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lt3519/lt3519-1/lt3519-2 1 3519fa typical application features applications description led driver with integrated schottky diode the lt ? 3519/lt3519-1/lt3519-2 are ? xed frequency step-up dc/dc converters designed to drive leds. they feature an internal 45v, 750ma low side switch and schottky diode. combining a traditional voltage feedback and a unique rail-to-rail current sense feedback allows these converters to operate as a constant-voltage source or constant-current source. internal compensation simpli? es applications. these devices feature rail-to-rail led current sense pins that provide the most ? exibility in choosing a converter con? guration to drive the leds. the led cur- rent is externally programmable with a sense resistor. the external pwm provides up to 3000:1 pwm dimming and the ctrl input provides analog dimming. l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. true color pwm is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 7199560 and 7321203. 4w boost automotive led driver n up to 3000:1 true color pwm ? dimming n wide input voltage range operation from 3v to 30v transient protection to 40v n rail-to-rail led current sense from 0v to 45v n 45v, 750ma internal switch n internal schottky diode n constant-current and constant-voltage regulation n boost, sepic, buck-boost mode or buck mode topology n open led protection and open led status pin n programmable undervoltage lockout with hysteresis n fixed frequency: 400khz (lt3519), 1mhz (lt3519-1), 2.2mhz (lt3519-2) n internal compensation n ctrl pin provides analog dimming n low shutdown current: <1a n 16-lead msop package n automotive n industrial n constant current source n current limited constant voltage source v in (v) 0 0 led current (ma) 20 40 60 80 100 120 10 20 30 3519 ta01b v in = 6v and above led current vs v in sw v in v ref ctrl shdn /uvlo isp isn fb openled anode lt3519 gnd 68h 1m v in 6v to 30v 243k 137k 100k 1m 1m 29.4k m1 2.49 4.7f 1f 38v led 100ma cathode pwm pwm 3519 ta01a v out
lt3519/lt3519-1/lt3519-2 2 3519fa pin configuration absolute maximum ratings v in , openled (note 3) .............................................40v shdn /uvlo (note 4) ...............................................40v sw, isp , isn, anode, cathode ..............................45v pwm, ctrl ..............................................................10v fb, v ref ......................................................................3v operating junction temperature range (note 2) .................................................. C40c to 125c maximum junction temperature........................... 125c storage temperature range ................... C65c to 125c (note 1) 1 2 3 4 5 6 7 8 gnd openled pwm shdn /uvlo v in sw anode gnd 16 15 14 13 12 11 10 9 gnd v ref ctrl fb isn isp cathode gnd top view ms package 16-lead plastic msop t jmax = 125c, ja = 130c/w parameter conditions min typ max units v in operating voltage range continuous operation (note 3) 3 30 v v in supply current shdn /uvlo = 0v (shutdown) pwm = 0v (idle) pwm > 1.5v, fb = 1.5v (active, not switching) 0.1 2.0 2.5 1 3.0 3.5 a ma ma current sense voltage (v isp -v isn ) isp = 24v isp = 0v l 240 250 250 260 mv mv zero current sense voltage (v isp -v isn ) isp = 24v, ctrl = 100mv l C15 C6 3 mv current sense voltage line regulation 2.5v < isp < 45v 0.02 %/v order information lead free finish tape and reel part marking* package description temperature range lt3519ems#pbf lt3519ems#trpbf 3519 16-lead plastic msop C40c to 125c lt3519ems-1#pbf lt3519ems-1#trpbf 35191 16-lead plastic msop C40c to 125c lt3519ems-2#pbf lt3519ems-2#trpbf 35192 16-lead plastic msop C40c to 125c lt3519ims#pbf lt3519ims#trpbf 3519 16-lead plastic msop C40c to 125c lt3519ims-1#pbf lt3519ims-1#trpbf 35191 16-lead plastic msop C40c to 125c lt3519ims-2#pbf lt3519ims-2#trpbf 35192 16-lead plastic msop C40c to 125c consult ltc marketing for parts speci? ed with wider operating temperature ranges. *the temperature grade is identi? ed by a label on the shipping container. 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/ electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 12v, shdn /uvlo = 12v, ctrl = 2v, pwm = 5v, unless otherwise noted.
lt3519/lt3519-1/lt3519-2 3 3519fa 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. the lt3519e/lt3519e-1/lt3519e-2 are guaranteed to meet speci? ed performance from 0c to 125c junction temperature range. speci? cations over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 12v, shdn /uvlo = 12v, ctrl = 2v, pwm = 5v, unless otherwise noted. statistical process controls. the lt3519i/lt3519i-1/lt3519i-2 are guaranteed to meet performance speci? cations over the C40c to 125c operating junction temperature range. note 3. absolute maximum voltage at v in and openled is 40v for nonrepetitive one second transients and 30v for continuous operation. note 4. for v in below 6v, the shdn /uvlo pin must not exceed v in for proper operation. parameter conditions min typ max units switching frequency 400khz (lt3519) 1mhz (lt3519-1) 2.2mhz (lt3519-2) l l l 320 0.80 1.9 400 1 2.2 440 1.10 2.4 khz mhz mhz maximum duty cycle 400khz (lt3519) 1mhz (lt3519-1) 2.2mhz (lt3519-2) l l l 94 86 72 97 93 83 % % % switch current limit l 750 980 1150 ma switch v cesat i sw = 500ma 300 mv switch leakage current sw = 45v, pwm = 0v 2 a ctrl for full-scale led current 1.2 v ctrl pin bias current current out of pin, ctrl = 0.1v 50 100 na pwm input high voltage l 1.5 v pwm input low voltage l 0.8 v pwm pin resistance to gnd 70 k fb regulation voltage (v fb ) l 1.190 1.220 1.250 v fb pin threshold voltage for openled falling v fb C 70mv v fb C 60mv v fb C 50mv v fb pin bias current current out of pin, fb = 1v 60 120 na isp , isn idle input bias current pwm = 0v, isp = isn = 24v 1 a isp , isn active input bias current isp = isn = 24v, current per pin 17 a schottky forward drop i schottky = 500ma 0.8 v schottky leakage current cathode = 24v, anode = 0v 4 a shdn /uvlo threshold voltage falling l 1.180 1.220 1.270 v shdn /uvlo input low voltage i vin drops below 1a 0.4 v shdn /uvlo pin bias current low shdn /uvlo = 1.15v 1.8 2.2 2.6 a shdn /uvlo pin bias current high shdn /uvlo = 1.30v 10 100 na v ref output voltage C100a i vref 0a l 1.96 2 2.04 v v ref output pin regulation 3v < v in < 40v 0.04 %/v openled output low (v ol )i openled = 1ma 240 mv openled leakage current fb = 0v, openled = 40v 1 a
lt3519/lt3519-1/lt3519-2 4 3519fa typical performance characteristics v isp -v isn threshold vs v ctrl switch current limit vs duty cycle v ref voltage vs temperature v isp- v isn threshold vs temperature switch current limit vs temperature oscillator frequency vs temperature (lt3519) v isp- v isn threshold vs v isp v ref voltage vs v in quiescent current vs v in v ctrl (v) 0 200 250 300 3519 g01 150 100 0.5 1.0 1.5 2.0 50 0 C50 v isp -v isn threshold (mv) v in = 12v v isp = 24v temperature (c) C50 v ref (v) 2.00 2.02 125 3519 g03 1.98 1.96 0 50 100 C25 25 75 2.04 1.99 2.01 1.97 2.03 v in = 12v temperature (c) C50 240 v isp -v isn threhsold (mv) 242 246 248 250 260 254 0 50 75 3519 g04 244 256 258 252 C25 25 100 125 v in = 12v v isp = 24v v ctrl = 2v temperature (c) C50 600 switch current limit (ma) 700 800 900 1000 050 100 125 3519 g05 1100 1200 C25 25 75 v in = 12v v isp (v) 0 v isp -v isn threshold (mv) 252 256 260 40 3519 g07 248 244 250 254 258 246 242 240 10 20 30 50 v in = 12v v ctrl = 2v v in (v) 0 v ref (v) 2.00 2.02 40 3519 g08 1.98 1.96 10 20 30 5 15 25 35 2.04 1.99 2.01 1.97 2.03 v in (v) 0 0 v in current (ma) 0.5 1.0 1.5 2.0 2.5 3.0 10 20 30 40 3519 g09 v pwm = 5v v fb = 1.5v duty cycle (%) 0 600 switch current limit (ma) 700 800 900 1000 1100 1200 25 50 75 100 3519 g02 temperature (c) C50 frequency (khz) 400 410 420 25 75 3519 g06 390 380 C25 0 50 100 125 370 360 (t a = 25c unless otherwise noted)
lt3519/lt3519-1/lt3519-2 5 3519fa fb regulation voltage vs temperature fb openled threshold vs temperature shdn /uvlo threshold vs temperature switch saturation voltage (v cesat ) schottky leakage current vs temperature schottky forward voltage drop temperature (c) C50 v fb (v) 1.23 1.24 1.25 25 75 125 3519 g10 1.22 1.21 1.20 C25 0 50 100 v in = 12v temperature (c) C50 0 v fb -v fb_ openled (mv) 10 30 40 50 100 70 0 50 75 3519 g11 20 80 90 60 C25 25 100 125 v in = 12v temperature (c) C50 shdn /uvlo threshld (v) 1.26 1.28 1.30 25 75 125 3519 g12 1.24 1.22 1.20 C25 0 50 100 v in = 12v shdn /uvlo rising shdn /uvlo falling switch current (ma) 0 switch voltage (v) 300 400 500 800 3519 g13 200 100 250 350 450 150 50 0 200 400 600 1000 temperature (c) C50 0 schottky leakage current (a) 1 3 4 5 10 7 0 50 75 3519 g14 2 8 9 6 C25 25 100 125 v r = 24v schottky forward voltage drop (mv) 0 0 schottky forward current (ma) 100 300 400 500 400 800 1000 900 3519 g15 200 200 600 600 700 800 typical performance characteristics (t a = 25c unless otherwise noted) oscillator frequency vs temperature (lt3519-1) oscillator frequency vs temperature (lt3519-2) temperature (c) C50 0.7 frequency (mhz) 0.8 50 100 125 1.2 3519 g16 25 0 C25 75 0.9 1.0 1.1 temperature (c) C50 1.9 frequency (mhz) 2.0 50 100 125 2.5 3519 g17 25 0 C25 75 2.1 2.3 2.2 2.4
lt3519/lt3519-1/lt3519-2 6 3519fa pin functions gnd (pins 1, 8, 9, 16): power ground and signal ground. tie to gnd plane for best thermal performance. openled (pin 2): open led status pin. the openled pin asserts if the fb input is greater than the fb regulation threshold minus 60mv (typical). the pin must have an external pull-up resistor to function. when the pwm input is low and the converter is idle, the openled condition is latched to the last valid state when the pwm input was high. when the pwm input goes high again, the openled pin will be updated. this pin may be used to report an open led fault. pwm (pin 3): pulse width modulated input. a signal low disables the oscillator and turns off the main switch. pwm has an internal pull-down resistor. tie pwm pin to v ref if not used. shdn /uvlo (pin 4): shutdown and undervoltage lockout pin. an accurate 1.22v falling threshold with externally programmable hysteresis detects when power is okay to enable switching. rising hysteresis is generated by the external resistor divider and an accurate internal 2.2a pull-down current. above the 1.25v (nominal) rising threshold (but below 6v), shdn /uvlo input bias current is sub-a. below the falling threshold, a 2.2a pull-down current is enabled so the user can de? ne the hysteresis with external resistor selection. tie to 0.4v or less to dis- able device and reduce v in quiescent current below 1a. pin may be tied to v in , but do not tie it to a voltage higher than v in if v in is less than 6v. v in (pin 5): input supply pin. this pin must be locally bypassed with a 1f ceramic capacitor (or larger) placed close to it. sw (pin 6): switch pin. connect the inductor at this pin. minimize the trace at this pin to reduce emi. anode (pin 7): internal schottky anode pin. cathode (pin 10): internal schottky cathode pin. isp (pin 11): current sense resistor positive pin. this input is the noninverting input of the internal current sense ampli? er. input bias current increases with v isp Cv isn increase. isn (pin 12): current sense resistor negative pin. this input is the inverting input of the internal current sense ampli? er. fb (pin 13): voltage loop feedback pin. it is used to connect to output resistor divider for constant voltage regulation or open led protection. the internal trans- conductance ampli? er will regulate fb to 1.22v (nominal) through the dc/dc converter. if the fb input is regulating the loop, the openled pull-down is asserted. this action may signal an open led fault. do not leave the fb pin open. if not used, connect to gnd. ctrl (pin 14): current sense threshold voltage adjust- ment pin. this pin sets the threshold voltage across the sense resistor between isp and isn. connect directly to the v ref pin or a voltage above 1.2v for full-scale thresh- old of 250mv, or use a voltage between 0.1v and 1.0v to linearly adjust the threshold. a voltage between 1.0v and 1.2v transitions to the full-scale threshold. tie ctrl pin to the v ref pin if not used. v ref (pin 15): reference output pin. typically 2v. this pin can supply up to 100a.
lt3519/lt3519-1/lt3519-2 7 3519fa block diagram C + + C + C + + + C + + C a1 C + a4 1.1v 1.22v 1.22v C + 1.16v fb gnd 1, 8, 9, 16 openled 2v 2.2a q3 ctrl 100mv isp r sense led array isn s 4 a2 a3 r c r s 3519 bd c c c out c in error amplifier pwm comparator 11 14 fb 13 shdn /uvlo 4 v in v ref 15 2 12 pwm pwm 3 cathode d1 10 anode 7 sw v in v in l1 6 5 g1 g3 main switch driver s rq bandgap and bias g4 v in 140a C + q2 C + ramp generator oscillator a5 q1 main switch a6 g2 q4 r1 r2 92k i q4 note: the maximum allowed q4 collector current i q4 is 2ma.
lt3519/lt3519-1/lt3519-2 8 3519fa operation the lt3519/lt3519-1/lt3519-2 are constant frequency, current mode regulators with an internal power switch and schottky. operation can be best understood by referring to the block diagram. at the start of each oscillator cycle, the sr latch is set, which turns on the q1 power switch. a voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the pwm comparator, a4. when this voltage exceeds the level at the negative input of a4, the sr latch is reset, turning off the power switch. the level at the negative input of a4 is set by the error ampli? er a3. a3 has two inputs, one from the voltage feedback loop and the other one from the current loop. whichever feedback input is lower takes precedence to set the v c node voltage, and forces the converter into either a constant-current or a constant-voltage mode. the lt3519/lt3519-1/lt3519-2 are designed to transi- tion cleanly between these two modes of operation. the current sense ampli? er senses the voltage across r sense and provides an 4 pre-gain to ampli? er a1. the output of a1 is simply an ampli? ed version of the difference be- tween the voltage across r sense and the lower of v ctrl or 1.1v. in this manner, the error ampli? er sets the correct peak switch current level to regulate the current through r sense . if the error ampli? ers output increases, more current is delivered to the output; if it decreases, less current is delivered. the current regulated in r sense can be adjusted by changing the input voltage v ctrl . the fb voltage loop is implemented by the ampli? er a2. when the voltage loop dominates, the v c node voltage is set by the ampli? ed difference of the internal reference of 1.22v and the fb pin. if fb voltage is lower than the reference voltage, the switch current will increase; if fb voltage is higher than the reference voltage, the switch demand current will decrease. the led current sense feedback interacts with the fb voltage feedback so that fb will not exceed the internal reference and the voltage between isp and isn will not exceed the threshold set by the ctrl pin. for accurate current or voltage regulation, it is necessary to be sure that under normal operating conditions the appropriate loop is dominant. to deactivate the voltage loop entirely, fb can be connected to gnd. to deactivate the led current loop entirely, the isp and isn should be tied together and the ctrl input tied to v ref . when the fb input exceeds a voltage about 60mv lower than the fb regulation voltage, the pull-down driver on the openled pin is activated. this function provides a status indicator that the load may be disconnected and the constant-voltage feedback loop is taking control of the switching regulator. dimming of the led array is accomplished by pulsing the current using the pwm pin. when the pwm pin is low, switching is disabled and the error ampli? er is turned off so that it does not drive the v c node. also, all internal loads on the v c node are disabled so that the charge state of the v c node will be saved on the internal compensation capacitor. this feature reduces transient recovery time. when the pwm input again transitions high, the demand current for the switch returns to the value just before pwm last transitioned low. to further reduce transient recovery time, an external mosfet should be used to disconnect the led array current loop when pwm is low, stopping c out from discharging.
lt3519/lt3519-1/lt3519-2 9 3519fa dimming control there are two methods to control the current source for dimming using the lt3519/lt3519-1/lt3519-2. the ? rst method, pwm dimming, uses the pwm pin to modulate the current source between zero and full current to achieve a precisely programmed average current. to make this method of current control more accurate, the switch de- mand current is stored on the internal v c node during the quiescent phase when pwm is low. this feature minimizes recovery time when the pwm signal goes high. to obtain best pwm dimming performance, it is necessary to use an external disconnect switch in the led current path to prevent the output capacitor from discharging during the pwm signal low phase. for best product of analog and pwm dimming, the minimum pwm low or high time should be at least six switching cycles (3s for f sw = 2mhz). maximum pwm period is determined by the system. the maximum pwm dimming ratio (pwm ratio ) can be calculated from the maximum pwm period (t max ) and the minimum pwm pulse width (t min ) as follows: pwm ratio = t max t min example: t max = 9ms, t min = 3s (f sw = 2mhz) pwm ratio = 9ms 3s = 3000:1 the second method of dimming control, analog dim- ming, uses the ctrl pin to linearly adjust the current sense threshold during the pwm high state. when the ctrl pin voltage is less than 1v but more than 100mv, the led current is: i led = v ctrl ? 100mv 4?r sense when v ctrl is higher than 1.2v, the led current is clamped to be: i led = 250mv r sense when v ctrl is more than 1v but less than 1.2v, the led current is in the nonlinear region of v isp -v isn threshold vs v ctrl as shown in the typical performance characteristics. the led current programming feature through the ctrl pin possibly increases the total dimming range by a factor of ten. in order to have the accurate led current, precision resistors are preferred (1% is recommended). the ctrl pin should not be left open. tie to v ref if not used. programming output voltage (constant voltage regulation) or open led/overvoltage threshold for a boost application, the output voltage can be set by selecting the values of r1 and r2 (see figure 1) according to the following equation: v out = r1 r2 + 1 ? ? ? ? ? ? ? 1.22v applications information r1 v out r2 3519 f01 lt3519/ lt3519-1/ lt3519-2 fb figure 1. fb resistor divider for boost led driver
lt3519/lt3519-1/lt3519-2 10 3519fa applications information for open led protection of a boost type led driver, set the resistor from the output to the fb pin such that the expected v fb during normal operation will not exceed 1.1v. for a buck mode or buck-boost mode led driver, the output voltage is typically level-shifted to a signal with respect to gnd as illustrated in figure 2. the open led voltage level can be expressed as: v out = v be(q1) + r1 r2 ? 1.22v programming the turn-on and turn-off thresholds with the shdn /uvlo pin the falling shdn /uvlo value can be accurately set by the resistor divider. a small 2.2a pull-down current is active when shdn /uvlo is below the 1.22v threshold. the purpose of this current is to allow the user to program the rising hysteresis. the following equations should be used to determine the values of the resistors: v in(falling) = r1 + r2 r2 ? 1.22v v in(rising) = 2.2a ? r1 + v in(falling) r1 r sense(ext) led array v out r2 100k C + 3519 f02 fb q1 lt3519/ lt3519-1/ lt3519-2 figure 2. open led protection fb resistor connector for buck mode or buck-boost mode led driver r1 v in r2 3519 f03 lt3519/ lt3519-1/ lt3519-2 shdn /uvlo figure 3. shdn /uvlo threshold programming
lt3519/lt3519-1/lt3519-2 11 3519fa applications information esl and have an adequate ripple current rating. a 2.2f ceramic type capacitor is usually suf? cient for lt3519 (400khz version). a capacitor of proportionately less value for lt3519-1/lt3519-2 (higher frequency version) can be used. output capacitor selection the selection of output capacitor depends on the load and converter con? guration, i.e., step-up or step-down and the operating frequency. for led applications, the equivalent resistance of the led is typically low, and the output ? lter capacitor should be sized to attenuate the current ripple. to achieve the same led ripple current, the required ? lter capacitor value is larger in the boost and buck-boost mode applications than that in the buck mode applications. lower operating frequencies will require proportionately higher capacitor values. for led buck mode applications, a 1f ceramic capacitor is usually suf? cient. for the led boost and buck-boost mode applications, a 2.2f ceramic ca- pacitor is usually suf? cient. very high performance pwm dimming applications may require a larger capacitor value to support the led voltage during pwm transitions. use only ceramic capacitors with x7r, x5r or better dielec- tric as they are best for temperature and dc bias stability of the capacitor value. all ceramic capacitors exhibit loss of capacitance value with increasing dc voltage bias, so it may be necessary to choose a higher value capacitor to get the required capacitance at the operation voltage. always check that the voltage rating of the capacitor is suf? cient. table 2. recommended ceramic capacitor vendors vendor phone web tdk (516)535-2600 www.tdk.com kemet (408)986-0424 www.kemet.com murata (814)237-1431 www.murata.com taiyo yuden (408)573-4150 www.t-yuden.com inductor selection the inductor used with the lt3519/lt3519-1/lt3519-2 should have a saturation current rating of 1a or greater. for buck mode led drivers, the inductor value should be chosen to give a ripple current 150ma or more. in the buck mode, the inductor value can be estimated using the formula: lh () = d buck ?v in ?v led () f osc (mhz) ? 0.15a h ? a ? mhz v ? ? ? ? ? ? d buck = v led v in v led is the voltage across the led string, v in is the input voltage to the converter, and f osc is the switching frequency. in the boost con? guration, the inductor can be estimated using the formula: lh () = d boost ?v in f osc (mhz) ? 0.15a h ? a ? mhz v ? ? ? ? ? ? d boost = v led ?v in () v led table 1. recommended inductor vendors vendor phone web sumida (408)321-9660 www.sumida.com toko (408)432-8281 www.toko.com cooper (561)998-4100 www.cooperet.com vishay (402)563-6866 www.vishay.com input capacitor selection for proper operation, it is necessary to place a bypass capacitor to gnd close to the v in pin of the lt3519/ lt3519-1/lt3519-2. a 1f or greater capacitor with low esr should be used. a ceramic capacitor is usually the best choice. in the buck mode con? guration, the capacitor at the input to the power converter has large pulsed currents. for best reliability, this capacitor should have low esr and
lt3519/lt3519-1/lt3519-2 12 3519fa applications information open led detection the lt3519/lt3519-1/lt3519-2 provide an open-collector status pin, openled , that pulls low when the fb pin is within ~60mv of its 1.22v regulated voltage. if the open led clamp voltage is programmed correctly using the fb pin, then the fb pin should never exceed 1.1v when leds are connected, therefore, the only way for the fb pin to be within 60mv of the 1.22v regulation voltage is for an open led event to have occurred. inrush current the lt3519/lt3519-1/lt3519-2 have a built-in schottky diode for a boost converter. when supply voltage is ap- plied to v in pin, the voltage difference between v in and v out generates inrush current ? owing from input through the inductor and the schottky diode to charge the output capacitor. the selection of inductor and capacitor value should ensure the peak of the inrush current to below 10a. in addition, the lt3519/lt3519-1/lt3519-2 turn-on should be delayed until the inrush current is less than the maximum current limit. if the peak of the inrush current is more than 10a, an external schottky diode should be used to bypass both the inductor and internal schottky. the recommended schottky diodes for hot plug are shown on table 3. table 3. schottky diodes recommended for hot plug vendor part number v r (v) i ave (a) diodes, inc dfls160 60 1 zetex zlls10000ta 40 1 international recti? er 10mq060n 60 1.5 board layout as with all switching regulators, careful attention must be paid to the pcb board layout and component placement. to prevent electromagnetic interference (emi) problems, proper layout of high frequency switching paths (see figure 4) is essential. minimize the length and area of all traces connected to the switching node pin (sw). keep the sense voltage pins (isp and isn) away from the switching node. the bypass capacitor on the v in supply to the lt3519 should be placed as close as possible to the v in pin and gnd. likewise, place c out next to the cathode pin. do not extensively route high impedance signals such as fb and ctrl, as they may pick up switching noise. figure 5 shows the recommended component placement. + load v out 3519 f04 v in d1 sw l1 figure 4. high frequency path gnd openled pwm shdn /uvlo v in sw anode gnd gnd v ref ctrl fb isn isp cathode gnd gnd v in v out r s c out c in l1 3519 f05 figure 5. suggested layout
lt3519/lt3519-1/lt3519-2 13 3519fa 4w boost automotive led driver 1000:1 pwm dimming at 120hz ef? ciency vs v in typical applications sw v in v ref ctrl shdn /uvlo isp isn fb openled anode lt3519 gnd l1 68h 1m v in 6v to 30v 243k 137k 100k 1m 1m 29.4k r sense 2.49 m1 c2 4.7f c1 1f 38v led 100ma c1: tdk c3216x7r1h105k c2: murata grm32er71h475ka88 l1: coiltronics dr74-680-r m1: vishay siliconix si2308ds r sense : stackpole electronics rhc 2512 2.49 note: v in = 8.2v rising turn on v in = 6.2v falling uvlo v in > 10v full led current and foldback below v out 42.7v overvoltage protection cathode pwm pwm 3519 ta02a v out 5v pwm 5v/div i led 0.1a/div i l 0.3a/div 2s/div 3519 ta02b v in = 12v v in (v) 6 84 efficiency (%) 86 88 90 92 94 10 14 18 22 3519 ta02c 26 30
lt3519/lt3519-1/lt3519-2 14 3519fa typical applications buck-boost mode 150ma led driver waveform for open led ef? ciency vs v in v in sw l1 47h r sense 1.65 v out 16v led 150ma v ref pwm ctrl 357k 24.3k 3519 ta03a 10k cathode shdn /uvlo isn isp fb openled lt3519 gnd 1m 1m 210k 100k 243k v in 6v to 24v c1 1f anode c2 1f c3 4.7f q1 c1: tdk c3216x7r1h105k c2: tdk c3216x7r1h105k c3: tdk c3216x7r1e475k l1: coiltronics dr73-470-r q1: diodes fmmt555 pnp note: v in = 8.2v rising turn on v in = 6.2v falling uvlo v in > 7v full led current and foldback below v out C v in 18.5v overvoltage protection v out 10v/div i led 0.1a/div openled 10v/div 50s/div 3519 ta03b v in = 12v v in (v) 6 efficiency (%) 72 74 76 15 21 3519 ta03c 70 68 66 912 18 78 80 82 24
lt3519/lt3519-1/lt3519-2 15 3519fa typical applications buck mode 500ma led driver 2000:1 pwm dimming at 120hz ef? ciency vs v in sw anode fb v in v ref ctrl shdn /uvlo isp shdn isn openled lt3519 gnd 1m 191k 100k 1m v in 12v to 30v (up to 40v transient) r sense 0.5 m1 v out c2 10f c1 4.7f 9v led 500ma cathode pwm pwm 3519 ta04a 1k 14.7k 10k 1.5k 130k q2 l1 47h q1 c1: murata grm32er71h475ka88 c2: tdk c3216x7r1c106m q1: diodes fmmt555 pnp q2: diodes fmmt494 npn l1: coiltronics dr73-470-r m1: vishay siliconix si2337ds 5v v in (v) 12 80 efficiency (%) 82 84 86 88 90 15 18 24 21 27 3519 ta04c 30 pwm 5v/div i led 0.5a/div i l 0.3a/div 1s/div 3519 ta04b v in = 20v
lt3519/lt3519-1/lt3519-2 16 3519fa typical applications boost 150ma led driver 3000:1 pwm dimming at 120hz ef? ciency vs v in i led 0.15a/div i l 0.5a/div pwm 5v/div 0.5s/div 3519 ta05b v in = 12v v in (v) 6 82 efficiency (%) 84 86 88 90 92 94 10 81216 14 18 3519 ta05c 20 sw l1 15h v ref ctrl shdn /uvlo isp isn fb openled lt3519-1 gnd 1m 243k 137k 100k 1m v in 6v to 20v r sense 1.65 v out m1 c2 2.2f c1 1f 24v led 150ma ? ? ? anode pwm pwm 3519 ta05a 40k 1m c1: tdk c3216x7r1h105k c2: murata grm31cr71h225ka88 l1: coiltronics dr74-150-r m1: vishay siliconix si2318ds r sense : stackpole electronics rhc 2512 2.49 and 4.99 note: v in = 8.2v rising turn-on v in = 6.2v falling uvlo v in > 10v full led current and foldback below v out = 31.7v overvoltage protection 5v cathode v in
lt3519/lt3519-1/lt3519-2 17 3519fa typical applications minimum bom buck mode 500ma led driver waveforms for open led ef? ciency vs v in v in C v out 5v/div openled 10v/div i led 0.5a/div 25s/div 3519 ta06b v in = 15v v in (v) 10 70 efficiency (%) 74 72 76 78 80 82 84 13 19 16 22 3519 ta06c 25 sw anode fb v in v ref ctrl pwm shdn /uvlo isp isn openled lt3519-2 gnd 140k 100k 1m v in 10v to 25v 0.5 v out c2 1f c1 2.2f 6v led 500ma cathode 3519 ta06a 23.2k 10k 130k l1 6.8h q1 c1: tdk c3216x7r1e225k c2: tdk c1608x7r1c105k q1: diodes fmmt555 pnp l1: coiltronics dr73-068-r
lt3519/lt3519-1/lt3519-2 18 3519fa package description ms package 16-lead plastic msop (reference ltc dwg # 05-08-1669 rev ?) msop (ms16) 1107 rev ? 0.53 p 0.152 (.021 p .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 C?0.27 (.007 C .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 16151413121110 12345678 9 note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.254 (.010) 0 o C 6 o typ detail a detail a gauge plane 5.23 (.206) min 3.20 C 3.45 (.126 C .136) 0.889 p 0.127 (.035 p .005) recommended solder pad layout 0.305 p 0.038 (.0120 p .0015) typ 0.50 (.0197) bsc 4.039 p 0.102 (.159 p .004) (note 3) 0.1016 p 0.0508 (.004 p .002) 3.00 p 0.102 (.118 p .004) (note 4) 0.280 p 0.076 (.011 p .003) ref 4.90 p 0.152 (.193 p .006)
lt3519/lt3519-1/lt3519-2 19 3519fa 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 nov 09 updated to add lt3519-1 and lt3519-2 parts 1-20
lt3519/lt3519-1/lt3519-2 20 3519fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2009 lt 1109 rev a ? printed in usa related parts typical applications sepic 150ma led driver waveforms for led shorted to ground ef? ciency vs v in part number description comments lt1618 constant-current, constant-voltage 1.24mhz, high ef? ciency boost regulator up to 16 white leds, v in : 1.6v to 18v, v out(max) = 34v, i q = 1.8ma, i sd < 1a, ms package lt3466/lt3466-1 dual full function, 2mhz diodes white led step-up converter with built-in schottkys up to 20 white leds, v in : 2.7v to 24v, v out(max) = 39v, dfn/tssop-16 packages lt3486 dual 1.3a white led converter with 1000:1 true color pwm dimming drives up to 16 100ma white leds. v in : 2.5v to 24v, v out(max) = 36v, dfn/tssop packages lt3491 2.3mhz white led driver with integrated schottky diode drives up to 6 leds. v in : 2.5v to 12v, v out(max) = 27v, sc70/dfn packages lt3497 dual full function 2.3mhz led driver with 250:1 true color pwm dimming with integrated schottky diodes drives up to 12 leds. v in : 2.5v to 10v, v out(max) = 32v, 3mm 2mm dfn package lt3517 full-featured led driver with 1.5a switch current v in : 3v to 40v, v out(max) = 45v, dimming = 5.000:1 true color pwm, i sd < 1a, 4mm 4mm qfn and tssop packages lt3518 full-featured led driver with 2.3a switch current v in : 3v to 40v, v out(max) = 45v, dimming = 3.000:1 true color pwm, i sd < 1a, 4mm 4mm qfn and tssop packages lt3591 constant-current, 1mhz, high ef? ciency white led step-up converter with built-in schottkys up to 10 white leds, v in : 2.5v to 12v, v out(max) = 45v, 3mm 2mm dfn package sw v in v ref ctrl shdn /uvlo isp isn fb openled anode lt3519 gnd l1a 68h c3 2.2f 1m v in 4v to 24v 432k 158k 100k 1m 1m 69.8k m1 r sense 1.65 c2 4.7f c1 1f 16v led 150ma cathode pwm pwm 3519 ta07a ? l1b 68h ? c1: tdk c3216x7r1h105k c2: tdk c3216x7r1e475k c3: tdk c3216x7r1e225k l1: coiltronics drq74-680-r (coupled inductor) m1: vishay siliconix si2318ds note: v in = 6v rising turn on v in = 4v falling uvlo v in > 9v full led current and foldback below v out 18.5v overvoltage protection v out 5v i led 0.1a/div i led_shorted 0.5a/div i l1a +i l1b 0.2a/div 50s/div 3519 ta07b v in = 12v v in (v) 4 84 86 88 20 3519 ta07c 82 80 81216 24 78 76 74 efficiency (%)

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