View LT3477EUFTR_8457109.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

lt3477 1 3477fc typical application description 3a, dc/dc converter with dual rail-to-rail current sense features applications n dual 100mv rail-to-rail current sense ampli? ers n wide input voltage range: 2.5v to 25v n 3a, 42v internal switch n high ef? ciency power conversion: up to 93% n drives leds in boost, buck-boost or buck mode n frequency set by external resistor: 200khz to 3.5mhz n programmable soft-start n low v cesat switch: 0.3v at 2.5a n capable of positive and negative output voltages (boost, inverting, sepic, flyback) n available in thermally enhanced 20-lead (4mm 4mm) qfn and 20-lead tssop packages the lt ? 3477 is a current mode, 3a dc/dc step-up con- verter with dual rail-to-rail current sense ampli? ers and an internal 3a, 42v switch. it combines a traditional voltage feedback loop and two unique current feedback loops to operate as a constant-current, constant-voltage source. both current sense voltages are set at 100mv and can be adjusted independently using the i adj1 and i adj2 pins. ef- ? c i e n c y o f u p t o 9 1% c a n b e a c h i e v e d i n t y p i c a l a p p l i c a t i o n s . the lt3477 features a programmable soft-start function to limit inductor current during start-up. both inputs of the error ampli? er are available externally allowing posi- tive and negative output voltages (boost, inverting, sepic, flyback). the switching frequency is programmable from 200khz to 3.5mhz through an external resistor. available in thermally enhanced 20-pin (4mm 4mm) qfn and 20-pin tssop packages, the lt3477 provides a complete solution for both constant-voltage and constant- current applications. ef? ciency 330ma led driver with open led protection i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 200k 3.3f 3.3f v in 5v 33nf 4.7nf 330ma 3477 ta01a 10k 22k 1k 0.3 sw 10h fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn i out (a) 0 efficiency (%) 70 75 80 0.4 3477 ta01b 6560 50 0.1 0.2 0.3 55 9085 n high power led driver n dsl modems n distributed power n input/output current limited boost, sepic, inverting, flyback converters n constant-voltage, constant-current source , lt, ltc and ltm are registered trademarks of linear technol ogy corporation. all other trademarks are the property of their respective owners. downloaded from: http:///
lt3477 2 3477fc absolute maximum ratings sw pin voltage ........................................................ 42v v in , shdn pin voltage ............................................. 25v fbp, fbn pin voltage ................................................. 6v v ref pin voltage......................................................... 6v r t , v c , ss pin voltage ............................................... 6v i adj1 , i adj2 pin voltage ............................................ 25v i sp1 , i sp2 , i sn1 , i sn2 pin voltage ...............................42v (note 1) junction temperature .......................................... 125c operating temperature range (note 2) lt3477e ...............................................C 40c to 85c lt3477i .............................................. C40c to 125c storage temperature range ...................C 65c to 125c lead temperature (soldering, 10 sec) tssop .............................................................. 300c the indicates speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 2.5v, v shdn = 2.5v. electrical characteristics parameter conditions min typ max units minimum input voltage l 2.3 2.5 v quiescent current v shdn = 0v v shdn = 2.5v, v c = 0.3v (not switching) 0.1 5.0 1.0 7.5 a ma reference voltage e grade i grade ll 1.216 1.210 1.235 1.235 1.250 1.260 vv reference voltage line regulation 2.5v < v in < 25v, v c = 0.3v 0.01 0.03 %/v fe package 20-lead plastic tssop 12 3 4 5 6 7 8 9 10 top view 2019 18 17 16 15 14 13 12 11 v in r t shdn ss v c fbn fbp v ref i adj2 i adj1 ncnc nc sw sw gnd i sn1 i sp1 i sn2 i sp2 21 t jmax = 125c, ja = 40c/w exposed pad (pin 21) is pgnd (must be soldered to pcb) 20 19 18 17 16 6 7 8 top view 21 uf package 20-lead (4mm 4mm) plastic qfn 9 10 5 4 3 2 1 11 12 13 14 15 ncnc v in r t shdn i sp1 i sn2 i sp2 i adj1 i adj2 ncsw sw gnd i sn1 ss v c fbn fbp v ref t jmax = 125c, ja = 37c/w exposed pad (pin 21) is pgnd (must be soldered to pcb) lead free finish tape and reel part marking package descriptio n temperature range lt3477efe#pbf lt3477efe#trpbf 20-lead plastic tssop C40c t o 85c lt3477ife#pbf lt3477ife#trpbf 20-lead plastic tssop C40c t o 125c lt3477euf#pbf lt3477euf#trpbf 3477 20-lead (4mm 4mm) plastic qfn C40c to 85c lt3477iuf#pbf lt3477iuf#trpbf 3477 20-lead (4mm 4mm) plastic qfn C40c to 125c consult ltc marketing for parts speci? ed with wider operating temp erature ranges. consult ltc marketing for information on non-standard lead based ? ni sh 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/ pin configurationorder information downloaded from: http:///
lt3477 3 3477fc electrical characteristics the indicates speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 2.5v, v shdn = 2.5v. parameter conditions min typ max units maximum v ref pin current out of pin 100 a soft-start pin current ss = 0.5v, out of pin 9 a fbp pin bias current 25 100 na fbn pin bias current 25 100 na feedback ampli? er offset voltage fbp C fbn, v c = 1v C2 2 6 mv feedback ampli? er voltage gain 500 v/v voltage feedback ampli? er transconductance 500 s feedback ampli? er sink current v fbp = 1.25v, v fbn = 1.5v, v c = 1v 10 a feedback ampli? er source current v fbp = 1.25v, v fbn = 1v, v c = 0.5v 10 a current sense ampli? er sense voltage positive rail, v cm = 25v, e grade positive rail, v cm = 25v, i grade ground 97.5 97.5 88 100 100 100 102.5 103 112 mvmv mv switching frequency r t = 17.2k r t = 107.4k r t = 2.44k 0.9 160 2.7 1 200 3.5 1.15 240 4.3 mhz khz mhz maximum switch duty cycle r t = 17.2k 87 93 % switch current limit (note 3) 3 4 5 a switch v cesat i sw = 1a (note 3) 150 200 mv switch leakage current sw = 40v 0.2 5 a shdn pin current v shdn = 5v v shdn = 0v 30 0.1 60 1 aa shdn pin threshold 0.3 1.5 2 v 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 lt3477e is guaranteed to meet performance speci? cations from 0c to 70c. speci? cations over the C 40c to 85c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the lt3477i is guaranteed over the full C40c to 125c operating junction temperature range. note 3: switch current limit and switch v cesat for uf package guaranteed by design and/or correlation to static test. typical performance characteristics switch v ce(sat) switch current limit v ref switch current (a) 0 0 v ce(sat) (v) 0.10 0.20 0.300.25 0.5 1 1.5 2 3477 g01 2.5 0.40 0.50 0.05 0.15 125c C50c 0.35 0.45 3 25c temperature (c) C50 C25 0 current (a) 2 5 0 50 75 3477 g02 1 4 3 25 100 125 temperature (c) C50 1.21 v ref (v) 1.22 1.23 1.24 1.25 05 0 100 150 3477 g03 1.26 1.27 C25 25 75 125 v in = 25v v in = 2.5v downloaded from: http:///
lt3477 4 3477fc temperature (c) C50 shdn threshold (v) 1.4 1.6 25 75 3477 g04 1.2 C25 0 50 100 125 1.0 v shdn (v) 0 shdn pin current (a) 30 40 50 20 3477 g05 20 10 0 5 10 15 C50c 25c 125c 25 temperature (c) C50 2 quiescent current (ma) 3 4 5 6 C25 0 25 50 3477 g06 75 100 125 150 v c = 0.3v temperature (c) C50 0 i ss (a) 5 10 15 20 C25 0 25 50 3477 g07 75 100 125 150 temperature (c) C50 frequency (mhz) 1.2 1.6 2.0 25 75 150 3477 g08 0.8 0.4 0 C25 0 50 100 125 r t = 10k r t = 15k r t = 20k temperature (c) C50 offset voltage (mv) 0 2 150 3477 g09 C2C4 0 50 100 C25 25 75 125 4 C1 1 C3 3 v c = 1v v c = 0.5v temperature (c) C50 fbp pin bias current (na) 30 40 50 25 75 3477 g10 20 10 C25 0 50 100 125 0 C10 + indicates the current flows out of pin temperature (c) C50 fbn pin bias current (na) 30 40 50 25 75 3477 g11 20 10 C25 0 50 100 125 0 C10 + indicates the current flows out of pin typical performance characteristics soft-start pin current oscillator frequency feedback ampli? er o ffset voltage shdn pin turn-on threshold shdn pin current quiescent current fbp pin bias current fbn pin bias current downloaded from: http:///
lt3477 5 3477fc i adj voltage (mv) 0 0 voltage sense (mv) 20 40 60 80 200 400 600 800 2477 g13 100 120 100 300 500 700 v cm = 10v temperature (c) C50 current sense voltage (mv) 103 25 3477 g14 100 98 C25 0 50 9796 104102 101 99 75 100 125 v cm = 10v v cm = 42v typical performance characteristics current sense voltage vs i adj current sense voltage vs temperature pin functions (qfn/tssop) nc (pins 1, 2, 20/pins 18, 19, 20): no connect pin. okay to connect to ground or v in , or to ? oat. v in (pin 3/pin 1): input supply. must be locally bypassed. powers the internal control circuitry. r t (pin 4/pin 2): timing resistor pin. adjusts the switch- ing frequency. connect a 17.2k resistor between r t and gnd for a 1mhz switching frequency. do not leave this pin open. see table 4 for additional r t values and switching frequencies. shdn (pin 5/pin 3): shutdown. tie to 2v or greater to enable the device. tie below 0.3v to turn off the device. ss (pin 6/pin 4): soft-start. place a soft-start capacitor here. leave ? oating if not in use. v c (pin 7/pin 5): compensation pin for error ampli? er. connect a series rc from this pin to gnd. typical values are 1k and 4.7nf. fbn (pin 8/pin 6): the inverting input to the error ampli- ? er. connect resistive divider tap here for positive output voltage. fbp (pin 9/pin 7): the noninverting input to the error ampli? er. connect resistive divider tap here for negative output voltage. v ref (pin 10/pin 8): bandgap voltage reference. inter- nally set to 1.235v. connect this pin to fbp if generat- ing a positive output or to an external resistor divider if generating a negative voltage. this pin can provide up to 100a of current and can be locally bypassed with a 100pf capacitor. i adj2 (pin 11/pin 9): second current sense adjustment. setting i adj2 t o b e l e s s t h a n 6 2 5 mv l e a d s t o a d j u s t m e n t o f the sensed voltage of the second current sense ampli? er linearly. if i adj2 is tied to higher than 650mv, the default current sense voltage is 100mv. if current sense ampli? er 2 is not used, always tie i adj2 to higher than 650mv. i adj1 (pin 12/pin 10): first current sense adjustment. setting i adj1 to be less than 625mv leads to adjustment of the sensed voltage of the ? rst current sense ampli? er linearly. if i adj1 is tied to higher than 650mv, the default current sense voltage is 100mv. if current sense ampli? er 1 is not used, always tie i adj1 to higher than 650mv. downloaded from: http:///
lt3477 6 3477fc pin functions (qfn/tssop) i sp2 (pin 13/pin 11): second current sense (+) pin. the noninverting input to the second current sense ampli? er. connect to i sn2 if not used. i sn2 (pin 14/pin 12): second current sense (C) pin. the inverting input to the second current sense ampli? er. connect to i sp2 if not used. i sp1 (pin 15/pin 13): first current sense (+) pin. the noninverting input to the ? rst current sense ampli? er. connect to i sn1 if not used. i sn1 (pin 16/pin 14): first current sense (C) pin. the in- verting input to the ? rst current sense ampli? er. connect to i sp1 if not used. gnd (pins 17/pin 15): ground. tie directly to local ground plane. sw (pins 18, 19/pins 16, 17): switch pins. collector of the internal npn power switch. connect the inductor and diode here and minimize the metal trace area connected to this pin to minimize electromagnetic interference. exposed pad (pin 21/pin 21): power ground. must be soldered to pcb ground for electrical contact and rated thermal performance. C + C + C + C ++ ia1 i sp1 i sn1 a1 v c sw ss a3 a4 slope v adj i adj1 i sp2 i sn2 fbpfbn shdn i adj2 v ref C + C ++ ia2 C + r t v in va a2 v adj v ref 1.25v s rq 1 3477 f01 q oscillator figure 1. lt3477 block diagram block diagram downloaded from: http:///
lt3477 7 3477fc operation the lt3477 uses a ? xed frequency, current mode control scheme to provide excellent line and load regulation. op- eration can be best understood by referring to the block diagram in figure 1. the start of each oscillator cycle sets the sr latch and turns on power switch q1. the signal at the noninverting input of the pwm comparator (a4 slope) is proportional to the sum of the switch current and oscillator ramp. when slope exceeds v c (the output of the feedback ampli? er), the pwm comparator resets the latch and turns off the power switch. in this manner, the feedback ampli? er and pwm comparators set the correct peak current level to keep the output in regula- tion. ampli? er a3 drives a4 inverting input. a3 has three inputs, one from the voltage feedback loop and the other two from the current feedback loop. whichever feedback input is higher takes precedence, forcing the converter into either a constant-current or a constant-voltage mode. the lt3477 is designed to transition cleanly between the two modes of operation. current sense ampli? er ia1 senses the voltage between the i sp1 and i sn1 pins and provides a pre-gain to ampli? er a1. when the voltage between i sp1 and i sn1 reaches 100mv, the output of ia1 provides v adj to the inverting input of a1 and the converter is in con- stant-current mode. if the current sense voltage exceeds 100mv, the output of ia1 will increase causing the output of a3 to decrease, thus reducing the amount of current delivered to the output. in this manner the current sense voltage is regulated to 100mv. the current sense level is also pin adjustable by i adj1 . forcing i adj1 to less than 625mv will overwrite v adj voltage thats set internally, thus providing current level control. the second current sense ampli? er, ia2, works the same as the ? rst current sense ampli? er ia1. both current sense ampli? ers provide rail-to-rail current sense operation. similarly, for positive output voltage operation where fbp is tied to v ref , if the fbn pin increases above v ref , the output of a3 will decrease to reduce the peak current level and regulate the output (constant-voltage mode). for negative output voltage operation where fbn is tied to gnd, if the fbp pin decreases below gnd level, the output of a3 will decrease to reduce the peak current level and regulate the output (constant-voltage mode). the lt3477 also features a soft-start function. during start-up, 9a of current charges the external soft-start capacitor. the ss pin directly limits the rate of voltage rise on the v c pin, which in turn limits the peak switch cur- rent. the switch current is constantly monitored and not allowed to exceed the nominal value of 3a. if the switch current reaches 3a, the sr latch is reset regardless of the output of the pwm comparator. current limit protects the power switch and external components. downloaded from: http:///
lt3477 8 3477fc applications information capacitor selection low esr (equivalent series resistance) ceramic capaci- tors should be used at the output to minimize the output ripple voltage. use only x5r or x7r dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges better than other dielectrics. a 4.7f to 10f output capacitor is suf? cient for most high output current designs. converters with lower output currents may need only a 1f or 2.2f output capacitor. table 1. ceramic capacitor manufacturers manufacturer phone web taiyo yuden (408) 573-4150 www.t-yuden.com avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com tdk (847) 803-6100 www.component.tdk.com inductor selection several inductors that work well with the lt3477 are listed in table 2. however, there are many other manufacturers and devices that can be used. consult each manufacturer for more detailed information and their entire range of parts. ferrite core inductors should be used to obtain the best ef? ciency. choose an inductor that can handle the necessary peak current without saturating, and ensure that the inductor has a low dcr (copper-wire resistance) to minimize i 2 r power losses. a 4.7h or 10h inductor will suf? ce for most lt3477 applications. inductor manufacturers specify the maximum current rating as the current where the inductance falls to some percentage of its nominal valuetypically 65%. an inductor can pass a current larger than its rated value without damaging it. aggressive designs where board space is precious will exceed the maximum current rat- ing of the inductor to save board space. consult each manufacturer to determine how the maximum inductor current is measured and how much more current the inductor can reliably conduct. diode selection schottky diodes, with their low forward voltage drop and fast switching speed, are ideal for lt3477 applications. table 3 lists several schottky diodes that work well with the lt3477. the diodes average current rating must exceed the average output current. the diodes maximum reverse voltage must exceed the output voltage. the diode conducts current only when the power switch is turned off (typically less than 50% duty cycle), so a 3a diode is suf? cient for most designs. the companies below also offer schottky diodes with higher voltage and current ratings. table 3. suggested diodes manufacturer part number max current (a) max reverse voltage (v) manufacturer ups340 ups315 33 4015 microsemi www.microsemi.com b220 b230 b240 b320 b330 b340 sbm340 22 2 3 3 3 3 2030 40 20 30 40 40 diodes, inc www.diodes.com table 2. suggested inductors manufacturer part number i dc (a) inductance (h) max dcr (m) l w h (mm) manufacturer cdrh6d283r0 cdrh6d28100 cdrh4d284r7 3 1.7 1.32 3 10 4.7 24 65 72 6.7 6.7 3.0 6.7 6.7 3.0 5.0 5.0 3.0 sumida www.sumida.com lm n 05d b4r7m lm n 05d b100k 2.2 1.6 4.7 10 49 10 5.9 6.1 2.8 5.9 6.1 2.8 taiyo yuden www.t-yuden.com lqh55dn4r7m01l lqh55dn100m01k 2.7 1.7 4.7 10 57 130 5.7 5.0 4.7 5.7 5.0 4.7 murata www.murata.com fdv0630-4r7m 4.2 4.7 49 7.0 7.7 3.0 toko www.toko.com downloaded from: http:///
lt3477 9 3477fc applications information setting positive output voltages to set a positive output voltage, select the values of r1 and r2 (see figure 2) according to the following equation: v out = 1.235v 1 + r1 r2 for designs needing an adjustable current level, the i adj1 and i adj2 pins are provided for the ? rst and the second current sense ampli? ers, respectively. with the i adj1 and i adj2 pins tied higher than 650mv, the nominal current sense voltage is 100mv (appearing between the i sp1 and i sn2 or i sp2 and i sn2 pins). applying a positive dc voltage less than 600mv to the i adj1 and i adj2 pins will decrease the current sense voltage according to the following formula: i mv r v mv sense sense iadj = 100 618 ? for example, if 309mv is applied to the i adj1 pin and r sense is 0.5, the current sense will be reduced from 200ma to 100ma. the adjustability allows the regulated current to be reduced without changing the current sense resistor (e.g., to adjust brightness in an led driver or to reduce the charge current in a battery charger). considerations when sensing input current in addition to regulating the dc output current for cur- rent-source applications, the constant-current loop of the lt3477 can also be used to provide an accurate input current limit. boost converters cannot provide output short-circuit protection, but the surge turn-on current can be drastically reduced using the lt3477 current sense at the input. sepics, however, have an output that is dc- isolated from the input, so an input current limit not only helps soft-start the output but also provides excellent short-circuit protection. when sensing input current, the sense resistor should be placed in front of the inductor (between the decoupling capacitor and the inductor). this will regulate the average inductor current and maintain a consistent inductor ripple current, which will, in turn, maintain a well regulated input current. do not place the sense resistor between the input source and the input decoupling capacitor, as this may allow the inductor ripple current to vary widely (even though the average input current and the average inductor current will still be regulated). since the inductor current is a triangular waveform (not a dc waveform like the output current) figure 2. positive output voltage feedback connections r4 r3 3477 f03 fbp v ref Cv out lt3477 fbn figure 3. negative output voltage feedback connections r2 r1 3477 f02 fbn v ref v out lt3477 fbp setting negative output voltages to s e t a n e g a t i v e o u t p u t v o l t a g e , s e l e c t t h e v a l u e s o f r 3 a n d r4 (see figure 3) according to the following equation: v out = ?1.235v r3 r4 selecting r sense /current sense adjustment using the following formula to choose the correct current sense resistor value (for constant current or fail-safe operation). r mv i sense sense = 100 downloaded from: http:///
lt3477 10 3477fc some tweaking of the compensation values (r c and c c on the v c pin) may be required to ensure a clean inductor ripple current while the constant-current loop is in effect. for these applications, the constant-current loop response can usually be improved by reducing the r c value or by adding a capacitor (with a value of approximately c c /10) in parallel with the r c and c c compensation network. frequency compensation the lt3477 has an external compensation pin (v c ), which allows the loop response to be optimized for each applica- tion. an external resistor and capacitor (or sometimes just a capacitor) are placed at the v c pin to provide a pole and a zero (or just a pole) to ensure proper loop compensation. several other poles and zeroes are present in the closed- loop transfer function of a switching regulator, so the v c pin pole and zero are positioned to provide the best loop response. a thorough analysis of the switching regulator control loop is not within the sc ope of this data sheet, and will not be presented here, but values of 1k and 4.7nf will be a good choice for many designs. for those wishing to optimize the compensation, use the 1k and 4.7nf as a starting point. board layout as with all switching regulators, careful attention must be paid to the pcb board layout and component place- ment. to maximize ef? ciency, switch rise and fall times are made as short as possible. to prevent radiation and high frequency resonance problems, proper layout of the high frequency switching path is essential. minimize the length and area of all traces connected to the sw pin and always use a ground plane under the switching regulator to minimize interplane coupling. the signal path including the switch, output diode d1 and output capacitor c out , contains nanosecond rise and fall times and should be kept as short as possible. soft-start for many applications, it is necessary to minimize the inrush current at start-up. the built-in soft-start circuit signi? cantly reduces the start-up current spike and out- put voltage overshoot. a typical value for the soft-start capacitor is 10nf. switching frequency the switching frequency of the lt3477 is set by an ex- ternal resistor attached to the r t pin. do not leave this pin open. a resistor must always be connected for proper operation. see table 4 and figure 4 for resistor values and corresponding frequencies. increasing switching frequency reduces output voltage ripple but also reduces ef? ciency. the user should set the frequency for the maximum tolerable output voltage ripple. figure 4. switch frequency r t (k) 0 1.51.0 0.5 3.53.0 2.5 2.0 3477 f04 switch frequency (mhz) 0.1 100 10 applications information table 4. switching frequency switching frequency (mhz) r t (k) 3.5 2.43 3 3.65 2.5 4.87 2 6.81 1.5 10.2 1 17.4 0.5 43.2 0.2 107 downloaded from: http:///
lt3477 11 3477fc applications information pwm dimming for led applications where a wide dimming range is required, two competing methods are available: analog dimming and pwm dimming. the easiest method is to simply vary the dc current through the ledanalog dimmingbut changing led current also changes its chromaticity, undesirable in many applications. the bet- ter method is pwm dimming, which switches the led on and off, using the duty cycle to control the average current. pwm dimming offers several advantages over analog dimming and is the method preferred by led manufacturers. by modulating the duty cycle of the pwm signal, the average led current changes proportionally as illustrated in figure 5. the chromaticity of the leds remains unchanged in this scheme since the led current is either zero or at programmed current. another advantage of pwm dimming over analog dimming is that a wider dimming range is possible. the lt3477 is a dc/dc converter that is ideally suited for led applications. for the lt3477, analog dimming offers a dimming ratio of about 10:1; whereas, pwm dimming with the addition of a few external components results in a wider dimming range of 500:1. the technique requires a pwm logic signal applied to the gate of both nmos (refer to figure 7). when the pwm signal is taken high the part runs in normal operation and i led = 100mv/r sense runs through the leds. when the pwm input is taken low, the leds are disconnected and turn off. this unique external circuitry produces a fast rise time for the led current, resulting in a wide dimming range of 500:1 at a pwm frequency of 100hz. the led current can be controlled by feeding a pwm signal with a broad range of frequencies. dimming below 80hz is possible, but not desirable, due to perceptible ? ashing of leds at lower pwm frequencies. the led current can be controlled at higher frequencies, but the dimming range decreases with increasing pwm frequency, as seen in figure 6. pwm dimming can be used in boost (shown in figure 7), buck mode (shown in figure 8) and buck-boost mode (shown in figure 9). for the typical boost topology, ef? ciency ex- ceeds 80%. buck mode can be used to increase the power handling capability for higher current led applications. a buck-boost led driver works best in applications where the input voltage ? uctuates to higher or lower than the total led voltage drop. in high temperature applications, the leakage of the schottky diode d1 increases, which in turn, discharges the output capacitor during the pwm off time. this results in a smaller effective led dimming ratio. consequently, the dimming range decreases to about 200:1 at 85c. figure 5. led current vs pwm duty cycle wide dimming range (500:1) figure 6. dimming range vs pwm frequency pwm duty cycle (%) 0.1 led current (ma) 1 10 100 1 10 100 3477 f05 0.01 0.1 v in = 5v boost4 leds pwm frequency = 100hz r t = 6.81k pwm frequency (khz) 0.1 1 dimming range: 1 100 1000 1 10 100 3477 f06 10 r t = 6.81k downloaded from: http:///
lt3477 12 3477fc applications information figure 7c. ef? ciency and led current vs pwm duty cycle figure 7b. pwm dimming waveforms 10s/div i led 200ma/div i l 1a/div pwm 5v/div 3477 f07b v in = 5v 4 leds300ma pwm freq = 100hz boost pwm duty cycle (%) 0 75 80 85 80 3477 f07c 7065 20 40 60 100 60 5550 250 300 350 200150 100 500 efficiency (%) v in = 5v boost4 leds, 300ma pwm frequency = 100hz efficiency led current i sn1 i sp1 v in i adj2 i adj1 fbn i sp2 fbp v ref 1m c210f c13.3f v in 5v c1: taiyo yuden emk316bj335ml c2: taiyo yuden udk325bj106mm l1: toko d53lc (pn# a915ay-2rom) d1: zetex zlls1000 d2: diodes inc 1n4148 nmos1: zetex 2n7002 nmos2: fairchild fdg327n led1 to led4: lumileds lxhl-bw02 c c 10nf c ss 33nf 300ma led1led2 led3 led4 3477 f07a 75k 6.81k nmos1 nmos2 out 100k 0 5v 100hz pwm r c 2.4k r sense 0.33 sw l1 2.0h d1 d2 ss gnd lt 3 4 7 7 i sn2 r t shdnv c figure 7a. 5v to 4 white leds: boost with pwm dimming downloaded from: http:///
lt3477 13 3477fc applications information figure 8a. 32v to 6 white leds: buck mode with pwm dimming figure 8b. pwm dimming waveforms 2ms/div i led 500ma/div i l 500ma/div pwm 5v/div 3477 f08b pv in = 32v 6 leds300ma pwm frequency = 100hz buck mode i sn1 i sp1 v in i adj2 i adj1 fbn i sp2 fbp v ref c33.3f c1 2.2f v in 3.3v c1: nippon nts40x5r1h225m c2: taiyo yuden gmk316bj105ml c3: taiyo yuden lmk316bj335kl l1: toko d53lc (pn# a915ay-100m) d1: zetex zlls400 d2: diodes inc 1n4148 nmos1, nm0s2: zetex 2n7002 pmos: siliconix si2303bds led1 to led6: lumileds lxhl-bw02 c c 0.1f c ss 33nf 300ma pmos 3477 f08a 6.81k nmos1 nmos2 100k 0 5v 100hz pwm 280k10k sw d2 ss gnd lt3477 i sn2 r t shdnv c r sense 0.33 pv in 32v l110h led1led6 c2 1f d1 1k 1k ?? ? pwm downloaded from: http:///
lt3477 14 3477fc applications information figure 9b. pwm dimming waveforms figure 9a. 10v to 2 white leds: buck-boost mode with pwm dimming 2ms/div i led 500ma/div i l 1a/div pwm 10v/div 3477 f09b v in = 10v 2 leds300ma pwm frequency = 100hz buck-boost mode 1m 1k1k c210f c13.3f v in 10v 300ma 49.9k l1 4.7h d1 i sn1 i sp1 v in i adj2 i adj1 fbn i sp2 fbp v ref c1: taiyo yuden lmk316bj335ml c2: taiyo yuden udk325bj106mm l1: toko d53lc (pn# a915ay-4r7m) d1: zetex zlls1000 d2: diodes inc 1n4148 nmos1, nmos2: zetex 2n7002 pmos: siliconix si2303bds led1, led2: lumileds lxhl-bw02 c c 10nf c ss 33nf 3477 f09a 6.81k nmos1 100k 0 5v 100hz pwm sw d2 ss gnd lt3477 i sn2 r t shdnv c r c 1.5k r sense 0.33 led2 led1 pwm nmos2 pmos downloaded from: http:///
lt3477 15 3477fc typical applications 800ma, 5v to 12v boost converter with accurate input current limit e f? ciency i sn1 i sp1 v in i adj1 i adj2 i sp2 i sn2 fbn r3200k r423.2k c12.2f v in 5v c310nf c1: taiyo yuden lmk316bj225md c2: avx 1206yd106mat d1: diodes inc. b320a l1: toko fdv0630-4r7m c210f 12v0.8a 3477 ta04a r217.8k sw l1 4.7h r1 0.033 d1 fbp ss gnd lt3477 r t v c shdnv ref shdn c c 4.7nf r c 1k i out (a) 0 efficiency (%) 70 75 80 0.4 0.5 0.6 0.7 0.8 3477 ta04b 6560 50 0.1 0.2 0.3 55 9085 5.5v sepic converter with short-circuit protection ef? ciency i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 r434.8k r3 0.15 r1 0.04 r510k c13.3f v in 3v to 16v c433nf c1: taiyo yuden lmk316bj335ml c2: taiyo yuden lmk325bj106mn c3: taiyo yuden lmk316bj106zl d1: diodes inc. dfls130l l1, l2: toko fdv0630-4r7m c310f c c 4.7nf 5.5v670ma 3477 ta02a r218.2k r c 1k sw l1 4.7h c2 10f l24.7h d1 fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn i out (a) 0 efficiency (%) 85 0.3 3477 ta02b 70 60 0.1 0.2 0.4 5550 9080 75 65 0.5 0.6 0.7 v in = 3v downloaded from: http:///
lt3477 16 3477fc typical applications 87% ef? cient, 4w led driver i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 r2200k c23.3f c13.3f v in 5v c333nf c1: taiyo yuden lmk316bj335ml c2: taiyo yuden tmk325bj335mn d1: diodes inc. dfls120l l1: toko a915ay-100m 330ma led1led2 led3 led4 3477 ta03a r110k r322k r60.3 sw l2 10h r4 0.05 d1 fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn c c 4.7nf r c 1k ef? ciency 1a buck mode high current led driver ef? ciency i out (a) 0 efficiency (%) 70 75 80 0.4 3477 ta01b 6560 50 0.1 0.2 0.3 55 9085 i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 r3280k r410k c12.2f r10.1 c33.3f pv in 32v v in 3.3v c433nf c1: nippon united chemicon nts40x5r1h225m c2: taiyo yuden gmk316bj105ml c3: taiyo yuden lmk316bj475 l1: toko a814ay-330m d1: diodes inc dfls140 3477 ta05a r222k sw l133h 1a ledstring c2 1f d1 led4 led1 ?? ? fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn c c 4.7nf r c 1k led current (a) 0 efficiency (%) 50 60 70 0.6 1 3477 ta05b 40 30 20 0.2 0.4 0.8 80 90 100 downloaded from: http:///
lt3477 17 3477fc typical applications i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 r3200k r1 0.1 r410k c13.3f led brightness control 0mv to 650mv v in 2.7v to 10v c333nf c24.7f c c 10nf c1: taiyo yuden lmk316bj335ml c2: murata grm31cr71e475ka88l d1: diodes, inc. b320a l1: toko fdv0630-4r7m 3477 ta06a r218k sw1 l1 4.7h d1 led1 fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn led2 buck-boost mode led driver ef? ciency i out (a) 0 efficiency (%) 65 70 75 0.6 1.0 3477 ta06b 60 55 50 0.2 0.4 0.8 80 85 90 v in = 8v v in = 4.2v v in (v) i out (a) 2.7 0.57 3.6 0.74 4.2 0.83 5 0.93 8 1.0 downloaded from: http:///
lt3477 18 3477fc package description uf package 20-lead plastic qfn (4mm 4mm) (reference ltc dwg # 05-08-1710) 4.00 0.10 (4 sides) note:1. drawing is proposed to be made a jedec package outline mo-220 variation (wggd-1)?to be approved 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 pin 1top mark (note 6) 0.38 0.10 20 19 12 bottom view?exposed pad 2.45 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 0.50 bsc 0.200 ref 0.00 ? 0.05 (uf20) qfn 10-04 recommended solder pad pitch and dimensions 0.70 0.05 0.25 0.05 0.50 bsc 2.45 0.05 (4 sides) 3.10 0.05 4.50 0.05 packageoutline pin 1 notchr = 0.30 typ downloaded from: http:///
lt3477 19 3477fc information furnished by linear technology corpor ation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technolo gy corporation makes no representa- t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s . package description fe package 20-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663) exposed pad variation cb fe20 (cb) tssop 0204 0.09 ? 0.20 (.0035 ? .0079) 0 ? 8 0.25 ref recommended solder pad layout 0.50 ? 0.75 (.020 ? .030) 4.30 ? 4.50* (.169 ? .177) 134 5 6 7 8910 11 12 14 13 6.40 ? 6.60* (.252 ? .260) 3.86 (.152) 2.74 (.108) 20 1918 17 16 15 1.20 (.047) max 0.05 ? 0.15 (.002 ? .006) 0.65 (.0256) bsc 0.195 ? 0.30 (.0077 ? .0118) typ 2 2.74 (.108) 0.45 0.05 0.65 bsc 4.50 0.10 6.60 0.10 1.05 0.10 3.86 (.152) millimeters (inches) *dimensions do not include mold flash. mold flash shall not exceed 0.150mm (.006") per side note:1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale see note 4 4. recommended minimum pcb metal size for exposed pad attachment 6.40 (.252) bsc downloaded from: http:///
lt3477 20 3477fc linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2005 lt 0309 rev c printed in usa related parts typical application part number description comments lt1618 constant current, constant voltage 1.4mhz, high ef? ciency boost regulator v in : 1.6v to 18v, v out(max) = 5.5v, i q = 2.5ma, i sd < 1a, qfn16 package lt3436 3a (i sw ), 800khz, 34v step-up dc/dc converter v in : 3v to 25v, v out(max) = 34v, i q = 0.9ma, i sd < 6a, tssop16e package ltc ? 3453 synchronous buck-boost high power white led driver v in : 2.7v to 5.5v, v out(max) = 5.5v, i q = 2.5ma, i sd < 1a, qfn16 package lt3466 dual constant current, 2mhz, high ef? ciency white led boost regulator with integrated schottky diode v in : 2.7v to 24v, v out(max) = 40v, i q = 5ma, i sd < 16a, dfn package lt3479 3a, 42v full featured boost/inverter converter with soft-start v in : 2.5v to 24v, v out(max) = 40v, i q = 5ma, i sd < 1a, dfn/tssop packages ltc3490 single cell 350ma, 1.3mhz led driver v in : 1v to 3.2v, v out(max) = 4.7v, i sd < 1a, dfn/so8 packages buck mode high current led driver ef? ciency led current (a) 0 efficiency (%) 50 60 70 0.6 1 3477 ta05b 40 30 20 0.2 0.4 0.8 80 90 100 i sn1 i sp1 v in i adj1 i adj2 fbn i sp2 r3280k r410k c12.2f r10.1 c33.3f pv in 32v v in 3.3v c433nf c1: nippon united chemicon nts40x5r1h225m c2: taiyo yuden gmk316bj105ml c3: taiyo yuden lmk316bj475 l1: toko a814ay-330m d1: diodes inc dfls140 c c 4.7nf 3477 ta07 r222k r c 1k sw l133h 1a ledstring c2 1f d1 led4 led1 ?? ? fbp ss gnd lt3477 i sn2 r t shdnv c v ref shdn downloaded from: http:///

▲Up To Search▲

Price & Availability of LT3477EUFTR

	To Download LT3477EUFTR Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .