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LTC3442 1 3442f , ltc and lt are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. burst mode is a registered trademark of linear technology corporation. 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 10 f 0.01 f v in 2.5v to 4.2v li-ion 340k 2.2k 22 f 220pf v out 3.3v 1.2a 200k 0.01 f 15k 470pf 3442 ta01a 4.7 h 1m 71.5k 200k typical applicatio u applicatio s u features descriptio u micropower synchronous buck-boost dc/dc converter with automatic burst mode operation the ltc ? 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 35 a 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 1 a 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. pda/smart phones handheld computers mp3 players handheld instruments digital cameras wireless handsets usb peripherals efficiency vs v in 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 = 4.7 h f = 600khz regulated output with input voltages above, below, or equal to the output single inductor, no schottky diodes required manual or programmable automatic burst mode operation programmable average input current limit up to 1.2a continuous output current from a single lithium-ion cell high efficiency: up to 95% output disconnect in shutdown 2.4v to 5.5v input range 2.4v to 5.25v output range 35 a quiescent current in burst mode operation programmable frequency from 300khz to 2mhz <1 a shutdown current small, thermally enhanced 12-lead (4mm 3mm) dfn package
LTC3442 2 3442f v in , v out voltage ........................................... C 0.3 to 6v sw1, sw2 voltage dc ................................................................. C 0.3 to 6v pulsed <100ns ............................................... C 0.3 to 7v shdn/ss, burst voltage ............................. C 0.3 to 6v operating temperature (note 2) ............. C 40 c to 85 c maximum junction temperature (note 4) ............ 125 c storage temperature range ................. C 65 c to 125 c order part number de part marking 3442 LTC3442ede absolute axi u rati gs w ww u package/order i for atio uu w (note 1) electrical characteristics the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = v out = 3.6v, r t = 64.9k, unless otherwise noted. parameter conditions min typ max units input start-up voltage 2.3 2.4 v output voltage adjust range 2.4 5.25 v feedback voltage 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 23 a reverse current limit 0.5 a burst mode operation current limit 0.9 a max duty cycle boost (% switch c on) 70 88 % buck (% switch a in) 100 % min duty cycle 0% frequency accuracy 570 670 770 khz error amp a vol 90 db error amp source current 11 a error amp sink current 300 a burst threshold (falling) 0.88 v burst threshold (rising) 1.12 v t jmax = 125 c ja = 53 c/w 1-layer board ja = 43 c/w 4-layer board jc = 4.3 c/w exposed pad is pgnd (pin 13) must be soldered to pcb 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 top view 13 de12 package 12-lead (4mm 3mm) plastic dfn
LTC3442 3 3442f v in (v) 2.5 % change (normalized) 4.0 5.0 3442 g05 3.0 3.5 4.5 8 6 4 2 0 C2 C4 C6 C8 v out = 3.3v 1mhz 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 frequency (mhz) 0.50 % change (normalized) 0.75 1.00 1.25 1.50 3442 ta01b 1.75 15 10 5 0 C5 C10 2.00 v in = 5v v out shorted v out drops 10% parameter conditions min typ max units 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 0.4 0.7 1.4 v when ea is at max boost duty cycle 2.2 2.4 v shdn/ss input current v shdn = 5.5v 0.01 1 a electrical characteristics the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = v out = 3.6v, r t = 64.9k, unless otherwise noted. note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the LTC3442e is guaranteed to meet performance specifications from 0 c to 70 c. specifications over C40 c to 85 c 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 125 c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. typical perfor a ce characteristics uw efficiency vs load efficiency and power loss vs load efficiency vs frequency input current mirror linearity average input current limit vs v in (normalized) 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 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 (t a = 25 c unless otherwise specified). average input current limit vs frequency (normalized)
LTC3442 4 3442f typical perfor a ce characteristics uw (t a = 25 c unless otherwise specified). quiescent current vs v in (fixed frequency mode) burst mode quiescent current vs v in peak current clamp vs v in 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 automatic burst mode threshold vs r burst minimum start voltage vs temperature average input current limit vs temperature (normalized) frequency change vs temperature (normalized) feedback voltage vs temperature (normalized) switch pins before entering boost mode 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) C55 minimum start voltage (v) C25 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) C55 change from 25 c 5% 4% 3% 2% 1% 0% C1% C2% C3% C4% C5% C15 25 45 125 3442 g12 C35 5 65 85 105 v in = v out = 3.3v temperature ( c) C55 change from 25 c 0.0% 0.5% 1.0% 105 3442 g13 C0.5% C1.0% C2.0% C15 25 65 C35 125 54585 C1.5% 2.0% 1.5% temperature ( c) C55 change from 25 c 1.0% 0.8% 0.6% 0.4% 0.2% 0.0% C2.0% C0.4% C0.6% C0.8% C1.0% C15 25 45 125 3442 g14 C35 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
LTC3442 5 3442f 200 s/div 3442 g22 c out = 100 f low esr tantalum inductor current 0.5a/div v out 50mv/div 1ms/div 3442 g23 r lim = 133k c lim = .001 f inductor current 0.5a/div r lim pin 0.5v/div v out 2v/div 20 s/div 3442 g21 c out = 100 f low esr tantalum inductor current 0.5a/div v out 50mv/div 50ns/div 3442 g17 sw1 2v/div sw2 2v/div v in = 4.2v 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 typical perfor a ce characteristics uw 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 pulsed overload using average input current limit transition from burst mode operation to fixed frequency mode 1 s/div 3442 g18 v out 20mv/div ac coupled v in = 4.2v v in = 3.3v v in = 2.7v 100 s/div 3442 g19 v in = 3.6v v out = 3.3v c out = 47 f, x5r ceramic load 0.5a/div v out 100mv/div 100 s/div 3442 g20 v in = 3.6v v out = 3.3v c out = 47 f, x5r ceramic + 100 f low esr tantalum load 0.5a/div v out 100mv/div (t a = 25 c unless otherwise specified).
LTC3442 6 3442f uu u pi fu ctio s 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. an rc network from the shut- down 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 oscil- lator. 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 con- nected from sw2 to v out for a moderate efficiency im- provement. minimize trace length to reduce emi. burst (pin 7): used to set the automatic burst mode operation 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 10 f 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 section 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.
LTC3442 7 3442f si plified w block diagra w C + C + C + C + C + C + C + 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 1v 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 C + 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
LTC3442 8 3442f the LTC3442 provides high efficiency, low noise power for applications such as portable instrumentation. the ltc 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 effi- ciency. 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 effi- ciency 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 35 a. 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 r khz tk () () , = ? 43 300 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 con- verter. for improved bandwidth, an additional rc feed- forward 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. operatio u internal current limit there are three different current limit circuits in the LTC3442. two 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 typical. 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 exter- nal 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 vv i c r lim k in out in amps lim f lim k () () () () ?. ?C . ? ? = + () ? ? ? ? ? ? ? ? 70 0 86 2 40 01
LTC3442 9 3442f 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 internal 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 v ns f in out = 1 150 C( ? ) 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 operatio u
LTC3442 10 3442f 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 v3, switch pair cd will alternately switch to pro- vide 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 35 a 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 (47 f or greater). another method of reducing burst mode operation ripple is to place a small feed-forward 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 v vv a out max burst in out in () .? + 02 note that the peak efficiency during burst mode operation is less than the peak efficiency during fixed frequency because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor current 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 re- quired to maintain the buck/boost function. the efficiency below 1ma becomes dominated primarily by the quies- cent current. the burst mode operation efficiency is given by: efficiency ni ai load load ? + ? 35 where n is typically 82% during burst mode operation. automatic burst mode operation control burst mode operation can be automatic or manually controlled 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 leave burst mode: i 22.4 r burst burst = = where r burst is in k ? and i burst is the load transition 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 C+ 8 v out d c 900ma i inductor 0ma 3442 f04 t2 b di dt v out l C 9 v in a 4 sw1 5 gnd 6 sw2 l +C 8 v out d c 900ma i inductor 0ma 3442 f03 t1 b di dt v in l operatio u
LTC3442 11 3442f current in amps. do not use values of r burst greater than 250k. 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 cv burst min out 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 automatically come out of burst mode operation and enter fixed fre- quency 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 operatio u
LTC3442 12 3442f figure 5. soft-start circuitry C + 12 11 v in error amp 1.22v 14 a fb r1 r2 c p1 v c v out 1 shdn/ss c ss 1v enable signal r ss soft-start clamp to pwm comparators chip enable 3442 f05 C + v ci operatio u 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 1v 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.
LTC3442 13 3442f applicatio s i for atio wu u u component selection 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 (814) 238-0490 www.murata.com (800) 831-9172 sumida usa: (847) 956-0666 usa: (847) 956-0702 www.sumida.com japan: 81(3) 3607-5111 japan: 81(3) 3607-5144 tdk (847) 803-6100 (847) 803-6296 www.component.tdk.com toko (847) 297-0070 (847) 699-7864 www.tokoam.com 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 vvv fiv h l vv v fiv h boost in min out in min l out buck out in max out l in max > ? > ? () () () () ?( C ) ?? ?( C ) ?? 2 2 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 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 for high efficiency, choose a ferrite inductor with a high frequency core material to reduce core loses. the inductor 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 = ivv cv f out max out in min out out () () ?( C )? ?? % 100 2 % ripple_buck = ivv cv vf out max in max out out in max out () () () ?( C )? ??? % 100 where c out = output filter capacitor in farads and f = switching frequency in hz.
LTC3442 14 3442f table 2. capacitor vendor information supplier phone fax web site avx (803) 448-9411 (803) 448-1943 www.avxcorp.com murata (814) 237-1431 (814) 238-0490 www.murata.com (800) 831-9172 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 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 ? /1nf series snubber is required between sw1 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 voltages, 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 capacitors, thus reducing board area and component height. how- ever, 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 the output capacitance is usually many times larger than the minimum value in order to handle the transient re- sponse 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 calcula- tions 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 recom- mended to place at least a 4.7 f, low esr ceramic bypass capacitor close to the v in and sgnd pins. it is also important to minimize any stray resistance from the con- verter to the battery or other power source. 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 output applicatio s i for atio wu uu
LTC3442 15 3442f 1.22v r1 r2 3442 f07 fb 12 v c c p1 v out 11 C + error amp where f = switching frequency in mhz. therefore fre- quency 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 lc filter pole out ?? ? = 1 2 hz (in buck mode) f v vlc filter pole in out out ???? = 2 hz (in boost mode) where l is in henries and c out is in farads. the output filter zero is given by: f rc filter zero esr out ?? ? = 1 2 hz where r esr is the equivalent series resistance of the output cap. a troublesome feature in boost mode is the right-half plane zero (rhp), given by: f v ilv rhpz in out out = 2 2? ? ? ? hz the loop gain is typically rolled off before the rhp zero frequency. a simple type i compensation network can be incorpo- rated 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 rc hz ug p = 1 21 1 ?? ? ?? ? ? = = = ?? ? ? () ?? ? ?? ? ?? ? where resistance is in ohms and capacitance is in farads. figure 7. error amplifier with type i compensation applicatio s i for atio wu uu figure 8. error amplifier with type iii compensation 1.22v r1 r2 3442 f08 fb 12 v c c p1 c z1 r z v out 11 c p2 C + error amp
LTC3442 16 3442f sw1 v in shdn/ss r lim r t sgnd sw2 v out fb v c burst pgnd LTC3442 0.01 f 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 0.01 f 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 10 f l1 4.7 h c out 22 f typical applicatio s u 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 10 f 0.01 f 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 3.3 h c out 22 f 220pf v out 3.3v 1.2a 200k 470pf 3442 ta02 43.2k burst fixed freq 1m 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
LTC3442 17 3442f 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 sw1 v in sd/ss r lim r t sgnd sw2 v out fb v c burst pgnd LTC3442 v in 2.5v to 4.2v lhxl-pw03 4.7 f v out 1nf 3442 ta04a 3.3 h 47pf 10 f r5 7.87k off on open led voltage limit = (r4+r5)*0.95/r4 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 typical applicatio s u high efficiency li-ion powered constant current led driver with open-led protection led driver efficiency vs led current
LTC3442 18 3442f 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 0.38 0.10 bottom viewexposed pad 1.70 0.10 (2 sides) 0.75 0.05 r = 0.115 typ r = 0.20 typ 0.25 0.05 3.30 0.10 (2 sides) 1 6 12 7 0.50 bsc pin 1 notch pin 1 top mark (note 6) 0.200 ref 0.00 C 0.05 (ue12/de12) dfn 0603 0.25 0.05 3.30 0.05 (2 sides) recommended solder pad pitch and dimensions 1.70 0.05 (2 sides) 2.20 0.05 0.50 bsc 0.65 0.05 3.50 0.05 package outline package descriptio u ue/de package 12-lead plastic dfn (4mm 3mm) (reference ltc dwg # 05-08-1695)
LTC3442 19 3442f sw1 v in sd/ss r lim r t sgnd sw2 v out fb v c burst pgnd LTC3442 v in 2.7v to 4.2v lhxl-pw03 10 f 6.3v v out 1nf 3442 ta05 3.3 h 1nf 10 f 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 typical applicatio s u typical applicatio s u high current led driver with low/high current range for pulsed applications; led current is 0.5a with 1.5a pulse 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.
LTC3442 20 3442f 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 1204 1k ? printed in usa 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 < 1 a, thinsot tm 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 < 1 a, 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 < 1 a, 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, i sd < 1 a, thinsot package lt1946/lt1946a 1.5a (i sw ), 1.2mhz/2.7mhz, high efficiency step-up v in : 2.45v to 16v, v out(max) = 34v, i q = 3.2ma, dc/dc converter i sd < 1 a, 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 = 6 a, 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 = 19 a/300 a, i sd < 1 a, 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 = 38 a, i sd < 1 a, 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 = 20 a, i sd 1 a, 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 = 20 a, i sd 1 a, thinsot package ltc3407 600ma (i out ), 1.5mhz dual synchronous step-down v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 40 a, dc/dc converter i sd 1 a, 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 = 60 a, i sd 1 a, 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 = 60 a, i sd 1 a, 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 = 12 a, i sd < 1 a, qfn package ltc3425 5a (i sw ), 8mhz multiphase synchronous step-up v in : 0.5v to 4.5v, v out(max) = 5.25v, i q = 12 a, dc/dc converter i sd < 1 a, 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 = 20 a, i sd < 1 a, qfn 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 ltc3440 600ma (i out ), 2mhz synchronous buck-boost dc/dc converter v in : 2.5v to 5.5v, v out(min) = 5.5v, i q = 25 a, i sd < 1 a, 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 = 25 a, i sd < 1 a, 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 = 28 a, i sd < 1 a, 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 < 1 a, thinsot package thinsot is a trademark of linear technology corporation.

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