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ltc3125 1 3125fa typical application features applications description 1.2a synchronous step-up dc/dc converter with input current limit the ltc ? 3125 is a high ef? ciency, synchronous step-up dc/dc converter with an accurate programmable average input current limit. the resistor programmable average input current limit is 5% accurate at 500ma and is suitable for a wide variety of applications. in mobile computing, gsm and gprs cards demand high current pulses well beyond the capability of the pc card and compactflash slots. the ltc3125 in concert with a reservoir capacitor, keeps the slot power safely within its capabilities providing a high performance and simple solution. synchronous recti? cation produces high ef? ciency while the 1.6mhz switching frequency minimizes the solution footprint. the current mode pwm design is internally com- pensated. output disconnect allows the load to discharge in shutdown, while also providing inrush current limiting. other features include a <1a shutdown current, short- circuit and thermal overload protection. the ltc3125 is offered in a low pro? le 0.75mm 2mm 3mm package. pcmcia/compactflash (3.3v/500ma max), 4v gsm pulsed load n programmable average input current limit n 5% input current accuracy n 200ma to 1000ma program range n v in : 1.8v to 5.5v, v out : 2v to 5.25v n supports high current gsm/gprs load burst n v in > v out operation n 1.6mhz fixed frequency operation n internal current sense resistor n 1.2a peak current limit n up to 93% ef? ciency n output disconnect in shutdown n soft-start n low quiescent current burst mode ? operation n available in 2mm 3mm 0.75mm dfn package n gsm/gprs pcmcia/compactflash pc card modems n wireless emergency locators n portable radios n supercap chargers l , lt, ltc, ltm and burst mode are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. cs 2.2h ltc3125 gnd v in 1.24m 2200f s2 tant 10f cer v out 4v 2a pulsed load v in 3.3v 500ma 536k 3125 ta01a shdn prog v out fb 44.2k sw off on ef? ciency vs load current load current (a) 0.001 40 efficiency (%) power loss (w) 50 60 70 80 0.01 0.1 1 3125 ta01b 30 20 10 0 90 100 0.1 0.01 0.001 1 v out = 4v v in = 3.3v v in = 2.4v
ltc3125 2 3125fa pin configuration absolute maximum ratings v in , v out voltage ......................................... C0.3v to 6v sw voltage .................................................. C0.3v to 6v sw voltage < 100ns .................................... C0.3v to 7v all other pins ............................................... C0.3v to 6v operating junction temperature range (notes 2, 5) ............................................ C40c to 125c junction temperature ........................................... 125c storage temperature range ................... C65c to 125c (note 1) top view sw v out shdn cs gnd fb prog v in dcb package 8-lead (2mm s 3mm) plastic dfn 9 3 4 2 1 6 5 7 8 t jmax = 125c, ja = 64c/w (note 6) exposed pad (pin 9) is gnd, must be soldered to pcb electrical characteristics parameter conditions min typ max units input voltage range 1.8 5.5 v minimum start-up voltage l 1.6 1.8 v output voltage adjust range l 2 5.25 v feedback voltage l 1.176 1.200 1.229 v feedback input current 150 na quiescent currentshutdown v shdn = 0v, not including switch leakage, v out = 0v 0.01 1 a quiescent current active measured on v out , nonswitching 300 500 a quiescent currentburst v in = v out = 3.3v, measured on v in , fb 1.230v, nonswitching 15 25 a n-channel mosfet switch leakage v sw = 5v, v in = 5v 0.1 10 a p-channel mosfet switch leakage v sw = 5v, v out = 0v, v in = 5v 0.1 20 a n-channel mosfet switch on-resistance v out = 3.3v 0.125 p-channel mosfet switch on-resistance v out = 3.3v 0.200 n-channel mosfet current limit l 1.2 1.8 a current limit delay to output (note 3) 60 ns average input current limit r prog = 44.2k r prog = 44.2k, (note 4) l 475 465 500 500 525 535 ma ma the l denotes the speci? cations which apply over the full operating junction temperature range, otherwise speci? cations are at t a = 25c. v in = 3.3v, v out = 4.5v unless otherwise noted (note 2). order information lead free finish tape and reel part marking package description temperature range ltc3125edcb#pbf ltc3125edcb#trpbf ldgy 8-lead (2mm 3mm) plastic dfn C40c to 125c consult ltc marketing for parts speci? ed with wider operating temperature ranges. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/
ltc3125 3 3125fa 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 ltc3125 is tested under pulsed load conditions such that t j t a . the ltc3125e (e grade) is guaranteed to meet speci? cations from 0c to 85c junction temperature. speci? cations over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the junction temperature (t j ) is calculated from the ambient temperature (t a ) and power dissipation (p d ) according to the formula: t j = t a + (p d ) ( ja c/w), where ja is the package thermal impedance. the maximum ambient temperature consistent with these speci? cations is determined by parameter conditions min typ max units prog current gain (note 3) 22.1 k-a/a maximum duty cycle v fb = 1.15v l 85 92 % minimum duty cycle v fb = 1.3v l 0% frequency l 1.3 1.6 1.9 mhz shdn input high 1v shdn input low 0.35 v shdn input current v shdn = 1.2v 0.3 1 a electrical characteristics the l denotes the speci? cations which apply over the full operating junction temperature range, otherwise speci? cations are at t a = 25c. v in = 3.3v, v out = 4.5v unless otherwise noted (note 2). speci? c operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. note 3: speci? cation is guaranteed by design and not 100% tested in production. note 4: current measurements are made when the output is not switching. note 5: 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 speci? ed maximum operating junction temperature may result in device degradation or failure. note 6: failure to solder the exposed backside of the package to the pc board ground plane will result in a thermal resistance much higher than 60c/w. typical performance characteristics ef? ciency vs load current, v out = 2.5v ef? ciency vs load current, v out = 3.3v (t a = 25c unless otherwise noted) load current (a) 0.001 40 efficiency (%) power loss (w) 50 60 70 80 0.01 0.1 1 3125 g01 30 20 10 0 90 100 0.1 0.01 0.0001 0.001 1 v in = 2.1v v in = 1.8v load current (a) 0.001 40 efficiency (%) power loss (w) 50 60 70 80 0.01 0.1 1 3125 g02 30 20 10 0 90 100 0.1 0.01 0.001 1 v in = 2.8v v in = 2.4v v in = 2v
ltc3125 4 3125fa burst mode threshold current vs v in oscillator frequency vs v out ef? ciency vs load current, v out = 5v average input current limit vs v in average input current limit vs temperature average input current vs r prog peak current limit vs v in typical performance characteristics (t a = 25c unless otherwise noted) no-load input current vs v in burst mode threshold current vs v in v in (v) 1.5 average input current limit change (%) C0.5 0 0.5 3.0 4.0 3125 g05 C1.0 C1.5 C2.0 2.0 2.5 3.5 1.0 1.5 2.0 normalized to 25c 4.5 temperature (c) C50 C1.50 average input current limit change (%) C1.00 C0.50 0 0.50 1.50 C25 02550 3125 g06 75 100 1.00 normalized to 25c v in (v) 1.5 input current (a) 2.15 2.45 2.50 2.55 3 4 4.5 3125 g08 2.05 2.35 2.25 2.10 2.40 2.00 2.30 2.20 2 2.5 3.5 5 5.5 v out = 3.8v r prog = 0 v out (v) 2.0 C8 frequency change (%) C7 C5 C4 C3 2 C1 2.5 3.5 4.0 3125 g11 C6 0 1 C2 3.0 4.5 5.0 normalized to v out = 3.3v load current (a) 0.001 40 efficiency (%) power loss (w) 50 60 70 80 0.01 0.1 1 3125 g03 30 20 10 0 90 100 0.1 0.01 0.001 1 v in = 4v v in = 3.3v v in (v) 1.5 i in (ma) 1.5 2.0 2.5 3 4 3125 g04 1.0 0.5 0 2 2.5 3.5 3.0 3.5 4.0 v out = 4v v out = 2.5v v out = 3.8v v out = 3.3v r prog (k) 10 20 30 40 50 70 80 90 100 0 average input current limit (a) 0.25 0.50 0.75 1.00 60 110 3125 g07 1.25 v in (v) 1.8 load current (ma) 30 40 2.6 3125 g09 20 10 2.0 2.2 2.4 2.8 50 v out = 3.3v c out = 1500f l = 2.2h v in (v) 1.8 20 load current (ma) 25 30 35 40 45 50 1.9 2.0 2.1 2.2 3125 g10 v out = 2.5v c out = 1500f l = 2.2h
ltc3125 5 3125fa r ds(on) vs v out r ds(on) vs temperature oscillator frequency vs temperature feedback vs temperature current sense voltage (v rprog ) vs temperature burst mode current vs v out typical performance characteristics (t a = 25c unless otherwise noted) v out and i in during soft-start v out and i in during soft-start v out (v) 1.5 rds(on) () 0.400 3 3125 g12 0.250 0.150 2 2.5 3.5 0.100 0.050 0.450 0.350 0.300 0.200 4 4.5 5 pmos nmos temperature (c) C50 180 200 240 10 50 3125 g13 160 140 C30 C10 30 70 90 120 100 220 r ds(on) (m) pmos nmos v out = 4v temperature (c) C50 C10 frequency change (%) C6 C2 2 C25 0 25 50 3125 g14 75 6 10 C8 C4 0 4 8 100 normalized to 25c temperature (c) C50 change in v fb (%) 0 0.25 0.50 10 50 3125 g15 C0.25 C0.50 C30 C10 30 70 90 C0.75 C1.00 normalized to 25c temperature (c) C50 change in v fb (%) 0 0.25 0.50 10 50 3125 g15 C0.25 C0.50 C30 C10 30 70 90 C0.75 C1.00 normalized to 25c v out (v) 1.5 i q (a) 15.0 15.5 16.0 34 3125 g17 14.5 14.0 2 2.5 3.5 4.5 5 13.5 13.0 v out 2v/div shdn 5v/div input current 200ma/div 20ms/div v in = 3.3v v out = 4.5v c out = 4.4mf l = 2.7h 3125 g18 burst current v out 2v/div shdn 5v/div input current 200ma/div 1s/div v in = 3.3v v out = 4.5v c out = 0.47f l = 2.7h 3125 g19
ltc3125 6 3125fa pin functions gnd (pin 1, exposed pad pin 9): ground. the exposed pad must be soldered to the pcb ground plane for electrical connection and for rated thermal performance. fb (pin 2): feedback input to the error ampli? er. connect the resistor divider tap to this pin. the top of the divider connects to v out and the bottom of the divider connects to gnd. the output voltage can be adjusted from 1.8v to 5.25v. prog (pin 3): programming input for average input cur- rent. this pin should be connected to ground through an external resistor (r prog ) to set input average current limit threshold. refer to the component selection section in applications information for details on selecting r prog . v in (pin 4): input voltage. the device is powered from v in until v out exceeds v in . once v out is greater than (v in + 0.25v), the device is powered from v out . place a ceramic bypass capacitor from v in to gnd. a minimum value of 1f is recommended. also connects to cs through 60m internal sense resistor. cs (pin 5): current sense resistor connection point. connect the inductor directly to cs. an internal 60m sense resistor is connected between cs and v in . shdn (pin 6): logic controlled shutdown input. bringing this pin above 1v enables the part, forcing this pin below 0.35v disables the part. v out (pin 7): output voltage sense and the output of the synchronous recti? er. connect the output ? lter capacitor from v out to gnd, close to the ic. a minimum value of 150f is recommended. due to the output disconnect feature, v out is disconnected from v in when shdn is low. sw (pin 8): switch pin. connect an inductor from this pin to cs. an internal anti-ringing resistor is connected across sw and cs after the inductor current has dropped near zero. typical performance characteristics (t a = 25c unless otherwise noted) v out and i in during soft-start v out 2v/div shdn 5v/div input current 200ma/div 2s/div v in = 3.3v v out = 4.5v c out = 1f l = 2.7h 3125 g20 ef? ciency vs v in v in (v) 2 50 efficiency (%) 60 65 70 75 80 85 3 4 3125 g21 90 95 100 55 5 i load = 200ma v out = 3.8v
ltc3125 7 3125fa block diagram 6 9 8 i pk comp i clmp comp i zero comp slope comp v ref r2 c out v out v out i clmp clk v ref averaging circuit i avg error amp exposed pad v ref good i zero wake tsd i pk + C + C logic v sel anti-ring gate drive and anti-cross conduction mode control v clamp thermal shutdown clk osc v bg v best r sense v b v sel sw l1 5 cs 4 v in shutdown input current sense amp v ref sd shdn prog 4m soft start 3125 bd + C well-switch + C 7 fb 2 r1 r prog + C g m 3 + C c in v in 1 gnd g m
ltc3125 8 3125fa operation the ltc3125 provides high ef? ciency, low noise power for applications in portable instrumentation and those with pulsed-load, power-limited requirements such as gsm modems. the ltc3125 directly and accurately controls the average input current. the high ef? ciency of the ltc3125 provides the maximum possible output current to the load without impacting the host. together with an external bulk capaci- tor the ltc3125 with average input current limit allows a gsm/gprs modem to be interfaced directly to a pcmcia or compactflash power bus without overloading it. the current mode architecture with adaptive slope com- pensation provides excellent transient load response, requiring minimal output ? ltering. internal soft-start and loop compensation simpli? es the design process while minimizing the number of external components. with its low r ds(on) and low gate charge internal n-chan- nel mosfet switch and p-channel mosfet synchronous recti? er, the ltc3125 achieves high ef? ciency over a wide range of load currents. automatic burst mode operation maintains high ef? ciency at very light loads, reducing the quiescent current to just 15a. error amplifier the noninverting input of the transconductance error ampli? er is internally connected to the 1.2v reference and the inverting input is connected to fb. clamps limit the minimum and maximum error amp output voltage for improved large-signal transient response. power converter control loop compensation is provided internally. an exter- nal resistive voltage divider from v out to ground programs the output voltage via fb from 2v to 5.25v. v out =1.2v 1+ r2 r1 ? ? ? ? ? ? internal current limit lossless current sensing converts the peak current signal of the n-channel mosfet switch into a voltage that is summed with the internal slope compensation. the summed signal is compared to the error ampli? er output to provide a peak current control command for the pwm. a second current limit comparator shuts off the n-chan- nel mosfet switch once the peak current signal clamp threshold is reached. the current limit comparator delay to output is typically 60ns. peak switch current is limited to approximately 1.8a, independent of input or output voltage, unless v out falls below 0.8v, in which case the current limit is cut in half. average input current limit a current proportional to the internally sensed input current is sourced out of the prog pin. the voltage across the external resistor on the prog pin is averaged and com- pared to a temperature stable internal reference, providing a signal to actively control the current limit comparators clamp threshold. the high gain of this loop forces the average input current to the limit set by the value of the external resistor, r prog . the ltc3125 is trimmed and tested at 500ma to obtain a 5% initial accuracy. at other current limit settings, non- idealities such as random offsets in the input current limit loop will degrade the accuracy in the application. r prog tolerance must also be considered when setting the input current limit as the accuracies listed in the electrical char- acteristics section do not include external resistor variation. traditional, internally compensated, current mode con- trolled boost converters can be unstable with the high capacitance and low esr values used in supercapacitor chargers and pulsed load applications. the internal loop compensation of the ltc3125 is optimized to be stable with output capacitor values greater than 150f with very low esr. output capacitor values below 150f will degrade transient response and can lead to instability. note that the ltc3125s input current averaging circuit may introduce a slightly higher inductor current ripple than expected. this is normal and has no affect on the average input current seen by the power source. zero current comparator the zero current comparator monitors the inductor cur- rent to the output and shuts off the synchronous recti? er when this current reduces to approximately 30ma. this
ltc3125 9 3125fa operation prevents the inductor current from reversing in polarity, improving ef? ciency at light loads. oscillator an internal oscillator sets the switching frequency to 1.6mhz. shutdown shutdown of the boost converter is accomplished by pulling shdn below 0.35v and enabled by pulling shdn above 1v. note that shdn can be driven above v in or v out , as long as it is limited to less than the absolute maximum rating. output disconnect the ltc3125 is designed to allow true output disconnect by eliminating body diode conduction of the internal p-channel mosfet recti? er. this allows for v out to go to zero volts during shutdown, drawing no current from the input source. it also limits inrush current at turn-on, minimizing surge currents seen by the input supply. note that to obtain the advantages of output disconnect, there cannot be an external schottky diode connected between the sw pin and v out . the output disconnect feature also allows v out to be pulled high, without any reverse current into the power source connected to v in . thermal shutdown if the die temperature exceeds 160c typical, the ltc3125 will go into thermal shutdown. all switches will be off and the soft-start capacitor will be discharged. the device will be enabled again when the die temperature drops by approximately 15c. synchronous rectifier to control inrush current and to prevent the inductor current from running away when v out is close to v in , the p-channel mosfet synchronous recti? er is only enabled when v out > (v in + 0.38v). anti-ringing control the anti-ringing control connects a resistor across the inductor to prevent high frequency ringing on the sw pin during discontinuous current mode operation. although the ringing of the resonant circuit formed by l and c sw (capacitance on sw pin) is low energy, it can cause emi radiation. soft-start the ltc3125 contains internal circuitry to provide soft- start operation. the soft-start circuitry slowly ramps the peak inductor current from zero to its peak value of 1.8a (typical) in approximately 0.5ms, allowing start-up into heavy loads. the soft-start circuitry is reset in the event of a shutdown command or a thermal shutdown. burst mode operation the ltc3125 will automatically enter burst mode opera- tion at light load and return to ? xed frequency pwm mode when the load increases. refer to the typical performance characteristics to see the output load burst mode thresh- old current vs v in . the load current at which burst mode operation is entered can be changed by adjusting the inductor value. raising the inductor value will lower the load current at which burst mode operation is entered. in burst mode operation, the ltc3125 still switches at a ? xed frequency of 1.6mhz, using the same error ampli? er and loop compensation for peak current mode control. this control method eliminates any output transient when switching between modes. in burst mode opera- tion, energy is delivered to the output until it reaches the nominal regulation value, then the ltc3125 transitions to sleep mode where the outputs are off and the ltc3125 consumes only 15a of quiescent current from v out . when the output voltage droops slightly, switching resumes. this maximizes ef? ciency at very light loads by minimizing switching and quiescent losses. as the load current increases, the ltc3125 will automati- cally leave burst mode operation. once the ltc3125 has left burst mode operation and returned to normal operation, it will remain there until the output load is reduced below the burst threshold.
ltc3125 10 3125fa applications information burst mode operation is inhibited during start-up and soft-start and until v out is at least 0.38v greater than v in . gsm and gprs modems have become a popular wire- less data transfer solution for use in notebook pcs and other mobile systems. gsm transmission requires large bursts of current that exceed the maximum peak current speci? cations for compactflash and pcmcia bus power. the gsm standard speci? es a 577s, 2a (typical) trans- mission burst within a 4.6ms period (12.5% duty cycle). during the receive and standby periods the current con- sumption drops to 70ma (typical), yielding an average current requirement of 320ma. other standards (such as gprs, class 10) de? ne a higher data rate. one popular requirement transmits two 2a bursts (3a worst case) within a 4.6ms frame period (70ma standby current) demanding an 800ma average input current. the ltc3125 external current limit programming resistor can be easily adjusted for this requirement. further, the gsm module is typically speci? ed to operate over an input power range that is outside that allowed in the pcmcia or compactflash bus power speci? cation. the ltc3125 is a high ef? ciency boost converter with programmable input average current limit that provides the needed ? exibility when designing a gsm/gprs power supply solution. the high ef? ciency of the converter maxi- mizes the average output power without overloading the bus. a bulk output capacitor is used to supply the energy and maintain the output voltage during the high current pulses. v in > v out operation the ltc3125 will maintain voltage regulation even when the input voltage is above the desired output voltage. note that the ef? ciency and the maximum output current capability are reduced. refer to the typical performance characteristics for details. short-circuit protection the ltc3125 output disconnect feature enables output short circuit protection although input current limit func- tionality is maintained. to reduce power dissipation under short-circuit conditions; the peak switch current limit is reduced to 800ma (typical). schottky diode although it is not necessary, adding a schottky diode from sw to v out will improve ef? ciency by about 4%. note that this defeats the output disconnect, short-circuit protection and average input limiting during start-up. pcb layout guidelines the high speed operation of the ltc3125 demands care- ful attention to board layout. a careless layout will result in reduced performance. a large ground pin copper area will help to lower the die temperature. a multilayer board with a separate ground plane is ideal, but not absolutely necessary. component selection inductor selection the ltc3125 can utilize small surface mount chip induc- tors due to its fast 1.6mhz switching frequency. inductor values between 2.2h and 4.7h are suitable for most applications. larger values of inductance will allow slightly greater output current capability (and lower the burst mode threshold) by reducing the inductor ripple current. increas- ing the inductance above 10h will increase size while providing little improvement in output current capability. the minimum inductance value is given by: l> v in(min) ?v out(max) Cv in(min) () ripple?v out(max) ?f sw where: ripple = allowable inductor current ripple (amps peak-peak) v in(min) = minimum input voltage v out(max) = maximum output voltage the inductor current ripple is typically set for 20% to 40% of the maximum inductor current. high frequency ferrite core inductor materials reduce frequency dependent
ltc3125 11 3125fa applications information power losses compared to cheaper powdered iron types, improving ef? ciency. the inductor should have low dcr (dc resistance of the windings) to reduce the i 2 r power losses, and must be able to support the peak inductor current without saturating. molded chokes and some chip inductors usually do not have enough core area to support the peak inductor currents of 1.8a seen on the ltc3125. to minimize radiated noise, use a shielded inductor. see table 1 for suggested components and suppliers. table 1. recommended inductors vendor part/style coilcraft (847) 639-6400 www.coilcraft.com lpo2506 lps4012, lps4018 mss6122 mss4020 mos6020 ds1605, do1608 coiltronics www.cooperet.com sd52, sd53, sd3114, sd3118 murata (714) 852-2001 www.murata.com lqh55d sumida (847) 956-0666 www.sumida cdh40d11 taiyo-yuden www.t-yuden.com np04sb nr3015 nr4018 tdk (847) 803-6100 www.component.tdk.com vlp , ltf vlf, vlcf wurth (201) 785-8800 www.we-online.com we-tpc type s, m, mh, ms output and input capacitor selection when selecting output capacitors for large pulsed loads, the magnitude and duration of the pulsing current, together with the ripple voltage speci? cation, determine the choice of the output capacitor. both the esr of the capacitor and the charge stored in the capacitor each cycle contribute to the output voltage ripple. the ripple due to the charge is approximately: v ripple (mv)= i pulse Ci standby () ?t on c out where i pulse and t on are the peak current and on time during transmission burst and i standby is the current in standby mode. the above is a worst-case approximation assuming all the pulsing energy comes from the output capacitor. the ripple due to the capacitor esr is: v ripple_esr = (i pulse C i standby ) ? esr low esr and high capacitance are critical to maintain low output voltage ripple. typically, two low pro? le 2200f parallel vishay tantamount ? tantalum, low esr capaci- tors are used. the capacitor has less than 40m esr. these capacitors can be used in parallel for even larger capacitance values. for applications requiring very high capacitance, the gs, gs2 and gw series from cap-xx, the bestcap tm series from avx and powerstor ? aerogel capacitors from cooper all offer very high capacitance and low esr in various package options. table 2 shows a list of several reservoir capacitor manufacturers. multilayer ceramic capacitors are an excellent choice for input decoupling of the step-up converter as they have extremely low esr and are available in small footprints. input capacitors should be located as close as possible to the device. while a 10f input capacitor is suf? cient for most applications, larger values may be used to re- duce input current ripple without limitations. consult the manufacturers directly for detailed information on their selection of ceramic capacitors. although ceramic capaci- tors are recommended, low esr tantalum capacitors may be used as well. table 2. capacitor vendor information supplier phone website vishay (402) 563-6866 www.vishay.com avx (803) 448-9411 www.avxcorp.com cooper bussman (516) 998-4100 www.cooperbussman.com cap-xx (843) 267-0720 www.cap-xx-com panasonic (800) 394-2112 www.panasonic.com
ltc3125 12 3125fa pc card (3.3v/1000ma maximum) 4.5v output, gsm pulsed load cs 2.7h* ltc3125 gnd v in 2.74m 2200f** s2 55m tant 10f cer v out 4.5v, 2a pulsed load (577s pw, 4.6ms period) v in pc card v cc 3.3v 10% 1000ma max 1m 3125 ta03a shdn prog v out fb 22.6k sw off on *wurth 7440420027 **vishay 592d228x6r3x220h waveforms of input current, v out for pulsed load current v out 100mv/div input current 500ma/div load current 2a/div 1ms/div v in = 3.3v v out = 4.5v c out = 4.4mf l = 2.7h r prog = 22.6k 3125 ta03b average input ilimit programming resistor selection the input current limit is user programmable by selection of an external resistor, r prog . it is important to locate the resistor as close to the pin as possible to minimize capacitance and noise pick-up. resistor tolerance directly affects the current limit accuracy so it must be factored in to the application requirements. table 3 shows standard resistors for typical current limit values. also refer to the graph, average input current vs r prog , in the typical performance characteristics section of this datasheet. applications information table 3. standard 1% resistor value (k) typical application input limit (a) 22.1 1.001 24.9 0.890 28.0 0.791 29.4 0.750 31.6 0.699 37.4 0.588 54.9 0.393 71.5 0.295 82.5 0.252 for most applications the loss in accuracy from standard 1% resistors is tolerated but for critical applications the use of 0.1% resistors is recommended. typical applications
ltc3125 13 3125fa pc card (3.3v/1000ma maximum) 4.5v output, gprs, class 10 pulsed load cs 2.7h* ltc3125 gnd v in 2.74m 2200f** s3 55m tant 10f cer v out 4.5v, 2a pulsed load (1154s pw, 4.6ms period) v in pc card v cc 3.3v 10% 1000ma max 1m 3125 ta04a shdn prog v out fb 22.6k sw off on *wurth 7440420027 **vishay 592d228x6r3x220h waveforms of input current, v out for pulsed load current v out 100mv/div input current 500ma/div load current 2a/div 1ms/div v in = 3.3v v out = 4.5v c out = 6.6mf l = 2.7h r prog = 22.6k 3125 ta04b single supercap charger cs 2.2h* ltc3125 gnd v in 1.07m sc** 10f 60m 10f cer v out 2.5v v in 3.3v 10% 1000ma max 1m 3125 ta05a shdn prog v out fb 22.6k sw off on *coiltronics sd3118-2r2-r **cooper b1325-2r5106-r waveforms of input current, v out for pulsed load current v out 500mv/div input current 500ma/div load current 1a/div 200ms/div v in = 3.3v v out = 2.5v c out = 10f l = 2.2h r prog = 22.6k 3125 ta05b typical applications
ltc3125 14 3125fa typical applications stacked supercap charger cs 2.2h* ltc3125 gnd v in 2.74m 100k 100k 10f cer v out 4.5v 30f** 2.3v v in 2.5v to 5v 500ma max 1m *tdk vlf4014st-2r2m1r9 **panasonic eechwod306 3125 ta06a shdn prog v out fb 44.2k sw off on + 30f** 2.3v + waveforms of input current, v out during charging v out 2v/div shdn 5v/div load current 200ma/div 20s/div v in = 4.5v v out = 4.5v c out_series = 15f l = 2.2h r prog = 44.2k 3125 ta06b
ltc3125 15 3125fa typical applications 3.3v to 5v with selectable input current limit cs 2.2h* ltc3125 gnd v in 3.2m c out 10f cer v out 5v v in 3.3v 10% 1m *tdk vlf4014st-2r2m1r9 3125 ta07a shdn prog m1 v out fb 44.2k 28.7k sw off on 300ma 500ma waveforms of input current, v out for pulsed input current limit input current 200ma/div m1 gate drive 5v/div 2ms/div v in = 3.3v v out = 5v c out = 4.4mf l = 2.2h i load = 500ma 3125 ta07b
ltc3125 16 3125fa package description dcb package 8-lead plastic dfn (2mm 3mm) (reference ltc dwg # 05-08-1718 rev a) 3.00 0.10 (2 sides) 2.00 0.10 (2 sides) note: 1. drawing is not a jedec package outline 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 viewexposed pad 0.75 0.05 r = 0.115 typ r = 0.05 typ 1.35 ref 1 4 8 5 pin 1 bar top mark (see note 6) 0.200 ref 0.00 C 0.05 (dcb8) dfn 0106 rev a 0.23 0.05 0.45 bsc pin 1 notch r = 0.20 or 0.25 s45 chamfer 0.25 0.05 1.35 ref recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 2.10 0.05 0.70 0.05 3.50 0.05 package outline 0.45 bsc 1.35 0.10 1.35 0.05 1.65 0.10 1.65 0.05
ltc3125 17 3125fa 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 a 12/10 text change to description change to electrical characteristics quiescent current-burst modi? cation of note 2 pin functions; change to gnd (pin 1), prog (pin 3) and v out (pin 7) replaced average input current limit section added average input limit programming resistor selection section updated related parts table 1 2 3 6 8 12 18
ltc3125 18 3125fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com linear technology corporation 2008 lt 1210 rev a ? printed in usa related parts part number description comments ltc3127 1a buck-boost converter with programmable input current limit 96% ef? ciency, 4% accurate average input current limit, v in : 1.8v to 5.5v, v out = 1.8v to 5.25v, i q = 35a, dfn package ltc3421 3a (i sw ), 3mhz, synchronous step-up dc/dc converter with output disconnect 94% ef? ciency, v in : 0.85v to 4.5v, v out(max) = 5.25v, i q = 12a, i sd < 1a, 4mm 4mm qfn24 package ltc3422 1.5a (i sw ), 3mhz synchronous step-up dc/dc converter with output disconnect 94% ef? ciency, v in : 0.85v to 4.5v, v out(max) = 5.25v, i q = 25a, i sd < 1a, 3mm 3mm dfn10 package ltc3459 80ma (i sw ), synchronous step-up dc/dc converter 92% ef? ciency, v in : 1.5v to 5.5v, v out(max) = 10v, i q = 10a, i sd < 1a, thinsot package ltc3523/ltc3523-2 600ma (i sw ), step-up and 400mhz synchronous step-down 1.2mhz/2.4mhz dc/dc converter with output disconnect 94% ef? ciency v in : 1.8v to 5.5v, v out(max) = 5.25v, i q = 45a, i sd < 1a, 3mm 3mm qfn16 package ltc3525-3/ ltc3525-3.3/ ltc3525-5 400ma (i sw ), micropower synchronous step-up dc/dc converter with output disconnect 94% ef? ciency, v in : 0.85v to 4v, v out(max) = 5v, i q = 7a, i sd < 1a, sc-70 package ltc3526/ltc3526l ltc3526b 500ma (i sw ), 1mhz synchronous step-up dc/dc converter with output disconnect 94% ef? ciency v in : 0.85v to 5v, v out(max) = 5.25v, i q = 9a, i sd < 1a, 2mm 2mm dfn6 package ltc3527/ltc3527-1 dual 800ma/400ma (i sw ), 2.2mhz synchronous step-up dc/dc converter with output disconnect 94% ef? ciency v in : 0.7v to 5v, v out(max) = 5.25v, i q = 12a, i sd < 1a, 3mm 3mm qfn16 package ltc3528/ltc3528b 1a (i sw ), 1mhz synchronous step-up dc/dc converter with output disconnect 94% ef? ciency v in : 0.7v to 5.5v, v out(max) = 5.25v, i q = 12a, i sd < 1a, 2mm 3mm dfn8 package ltc3537 600ma (i sw ), 2.2mhz synchronous step-up dc/dc converter with output disconnect and 100ma ldo 94% ef? ciency v in : 0.7v to 5v, v out(max) = 5.25v, i q = 30a, i sd < 1a, 3mm 3mm qfn16 package ltc3539/ltc3539-2 2a (i sw ), 1mhz, 2.2mhz synchronous step-up dc/dc converter with output disconnect 94% ef? ciency, v in : 0.7v to 5v, v out(max) = 5.25v, i q = 10a, i sd < 1a, 2mm 3mm dfn package pc card or compactflash (3.3v/500ma maximum) 4.5v output, gsm pulsed load cs 2.2h* ltc3125 gnd v in 2.74m 2200f** 2 55m tant 10f cer v out 4.5v, 2a pulsed load (577s pw, 4.6ms period) v in pc card v cc 3.3v 10% 500ma max 1m *coiltronics sd3118-2r2-r **vishay 592d228x6r3x220h 3125 ta02a shdn prog v out fb 44.2k sw off on waveforms of input current, v out for pulsed load current v out 100mv/div input current 200ma/div load current 2a/div 1ms/div v in = 3.3v v out = 4.5v c out = 4.4mf l = 2.2h r prog = 44.2k 3125 ta02b typical application

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