5 v in (v) 2.5 2.0 2.5 3.0 4.0 5.0 3442 g09 1.5 1.0 3.0 3.5 4.5 5.5 0.5 0.0 input current (a) 3.5 r burst (k) 150 60 load current (ma) 70 90 100 110 160 130 175 225 3442 g10 80 140 150 120 200 250 enter burst mode operation leave burst mode operation temperature (c) ?55 minimum start voltage (v) ?25 5 35 65 3442 g11 95 2.30 2.29 2.28 2.27 2.26 2.25 2.24 2.23 2.22 2.21 2.20 125 temperature (c) ?55 change from 25c 5% 4% 3% 2% 1% 0% ?1% ?2% ?3% ?4% ?5% ?15 25 45 125 3442 g12 ?35 5 65 85 105 v in = v out = 3.3v
ltc 3442 5 3442fb for more information www.linear.com/ltc3442 typical performance characteristics switch pins in buck-boost mode switch pins entering buck-boost mode output ripple at 1a load load transient response in fixed frequency mode, no load to 1a load transient response in auto burst mode operation, no load to 1a burst mode operation frequency change vs temperature (normalized) feedback voltage vs temperature (normalized) switch pins before entering boost mode (t a = 25c unless otherwise specified). temperature (c) ?55 change from 25c 1.0% 0.8% 0.6% 0.4% 0.2% 0.0% ?2.0% ?0.4% ?0.6% ?0.8% ?1.0% ?15 25 45 125 3442 g14 ?35 5 65 85 105 v in = v out = 3.3v 50ns/div 3442 g15 sw1 2v/div sw2 2v/div v in = 2.9v v out = 3.3v at 500ma 50ns/div 3442 g16 sw1 2v/div sw2 2v/div v in = 3.3v v out = 3.3v at 500ma 50ns/div 3442 g17 sw1 2v/div sw2 2v/div v in = 4.2v v out = 3.3v at 500ma 1s/div 3442 g18 v out 20mv/div ac coupled v in = 4.2v v in = 3.3v v in = 2.7v 100s/div 3442 g19 v in = 3.6v v out = 3.3v c out = 47f, x5r ceramic load 0.5a/div v out 100mv/div 100s/div 3442 g20 v in = 3.6v v out = 3.3v c out = 47f, x5r ceramic + 100f low esr tantalum load 0.5a/div v out 100mv/div 20s/div 3442 g21 c out = 100f low esr tantalum inductor current 0.5a/div v out 50mv/div temperature (c) ?55 change from 25c 0.0% 0.5% 1.0% 105 3442 g13 ?0.5% ?1.0% ?2.0% ?15 25 65 ?35 125 5 45 85 ?1.5% 2.0% 1.5%
ltc 3442 6 3442fb for more information www.linear.com/ltc3442 pin functions typical performance characteristics (t a = 25c unless otherwise specified). t ransition from burst mode operation to fixed frequency mode pulsed overload using average input current limit 200s/div 3442 g22 c out = 100f low esr tantalum inductor current 0.5a/div v out 50mv/div 1ms/div 3442 g23 r lim = 133k c lim = .001f inductor current 0.5a/div r lim pin 0.5v/div v out 2v/div shdn/ss (pin 1): combined soft-start and shutdown. applied voltage <0.4v shuts down the ic. tie to >1.4v to enable the ic and >2.4v to ensure the error amp is not clamped from soft-start. for burst mode operation, this pin must be pulled up to within 0.5v of v in . an rc network from the shutdown command signal to this pin will provide a soft-start function by limiting the rise time of the v c pin. r t (pin 2): programs the frequency of the internal os- cillator. place a resistor from this pin to ground. see the applications information section for component value selection. sgnd (pin 3): signal ground for the ic. sw1 (pin 4): switch pin where internal switches a and b are connected. connect inductor from sw1 to sw2. an optional schottky diode can be connected from sw1 to ground for a moderate efficiency improvement. minimize trace length to reduce emi. pgnd (pin 5, 13): power ground for the internal nmos power switches. the exposed pad must be soldered to pcb ground to provide both electrical contact and a good thermal contact to the pcb. sw2 (pin 6): switch pin where internal switches c and? d are connected. an optional schottky diode can be connected from sw2 to v out for a moderate efficiency improvement. minimize trace length to reduce emi. burst (pin 7): used to set the automatic burst mode op- eration threshold. place a resistor and capacitor in parallel from this pin to ground. see the applications information section for component value selection . for manual control , ground the pin to force burst mode operation, connect to v out to force fixed frequency mode. v out (pin 8): output of the synchronous rectifier. a filter capacitor is placed from v out to gnd. a ceramic bypass capacitor is recommended as close to the v out and gnd pins as possible. v in (pin 9): input supply pin. internal v cc for the ic. a 10f ceramic capacitor is recommended as close to v in and sgnd as possible. r lim (pin 10): sets the average input current limit threshold. place a resistor and capacitor in parallel from this pin to ground. see the applications information sec- tion for component value selection. v c (pin 11): error amp output. a frequency compensation network is connected from this pin to fb to compensate the loop. during burst mode operation, v c is internally connected to a hold circuit. fb (pin 12): feedback pin. connect resistor divider tap here. the output voltage can be adjusted from 2.4v to 5.25v. the feedback reference voltage is typically 1.22v.
ltc 3442 7 3442fb for more information www.linear.com/ltc3442 block diagram ? + ? + ? + ? + ? + ? + ? + 9 pwm logic gate drivers and anticross conduction pgnd uvlo 5a 2.3v osc peak current limit sw a sw1 v in v cc v in v in sw2 sw d error amp 1.22v reverse amp sw b 0.95v average i lim sw c 2 4 6 sgnd 6 v out 8 fb 12 burst 7 v c 11 1 shdn/ss 2 r t 3442 bd pwm comparators ? + thermal shutdown a v = 6 shutdown soft-start shutdown 1.22v v ref 10 r lim automatic burst mode control and vc hold g m = 1/60k 3a v ref sleep ss
ltc 3442 8 3442fb for more information www.linear.com/ltc3442 operation the ltc3442 provides high efficiency, low noise power for applications such as portable instrumentation. the lt c proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. the error amp output voltage on v c determines the output duty cycle of the switches. since v c is a filtered signal, it provides rejection of frequencies from well below the switching frequency. the low r ds(on) , low gate charge synchronous switches provide high frequency pulse width modulation control at high efficiency . schottky diodes across the synchronous switch d and synchronous switch b are not required, but provide a lower voltage drop during the break-before-make time (typically 15ns). schottky diodes will improve peak efficiency by typically 1% to 2%. high efficiency is achieved at light loads when burst mode operation is entered and the ics quiescent current drops to a low 35a. low noise fixed frequency operation oscillator the frequency of operation is programmed by an external resistor from r t to ground, according to the following equation: f (khz) = 43,300 r t(k ? ) error amp the error amplifier is a voltage mode amplifier. the loop compensation components are configured around the amplifier ( from fb to v c ) to obtain stability of the converter . for improved bandwidth, an additional rc feedforward network can be placed across the upper feedback divider resistor. the voltage on shdn/ss clamps the error amp output, v c , to provide a soft-start function. internal current limit there are three different current limit circuits in the ltc3442. tw o have internally fixed thresholds which vary inversely with v in , the third is externally programmable, and does not vary with input voltage. the first circuit is a high speed peak current limit amplifier that will shut off switch a if the current exceeds 5a typi- cal. the delay to output of this amplifier is typically 50ns. a second amplifier will begin to source current into the fb pin to drop the output voltage once the peak input current exceeds 3a typical. this method provides a closed loop means of clamping the input current. during conditions where v out is near ground, such as during a short- circuit or during startup, this threshold is cut in half, providing a foldback feature. for this current limit feature to be most effective , the thevenin resistance from fb to ground should be greater than 100k. externally programmable current limit the third current limit circuit is programmed by an external resistor on r lim . this circuit works by mirroring the input current in switch a, averaging it by means of the external rc network on r lim , and comparing the resulting voltage with an internal reference. if the voltage on r lim starts to exceed 0.95v, a g m amplifier will clamp v c , lowering v out to maintain control of the input current. this allows the user to program a maximum average input current, for applications such as usb, where the current draw from the bus must be limited to 500ma. the resistor and capacitor values are determined by the following equations: r lim(k ? ) = 70 ? 0.86 + 2 ? v in ? v out ( ) 40 ? ? ? ? ? ? i in(amps) c lim( f) 0.1 r lim(k ? ) the programmable current limit feature is disabled in burst mode operation.
ltc 3442 9 3442fb for more information www.linear.com/ltc3442 operation reverse current limit during fixed frequency operation, the ltc3442 operates in forced continuous conduction mode. the reverse cur - rent limit amplifier monitors the inductor current from the output through switch d. once the negative inductor current exceeds 500ma typical, the ic will shut off switch? d . four-switch control figure 1 shows a simplified diagram of how the four in- ternal switches are connected to the inductor, v in , v out and gnd. figure 2 shows the regions of operation for the ltc3442 as a function of the internal control voltage, v ci . depending on the control voltage, the ic will operate in either buck, buck/boost or boost mode. the v ci voltage is a level shifted voltage from the output of the error amp (v c ) (see figure 5). the four power switches are properly phased so the transfer between operating modes is con- tinuous, smooth and transparent to the user. when v in approaches v out the buck/boost region is reached where the conduction time of the four switch region is typically 150ns. referring to figures 1 and 2, the various regions of operation will now be described. buck region (v in > v out ) switch d is always on and switch c is always off during this mode. when the internal control voltage, v ci , is above voltage v1, output a begins to switch. during the off-time of switch a, synchronous switch b turns on for the remainder of the time. switches a and b will alternate similar to a typical synchronous buck regulator. as the control voltage increases, the duty cycle of switch a increases until the maximum duty cycle of the converter in buck mode reaches dmax_buck, given by: dmax_buck = 100 C d4 sw % where d4 sw = duty cycle % of the four switch range. d4 sw = (150ns ? f) ? 100 % where f = operating frequency, hz. beyond this point the four switch, or buck/boost region is reached. buck/boost or four switch (v in ~ v out ) when the internal control voltage, v ci , is above voltage v2, switch pair ad remain on for duty cycle dmax_buck, and the switch pair ac begins to phase in. as switch pair ac phases in, switch pair bd phases out accordingly. when the v ci voltage reaches the edge of the buck/boost range, at voltage v3, the ac switch pair completely phase out the bd pair, and the boost phase begins at duty cycle d4 sw . the input voltage, v in , where the four switch region begins is given by: v in = v out 1? (150ns s f) the point at which the four switch region ends is given by: v in = v out (1 C d) = v out (1 C 150ns ? f) v 4 sw1 6 sw2 pmos a nmos b 9 v in pmos d nmos c 3442 f01 8 v out figure 1. simplified diagram of output switches figure 2. switch control vs internal control voltage, v ci 88% d max boost d min boost d max buck duty cycle 0% v4 (2.05v) v3 (1.65v) boost region buck region buck/boost region v2 (1.55v) v1 (0.9v) 3442 f02 a on, b off pwm cd switches d on, c off pwm ab switches four switch pwm internal control voltage, v ci
ltc 3442 10 3442fb for more information www.linear.com/ltc3442 operation boost region (v in < v out ) switch a is always on and switch b is always off during this mode. when the internal control voltage, v ci , is above voltage v 3, switch pair cd will alternately switch to provide a boosted output voltage. this operation is typical to a synchronous boost regulator. the maximum duty cycle of the converter is limited to 88% typical and is reached when v ci is above v4. burst mode operation burst mode operation occurs when the ic delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the ic is consuming only 35a of quiescent current from v in . in this mode the output ripple has a variable frequency component that depends upon load current, and will typically be about 2% peak-to-peak. burst mode operation ripple can be reduced slightly by using more output capacitance (47f or greater). another method of reducing burst mode operation ripple is to place a small feedforward capacitor across the upper resistor in the v out feedback divider network (as in type?iii compensation). during the period where the device is delivering energy to the output, the peak switch current will be equal to 900ma typical and the inductor current will terminate at zero current for each cycle. in this mode the typical maximum average output current is given by: i out(max)burst 0.2 ? v in v out + v in a note that the peak efficiency during burst mode operation is less than the peak efficiency during fixed frequency 9 v in a 4 sw1 5 gnd 6 sw2 l + ? 8 v out d c 900ma i inductor 0ma 3442 f03 t1 b di dt v in l figure 3. inductor charge cycle during burst mode operation figure 4. inductor discharge cycle during burst mode operation 9 v in a 4 sw1 5 gnd 6 sw2 l ? + 8 v out d c 900ma i inductor 0ma 3442 f04 t2 b di dt v out l ? because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor cur - rent as illustrated in figures 3 and 4. during burst mode operation, the control loop is nonlinear and cannot utilize the control voltage from the error amp to determine the control mode, therefore full- time 4-switch mode is required to maintain the buck/boost function. the efficiency below 1ma becomes dominated primarily by the quiescent cur - rent. the burst mode operation efficiency is given by: efficiency ? n ? i load 35a + i load where n is typically 82% during burst mode operation. automatic burst mode operation control burst mode operation can be automatic or manually con- trolled with a single pin. in automatic mode, the ic will enter burst mode operation at light load and return to fixed frequency operation at heavier loads. the load current at which the mode transition occurs is programmed using a single external resistor from the burst pin to ground, according to the following equations: enter burst mode: i = 17.6 r burst leave burst mode: i = 22.4 r burst where r burst is in k and i burst is the load transition current in amps. do not use values of r burst greater than 250k.
ltc 3442 11 3442fb for more information www.linear.com/ltc3442 operation for automatic operation, a filter capacitor should also be connected from burst to ground to prevent ripple on burst from causing the ic to oscillate in and out of burst mode operation. the equation for the minimum capacitor value is: c burst(min) c out ? v out 60,000 where c burst(min) and c out are in f. in the event that a load transient causes the feedback pin to drop by more than 4% from the regulation value while in burst mode operation, the ic will immediately switch to fixed frequency mode and an internal pull-up will be momentarily applied to burst , rapidly charging the burst cap. this prevents the ic from immediately re- entering burst mode operation once the output achieves regulation. manual burst mode operation for manual control of burst mode operation, the rc network connected to burst can be eliminated. to force fixed frequency mode, burst should be connected to v out . to force burst mode operation, burst should be grounded . when commanding burst mode operation manually, the circuit connected to burst should be able to sink up to 2ma. for optimum transient response with large dynamic loads, the operating mode should be controlled manually by the host. by commanding fixed frequency operation prior to a sudden increase in load, output voltage droop can be minimized. note that if the load current applied during forced burst mode operation (burst pin is grounded) exceeds the current that can be supplied, the output voltage will start to droop and the ic will automati- cally come out of burst mode operation and enter fixed frequency mode, raising v out . once regulation is achieved , the ic will then enter burst mode operation once again, and the cycle will repeat, resulting in about 4% output ripple. note that burst mode operation is inhibited during soft-start. burst mode operation to fixed frequency transient response in burst mode operation, the compensation network is not used and v c is disconnected from the error amplifier. during long periods of burst mode operation, leakage currents in the external components or on the pc board could cause the compensation capacitor to charge (or discharge), which could result in a large output transient when returning to fixed frequency mode of operation, even at the same load current. to prevent this, the ltc3442 incorporates an active clamp circuit that holds the voltage on v c at an optimal voltage during burst mode operation. this minimizes any output transient when returning to fixed frequency mode operation. for optimum transient response, type 3 compensation is also recommended to broad band the control loop and roll off past the two pole response of the output lc filter. (see closing the feedback loop.) soft -start the soft-start function is combined with shutdown. when the shdn/ss pin is brought above 0.7v typical, the ic is enabled but the ea duty cycle is clamped from v c . a detailed diagram of this function is shown in figure 5. the components r ss and c ss provide a slow ramping voltage on shdn/ss to provide a soft-start function. to ensure that v c is not being clamped, shdn/ss must be raised above 2.4v. to enable burst mode operation, shdn/ss must be raised to within 0.5v of v in .
ltc 3442 12 3442fb for more information www.linear.com/ltc3442 operation applications information ? + 12 11 v in error amp 1.22v 14a fb r1 r2 c p1 v c v out 1 shdn/ss c ss 0.7v enable signal r ss soft-start clamp to pwm comparators chip enable 3442 f05 ? + v ci figure 5. soft-start circuitry component selection 12 11 10 9 8 7 1 2 3 4 5 6 fb v c r lim v in v out burst shdn/ss rt sgnd sw1 pgnd sw2 v in v out gnd r t multiple vias 3442 f06 v in figure 6. recommended component placement. traces carrying high current should be short and wide. trace area at fb and v c pins are kept low. lead length to battery should be kept short. v out and v in ceramic capacitors close to the ic pins. inductor selection the high frequency operation of the ltc3442 allows the use of small surface mount inductors. the inductor ripple current is typically set to 20% to 40% of the maximum inductor current. for a given ripple the inductance terms are given as follows: l boost > v in(min) ? (v out ? v in(min) ) f ? ? i l ? v out h l buck > v out ? (v in(max) ? v out ) f ? ? i l ? v in(max) h where f = operating frequency, hz ?i l = maximum allowable inductor ripple current, a v in(min) = minimum input voltage, v v in(max) = maximum input voltage, v v out = output voltage, v i out(max) = maximum output load current
ltc 3442 13 3442fb for more information www.linear.com/ltc3442 applications information table 1. inductor vendor information supplier phone fax web site coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com coev magnetics (800) 227-7040 (650) 361-2508 www. circuitprotection.com/magnetics.asp murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com sumida usa: (847) 956-0666 japan: 81(3) 3607-5111 usa: (847) 956-0702 japan: 81(3) 3607-5144 www.sumida.com tdk (847) 803-6100 (847) 803-6296 www.component.tdk.com toko (847) 297-0070 (847) 699-7864 www.tokoam.com for high efficiency, choose a ferrite inductor with a high frequency core material to reduce core loses. the induc- tor should have low esr (equivalent series resistance) to reduce the i 2 r losses, and must be able to handle the peak inductor current without saturating . molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1a to 2a region. to minimize radiated noise, use a shielded inductor. see table 1 for a suggested list of inductor suppliers. output capacitor selection the bulk value of the output filter capacitor is set to reduce the ripple due to charge into the capacitor each cycle. the steady-state ripple due to charge is given by: % ripple_boost= i out(max) ? v out ? v in(min) ( ) ? 100 c out ? v out 2 ? f % % ripple_buck = i out(max) ? v in(max) ? v out ( ) ? 100 c out ? v in(max) ? v out ? f % where c out = output filter capacitor in farads and f = switching frequency in hz. the output capacitance is usually many times larger than the minimum value in order to handle the transient response requirements of the converter . for a rule of thumb , the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the above calculations in order to maintain the desired transient response. the other component of ripple is due to the esr (equiva- lent series resistance) of the output capacitor. low esr capacitors should be used to minimize output voltage ripple. for surface mount applications, taiyo yuden or tdk ceramic capacitors, avx tps series tantalum capaci- tors or sanyo poscap are recommended. see table 2 for contact information. input capacitor selection since v in is the supply voltage for the ic, as well as the input to the power stage of the converter, it is recommended to place at least a 4.7f, low esr ceramic bypass capacitor close to the v in and sgnd pins. it is also important to minimize any stray resistance from the converter to the battery or other power source. table 2. capacitor vendor information supplier phone fax web site avx (803) 448-9411 (803) 448-1943 www.avxcorp.com murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com taiyo yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com tdk (847) 803-6100 (847) 803-6296 www.component.tdk.com
ltc 3442 14 3442fb for more information www.linear.com/ltc3442 optional schottky diodes the schottky diodes across the synchronous switches? b and d are not required (v out < 4.3v), but provide a lower drop during the break-before-make time (typically 15ns) improving efficiency. use a surface mount schottky diode such as an mbrm120t3 or equivalent. do not use ordi- nary rectifier diodes, since the slow recovery times will compromise efficiency. for applications with an output voltage above 4.3v, a schottky diode is required from sw2 to v out . output voltage < 2.4v the ltc3442 can operate as a buck converter with out- put voltages as low as 0.4v. the part is specified at 2.4v minimum to allow operation without the requirement of a schottky diode. synchronous switch d is powered from v out and the r ds(on) will increase at low output voltages, therefore a schottky diode is required from sw2 to v out to provide the conduction path to the output. note that burst mode operation is inhibited at output voltages below 1.6v typical. output voltage > 4.3v a schottky diode from sw2 to v out is required for output voltages over 4.3v. the diode must be located as close to the pins as possible in order to reduce the peak voltage on sw2 due to the parasitic lead and trace inductance. input voltage > 4.5v for applications with input voltages above 4.5v which could exhibit an overload or short- circuit condition, a 2/1 nf series snubber is required between sw 1 and gnd . a schottky diode from sw1 to v in should also be added as close to the pins as possible. for the higher input volt- ages, v in bypassing becomes more critical; therefore, a ceramic bypass capacitor as close to the v in and sgnd pins as possible is also required. operating frequency selection higher operating frequencies allow the use of a smaller inductor and smaller input and output filter capaci - tors, thus reducing board area and component height. applications information however, higher operating frequencies also increase the ics total quiescent current due to the gate charge of the four switches, as given by: buck : iq = (0.8 ? v in ? f) ma boost : iq = [0.4 ? (v in + v out ) ? f] ma buck/boost : iq = [f ? (1.2 ? v in + 0.4 ? v out )] ma where f = switching frequency in mhz . therefore frequency selection is a compromise between the optimal efficiency and the smallest solution size. closing the feedback loop the ltc3442 incorporates voltage mode pwm control . the control to output gain varies with operation region (buck, boost, buck/boost), but is usually no greater than 15. the output filter exhibits a double pole response, as given by: f filter ? pole = 1 2 s l s c out hz ( in buck mode) f filter ? pole = v in 2 s v out s l s c out hz ( in boost mode) where l is in henries and c out is in farads. the output filter zero is given by: f filter ? zero = 1 2 s r esr s c out hz where r esr is the equivalent series resistance of the output capacitor. a troublesome feature in boost mode is the right -half plane zero (rhp), given by: f rhpz = v in 2 2 s i out s l s v out hz the loop gain is typically rolled off before the rhp zero frequency.
ltc 3442 15 3442fb for more information www.linear.com/ltc3442 applications information typical applications a simple type i compensation network can be incorporated to stabilize the loop, but at a cost of reduced bandwidth and slower transient response. to ensure proper phase margin using type i compensation, the loop must be crossed over a decade before the lc double pole. the unity-gain frequency of the error amplifier with the type ? i compensation is given by: f ug = 1 2 ? ? r1 ? c p1 hz referring to figure 7. most applications demand an improved transient response to allow a smaller output filter capacitor. to achieve a higher bandwidth, type iii compensation is required, providing two zeros to compensate for the double-pole response of the output filter. referring to figure 8, the location of the poles and zeros are given by: f pole1 ? 1 2 ? ? 32e 3 ? r1 ? cp1 hz (which is extremely close to dc) f zero1 = 1 2 ? ? r z ? c p1 hz f zero2 = 1 2 ? ? r1 ? c z1 hz f pole2 = 1 2 ? ? r z ? c p2 hz where resistance is in ohms and capacitance is in farads. 1.22v r1 r2 3442 f07 fb 12 v c c p1 v out 11 ? + error amp 1.22v r1 r2 3442 f08 fb 12 v c c p1 c z1 r z v out 11 c p2 ? + error amp figure 7. error amplifier with type i compensation figure 9. error amplifier with type iii compensation 1mhz li-ion to 3.3v at 1.2a converter with manual mode control (and peak current limit only) sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd ltc3442 c in 10f 0.01f c in : taiyo yuden jmk212bj106mg c out : taiyo yuden jmk325bj226mm l1: tdk rlf7030t-3r3m4r 2.5v to 4.2v li-ion 15k 340k 2.2k l1 3.3h c out 22f 220pf v out 3.3v 1.2a 200k 470pf 3442 ta02 + 43.2k burst fixed freq 1m
ltc 3442 16 3442fb for more information www.linear.com/ltc3442 typical applications multi-input 3.3v at 600ma boost converter for portable applications with automatic burst mode operation and average input current limit for usb powered devices sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd ltc3442 0.01f c in : taiyo yuden jmk212bj106mg c out : taiyo yuden jmk325bj476mm l1: tdk rlf7030t-4r7m3r4 2.5v to 5.5v li-ion 15k 340k 200k 2.2k 0.01f 220pf v out 3.3v 600ma 200k 470pf 3442 ta03 64.9k 143k 1m 1nf r snub ** 1 usb/5v 2 d1 mbrm120t3 1nf a snubber resistor is required to prevent ringing if there is significant input inductance, such as from a usb cable ** usb present 2n7002 143k c in 10f l1 4.7h c out 22f high efficiency li-ion powered constant current led driver with open-led protection led driver efficiency vs led current sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd ltc3442 v in 2.5v to 4.2v lhxl-pw03 4.7f v out 1nf 3442 ta04a 3.3h 47pf 10f r5 7.87k *off on open led voltage limit = (r4 + r5) ? 0.95/r4 * note: the shdn/ss voltage must be no more than 0.5v below v in when enabled. r2 = r1/1.5 i led = 24 ? (r1 + r2 + r3)/(r1 ? r3) amps r3 95.3k r2 200k r1 301k 57.6k r4 2k i led = 500ma led current (a) 0.1 efficiency (%) 1.0 3442 ta04b 80 84 88 92 96 82 86 90 94 98 100 v in = 3.6v 750khz
ltc 3442 17 3442fb for more information www.linear.com/ltc3442 typical applications high current led driver with low/high current range for pulsed applications; led current is 0.5a with 1.5a pulse sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd ltc3442 v in 2.7v to 4.2v lhxl-pw03 10f 6.3v v out 1nf 3442 ta05 3.3h 1nf 10f 6.3v r5 7.87k i led = 500ma/1.5a open led voltage limit = (r4 + r5) ? 0.95/r4 r2 = r1/1.5 i led = 24 ? (r1 + r2 + r3)/(r1 ? r3) amps (or: i led = 40/r3 + .08) 95.3k 40.2k 2n7002 r2 200k r1 301k 57.6k r4 2k r2 20k *off on low hi * note: the shdn/ss voltage must be no more than 0.5v below v in when enabled.
ltc 3442 18 3442fb for more information www.linear.com/ltc3442 package description please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. 4.00 0.10 (2 sides) 3.00 0.10 (2 sides) note: 1. drawing proposed to be a variation of version (wged) in jedec package outline m0-229 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom view?exposed pad 1.70 0.10 0.75 0.05 r = 0.115 typ r = 0.05 typ 2.50 ref 1 6 12 7 pin 1 notch r = 0.20 or 0.35 45 chamfer pin 1 top mark (note 6) 0.200 ref 0.00 ? 0.05 (ue12/de12) dfn 0806 rev d 2.50 ref recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 2.20 0.05 0.70 0.05 3.60 0.05 package outline 3.30 0.10 0.25 0.05 0.50 bsc 1.70 0.05 3.30 0.05 0.50 bsc 0.25 0.05 de/ue package 12-lead plastic dfn (4mm 3mm) (reference ltc dwg # 05-08-1695 rev d)
ltc 3442 19 3442fb for more information www.linear.com/ltc3442 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. revision history rev date description page number b 05/13 modified the absolute maximum ratings section and added new order information modified the electrical characteristics table and note 2 simplified block diagram, update 1v to 0.95v changed operation section, 1v to 0.7v for soft-start 2 2, 3 7 12 (revision history begins at rev b)
ltc 3442 20 3442fb for more information www.linear.com/ltc3442 ? linear technology corporation 2013 lt 0613 rev b ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/ltc3442 related parts part number description comments lt ? 1613 550ma (i sw ), 1.4mhz, high efficiency step-up dc/dc converter v in : 0.9v to 10v, v out(max) = 34v, i q = 3ma, i sd < 1a, thinsot? package lt1618 1.5a (i sw ), 1.25mhz, high efficiency step-up dc/dc converter v in : 1.6v to 18v, v out(max) = 35v, i q = 1.8ma, i sd < 1a, ms10 package lt1930/lt1930a 1a (i sw ), 1.2mhz/2.2mhz, high efficiency step- up dc/dc converter v in : 2.6v to 16v, v out(max) = 34v, i q = 4.2ma/5.5ma, i sd < 1a, thinsot package lt1935 2a (i sw ), 1.2mhz, 38v step-up dc/dc converter v in : 2.3v to 16v, v out(max) = 38v, i q = 3ma, s d < 1a, thinsot package lt1946/lt1946a 1.5a (i sw ), 1.2mhz/2.7mhz, high efficiency step-up dc/dc converter v in : 2.45v to 16v, v out(max ) = 34v, i q = 3.2ma, i sd < 1a, ms8 package lt1961 1.5a (i sw ), 1.25mhz, high efficiency step-up dc/dc converter v in : 3v to 25v, v out(max) = 35v, i q = 0.9ma, i sd = 6a, ms8e package ltc3400/ltc3400b 600ma (i sw ), 1.2mhz synchronous step-up dc/dc converter v in : 0.85v to 5v, v out(max) = 5v, i q = 19a/300a, i sd < 1a, thinsot package ltc3401/ ltc3402 1a/2a (i sw ), 3mhz synchronous step-up dc/dc converter v in : 0.5v to 5v, v out(max) = 6v, i q = 38a, i sd < 1a, ms package ltc3405/ltc3405a 300ma (i out ), 1.5mhz synchronous step-down dc/dc converter v in : 2.7v to 6v, v out(min) = 0.8v, i q = 20a, i sd 1a, ms10 package ltc3406/ltc3406b 600ma (i out ), 1.5mhz synchronous step-down dc/dc converter v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 20a, i sd 1a, thinsot package ltc3407 600ma (i out ), 1.5mhz dual synchronous step-down dc/dc converter v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 40a, i sd 1a, ms package ltc3411 1.25a (i out ), 4mhz synchronous step-down dc/dc converter v in : 2.5v to 5.5v, v out(min) = 0.8v, i q = 60a, i sd 1a, ms package ltc3412 2.5a (i out ), 4mhz synchronous step-down dc/dc converter v in : 2.5v to 5.5v, v out(min) = 0.8v, i q = 60a, i sd 1a, tssop16e package ltc3421 3a (i sw ), 3mhz synchronous step-up dc/dc converter v in : 0.5v to 4.5v, v out(max) = 5.25v, i q = 12a, i sd < 1a, qfn package ltc3425 5a (i sw ), 8mhz multiphase synchronous step-up dc/dc converter v in : 0.5v to 4.5v, v out(max) = 5.25v, i q = 12a, i sd < 1a, qfn package ltc3429 600ma (i sw ), 500khz synchronous step-up dc/dc converter v in : 0.5v to 4.4v, v out(min) = 5v, i q = 20a, i sd < 1a, qfn package lt3436 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 < 6a, tssop-16e package ltc3440 600 ma (i out ), 2mhz synchronous buck-boost dc/dc converter v in : 2.5v to 5.5v, v out(min) = 5.5v, i q = 25a, i sd < 1a, ms, dfn packages ltc3441 600ma (i out ), 2mhz synchronous buck-boost dc/dc converter v in : 2.5v to 5.5v, v out(min) = 5.5v, i q = 25a, i sd < 1a, dfn package ltc3443 1.2a (i out ), 600khz synchronous buck-boost dc/dc converter v in : 2.4v to 5.5v, v out( min) = 5.25v, i q = 28a, i sd < 1a, ms package lt3467 1.1a (i sw ), 1.3mhz, high efficiency step-up dc/dc converter v in : 2.6v to 16v, v out(max) = 40v, i q = 1.2ma, i sd < 1a, thinsot package

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