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ltc3458 1 3458fa features descriptio u applicatio s u typical applicatio u high efficiency: up to 93% inrush current limiting and output disconnect programmable output voltages up to 7.5v 1.5v to 6v input range programmable/synchronizable fixed frequency operation up to 1.5mhz programmable automatic burst mode operation current mode control with programmable soft-start period and peak current limit 700ma at 7v from 5v input 0.3 n-channel and 0.4 p-channel 1.4a switches at 5v out ultralow quiescent currents: 15 a sleep, <1 a in shutdown 3mm 4mm thermally enhanced dfn package point-of-load regulators usb v bus power lcd bias oled displays 1.4a, 1.5mhz synchronous step-up dc/dc converter with output disconnect the ltc 3458 is a high efficiency, current mode, fixed frequency, step up dc/dc converter with true output disconnect and inrush current limiting. the ltc3458 is rated for a 7.5v output and includes a 0.3 n-channel mosfet switch and a 0.4 p-channel mosfet synchro- nous rectifier. the ltc3458 is well suited for battery powered applications and includes programmable output voltage, switching frequency and loop compensation. the oscillator frequency can be set up to 1.5mhz or synchro- nized to an external clock. quiescent current is only 15 a during burst mode opera- tion maximizing battery life in portable applications. the burst mode current threshold, peak current limit, and soft- start are externally programmable. other features include <1 a shutdown current, antiringing control, and thermal limit. the ltc3458 is available in a low profile (0.75mm), 3mm 4mm 12-pin dfn package. usb to 7v at 1mhz burst mode is a registered trademark of linear technology corporation. usb to 7v out v in gnd/pgnd shdn sync r t i lim sw v out fb comp ss burst ltc3458 usb 4.35v to 5.25v 2.2 f coev 10 h dq7545 on off 200k 124k 133k 316k 33k 0.01 f 0.01 f 560pf 10pf 10pf 1.5m 22 f x5r v out 7v 500ma 3458 ta01a load current (ma) efficiency power loss (mw) 100 95 90 85 80 75 70 1000 10 0.1 0.1 10 100 1000 3458 ta01b 1 5.25v in 4.35v in power loss , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners.
ltc3458 2 3458fa v in , ss, sync voltages ................................. e0.3 to 7v burst, shdn, v out voltages ....................... e0.3 to 8v operating temperature range (notes 2, 3) .........................................e40 c to 85 c storage temperature range ..................e65 c to 125 c sw voltage dc ........................................................... e0.3v to 8v pulsed <100ns ...................................... e0.3v to 10v absolute axi u rati gs w ww u (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 = 3.3v, v out = 5v, r t = 200k, unless otherwise noted. parameter conditions min typ max units minimum v in operating voltage t a = 0 c to 85 c 1.4 1.5 v t a = e40 c to 0 c 1.4 1.7 v output voltage adjust range 2.0 7.5 v feedback voltage 0 c to 85 c, v out = 3.3v 1.21 1.23 1.25 v e40 c to 0 c 1.20 1.25 v undervoltage (exit burst mode operation) below feedback voltage e4% v feedback input current v fb = 1.23v 1 50 na quiescent current - burst mode operation v in current at 3.3v 15 30 r a v out current at 5v 5 10 r a quiescent current - shutdown v in current at 3.3v 0.5 1 r a v out current at 0v 1 3 r a quiescent current - active v in current switching 1 3 ma nmos switch leakage 0.05 5 r a pmos switch leakage 0.05 5 r a nmos switch on resistance v out = 5v 0.3 < pmos switch on resistance v out = 5v 0.4 < fixed nmos current limit r ilim = 124k 1.4 1.6 a maximum duty cycle v in = 3.3v, f osc = 1mhz 80 90 % minimum duty cycle 0% frequency accuracy r t = 200k 0.85 1 1.15 mhz error amplifier transconductance 100 r a/v error amplifier source current 7 r a pin configuration t jmax = 125 c, v ja = 45 c/w 12 11 10 9 8 7 1 2 3 4 5 6 v out burst ss gnd comp fb sw v in sync shdn i lim r t top view de12 package 12-lead (4mm 3mm) plastic dfn exposed pad is pgnd (pin 13), must be soldered to pcb 13 order information lead free finish tape and reel part marking package description temperature range ltc3458ede#pbf ltc3458ede#trpbf 3458 12-lead (4mm x 3mm) plastic dfn e40?c to 85?c consult ltc marketing for parts specified with wider operating temperature ranges. consult ltc for information on nonstandard lead based finish parts. 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/
ltc3458 3 3458fa parameter conditions min typ max units error amplifier sink current 7 a sync input high 1.5 v sync input low 0.35 v shdn input high 1.25 v shdn input low 0.3 v burst mode peak current r ilim = 124k 0.4 a burst threshold voltage 1.10 v the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3.3v, v out = 5v, r t = 200k, unless otherwise noted. electrical characteristics 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: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed 125 c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may impair device reliability. note 3: the ltc3458 is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the 40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. typical perfor a ce characteristics uw temperature ( c) temperature ( c) v in (v) ?0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 current ( a) 10 15 60 3458 g03 3458 g01 3458 g02 5 0 ?5 10 35 85 20 current (ma) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 ?00 i limit i burst peak i zero i vin i vout v out = 7v l = 10 h r ilim = 124k v in = 3.3v v out = 5v 3458 g04 3458 g05 3458 g06 r burst (k ) 50 current (ma) 200 300 100 150 250 160 140 120 100 80 60 40 20 0 v in (v) 1.5 current (ma) 250 200 150 100 50 0 3.0 4.0 5.5 2.0 2.5 3.5 4.5 5.0 oscillator frequency (khz) 400 rt (k ) 600 550 500 450 400 350 300 250 200 150 100 1200 600 800 1000 1400 out of burst into burst 3.3v out 5v out 7.5v out r ilim = 124k ?5 1.4 current (a) 1.5 1,7 1.8 ?5 15 30 90 1.6 ?0 0 45 60 75 r ilimit = 124k i limit , i burst , t zero currents burst mode quiescent current maximum load current in burst oscillator programming resistor current limit accuracy typical burst mode threshold and hysteresis vs r burst (t a = 25 c unless otherwise specified)
ltc3458 4 3458fa typical perfor a ce characteristics uw 3458 g12 3458 g11 3458 g13 3458 g07 3458 g08 frequency (khz) 500 efficiency (%) 95 93 91 89 87 85 1300 700 900 1100 1500 temperature ( c) ?0 r ds(on) ( ) 0.5 0.4 0.3 0.2 0.1 0 60 3458 g09 ?5 10 35 85 v in (v) max load current (ma) 3458 g10 1200 1000 800 600 400 200 0 1.5 2.5 3.5 4.0 2.0 3.0 4.5 5.0 5.5 3.3v out 5v out 7.5v out p-channel n-channel 1.8 to 5.5v in at 700khz r ilim = 124k v in = 3.3v v out = 5v v in = 3.3v v out = 5v at 100ma temperature ( c) ?5 0.95 frequency (mhz) 0.97 1.01 1.03 1.05 ?5 15 30 90 0.99 ?0 0 45 60 75 temperature ( c) ?5 ?5 15 30 90 ?0 0 45 60 75 temperature ( c) ?5 ?5 15 30 90 ?0 0 45 60 75 0.5 voltage (v) 0.6 0.8 0.9 1.0 0.7 1.20 voltage (v) 1.21 1.23 1.24 1.25 1.22 temperature ( c) ?5 ?5 15 30 90 ?0 0 45 60 75 voltage (v) 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 operating shutdown rt = 200k efficiency vs frequency maximum load current n-channel and p-channel r ds(on) (t a = 25 c unless otherwise specified) shdn pin threshold and hysteresis sync pin threshold fb voltage frequency accuracy
ltc3458 5 3458fa typical perfor a ce characteristics uw sw 2v/div i l 100ma/div sw 2v/div sw 5v/div i l 200ma/div v out 100mv/div i l 200ma/div sw 5v/div v out 100mv/div i l 200ma/div ss 200mv/div v out 2v/div 2v/div v in i l 200ma/div sw 2v/div i l 0.5a/div 0ma 200ns/div 1 s/div 200ns/div 50 s/div 5ms/div 2 s/div v in = 3.3v v out = 7v l = 10 h v in = 3.3v v out = 7v l = 10 h v in = 3.3v v out = 7v l = 10 h r ilim = 133k v in = 3.3v v out = 7v l = 10 h c out = 22 f c ff = 22pf 0ma 0ma 0ma 0ma v in = 3.3v v out = 7v l = 10 h c out = 22 f c ff = 22pf v in = 3.3v v out = 7v l = 10 h fixed frequency (ff) discontinuous current fixed frequency (ff) continuous current over-current with 1.5a i limit burst mode operation burst mode operation close-up soft-start into 50 load
ltc3458 6 3458fa typical perfor a ce characteristics uw ff mode 100-300ma load step sync operation at 1.33mhz burst mode operation 10ma to 50ma load step auto mode 10ma to 100ma load step 10ma to 200ma load step showing uv trip forced burst to ff mode switch with 50ma load burst 1v/div v out 200mv/div load i l 200ma/div 500 s/div 100ma 10ma v out 200mv/div v out 200mv/div i l 200ma/div i l 500ma/div 200 s/div 200 s/div fixed frequency burst ?% sw 5v/div sync 2v/div i l 200ma/div 500ns/div comp 500mv/div burst 500mv/div v out 200mv/div v out 200mv/div load i l 200ma/div i l 0.5a/div 200 s/div 200 s/div 50ma 10ma v in = 3.3v v out = 7v r osc = 200k v in = 3.3v v out = 5v l = 10 h c out = 22 f v in = 3.3v v out = 5v l = 10 h c burst = 0.015 f r burst = 133k v in = 3.3v v out = 5v l = 10 h c burst = 0.015 f r burst = 133k v in = 3.3v v out = 5v r z = 33k cc1 = 270pf cc2 = 10pf c out = 22 f 0ma 0ma v in = 3.3v v out = 5v l = 10 h r z = 33k cc1 = 270pf cc2 = 10pf c out = 22 f l = 10 h f = 1mhz
ltc3458 7 3458fa uu u pi fu ctio s sw (pin 1): switch pin for inductor connection. during discontinuous conduction mode an antiring resistor con- nects sw to v in to reduce noise. v in (pin 2): input supply pin. connect this to the input supply and decouple with 1 f minimum. sync (pin 3): oscillator synchronization pin. a clock pulse width of 100ns to 2 s is required to synchronize the internal oscillator. this pin is disabled when grounded. shdn (pin 4): shutdown pin. grounding this pin shuts down the ic. connect to >1.25v to enable. i lim (pin 5): adjustable peak current limit. connect a resistor from i lim to gnd to program the peak inductor current according to the following formula: i r limit ilim = 200 where i limit is in amps and r ilim is in k . r t (pin 6): connect a resistor to ground to program the oscillator frequency, according to the formula: f r osc t = + 1 02 0004 .. where f osc is in mhz and r t is in k . fb (pin 7): connect resistor divider tap here. the output voltage can be adjusted from 2v to 7.5v. feedback refer- ence voltage is typically 1.23v. comp (pin 8): g m error amp output. a frequency com- pensation network is connected from this pin to ground to compensate the loop. see the section ?ompensating the feedback loop?for guidelines. gnd (pin 9): signal ground pin. ss (pin 10): connect a capacitor between this pin and ground to set soft-start period. 5 a of current is sourced from ss during soft-start. t(msec) = c ss ( f )?200 burst (pin 11): burst mode threshold adjust pin. a resistor/capacitor combination from this pin to ground programs the average load current at which automatic burst mode operation is entered, according to the formula: r i burst burst = 10 where r burst is in k and i burst is in amps. c cv burst out out = , 10 000 where c burst(min) and c out are in f. to force fixed frequency pwm mode, connect burst to v out through a 50k resistor. v out (pin 12): output of the synchronous rectifier and internal gate drive source for the power switches. v r r out =+ ? ? ? ? ? ? 123 1 2 1 . exposed pad (pgnd) (pin 13): must be soldered to pcb ground, for electrical contact and optimum thermal performance.
ltc3458 8 3458fa detailed description the ltc3458 provides high efficiency, low noise power for boost applications with output voltages up to 7.5v. the true output disconnect feature eliminates inrush current, and allows v out to go to zero during shutdown. the current mode architecture with adaptive slope compensa- tion provides ease of loop compensation with excellent transient load response. the low r ds(on) , low gate charge synchronous switches eliminate the need for an external schottky rectifier, and provide efficient high frequency pulse width modulation (pwm) control. high efficiency is achieved at light loads when burst mode operation is entered, where the ic? quiescent current is a low 15 a typical on v in . the ltc3458 is designed to provide custom performance in a variety of applications with program- mable feedback, current limit, oscillator frequency, soft- start, and burst mode threshold. block diagra w pgnd pgnd v best v best v select 3 6 9 osc/sync max duty sync gnd i lim pgnd ss comp shdn r t v cc v cc v cc sw v out fb burst pwm and burst mode drive logic p-drive p-drive p-drive n-drive n-drive n-drive i zero detect burst mode control fixed frequency burst mode mux soft-start thermal sd 4% undervoltage reference/ bias peak current comparator i comp , i limit , i burst_peak , slope comp sleep sleep control mode mode mode i comp/limit_peak i burst_peak slope slope sleep to all blocks i_sense burst active (disabled in burst mode) + + tsd 5 13 10 8 4 11 1 2 12 7 antiring sw1 under under sd to all blocks sdb i peak clock bias currents uvlo i zero 3458 bd error amplifier/ burst comparator applicatio s i for atio wu uu ltc3458 programmable functions current limit/peak burst current. the programmable current limit circuit sets the maximum peak current in the internal n-channel mosfet switch. this clamp level is programmed using a resistor to ground on i lim . in burst mode operation, the current limit is automatically set to ~1/4 of the programmed current limit for optimal effi- ciency. a 124k r ilim resistor is recommended in most applications unless a lower limit is needed to prevent the external inductor from saturating. i r lim = 200 i is in amps and r is in k . ii burstpeak lim 1 4
ltc3458 9 3458fa applicatio s i for atio wu u u current sensing. lossless current sensing converts the peak current signal to a voltage to sum in with the internal slope compensation. this summed signal is compared to the error amplifier output to provide a peak current control command for the pwm. the slope compensation in the ic is adaptive to the input and output voltage, therefore the converter provides the proper amount of slope compensa- tion to ensure stability, but not an excess to cause a loss of phase margin in the converter. output disconnect and inrush limiting. the ltc3458 is designed to allow true output disconnect by eliminating body diode conduction of the internal p-channel mosfet rectifier. this allows v 0ut to go to zero volts during shutdown, drawing no current from the input source. it also allows for inrush current limiting at turn-on, minimiz- ing surge currents seen by the input supply. note that to obtain the advantages of output disconnect, there must be no external schottky diodes connected between sw and v out . shutdown. the part is shut down by pulling shdn below 0.3v, and made active by pulling the pin above 1.25v. note that shdn can be driven above v in or v out , as long as it is limited to less than 8v. synchronous rectifier. to prevent the inductor current from running away, the p-channel mosfet synchronous rectifier is only enabled when v out > (v in + 0.25v). thermal shutdown. if the die temperature reaches ap- proximately 150 c, the part will go into thermal shutdown and all switches will be turned off and the soft-start capacitor will be reset. the part will be enabled again when the die temperature has dropped by 10 c (nominal). zero current amplifier. the zero current amplifier moni- tors the inductor current to the output and shuts off the synchronous rectifier once the current is below 50ma typical, preventing negative inductor current. burst mode operation burst mode operation can be automatic or user controlled. in automatic operation, the ic will automatically enter burst mode operation at light load and return to fixed frequency pwm mode for heavier loads. the user can program the average load current at which the mode error amp. the error amplifier is a transconductance type, with its positive input internally connected to the 1.23v reference, and its negative input connected to fb. a simple compensation network is placed from comp to ground. internal clamps limit the minimum and maximum error amp output voltage for improved large signal transient response. during sleep (in burst mode), the compensa- tion pin is high impedance, however clamps limit the voltage on the external compensation network, preventing the compensation capacitor from discharging to zero during the sleep time. oscillator. the frequency of operation is set through a resistor from r t to ground. an internally trimmed timing capacitor resides inside the ic. the oscillator frequency is calculated using the following formula: f r osc t = + 1 02 0004 .. where f osc is in mhz and r t is in k the oscillator can be synchronized with an external clock applied to the sync pin. when synchronizing the oscilla- tor, the free running frequency must be set to approxi- mately 30% lower than the desired synchronized fre- quency. soft-start. the soft-start time is programmed with an external capacitor to ground on ss. an internal current source charges it with a nominal 5 a. the voltage on the ss pin (in conjunction with the external resistor on i lim ) is used to control the peak current limit until the voltage on the capacitor exceeds ~1v, at which point the external resistor sets the peak current. in the event of a com- manded shutdown, severe short-circuit, or a thermal shutdown, the capacitor is discharged automatically. t (msec) = c ss ( f) ?200 other ltc3458 features and functions antiringing control. the antiringing control places a resistor across the inductor to damp the ringing on sw pin discontinuous conduction mode. the lc ringing (l = inductor, c sw = capacitance on sw pin) is low energy, but can cause emi radiation.
ltc3458 10 3458fa transition occurs using a single resistor. during burst mode operation, the oscillator is shut down, since the on time is determined by the time it takes the inductor current to reach a fixed peak current, and the off time is deter- mined by the time it takes for the inductor current to return to zero. in burst mode operation, 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 15 a of quiescent current. in this mode the output ripple voltage has a variable frequency component with load current and will be typically 2% peak-to-peak. this maxi- mizes efficiency at very light loads by minimizing switch- ing and quiescent losses. burst mode ripple can be re- duced slightly by using more output capacitance (22 f or greater). this capacitor does not need to be a low esr type if low esr ceramics are also used. another method of reducing burst mode ripple is to place a small feed- forward capacitor across the upper resistor in the v out feedback divider network. during burst mode operation, comp is disconnected from the error amplifier in an effort to hold the voltage on the external compensation network where it was before entering burst mode operation. to minimize the effects of leakage current and stray resistance, voltage clamps limit the minimum and maximum voltage on comp during burst mode operation. this minimizes the transient expe- rienced when a heavy load is suddenly applied to the converter after being in burst mode operation for an extended period of time. for automatic operation, an rc network should be con- nected from burst to ground. the value of the resistor will control the average load current (i burst ) at which burst mode operation will be entered and exited (there is hysteresis to prevent oscillation between modes). the equation given for the capacitor on burst is for the minimum value, to prevent ripple on the burst pin from causing the part to oscillate in and out of burst mode operation at the current where the mode transition occurs. r i burst burst = 10 where r burst is in k and i burst is in amps. c cv burst out out = , 10 000 where c burst(min) and c out are in f. note: the burst pin only sources current based on current delivered to v out through the p-channel mosfet. if current in the inductor is allowed to go negative (this can occur at very light loads and high step-up ratios), the burst threshold may become inaccurate, preventing the ic from entering burst mode operation. for r burst values greater than 200k, a larger than recommended inductor value may be needed to ensure positive inductor current and auto- matic burst mode operation. in the event that a sudden load transient causes the voltage level on fb to drop by more than 4% from the regulation value, an internal pull-up is applied to burst, forcing the part quickly out of burst mode operation. for optimum transient response when going between burst mode op- eration and pwm mode, burst can be controlled manually by the host. this way pwm mode can be commanded before the load step occurs, minimizing output voltage drop. note that burst mode operation is inhibited during start-up and soft-start. manual control for applications requiring fixed frequency operation at all load currents, connect the burst pin to v out through a 50k resistor. to force burst mode operation, ground the burst pin. for applications where a large load step can be anticipated, the circuit below can be used to reduce the voltage transient on v out . automatic operation is achieved when the external pmos is off and fixed frequency operation is commanded when the external pmos is on. in shutdown, the pmos should be off. applicatio s i for atio wu uu figure 1 0.01 f v in burst 133k pmos high: auto mode low: fixed frequency 3458 fo2
ltc3458 11 3458fa component selection inductor selection the high frequency operation of the ltc3458 allows for the use of small surface mount inductors. since the internal slope compensation circuit relies on the inductor? current slope and frequency, table 1 should be used to select an inductor value for a given frequency of operation ( 25%). the recommended value will yield optimal tran- sient performance while maintaining stable operation. inductor values larger than listed in table 1 are permis- sible to reduce the current ripple. table 1. recommended inductor values frequency inductor value( h) 1.5mhz 3.3 to 4.7 1.25mhz 4.7 to 6.8 1mhz 6.8 to 10 750hz 10 to 15 500khz 15 to 22 for high efficiency, choose an inductor with high fre- quency core material, such as ferrite, to reduce core losses. 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 saturat- ing. molded chokes or chip inductors usually do not have enough core to support peak inductor currents in the 1a to 3a region. to minimize radiated noise, use a toroidal or shielded inductor. (note that the inductance of shielded types will drop more as current increases, and will saturate more easily). see table 2 for a list of inductor manufacturers. table 2. inductor vendor information supplier phone website coilcraft (847) 639-6400 www.coilcraft.com tdk (847) 803-6100 www.component.tdk.com murata usa: (814) 237-1431 (800) 831-9172 www.murata.com sumida usa: (847) 956-0666 japan: 81-3-3607-5111 www.japanlink.com/sumida coev (800) 227-7040 www.coev.net toko (847) 297-0070 www.tokoam.com wurth (202) 785-8800 www.we-online.com applicatio s i for atio wu uu some example inductor part types are: coilcraft: do1608 and mss5131 series tdk: rlf5018t and slf7045 series murata: lqh4c and lqn6c series sumida: cdrh4d28 and cdrh6d28 series coev: dq7545 series toko: d62cb and d63lcb series wurth: we-pd2 series output capacitor selection the output voltage ripple has three components to it. the bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. the max ripple due to charge is given by: v iv cvf rbulk pin out out = where i p = peak inductor current and f = switching frequency. the esr (equivalent series resistance) is usually the most dominant factor for ripple in most power converters. the ripple due to capacitor esr is given by: v rcesr = i p ?c esr where c esr = capacitor series resistance. the esl (equivalent series inductance) is also an impor- tant factor for high frequency converters. using small, surface mount ceramic capacitors, placed as close as possible to the v out pins, will minimize esl. low esr/esl capacitors should be used to minimize output voltage ripple. for surface mount applications, avx tps series tantalum capacitors, sanyo poscap, or taiyo yuden x5r type ceramic capacitors are recommended. for through-hole applications, sanyo os-con capacitors offer low esr in a small package size. in all applications, a minimum of 4.7 f (generally 22 f is recommended), low esr ceramic capacitor should be placed as close to the v out pin as possible, and grounded to a local ground plane. .. ..
ltc3458 12 3458fa input capacitor selection the input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. in most applications >1 f per amp of peak input current is recommended. see table 3 for a list of capacitor manufacturers for input and output capacitor selection. table 3. capacitor vendor information supplier phone website avx (803) 448 - 9411 www.avxcorp.com sanyo (619) 661 - 6322 www.sanyovideo.com tdk (847) 803 - 6100 www.component.tdk.com murata usa: (814) 237-1431 (800) 831-9172 www.murata.com taiyo yuden (408) 573 - 4150 www.t-yuden.com operating frequency selection there are several considerations in selecting the operating frequency of the converter. the first is staying clear of sensitive frequency bands, which cannot tolerate any spectral noise. for example in products incorporating rf communications the 455khz if frequency is sensitive to any noise, therefore switching above 600khz is desired. some communications have sensitivity to 1.1mhz and in that case a 1.5mhz switching converter frequency may be employed. the second consideration is the physical size of the converter. as the operating frequency goes up, the inductor and filter capacitors go down in value and size. the trade off is in efficiency, since the switching losses due to gate charge increase proportional with frequency. thermal considerations for the ltc3458 to deliver its full output power, it is imperative that a good thermal path be provided to dissi- pate the heat generated within the package. this can be accomplished by taking advantage of the large thermal pad on the underside of the ic. it is recommended that multiple vias in the printed circuit board be used to conduct heat away from the ic and into a copper plane with as much area as possible. if the junction temperature rises above ~150 c, the part will go into thermal shutdown, and all switching will stop until the temperature drops. compensating the feedback loop the ltc3458 uses current mode control, with internal adaptive slope compensation. current mode control elimi- nates the 2nd order filter due to the inductor and output capacitor exhibited in voltage mode controllers, and sim- plifies the power loop to a single pole filter response. the product of the modulator control to output dc gain, and the error amp open-loop gain gives the dc gain of the system: gg g v v g g v i gg r dc control ea ref out current sense control in out ea current sense ds on = = = , , _ _ () 2 1000 1 the output filter pole is given by: f i vc filter pole out out out _ , = where c out is the output filter capacitor. the output filter zero is given by: f rc filter zero esr out _ , = 1 2 where r esr is the output capacitor equivalent series resistance. a troublesome feature of the boost regulator topology is the right half plane zero (rhp), and is given by: f v ivl rhpz in out out = 2 2 at heavy loads this gain increase with phase lag can occur at a relatively low frequency. the loop gain is typically applicatio s i for atio wu uu
ltc3458 13 3458fa rolled off before the rhp zero frequency. the typical error amp compensation is shown in figure 2. the equations for the loop dynamics are as follows: f ecc which is close to dc f rcc f rcc pole zero z pole z 1 6 1 2 1 210 1 1 21 1 22 = + 7 8 comp fb error amp 1.25v v out r1 r2 cc1 cc2 r z 3458 f01 figure 2 applicatio s i for atio wu uu
ltc3458 14 3458fa typical applicatio s u v in gnd/pgnd shdn sync r t i lim sw v out fb comp ss burst ltc3458 li-ion 2.5v to 4.2v 2.2 f wurth 12 h 774775112 on off 243k 124k 133k 324k 33k 0.01 f 0.01 f 560pf 10pf 10pf 1m 22 f x5r v out 5v 450ma 3458 ta03a v in gnd/pgnd shdn sync r t i lim sw v out fb comp ss burst ltc3458 2 alkaline 1.8v to 3.3v 2.2 f wurth 12 h 774775112 on off 243k 124k 133k 324k 33k 0.01 f 0.01 f 560pf 10pf 1m 22 f x5r v out 5v 200ma 3458 ta04a 10pf v in gnd/pgnd shdn sync r t i lim sw v out fb comp ss burst ltc3458 li-ion 2.5v to 4.2v 2.2 f coev 10 h dq7545 on off 200k 124k 133k 316k 33k 0.01 f 0.01 f 560pf 10pf 1.5m 22 f x5r v out 7v 250ma 3458 ta05a 10pf lithium-ion to 5v, 500ma at 850khz two cell to 5v out , 200ma at 850khz lithium-ion battery to 7v out , 250ma at 1mhz load current (ma) efficiency 100 95 90 85 80 75 70 65 0.1 10 100 1000 3458 ta03b 1 4.2v in 3.6v in 2.5v in load current (ma) efficiency 100 95 90 85 80 75 70 65 0.1 10 100 1000 3458 ta04b 1 3.3v in 1.8v in load current (ma) efficiency 100 95 90 85 80 75 70 65 0.1 10 100 1000 3458 ta05b 1 4.2v in 3.6v in 2.5v in li-ion to 5v out two alkaline to 5v out li-ion to 7v out
ltc3458 15 3458fa de/ue package 12-lead plastic dfn (4mm 3mm) (reference ltc dwg # 05-08-1695) package descriptio u 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. 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?xposed 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
ltc3458 16 3458fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2004 lt0807 rev a ?printed in usa related parts typical applicatio u part number description comments lt1310 1.5a i sw , 4.5mhz, high efficiency step-up dc/dc converter v in : 2.75v to 18v, v out(max) = 35v, i q = 12ma, i sd < 1 a, ms10e lt1613 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 lt1615/ 300ma/80ma i sw , constant off-time, high efficiency v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, lt1615-1 step-up dc/dc converter thinsot lt1618 1.5a i sw , 1.4mhz, 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 lt1944 (dual) dual output 350ma i sw , constant off-time, high efficiency v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, ms10 step-up dc/dc converter lt1945 (dual) dual output pos/neg 350ma i sw , constant off-time, v in : 1.2v to 15v, v out(max) = 34v, i q = 20 a, i sd < 1 a, ms10 high efficiency step-up dc/dc converter 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, i sd < 1 a, ms8 dc/dc converter lt1949/ 550ma i sw , 600khz/1.1mhz, high efficiency step-up v in : 1.5v to 12v, v out(max) = 28v, i q = 4.5ma, i sd < 25 a, so-8, lt1949-1 dc/dc converter ms8 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 ltc3400/ 600ma i sw , 1.2mhz, synchronous step-up dc/dc converter v in : 0.5v to 5v, v out(max) = 5v, i q = 19 a/300 a i sd < 1 a, ltc3400b thinsot ltc3401 1a 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, ms10 ltc3402 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, ms10 ltc3425 5a i sw , 8mhz, 4-phase 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, qfn32 ltc3429 600ma, 500khz, synchronous step-up dc/dc converter v in : 0.5v to 5v, v out(max) = 5v, i q = 20 a/300 a i sd < 1 a, with output disconnect and soft-start thinsot ltc3459 70ma i sw , 10v micropower synchronous boost/output disconnect v in : 1.5v to 5.5v, v out(max) = 10v, i q = 10 a, thinsot lt3460 320ma i sw , 1.3mhz, high efficiency step-up dc/dc converter v in : 2.5v to 16v, v out(max) = 36v, i q = 2ma, i sd < 1 a, sc70, thinsot lt3464 85ma i sw , constant off-time, high efficiency step-up dc/dc v in : 2.3v to 10v, v out(max) = 34v, i q = 25 a, i sd < 1 a, converter with integrated schottky/output disconnect thinsot dual lumiled application with burst pin current regulation v in gnd/pgnd shdn sync r t i lim sw v out fb comp ss burst ltc3458 li-ion 2.7v to 4.2v c in 2.2 f l1 z1 d1 d2 on off 243k 124k r burst 33k 0.01 f 0.01 f 0.01 f c out 2.2 f v out 6.4v to 6.8v 3458 ta06a c in , c out : taiyo yuden jmk107bj225ma d1, d2: luxeon emitter lumiled white lxhlmw1d (2.9v at 350ma) l1: wurth 12 h 774775112 r burst : 35.7k for 350ma, 47.5k for 250ma, 82.5k for 150ma z1: central semi 6.8v zener diode sot-23 cmpz5235b f osc = 850khz input voltage (v) efficiency (%) 100 90 80 70 60 50 2.5 3.5 4.0 3458 ta06b 2.0 3.0 4.5 5.0 5.5 350ma, 6.8v 150ma, 6.4v 250ma, 6.6v note: lumiled current regulation ~10% over v in range 2-lumileds in series

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