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lt3496 1 3496ff features applications description triple output led driver the lt ? 3496 is a triple output dc/dc converter designed to operate as a constant-current source and is ideal for driving leds. the lt3496 works in buck, boost or buck- boost mode. the lt3496 uses a fixed frequency, current mode architecture resulting in stable operation over a wide range of supply and output voltages. a frequency adjust pin allows the user to program switching frequency between 330khz and 2.1mhz to optimize efficiency and external component size. the lt3496 supports 3000:1 dimming control on each channel. each of the three regulators is independently operated by that channels pwm signal. the pwm feature allows precise adjustment of the color mixing or dimming ratio of the led source. each of the three channels has a built-in gate driver to drive an external led-disconnect p-channel mosfet, allowing high dimming range. the output current range of each channel of the lt3496 is programmed with an external sense resistor. the ctrl pins are used to adjust the led currents either for analog dimming or overtemperature protection. l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks and thinsot and true color pwm are trademarks of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 7199560, 7321203, and others pending. n true color pwm? dimming delivers up to 3000:1 dimming ratio n built-in gate driver for pmos led disconnect n three independent driver channels with 750ma, 45v internal switches n operates in buck, boost, buck-boost modes n ctrl pin accurately sets led current sense threshold over a range of 10mv to 100mv n adjustable frequency: 330khz to 2.1mhz n open led protection n wide v in supply range: operation from 3v to 30v transient protection to 40v n surface mount components n 28-lead (4mm 5mm) qfn and tssop packages n rgb lighting n billboards and large displays n automotive and avionic lighting n constant-current sources high dimming ratio triple output led power supply 3000:1 pwm dimming at 120hz typical application pwm 5v/div 0.5s/div 3496 ta01b i led 0.5a/div i l 0.5a/div 0.5a 0.47f 0.47f led1 200m 200m tg1 pv in 42v 7 leds 18h cap1 0.5a led2 tg2 18h cap2 0.5a 0.47f led3 1f 3 200m 470pf 3496 ta01a tg3 18h cap3 sw1 sw2 lt3496 gnd sw3 tg1, tg2, tg3 vc1, vc2, vc3 v ref ctrl1, ctrl2, ctrl3 f adj ovp1, ovp2, ovp3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm1, pwm2, pwm3 shdn v in 3v to 24v 1f 22k downloaded from: http:///
lt3496 2 3496ff absolute maximum ratings v in (note 4) ...............................................................40v sw1, sw2, sw3, led1, led2, led3, cap1, cap2, cap3....................................................45v tg1, tg2, tg3 .................................... cap C 10v to cap pwm1, pwm2, pwm3 ..............................................20v v ref , ctrl1, ctrl2, ctrl3, f adj , vc1, vc2, vc3, ovp1, ovp2, ovp3 ..................................................2.5v shdn (note 4) ...........................................................v in (note 1) pin configuration 12 3 4 5 6 7 8 9 1011 12 13 14 top view fe package 28-lead plastic tssop 2827 26 25 24 23 22 21 20 19 18 17 16 15 shdn pwm3pwm2 pwm1 v ref ctrl3ctrl2 ctrl1 f adj vc3vc2 vc1 ovp3ovp2 v in tg3led3 cap3 sw3 sw2 cap2 led2 tg2 sw1 cap1 led1 tg1 ovp1 29 ja = 30c/w, jc = 10c/w exposed pad (pin 29) is gnd, must be soldered to pcb 9 10 top view 29 ufd package 28-lead (4mm 5mm) plastic qfn 11 12 13 28 27 26 25 24 14 23 6 5 4 3 2 1 pwm1 v ref ctrl3ctrl2 ctrl1 f adj vc3vc2 cap3sw3 sw2 cap2 led2 tg2 sw1 cap1 pwm2pwm3 shdn v in tg3led3 vc1 ovp3ovp2 ovp1 tg1 led1 7 17 18 19 20 21 2216 8 15 ja = 34c/w, jc = 2.7c/w exposed pad (pin 29) is gnd, must be soldered to pcb lead free finish tape and reel part marking* package description temperature range lt3496efe#pbf lt3496efe#trpbf 3496fe 28-lead plastic tssop C40c to 125c lt3496ife#pbf lt3496ife#trpbf 3496fe 28-lead plastic tssop C40c to 125c lt3496eufd#pbf lt3496eufd#trpbf 3496 28-lead (4mm 5mm) plastic qfn C40c to 125c lt3496iufd#pbf lt3496iufd#trpbf 3496 28-lead (4mm 5mm) plastic qfn C40c to 125c lt3496hufd#pbf lt3496hufd#trpbf 3496 28-lead (4mm 5mm) plastic qfn C40c to 150c consult ltc marketing for parts specified with wide r operating temperature ranges. *the temperature gr ade is identified by a label on the shipping contai ner. consult ltc marketing for information on non-standard 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/ order information operating junction temperature range (notes 2, 6) lt3496e ............................................ C40c to 125c lt3496i ............................................. C40c to 125c lt3496h ............................................ C40c to 150c storage temperature range qfn .................................................... C65c to 150c tssop ................................................. 65c to 125c lead temperature (soldering, 10 sec) tssop .............................................................. 300c downloaded from: http:///
lt3496 3 3496ff the l denotes the specifications which apply over the fu ll operating temperature range, otherwise specifications are at t a = 25c. v in = 5v, v shdn = 5v, cap1, cap2, cap3 = 5v, pwm1, pwm2, pwm3 = 5v , f adj = 0.5v, ctrl1, ctrl2, ctrl3 = 1.5v, ovp1, ovp2, ov p3 = 0v, unless otherwise noted. electrical characteristics parameter conditions min typ max units v in operation voltage (note 4) 3 30 v v in undervoltage lockout 2.1 2.4 v full-scale led current sense voltage (v cap1-led1 , v cap2-led2 , v cap3-led3 ) cap1, cap2, cap3 = 24v l 98 97 100 103 104 mv mv one-tenth scale led current sense voltage (v cap1-led1 , v cap2-led2 , v cap3-led3 ) ctrl1, ctrl2, ctrl3 = 100mv, cap1, cap2, cap3 = 24v h-grade e-grade, i-grade l l 7.5 7.5 10 10 13.5 12.5 mv mv cap1, cap2, cap3 operating voltage 0v v cap1-led1 104mv 0v v cap2-led2 104mv 0v v cap3-led3 104mv 2.5 45 v v ref output voltage i ref = 200a, current out of pin l 1.96 2 2.04 v v ref line regulation 3v v in 40v, i ref = 10a 0.03 %/v quiescent current in shutdown shdn = 0v 0.1 10 a quiescent current idle pwm1, pwm2, pwm3 = 0v 6 7.5 ma quiescent current active (not switching) 11 14 ma switching frequency f adj = 1.5v f adj = 0.5v f adj = 0.1v 1900 2100 1300 330 2300 khz khz khz maximum duty cycle f adj = 1.5v (2.1mhz) f adj = 0.5v (1.3mhz) f adj = 0.1v (330khz) l 70 78 87 97 % % % ctrl1, ctrl2, ctrl3 input bias current current out of pin, ctrl1, ctrl2, ctrl3 = 0.1v 20 100 na f adj input bias current current out of pin, f adj = 0.1v 20 100 na ovp1, ovp2, ovp3 input bias current current out of pin, ovp1, ovp2, ovp3 = 0.1v 10 100 na ovp1, ovp2, ovp3 threshold 0.95 1 1.05 v vc1, vc2, vc3 idle input bias current pwm1, pwm2, pwm3 = 0v ?20 0 20 na vc1, vc2, vc3 output impedance cap1, cap2, cap3 = 24v 10 m eamp g m ( i vc / v cap-led ) cap1, cap2, cap3 = 24v 200 s sw1, sw2, sw3 current limit (note 3) 750 1000 1250 ma sw1, sw2, sw3 v cesat i sw = 500ma (note 3) 260 mv sw1, sw2, sw3 leakage current shdn = 0v, sw = 5v 2 a cap1, cap2, cap3 input bias current 180 250 a cap1, cap2, cap3, led1, led2, led3 idle input bias current pwm1, pwm2, pwm3 = 0v 1 a cap1, cap2, cap3, led1, led2, led3 input bias current in shutdown shdn = 0v 1 a downloaded from: http:///
lt3496 4 3496ff the l denotes the specifications which apply over the fu ll operating temperature range, otherwise specifications are at t a = 25c. v in = 5v, v shdn = 5v, cap1, cap2, cap3 = 5v, pwm1, pwm2, pwm3 = 5v , f adj = 0.5v, ctrl1, ctrl2, ctrl3 = 1.5v, ovp1, ovp2, ov p3 = 0v, unless otherwise noted. 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 lt3496e is guaranteed to meet performance specifications from 0c to 125c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the lt3496i is guaranteed over the full C40c to 125c operating junction temperature range. the lt3496h is guaranteed over the full C40c to 150c operating junction temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. electrical characteristics note 3: current flows into pin. current limit and switch v cesat is guaranteed by design and/or correlation to static test.note 4: absolute maximum voltage at the v in and shdn pins is 40v for nonrepetitive 1 second transients, and 30v for continuous operation.note 5: gate turn-on/turn-off delay is measured from 50% level of pwm voltage to 90% level of gate on/off voltage.note 6: the lt3496 includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed the maximum operating junction temperature when overtemperature protection is active. continuous operating above the specified maximum operating junction temperature may impair device reliability. parameter conditions min typ max units shdn input low voltage 0.4 v shdn input high voltage 1.5 v shdn pin current v shdn = 5v, current into pin 65 100 a pwm1, pwm2, pwm3 input low voltage 0.4 v pwm1, pwm2, pwm3 input high voltage 1.2 v pwm1, pwm2, pwm3 pin current current into pin 160 210 a gate off voltage (cap1 C tg1, cap2 C tg2, cap3 C tg3) cap1, cap2, cap3 = 40v, pwm1, pwm2, pwm3 = 0v 0.1 0.3 v gate on voltage (cap1 C tg1, cap2 C tg2, cap3 C tg3) cap1, cap2, cap3 = 40v 5.5 6.5 7.5 v gate turn-on delay c load = 300pf, cap1, cap2, cap3 = 40v (note 5) 110 ns gate turn-off delay c load = 300pf, cap1, cap2, cap3 = 40v (note 5) 110 ns downloaded from: http:///
lt3496 5 3496ff quiescent current switch on voltage switch frequency vs f adj switch current limit vs duty cycle reference voltage vs temperature switch current limit vs temperature (t a = 25c unless otherwise noted) typical performance characteristics v in (v) 0 8 10 14 30 3496 g01 6 4 10 20 40 20 12 input current (ma) pwm1, pwm2, pwm3 = 5v pwm1, pwm2, pwm3 = 0v v c = gnd, not switching switch current (ma) 0 switch voltage (mv) 300 400 500 800 3496 g02 200 100 0 200 400 600 1000 duty cycle (%) 0 switch current limit (ma) 600 800 1000 80 3496 g03 400 200 0 20 40 60 100 C50 25 C25 0 50 75 100 125 150 temperature (c) current limit (ma) 800 1000 1200 3496 g04 600 400 200 0 temperature (c) C50 v ref (v) 2.03 25 3496 g05 2.00 1.98 C25 0 50 1.971.96 2.042.02 2.01 1.99 75 100 125 150 f adj (v) 0 0 switch frequency (khz) 250 750 1000 1250 0.8 2250 3496 g06 500 0.4 0.2 1.0 0.6 1.2 1500 1750 2000 downloaded from: http:///
lt3496 6 3496ff v cap-led threshold vs temperature pmos turn on waveforms pmos turn off waveforms (t a = 25c unless otherwise noted) typical performance characteristics C50 25 C25 0 50 75 100 125 150 temperature (c) v cap-led threshold (mv) 101 102 103 3496 g10 100 99 98 97 ctrl = 1.2vv cap = 24v 5v0v pwm 40v30v tg 200ns/div v cap = 40v 3496 g11 200ns/div v cap = 40v 3496 g12 5v0v pwm 40v30v tg switch frequency vs temperature v cap-led threshold vs ctrl v cap-led threshold vs v cap C50 25 C25 0 50 75 100 125 150 temperature (c) switch frequency (mhz) 2.1 2.2 2.3 2.4 3496 g07 2.0 1.9 1.8 f adj = 1.2v ctrl (v) 0 0 v cap-led threshold (mv) 20 40 60 80 120 0.2 0.4 0.6 0.8 3496 g08 1 1.2 100 v cap = 24v v cap (v) 0 97 v cap-led trheshold (mv) 98 99 100 101 102 103 10 20 30 40 3496 g09 50 ctrl = 1.2v downloaded from: http:///
lt3496 7 3496ff pwm1, pwm2, pwm3: pulse width modulated inputs. signal low turns off the respective converter, reduces quiescent supply current and causes the vc pin for that converter to become high impedance. pwm pin must not be left floating; tie to v ref if not used. v ref : reference output pin. can supply up to 200a. the nominal output voltage is 2v. ctrl1, ctrl2, ctrl3: led current adjustment pins. sets voltage across external sense resistor between cap and led pins of the respective converter. setting ctrl voltage to be less than 1v will control the current sense voltage to be one-tenth of ctrl voltage. if ctrl voltage is hi gher than 1v, the default current sense voltage is 100mv. the ctrl pin must not be left floating. f adj : switching frequency adjustment pin. setting f adj voltage to be less than 1v will adjust switching frequency up to 2.1mhz. if f adj voltage is higher than 1v, the default switching frequency is 2.1mhz. the f adj pin must not be left floating. vc1, vc2, vc3: error amplifier compensation pins. con- nect a series rc from these pins to gnd. ovp1, ovp2, ovp3: open led protection pins. a voltage higher than 1v on ovp turns off the internal main switch of the respective converter. tie to ground if not used. tg1, tg2, tg3: the gate driver output pins for dis- connnect p -channel mosfets. one for each converter. when the pwm pin is low, the tg pin pulls up to cap to turn off the external mosfet. when the pwm pin is high, the external mosfet turns on. respective cap-tg is limited to 6.5v to protect the mosfet. leave open if the external mosfet is not used. led1, led2, led3: noninverting inputs of current sense error amplifiers. connect directly to led current sense resistor terminal for current sensing of the respective converter cap1, cap2, cap3: inverting inputs of current sense error amplifiers. connect directly to other terminal of l ed current sense resistor terminal of the respective converter. sw1, sw2, sw3: switch pins. collector of the internal npn power switch of the respective converter. connect to external inductor and anode of external schottky recti- fier of the respective converter. minimize the metal trace area connected to this pin to minimize electromagnetic interference. v in : input supply pin. must be locally bypassed. powers the internal control circuitry. shdn : shutdown pin. used to shut down the switching regulator and the internal bias circuits for all three convert- ers. tie to 1.5v or greater to enable the device. tie below 0.4v to turn off the device. exposed pad: signal ground and power ground. solder paddle directly to ground plane. pin functions downloaded from: http:///
lt3496 8 3496ff figure 1. lt3496 block diagram working in boost configuration block diagram C + C ++ eamp a1 C + v1 pwm1 vc 1v pwm comparator slope r1 2k C + v sense i led led1 m1 r sense 0.2 a8 ctrl buffer q3 1v ctrl1 vc1 q1 gnd r220k r6 r5 C + C + a3 sr latch isens2 replicated for each channel shared components s r q a2 C + a9 a6 npn driver C + a10 a4 a7 mosfet driver a5 v in v ref f adj 3496 bd shdn ovp1 r3 r4 r c pwm1 tg1 led1 cap1 sw1 d1 l1 v in c2 c1 c c v in c3 c4 internal regulator and uvlo 2v reference ramp generator oscillator q2 v in isrc200a downloaded from: http:///
lt3496 9 3496ff applications information operation the lt3496 uses a fixed 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 oscillator, ramp generator, refer- ence, internal regulator and uvlo are shared among the three converters. the control circuitry, power switch etc., are replicated for each of the three converters. figure 1 shows the shared circuits and only converter 1 circuits. if the shdn pin is tied to ground, the lt3496 is shut down and draws minimal current from v in . if the shdn pin exceeds 1.5v, the internal bias circuits turn on. the switching regulators start to operate when their respective pwm signal goes high. the main control loop can be understood by following the operation of converter 1. the start of each oscillator cycle sets the sr latch, a3, and turns on power switch q1. the signal at the noninverting input (slope node) of the pwm comparator a2 is proportional to the sum of the switch current and oscillator ramp. when slope exceeds vc1 (the output of the error amplifier a1), a2 resets the latch and turns off the power switch q1 through a4 and a5. in this manner, a10 and a2 set the correct peak current level to keep the output in regulation. amplifier a8 has two noninverting inputs, one from the 1v internal voltage reference and the other one from the ctrl1 pin. whi chever input is lower takes precedence. a8, q3 and r1 force v1, the voltage across r1, to be one tenth of either 1v or the voltage of ctrl1 pin, whichever is lower. v sense is the voltage across the sensing resistor, r sense , which is con- nected in series with the leds. v sense is compared to v1 by a1. if v sense is higher than v1, the output of a1 will decrease, thus reducing the amount of current delivered to leds. in this manner the current sensing voltage v sense is regulated to v1.converters 2 and 3 are identical to converter 1. pwm dimming control led1 can be dimmed with pulse width modulation us- ing the pwm1 pin and an external p-channel mosfet, m1. if the pwm1 pin is pulled high, m1 is turned on by internal driver a7 and converter 1 operates nominally. a7 limits cap1-tg1 to 6.5v to protect the gate of m1. if the p wm1 pin is pulled low, q1 is turned off. converter 1 stops operating, m1 is turned off, disconnects led1 and stops current draw from output capacitor c2. the vc1 pin is also disconnected from the internal circuitry and draws minimal current from the compensation capacitor c c . the vc1 pin and the output capacitor store the state of the led1 current until pwm1 is pulled up again. this leads to a highly linear relationship between pulse width and output light, and allows for a large and accurate dim- ming range. a p-channel mosfet with smaller total gate charge (q g ) improves the dimming performance, since it can be turned on and off faster. use a mosfet with a q g lower than 10nc, and a minimum v th of C1v to C2v. dont use a low v th pmos. to optimize the pwm control of all the three channels, the rising edge of all the three pwm signals should be synchronized. in the applications where high dimming ratio is not required, m1 can be omitted to reduce cost. in these conditions, tg1 should be left open. the pwm dimming range can be further increased by using ctrl1 pin to linearly adjust the current sense threshold during the pwm1 high state. loop compensation loop compensation determines the stability and transient performance. the lt3496 uses current mode control to regulate the output, which simplifies loop compensation. to compensate the feedback loop of the lt3496, a series resistor-capacitor network should be connected from the vc pin to gnd. for most applications, the compensation capacitor should be in the range of 100pf to 1nf. the com- pensation resistor is usually in the range of 5k to 50k. to obtain the best performance, tradeoffs should be made in the compensation network design. a higher value of compensation capacitor improves the stability and dim- ming range (a larger capacitance helps hold the vc voltage when the pwm signal is low). however, a large compen- sation capacitor also increases the start-up time and the time to recover from a fault condition. similarly, a larger compensation resistor improves the transient response but may reduce the phase margin. a practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. the stability, pwm downloaded from: http:///
lt3496 10 3496ff dimming waveforms and the start-up time should be checked across all operating conditions. open-led protection the lt3496 has open-led protection for all the three converters. as shown in figure 1, the ovp1 pin receives the output voltage (the voltage across the output c apacitor) feedback signal from an external resistor divider. ovp1 voltage is compared with a 1v internal voltage reference by comparator a6. in the event the led string is disconnected or fails open, converter 1 output voltage will incr ease, caus- ing ovp1 voltage to increase. when ovp1 voltage exceeds 1v, the power switch q1 will turn off, and cause the output voltage to decrease. eventually, ovp1 will be regulated to 1v and the output voltage will be limited. in the event one of the converters has an open-led protection, the other converters will continue functioning properly. switching frequency and soft-start the lt3496 switching frequency is controlled by f adj pin voltage. setting f adj voltage to be less than 1v will reduce switching frequency. if f adj voltage is higher than 1v, the default switching frequency is 2.1mhz. in general, a lower switching fre- quency should be used where either very high or very low switch duty cycle is required or higher efficiency is desired. selection of a higher switching frequency will allow use of low value external components and yield a smaller solution size and profile. connecting f adj pin to a lowpass filter (r5 and c4 in figure 1) from the ref pin provides a soft-start function. during start-up, f adj voltage increases slowly from 0v to the setting voltage. as a result, the switching frequency increases slowly to the setting frequency. this function limits the inrush current during start-up. undervoltage lockout the lt3496 has an undervoltage lockout circuit that shuts down all the three converters when the input volt- age drops below 2.4v. this prevents the converter from switching in an erratic mode when powered from a low supply voltage. input capacitor selection for proper operation, it is necessary to place a bypass capacitor to gnd close to the v in pin of the lt3496. a 1f or greater capacitor with low esr should be used. a ceramic capacitor is usually the best choice. in the buck mode configuration, the capacitor at pv in has large pulsed currents due to the current returned though the schottky diode when the switch is off. for the best reliability, this capacitor should have low esr and esl and have an adequate ripple current rating. the rms input current is: i in(rms) = i led 1C d ( ) d where d is the switch duty cycle. a 1f ceramic type ca- pacitor placed close to the schottky diode and the ground plane is usually sufficient for each channel. output capacitor selection the selection of output filter capacitor depends on the load and converter configuration, i.e., step-up or step-down. for led applications, the equivalent resistance of the led is typically low, and the output filter capacitor should be large enough to attenuate the current ripple. to achieve the same led ripple current, the required filter capacitor value is larger in the boost and buck-boost mode applications than that in the buck mode application s. for the led buck mode applications, a 0.22f ceramic capacitor is usually sufficient for each channel. for the led boost and buck-boost applications, a 1f ceramic capacitor is usually sufficient for each channel. if higher led current ripple can be tolerated, a lower output capacitance can be selected to reduce the capacitors cost and size. use only ceramic capacitors with x7r or x5r dielectric, as they are good 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 sufficient. table 1 shows some recommended capacitor vendors. applications information downloaded from: http:///
lt3496 11 3496ff table 1. ceramic capacitor manufacturers vendor type series taiyo yuden ceramic x5r, x7r avx ceramic x5r, x7r murata ceramic x5r, x7r kemet ceramic x5r, x7r inductor selection several inductors that work well with the lt3496 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 efficiency. choose an inductor that can handle the necessary peak current without saturating, and ensu re that the inductor has a low dcr (copper-wire resistance) to minimize i 2 r power losses. an inductor with a magnetic shield should be used to prevent noise radiation and cross coupling among the three channels. diode selection the schottky diode conducts current during the interval when the switch is turned off. select a diode v r rated for the maximum sw voltage. it is not necessary that the forward current rating of the diode equal the switch current limit. the average current, i f , through the diode is a function of the switch duty cycle. select a diode with forward current rating of: i f = i l (1 C d) where i l is the inductor current. if using the pwm feature for dimming, it is important to consider diode leakage, which increases with the tem- perature from the output during the pwm low interval. therefore, choose the schottky diode with sufficient low leakage current. table 3 shows several schottky diodes that work well with the lt3496. table 3. schottky diodes part number v r (v) i f (a) package zetex zlls350 40 0.38 sod523 zlls400 40 0.52 sod323 applications information table 2. surface mount inductors part number value (h) dcr ( max) i rms (a) size w l h (mm3) sumida cmd4d06 2.2 0.116 0.95 3.5 4.3 0.8 3.3 0.174 0.77 cdrh3d16 2.2 0.072 1.20 3.8 3.8 1.8 3.3 0.085 1.10 4.7 0.105 0.90 cdrh4d28 10 0.128 1.00 5.0 5.0 3.0 15 0.149 0.76 cdrh5d28 22 0.122 0.9 6.0 6.0 3.0 33 0.189 0.75 cooperet sd3112 2.2 0.140 0.97 3.1 3.1 1.2 3.3 0.165 0.90 4.7 0.246 0.74 sd14 10 0.2058 1.1 5.0 5.0 1.4 sd20 15 0.1655 1.25 5.0 5.0 2.0 22 0.2053 1.12 sd25 33 0.2149 1.11 5.0 5.0 2.5 taiyo yuden nr3015 2.2 0.06 1.48 3.0 3.0 1.5 4.7 0.12 1.02 np04szb 4.7 0.075 1.6 4.0 4.0 1.8 10 0.100 1.2 15 0.180 0.95 22 0.210 0.77 downloaded from: http:///
lt3496 12 3496ff applications information programming the led current the led current of each channel is programmed by con- necting an external sense resistor r sense in series with the led load, and setting the voltage regulation threshold across that sense resistor using ctrl input. if the ctrl voltage, v ctrl , is less than 1v, the led current is: i led = v ctrl 10 r sense if v ctrl is higher than 1v, the led current is: i led = 100mv r sense the ctrl pins should not be left open. the ctrl pin can also be used in conjunction with a ptc thermistor to provide overtemperature protection for the led load as shown in figure 2. voltages to ensure that a junction temperature of 125c is not exceeded. this is especially important when operat- ing at high ambient temperatures. the exposed pad on the bottom of the package must be soldered to a ground plane. this ground should then be connected to an internal copper ground plane with thermal vias placed directly under the package to spread out the heat dissipated by the lt3496. board layout the high speed operation of the lt3496 demands careful attention to board layout and component placement. the exposed pad of the package is the only gnd terminal of the ic and is important for thermal management of the ic. therefore, it is crucial to achieve a good electrical and thermal contact between the exposed pad and the ground plane of the board. also, in boost configuration, the schottky rectifier and the capacitor between gnd and the cathode of the schottky are in the high frequency switching path where current flow is discontinuous. these elements should be placed so as to minimize the path between sw and the gnd of the ic. to reduce electro- magnetic interference (emi), it is important to minimize the area of the sw node. use the gnd plane under sw to minimize interplane coupling to sensitive signals. to obtain good current regulation accuracy and eliminate sources of channel to channel coupling, the cap and led inputs of each channel of the lt3496 should be run as separate lines back to the terminals of the sense resistor. any resistance in series with cap and led inputs should be minimized. finally, the bypass capacitor on the v in sup- ply to the lt3496 should be placed as close as possible to the v in terminal of the device. figure 2 50k 3496 f02 45k 2v v ref 5k ptc ctrl1 to ctrl3 thermal considerations the lt3496 is rated to a maximum input voltage of 30v for continuous operation, and 40v for nonrepetitive one second transients. careful attention must be paid to the internal power dissipation of the lt3496 at higher input downloaded from: http:///
lt3496 13 3496ff typical applications minimum bom buck mode led driver 300:1 pwm dimming at 120hz efficiency 0.3a c4 0.22f c5 0.22f c6 0.22f led1 330m 330m pv in 42v 7 leds l1 15h l215h l3 15h cap1 0.3a led2 cap2 0.3a led3 c1-c3 1f 3 330m 22k 470pf 3496 ta07a cap3 sw1 d1 d2 d3 open sw2 lt3496 gnd sw3 tg1, tg2, tg3 vc1, vc2, vc3 v ref ctrl1, ctrl2, ctrl3 f adj ovp1, ovp2, ovp3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm1, pwm2, pwm3 shdn v in 3v c7 1f c1-c3, c7: murata grm31mr71h105ka88 c4-c6: murata grm21br71h224ka01 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 150m pwm 5v/div i l 0.5a/div i led 0.5a/div 5s/div 3496 ta07b i led (ma) 0 75 efficiency (%) 80 85 90 95 100 50 100 150 200 3496 ta07c 250 300 pwm = 3v ctrl = 0v to 1.2v downloaded from: http:///
lt3496 14 3496ff 3000:1 pwm dimming at 120hz pwm 5v/div i l 0.5a/div i led 0.1a/div 0.5s/div 3496 ta03b typical applications triple boost 100ma 10 led driver efficiency vs pwm duty cycle 10 leds c2 1f c3 1f c4 1f pv in 12v 100ma 825k20k ovp1 led1 tg1 1 470pf 3496 ta03a l1 10h l2 10h l3 10h cap1 d1 d2 d3 m1 m2 m3 sw1 sw2 lt3496 gnd sw3 tg1, tg2, tg3 ovp1, ovp2, ovp3 vc1, vc2, vc3 v ref f adj ctrl1, ctrl2, ctrl3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm1, pwm2, pwm3 shdn v in 3v c1: murata grm31mr71c225ka35 c2-c5: murata grm31mr71h105ka88 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 100m m1-m3: zetex zxmp6a13f c5 1f 10 leds 100ma 825k20k ovp2 led2 tg2 1 cap2 10 leds 100ma 825k20k ovp3 10k led3 tg3 1 cap3 c1 2.2f pwm duty cycle (%) 0 50 efficiency (%) 55 65 70 75 40 80 100 95 3496 ta03d 60 20 60 80 85 90 ctrl = 2v downloaded from: http:///
lt3496 15 3496ff typical applications dual boost led driver triple boost 20ma 8 led driver c2 1f c3 1f c4 1f pv in 12v led1 m1 1 470pf open 3496 ta04 l1 10h l2 10h l3 10h cap1 d1 d2 d3 sw1 tg1 sw2 lt3496 gnd sw3 tg2 ovp1, ovp2, ovp3 tg3 vc1, vc2, vc3 v ref f adj ctrl1, ctrl2, ctrl3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm shdn v in 3v to 12v c5 1f c1 2.2f led2 1 cap2 10 leds 200ma 20k ovp2-3 10k led3 m2 1 cap3 10 leds 100ma 825k 825k 20k ovp1 c1: murata grm31mr71c225ka35 c2-c5: murata grm31mr71h105ka88 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 100m m1, m2: zetex zxmp6a13f 8 leds c2 1f c3 1f c4 1f pv in 5v 20ma 825k20k ovp1 led1 tg1 5 470pf 3496 ta08a l1 22h l2 22h l3 22h cap1 d1 d2 d3 m1 m2 m3 sw1 sw2 lt3496 gnd sw3 tg1, tg2, tg3 ovp1, ovp2, ovp3 vc1, vc2, vc3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm1, pwm2, pwm3 shdn v in 5v c1: murata grm31mr71c225ka35 c2-c5: murata grm31mr71h105ka88 d1-d3: zetex zlls350 l1-l3: taiyo yuden np04szb 220m m1-m3: zetex zxmp6a13f c5 1f 8 leds 20ma 825k20k ovp2 led2 tg2 5 cap2 8 leds 20ma 825k 82k ovp3 20k 10k 20k led3 tg3 5 cap3 c1 2.2f v ref ctrl1, ctrl2, ctrl3 f adj downloaded from: http:///
lt3496 16 3496ff typical applications buck-boost mode 300ma 6 led driver triple buck mode led driver with open led protection pv in 10v to 16v 470pf open 3496 ta05 sw1 sw2 pv in pv in lt3496 gnd sw3 tg1 ovp1, ovp2, ovp3 tg1, tg2, tg3 vc1, vc2, vc3 v ref f adj ctrl1, ctrl2, ctrl3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm shdn v in 3v to 16v c8 1f 6 leds 300ma 825k m1 d2 d3 20k ovp1-3 10k led3 1 l1 10h l2 10h l3 10h cap3 led2 1 cap2 d1 c2 0.1f c4 0.1f c6 0.1f c3 1f led1 1 cap1 c1 2.2f c5 1f pv in c7 1f c1: murata grm31mr71e225ka93 c2, c4, c6: murata grm21br71h104ka01b c3, c5, c7: murata grm31mr71h105ka88 c8: murata grm31mr71e105ka93 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 100m m1: zetex zxmp6a13f 0.5a c4 0.47f c5 0.47f c6 0.47f d1 d2 d3 5.6k 5.6k 20k 20k 2k 2k led1 m1 m2 m3 200m 200m tg1 pv in 12v to 40v l1 10h l210h l3 10h m4 ovp1 ovp2 m5 m6 cap1 0.5a led2 tg2 cap2 0.5a led3 c1-c3 1f 3 200m 470pf 3496 ta02 tg3 cap3 sw1 sw2 lt3496 gnd sw3 tg1, tg2, tg3 ovp1, ovp2, ovp3 vc1, vc2, vc3 v ref f adj ctrl1, ctrl2, ctrl3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm1, pwm2, pwm3 shdn v in 3v to 24v c7 1f 5.6k 20k 2k 22k ovp1 c1-c3, c7: murata grm31mr71h105ka88 c4-c6: murata grm188r71c474ka88 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 100m m1-m3: zetex zxmp6a13f m4-m6: philips bc858b downloaded from: http:///
lt3496 17 3496ff package description fe28 (eb) tssop 0204 0.09 C 0.20 (.0035 C .0079) 0 C 8 0.25 ref 0.50 C 0.75 (.020 C .030) 4.30 C 4.50* (.169 C .177) 1 3 4 5 6 7 8 9 10 11 12 13 14 19 20 22 21 15 16 18 17 9.60 C 9.80* (.378 C .386) 4.75 (.187) 2.74 (.108) 28 2726 25 24 23 1.20 (.047) max 0.05 C 0.15 (.002 C .006) 0.65 (.0256) bsc 0.195 C 0.30 (.0077 C .0118) typ 2 recommended solder pad layout exposed pad heat sink on bottom of package 0.45 ? 0.05 0.65 bsc 4.50 ? 0.10 6.60 ? 0.10 1.05 ? 0.10 4.75 (.187) 2.74 (.108) 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 fe package 28-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663) exposed pad variation eb downloaded from: http:///
lt3496 18 3496ff 4.00 0.10 (2 sides) 2.50 ref 5.00 0.10 (2 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wxxx-x). 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) 0.40 0.10 27 28 12 bottom viewexposed pad 3.50 ref 0.75 0.05 r = 0.115 typ r = 0.05 typ pin 1 notch r = 0.20 or 0.35 45 chamfer 0.25 0.05 0.50 bsc 0.200 ref 0.00 C 0.05 (ufd28) qfn 0506 rev b recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 ? 0.05 0.25 ? 0.05 0.50 bsc 2.50 ref 3.50 ref 4.10 0.05 5.50 0.05 2.65 0.05 3.10 0.05 4.50 0.05 package outline 2.65 0.10 3.65 0.10 3.65 0.05 package description ufd package 28-lead plastic qfn (4mm 5mm) (reference ltc dwg # 05-08-1712 rev b) downloaded from: http:///
lt3496 19 3496ff 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 f 4/10 added h-grade and revised entire data sheet 1 through 20 (revision history begins at rev f) downloaded from: http:///
lt3496 20 3496ff linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com ?? linear technology corporation 2007 lt 0510 rev f ? printed in usa typical application part number description comments lt1618 constant current, 1.4mhz, 1.5a boost converter v in : 1.6v to 18v, v out(max) = 36v, i q = 1.8ma, i sd < 1a, 10-pin ms package lt3453 1mhz, 800ma synchronous buck-boost high power led driver v in : 2.7v to 5.5v, v out(max) = 5.5v, i q = 2.5ma, i sd < 6a, qfn package lt3466 dual constant current, 2mhz, high efficiency 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 lt3467/lt3467a 1.1a (isw), 1.3mhz/2.1mhz, high efficiency step-up dc/dc converters with integrated soft-start v in : 2.4v to 16v, v out(max) = 40v, i q = 1.2ma, i sd < 1a, thinsot? package lt3474 step-down 1a 2mhz led driver v in : 4v to 36v, v out(max) = 15v, i q = 2.6ma, i sd < 1a, tssop package lt3475 dual step-down 1.5a, 2mv led driver v in : 4v to 36v, i q = 6ma, i sd < 1a, 20-lead tssope package lt3476 high current 2mhz quad 1.5a output led driver v in : 2.8v to 16v, v out(max) = 33.5v, i q = 5.5ma, i sd < 1a, 38-lead 5mm 7mm qfn package lt3477 3a, 42v, 3mhz step-up regulator with dual rail-to-rail current sense v in : 2.5v to 2.5v, v out(max) = 40v, i q = 5ma, i sd < 1a, qfn, 16-pin tssope packages lt3478/lt3478-1 4.5a, 2.25mhz led driver with 3000:1 ture color pwm? dimming v in : 2.8v to 36v, v out(max) = 40v, i q = 6.1ma, i sd < 3a, 16-pin tssope package lt3479 3a, full-featured dc/dc converter with soft-start and inrush current protection v in : 2.5v to 24v, v out(max) = 40v, i q = 6.5ma, i sd < 1a, dfn, tssop packages triple buck-boost mode 100ma 6 led driver 3000:1 pwm dimming at 120hz pv in 10v to 16v 470pf 3496 ta06 sw1 sw2 pv in lt3496 gnd sw3 tg1, tg2, tg3 ovp1, ovp2, ovp3 vc1, vc2, vc3 v ref f adj ctrl1, ctrl2, ctrl3 cap1, cap2, cap3led1, led2, led3 v in pwm1, pwm2, pwm3 shdn pwm shdn v in 3v to 16v c8 1f 6 leds 100ma 3.9m100k ovp3 10k led3 tg3 1 l1 10h l2 10h l3 10h cap3 led2 1 cap2 c2 0.1f c4 0.1f c6 0.1f c5 1f pv in c3 1f pv in c7 1f led1 d1 d2 d3 1 cap1 3.9m100k ovp2 3.9m100k ovp1 c1 2.2f 6 leds 100ma tg2 tg1 6 leds 100ma m1 m2 m3 c1: murata grm31mr71e225ka93 c2, c4, c6: murata grm21br71h104ka01b c3, c5, c7: murata grm31mr71h105ka88 c8: murata grm31mr71e105ka93 d1-d3: diodes dfls160 l1-l3: taiyo yuden np04szb 100m m1-m3: zetex zxmp6a13f pwm 5v/div i l 0.5a/div i led 0.1a/div 0.5s/div 3496 ta06b related parts downloaded from: http:///

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