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lt3497 1 3497f typical application features applications description dual full function white led driver with integrated schottky diodes the lt ? 3497 is a dual full function step-up dc/dc con- verter speci? cally designed to drive up to 12 white leds (6 white leds in series per converter) from a li-ion cell. se- ries connection of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors and expensive factory calibration. the two independent converters are capable of driving asymmetric led strings. accurate led dimming and shutdown of the two led strings can also be controlled independently. the lt3497 features a unique high side led current sense that enables the part to function as a one wire current source; one side of the led string can be returned to ground anywhere, allowing a simpler 1-wire led connection. traditional led drivers use a grounded resistor to sense led current, requiring a 2-wire connec- tion to the led string. the 2.3mhz switching frequency allows the use of tiny inductors and capacitors. few external components are needed for the dual white led driver: open-led protection and the schottky diodes are all contained inside the 3mm 2mm dfn package. with such a high level of integra- tion, the lt3497 provides a high ef? ciency dual white led driver solution in the smallest of spaces. li-ion power driver for 4/4 white leds drives up to 12 white leds (6 in series per converter) from a 3v supply two independent boost converters capable of driving asymmetric led strings independent dimming and shutdown control of the two led strings high side sense allows one wire current source per converter internal schottky diodes open led protection (32v) 2.3mhz switching frequency 5% reference accuracy v in range: 2.5v to 10v dual wide 250:1 true color pwm tm dimming requires only 1f output capacitor per converter available in a 3mm 2mm 10-pin dfn package cellular phones pdas, handheld computers digital cameras mp3 players gps receivers , lt, ltc and ltm 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. ef? ciency sw1 v in lt3497 gnd sw2 15 h 10 ? 10 ? 1 f 1 f 3497 ta01a 1 f v in 3v to 5v 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on led current (ma) 0 50 efficiency (%) 55 60 65 70 75 80 v in = 3.6v 4/4leds 51 01 52 0 3497 ta01b downloaded from: http:///
lt3497 2 3497f electrical characteristics package/order information absolute maximum ratings input voltage (vin) ...................................................10v sw1, sw2 voltages ..................................................35v cap1, cap2 voltages ................................................35v ctrl1, ctrl2 voltages ............................................10v led1, led2 voltages ................................................35v operating temperature range ................. C40c to 85c maximum junction temperature .......................... 125c storage temperature range ................... C65c to 125c (note 1) parameter conditions min typ max units minimum operating voltage 2.5 v led current sense voltage (v cap1 C v led1 )v cap1 = 16v 190 200 210 mv led current sense voltage (v cap2 C v led2 )v cap2 = 16v 190 200 210 mv offset voltage (v os ) between (v cap1 C v led1 ) C (v cap2 C v led2 ) voltages v os = |(v cap1 C v led1 ) C (v cap2 C v led2 )| 0 2 8 mv cap1, led1 pin bias current v cap1 = 16v, v led1 = 16v 20 40 a cap2, led2 pin bias current v cap2 = 16v, v led2 = 16v 20 40 a v cap1 , v led1 common mode minimum voltage 2.5 v v cap2 , v led2 common mode minimum voltage 2.5 v supply current v cap1 = v cap2 = 16v, v led1 = v led2 = 15v, v ctrl1 = v ctrl2 = 3v 6 8.5 ma v ctrl1 = v ctrl2 = 0v 12 18 a switching frequency 1.8 2.3 2.8 mhz maximum duty cycle 88 92 % converter 1 switch current limit sw1 300 400 ma converter 2 switch current limit sw2 300 400 ma converter 1 v cesat i sw1 = 200ma 200 mv converter 2 v cesat i sw2 = 200ma 200 mv switch 1 leakage current v sw1 = 16v 0.1 5 a switch 2 leakage current v sw2 = 16v 0.1 5 a top view 11 ddb package 10-lead (3mm 2mm) plastic dfn led1 ctrl1 gnd ctrl2 led2 cap1sw1 v in sw2cap2 6 8 7 9 10 5 4 2 3 1 t jmax = 125c, ja = 76c/w, jc = 13.5c/w exposed pad (pin 11) is gnd, must be soldered to pcb order part number ddb part marking lt3497eddb lcgt order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/ consult ltc marketing for parts speci? ed with wider operating temperature ranges. the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 3v, v ctrl1 = v ctrl2 = 3v. downloaded from: http:///
lt3497 3 3497f 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. parameter conditions min typ max units v ctrl1 voltage for full led current v cap1 = 16v 1.5 v v ctrl2 voltage for full led current v cap2 = 16v 1.5 v v ctrl1 or v ctrl2 voltage to turn on the ic 100 mv v ctrl1 and v ctrl2 voltages to shut down the ic 50 mv ctrl1, ctrl2 pin bias current 100 na cap1 pin overvoltage protection 30 32 34 v cap2 pin overvoltage protection 30 32 34 v schottky 1 forward drop i schottky1 = 100ma 0.8 v schottky 2 forward drop i schottky2 = 100ma 0.8 v schottky 1 reverse leakage current v r1 = 25v 4 a schottky 2 reverse leakage current v r2 = 25v 4 a electrical characteristics the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 3v, v ctrl1 = v ctrl2 = 3v. note 2: the lt3497e is guaranteed to meet performance speci? cations from 0c to 85c. speci? cations over the C40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. downloaded from: http:///
lt3497 4 3497f typical performance characteristics switch saturation voltage (v cesat ) schottky forward voltage drop shutdown current (v ctrl1 = v ctrl2 = 0v) sense voltage (v cap C v led ) vs v ctrl open-circuit output clamp voltage input current in output open circuit switching waveform transient response (t a = 25c unless otherwise speci? ed) switch current (ma) 0 switch saturation voltage (mv) 200 250 300 350 400 3497 g01 150 100 0 100 200 300 50 150 250 350 50 450 400 50 c 125 c 25 c scottky forward drop (mv) 0 schottky forward current (ma) 150 200 250 600 1000 3497 g02 100 50 0 200 400 800 300 350 400 50 c 125 c 25 c v in (v) 0 shutdown current ( a) 9 12 15 8 3497 g03 6 3 0 2 4 6 10 50 c 125 c 25 c v ctrl (mv) 0 0 sense voltage (mv) 40 80 120 160 200 240 500 1000 1500 2000 3497 g04 50 c 125 c 25 c v in (v) 0 output clamp voltage (v) 32 33 8 3497 g05 3130 2 4 6 10 34 50 c 125 c 25 c v in (v) 2 0 input current (ma) 5 10 15 20 25 30 46 81 0 3497 g06 50 c 150 c 25 c v sw 10v/div v cap 50mv/div i l 100ma/div 200ms/div 3497 g07 v in = 3.6v front page application circuit v cap 5v/div v ctrl 5v/div i l 200ma/div 1ms/div 3497 g08 v in = 3.6v front page application circuit downloaded from: http:///
lt3497 5 3497f typical performance characteristics quiescent current current limit vs temperature schottky leakage current vs temperature (C50c to 125c) open-circuit output clamp voltage vs temperature (C50c to 125c) input current in output open circuit vs temperature (C50c to 125c) (t a = 25c unless otherwise speci? ed) switching frequency vs temperature sense voltage (v cap C v led ) vs v cap sense voltage vs temperature v in (v) 0 5 6 7 8 3497 g09 43 246 1 0 2 10 quiescent current (ma) 50 c 125 c 25 c temperature ( c) 50 300 current limit (ma) 350 400 450 500 25 0 25 50 3497 g11 75 100 125 temperature ( c) 0 schottky leakage current ( a) 1 2 3 50 25 0 25 50 3497 g12 75 100 125 24v 16v temperature ( c) 50 28 output clamp voltage (v) 30 32 34 36 25 0 25 50 3497 g13 75 100 125 temperature ( c) 50 input current (ma) 20 25 30 25 75 3497 g14 15 10 25 0 50 100 125 5 0 v in = 3v temperature ( c) 50 switching frequency (mhz) 2.50 25 3497 g15 2.20 2.00 25 0 50 1.901.80 2.602.40 2.30 2.10 75 100 125 v in = 3.6v v cap (v) 5 sense voltage (mv) 200 204 208 25 3497 g16 196 192 188 10 15 20 30 50 c 125 c 25 c temperature ( c) 50 190 sense voltage (mv) 194 198 202 206 25 0 25 50 3497 g17 75 100 125 downloaded from: http:///
lt3497 6 3497f pin functions led1 (pin 1): connection point for the anode of the ? rst led of the ? rst set of leds and the sense resistor (r sense1 ). the led current can be programmed by: i mv r led sense 1 1 200 = ctrl1 (pin 2): dimming and shutdown pin. connect ctrl1 below 50mv to disable converter 1. as the pin volt- age is ramped from 0v to 1.5v, the led current ramps from 0 to (i led1 = 200mv/r sense1 ). the ctrl1 pin must not be left ? oating. gnd (pin 3): connect the gnd pin to the pcb system ground plane.ctrl2 (pin 4): dimming and shutdown pin. connect ctrl2 below 50mv to disable converter 2. as the pin volt- age is ramped from 0v to 1.5v, the led current ramps from 0 to (i led2 = 200mv/r sense2 ). the ctrl2 pin must not be left ? oating. led2 (pin 5): connection point for the anode of the ? rst led of the second set of leds and the sense resistor (r sense2 ). the led current can be programmed by: i mv r led sense 2 2 200 = cap2 (pin 6): output of converter 2. this pin is connected to the cathode of internal schottky diode 2. connect the output capacitor to this pin and the sense resistor (r sense2 ) from this pin to led2 pin.sw2 (pin 7): switch pin. minimize trace area at this pin to minimize emi. connect the inductor at this pin.v in (pin 8): input supply pin. this pin must be locally bypassed.sw1 (pin 9): switch pin. minimize trace area at this pin to minimize emi. connect the inductor at this pin.cap1 (pin 10): output of converter 1. this pin is connected to the cathode of internal schottky diode 1. connect the output capacitor to this pin and the sense resistor (r sense1 ) from this pin to led1 pin.exposed pad (pin 11): ground. must be soldered to pcb. downloaded from: http:///
lt3497 7 3497f block diagram figure 1. lt3497 block diagram + + + 8 overvoltage protect ramp generator start-up start-up 2.3mhz oscillator r r q s v in 9 sw1 q1 cap1 1 2 led1 r a3 a = 6.25 + + a1 1.25v 1.25v ctrl1 ctrl2 3497 f01 r c r c c c c c c out1 1 f c in 1 f l1 15 h l2 15 h g m amp g m amp converter 1 converter 2 a2 10 r sense1 10 ? + + + overvoltage protect r r q s q2 driver driver 5 4 gnd 3 r led2 cap2 a3 + + a2 6 sw2 7 a1 c out2 1 f r sense2 10 ? a = 6.25 downloaded from: http:///
lt3497 8 3497f operation main control loop the lt3497 uses a constant frequency, current mode con- trol scheme to provide excellent line and load regulation. it incorporates two identical, but fully independent pwm converters. operation can be best understood by referring to the block diagram in figure 1. the oscillator, start-up bias and the band gap reference are shared between the two converters. the control circuitry, power switch, schottky diode etc., are identical for both the converters. at power up, the capacitors at cap1 and cap2 pins are charged up to v in (input supply voltage) via their respective inductor and the internal schottky diode. if either ctrl1 and ctrl2 or both are pulled higher than 100mv, the bandgap reference, the start-up bias and the oscillator are turned on. the main control loop can be understood by following the operation of converter 1. at the start of each oscillator cycle, the power switch, q1, is turned on. 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, a2. when this voltage exceeds the level at the negative input of a2, the pwm logic turns off the power switch. the level at the negative input of a2 is set by the error ampli? er, a1, and is simply an ampli? ed version of the difference between the v cap1 and v led1 voltage and the bandgap reference. in this manner the error ampli? er, a1, sets the correct peak current level in inductor l1 to keep the output in regulation. the ctrl1 pin is used to adjust the led current. if only one of the converters is turned on, the other converter will stay off and its output will remain charged up to v in (input supply voltage). the lt3497 enters into shutdown when both ctrl1 and ctrl2 pins are pulled lower than 50mv. the ctrl1 and ctrl2 pins perform independent dimming and shutdown control for the two converters. minimum output current the lt3497 can drive a 4-led string at 2ma led current without pulse skipping. as current is further reduced, the device may begin skipping pulses. this will result in some low frequency ripple, although the average led current remains regulated down to zero. the photo in figure 2 details circuit operation driving 4 white leds at 2ma. peak inductor current is less than 50ma and the regulator operates in discontinuous mode, meaning the inductor current reaches zero during the discharge phase. after the inductor current reaches zero, the sw pin exhibits ringing due to the lc tank circuit formed by the inductor in combination with the switch and the diode capacitance. this ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. figure 2. switching waveforms i l 50ma/div v sw 10v/div v in = 4.2v i led = 2ma 4 leds 200ns/div 3497 f02 downloaded from: http:///
lt3497 9 3497f applications information duty cyclethe duty cycle for a step-up converter is given by: d vvv vvv out d in out d cesat = + + where: v out = output voltage v d = schottky forward voltage drop v cesat = saturation voltage of the switch v in = input voltage the maximum duty cycle achievable for lt3497 is 88% when running at 2.3mhz switching frequency. always ensure that the converter is not duty-cycle limited when powering the leds at a given frequency. inductor selection a 15h inductor is recommended for most lt3497 ap- plications. although small size and high ef? ciency are major concerns, the inductor should have low core losses at 2.3mhz and low dcr (copper wire resistance). some inductors in this category with small size are listed in table 1. the ef? ciency comparison of different inductors is shown in figure 3. table 1: recommended inductors part l (h) max dcr () current rating (ma) vendor lqh32cn150k53lqh2mcn150k02 lqh32cn100k53 lqh2mcn100k02 1515 10 10 0.58 1.60.3 1.2 300200 450 225 murata www.murata.com sd3112-150 15 0.654 440 cooper www.cooperet.com 1001as-150m(type d312c) 15 0.80 360 toko www.toko.com cdrh2d11/hp 15 0.739 410 sumida www.sumida.com capacitor selection the small size of ceramic capacitors make them ideal for lt3497 applications. use only x5r and x7r types because they retain their capacitance over wider temperature ranges than other types such as y5v or z5u. a 1f input capacitor and a 1f output capacitor are suf? cient for most applica- tions. table 2 shows a list of several ceramic capacitor manufacturers. consult the manufacturers for detailed information on their entire selection of ceramic parts. table 2: recommended ceramic capacitor manufacturers taiyo yuden (800) 368-2496 www.t-yuden.com avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com overvoltage protection the lt3497 has an internal open-circuit protection circuit for both converters. in the cases of output open circuit, when the leds are disconnected from the circuit or the leds fail open circuit, the converter v cap voltage is clamped at 32v (typ). figure 4a shows the transient response of the front page application step-up converter with led1 disconnected. with led1 disconnected, the converter starts switching at the peak inductor current limit. the converter output starts ramping up and ? nally gets clamped at 32v (typ). the converter will then switch at low inductor current to regulate the converter output at the clamp voltage. the v cap and input current during output open circuit are shown in the typical performance characteristics. figure 3. ef? ciency comparison of different inductors led current (ma) 0 65 70 80 15 h murata lqh32cn150k53 15 h murata lqh2mcn150k02 15 h cooper sd3112-150 15 h toko 1001as-150m type d312c 15 h sumida cdrh2d11/hp 15 3497 f03 60 55 51 0 2 0 5045 75 efficiency (%) downloaded from: http:///
lt3497 10 3497f applications information in the event one of the converters has an output open circuit, its output voltage will be clamped at 32v. however, the other converter will continue functioning properly. the photo in figure 4b shows circuit operation with converter 2 output open circuit and converter 1 driving 4 leds at 20ma. converter 2 starts switching at a lower peak inductor current and begins skipping pulses, thereby reducing its input current. inrush current the lt3497 has built-in schottky diodes. when supply voltage is applied to the v in pin, an inrush current ? ows through the inductor and the schottky diode and charges up the cap voltage. both the schottky diodes in the lt3497 can sustain a maximum current of 1a. the selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1a. for low dcr inductors, which are usually the case for this application, the peak inrush current can be simpli? ed as follows: = = = r l lc r l i v l pk in 2 1 4 06 2 2 ? ? ? . ? ? exp ? 22 ?? ? ?? ? where l is the inductance, r is the dcr of the inductor and c is the output capacitance. table 3 gives inrush peak currents for some component selections. table 3: inrush peak currents v in (v) r ( )l ( h )c out (f) i p (a) 4.2 0.58 15 1 0.828 4.2 1.6 15 1 0.682 4.2 0.8 15 1 0.794 4.2 0.739 15 1 0.803 programming led currentthe led current of each led string can be set indepen- dently by the choice of resistors r sense1 and r sense2 , respectively. for each led string, the feedback resistor (r sense ) and the sense voltage (v cap C v led ) control the led current. for each independent led string, the ctrl pin controls the sense reference voltage as shown in the typical performance characteristics. for ctrl higher than 1.5v, the sense reference is 200mv, which results in full led current. in order to have accurate led current, precision resistors are preferred (1% is recommended). the formula and table 4 for r sense selection are shown below. r mv i sense led = 200 figure 4a. transient response of switcher 1 with led1 disconnected from the output figure 4b. switching waveforms with output 1 open circuit i sw 200ma/div v cap 10v/div v in = 3.6v front pageapplication circuit 500 s/div 3497 f04a leds disconnectedat this instant i l1 50ma/div i l2 50ma/div v sw1 20v/div v sw2 20v/div v in = 3.6v 4 leds led 2 disconnected 200ms/div 3497 f04b downloaded from: http:///
lt3497 11 3497f applications information table 4: r sense value selection for 200mv sense i led (ma) r sense ( ) 54 0 10 20 15 13.3 20 10 dimming control there are three different types of dimming control circuits. the led current can be set by modulating the ctrl pin with a dc voltage, a ? ltered pwm signal or directly with a pwm signal. using a dc voltage for some applications, the preferred method of brightness control is a variable dc voltage to adjust the led current. the ctrl pin voltage can be modulated to set the dim- ming of the led string. as the voltage on the ctrl pin increases from 0v to 1.5v, the led current increases from 0 to i led . as the ctrl pin voltage increases beyond 1.5v, it has no effect on the led current. the led current can be set by: i mv r v i v led sense led ctrl > 200 15 6 . when v ctrl .. ? . 25 125 r v sense when v ctrl < feedback voltage variation versus control voltage is given in the typical performance characteristics. using a filtered pwm signal a ? ltered pwm can be used to control the brightness of the led string. the pwm signal is ? ltered (figure 5) by a rc network and fed to the ctrl1, ctrl2 pins. the corner frequency of r1, c1 should be much lower than the frequency of the pwm signal. r1 needs to be much smaller than the internal impedance in the ctrl pins which is 10m (typ). direct pwm dimming changing the forward current ? owing in the leds not only changes the intensity of the leds, it also changes the color. the chromaticity of the leds changes with the change in forward current. many applications cannot tolerate any shift in the color of the leds. controlling the intensity of the leds with a direct pwm signal allows dimming of the leds without changing the color. in addition, direct pwm dimming offers a wider dimming range to the user. dimming the leds via a pwm signal essentially involves turning the leds on and off at the pwm frequency. the typical human eye has a limit of ~60 frames per second. by increasing the pwm frequency to ~80hz or higher, the eye will interpret that the pulsed light source is con- tinuously on. additionally, by modulating the duty cycle (amount of on time) the intensity of the leds can be controlled. the color of the leds remains unchanged in this scheme since the led current value is either zero or a constant value. figure 6 shows a li-ion powered 4/4 white led driver. direct pwm dimming method requires an external nmos tied between the cathode of the lowest led in the string and ground as shown in figure 6. si2318ds mosfets can be used since its sources are connected to ground. the pwm signal is applied to the (ctrl1 and ctrl2) control pins of the lt3497 and the gate of the mosfet. the pwm signal should traverse between 0v to 5v to ensure proper turn on and off of the converters and the nmos transistors (q1 and q2). when the pwm signal goes high, leds are con- nected to ground and a current of i led = (200mv/r sense ) ? ows through the leds. when the pwm signal goes low, the leds are disconnected and turn off. the low pwm input applied to the lt3497 ensures that the respective figure 5. dimming control using a filtered pwm signal lt3497 ctrl1,2 c10.1 f pwm 10khz typ 3497 f05 r1 100k downloaded from: http:///
lt3497 12 3497f converter turns off. the mosfets ensure that the leds quickly turn off without discharging the output capacitors which in turn allows the leds to turn on faster. figures 7 and 8 show the pwm dimming waveforms and ef? ciency for the figure 6 circuit. the time it takes for the leds current to reach its pro- grammed value sets the achievable dimming range for a given pwm frequency. for example, the settling time of the leds current in figure 7 is approximately 40s for a 3v input voltage. the achievable dimming range for this application and 100hz pwm frequency can be determined using the following method. example: ? = 100hz, t settle = 40s t period = 1/? = 1/100 = 0.01s dim range = t period /t settle = 0.01s/40s = 250:1 min duty cycle = t settle /t period ? 100 = 40s/0.01s = 0.4% duty cycle range = 100% 0.4% at 100hz the calculations show that for a 100hz signal the dimming range is 250 to 1. in addition, the minimum pwm duty cycle of 0.4% ensures that the leds current has enough figure 6. li-ion to 4/4 white leds with direct pwm dimming figure 7. direct pwm dimming waveforms applications information sw1 v in lt3497 gnd sw2 l215 h r sense1 10 ? q1 si2318ds q2si2318ds r sense2 10 ? 1 f 1 f 3497 f06 1 f 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 ctrl2 100k 100k 0v pwm freq 5v pwm freq 0v 5v i led 20ma/div i l 200ma/div pwm 5v/div v in = 3.6v 4 leds 2ms/div 3497 f07 led current (ma) 0 efficiency (%) 74 76 20 3497 f08 7270 5 10 15 80 v in = 3.6v 4/4 leds 78 figure 8. ef? ciency downloaded from: http:///
lt3497 13 3497f time to settle to its ? nal value. figure 9 shows the avail- able dimming range for different pwm frequencies with a settling time of 40s. figure 9. dimming ratio vs frequency lower battery voltage. this technique allows the leds to be powered off two alkaline cells. most portable devices have a 3.3v supply voltage which can be used to power the lt3497. the leds can be driven straight from the battery, resulting in higher ef? ciency. figure 11 shows 3/3 leds powered by two aa cells. the battery is connected to the inductors and the chip is powered off a 3.3v logic supply voltage. the dimming range can be further extended by changing the amplitude of the pwm signal. the height of the pwm signal sets the commanded sense voltage across the sense resistor through the ctrl pin. in this manner both analog dimming and direct pwm dimming extend the dimming range for a given application. the color of the leds no longer remains constant because the forward current of the led changes with the height of the ctrl signal. for the 4-led application described above, the leds can be dimmed ? rst, modulating the duty cycle of the pwm signal. once the minimum duty cycle is reached, the height of the pwm signal can be decreased below 1.5v down to 100mv. the use of both techniques together allows the average led current for the 4-led application to be varied from 20ma down to less than 20a. figure 10 shows the application for dimming using both analog dimming and pwm dim- ming. a potentiometer must be added to ensure that the gate of the nmos receives a logic-level signal, while the ctrl signal can be adjusted to lower amplitudes. low input voltage applications the lt3497 can be used in low input voltage applica- tions. the input supply voltage to the lt3497 must be 2.5v or higher. however, the inductors can be run off a figure 11. 2 aa cells to 3/3 white leds applications information pwm frequency (hz) 10 pwm dimming range 100 1000 10000 100 1000 10000 3497 f09 1 10 pulsing may be visible sw1 v in lt3497 gnd sw2 l215 h r sense1 10 ? q1 si2318ds q2si2318ds r sense2 10 ? 1 f 1 f 3497 f10 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 ctrl2 1 f 100k 100k 0v pwm freq 5v pwm freq 0v 5v figure 10. li-ion to 4/4 white leds with both pwm dimming and analog dimming sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c21 f c1 1 f c41 f c1, c2: taiyo yuden lmk212bj105mg c3, c4: taiyo yuden gmk212bj105kg l1, l2: murata lqh32cn150k53 c3 1 f 3497 f11 3.3v l1 15 h 2 aa cells 2v to 3.2v cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on downloaded from: http:///
lt3497 14 3497f li-ion to 1/2 white leds conversion ef? ciency board layout considerations 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 is essential. minimize the length and area of all traces connected to the switching node pins (sw1 and sw2). keep the sense voltage pins (cap1, cap2, led1 and led2) away from applications information 5 41 2 3 76 8 9 10 cap2 sw2sw1 cap1 vias to ground plane via to ground plane via to ground plane l1 l2 led2led1 3497 f12 c out2 c out1 gnd ctrl2ctrl1 c in v in the switching node. place the output capacitors (c out1 and c out2 ) next to the output pins (cap1 and cap2). the placement of a bypass capacitor on v in needs to be in close proximity to the ic to ? lter emi noise from sw1 and sw2. always use a ground plane under the switching regulator to minimize interplane coupling. recommended component placement is shown in figure 12. figure 12. recommended component placement sw1 v in lt3497 gnd sw2 l210 h r sense2 10 ? r sense1 10 ? c31 f c1 1 f c21 f 3497 ta02a v in 3v to 5v l1 10 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn100k53 led current (ma) 0 efficiency (%) 50 55 60 20 3497 ta02b 4540 30 5 10 15 35 7065 v in = 3.6v 1/2leds typical applications downloaded from: http:///
lt3497 15 3497f typical applications li-ion to 2/2 white leds conversion ef? ciency sw1 v in lt3497 gnd sw2 l210 h r sense2 10 ? c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn100k53 r sense1 10 ? c31 f c1 1 f c21 f 3497 ta12a v in 3v to 5v l1 10 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on li-ion to 2/2 white leds conversion ef? ciency sw1 v in lt3497 gnd sw2 l210 h r sense1 10 ? r sense2 10 ? c31 f c21 f c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn100k53 c11 f 3497ta13a 3v to 5v l1 10 h cap1 cap2 led1 led2 ctrl1 ctrl2 shutdown and dimming control 1 shutdown and dimming control 2 off on off on led current (ma) 0 40 efficiency (%) 45 50 55 60 65 70 51 01 52 0 3497 ta12b v in = 3.6v 2/2 leds led current (ma) 0 efficiency (%) 60 65 70 20 3497 ta13b 5550 40 5 10 15 45 80 v in = 3.6v 2/2leds 75 downloaded from: http:///
lt3497 16 3497f typical applications li-ion to 3/3 white leds conversion ef? ciency li-ion to 2/4 white leds conversion ef? ciency sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c1 1 f c21 f c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1: murata lqh32cn100k53 l2: murata lqh32cn150k53 3497 ta03a v in 3v to 5v l1 10 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on led current (ma) 0 65 70 80 15 3497 ta03b 60 55 51 0 2 0 5045 75 efficiency (%) v in = 3.6v 2/4leds sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn150k53 c21 f 3497 ta04a c1 1 f v in 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on led current (ma) 0 65 70 80 15 3497 ta04b 60 55 51 0 2 0 5045 75 efficiency (%) v in = 3.6v 3/3leds downloaded from: http:///
lt3497 17 3497f li-ion to 4/6 white leds conversion ef? ciency typical applications li-ion to 5/5 white leds conversion ef? ciency sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c21 f 3497 ta05a c1 1 f v in 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn150k53 led current (ma) 0 50 efficiency (%) 55 60 65 70 75 80 v in = 3.6v 4/6leds 51 01 52 0 3497 ta05b sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c21 f 3497 ta06a c1 1 f v in 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn150k53 led current (ma) 0 50 efficiency (%) 55 60 65 70 75 80 v in = 3.6v 5/5leds 51 01 52 0 3497 ta06b downloaded from: http:///
lt3497 18 3497f typical applications li-ion to 6/6 white leds conversion ef? ciency 2-cell li-ion movie and flash mode/6 white leds control conversion ef? ciency sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c21 f 3497 ta07a c1 1 f v in 3v to 5v l1 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn150k53 led current (ma) 0 50 efficiency (%) 55 60 65 70 75 80 v in = 3.6v 6/6leds 51 01 52 0 3497 ta07b cap1 v in lt3497 gnd sw2 l215 h l1 15 h flash movie r sense2 10 ? r sense1 1 ? c31 f c21 f 3497 ta08a c1 4.7 f v in 6v to 9v led1 d1 cap2 sw1 led2 1.5v 680mv v ctrl1 ctrl1 shutdown and dimming control 2 ctrl2 off on mode movie flash i led 100ma200ma c1: taiyo yuden lmk212bj475kd c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg d1: aot-2015 hpw1751b l1, l2: murata lqh32cn150k53 v in (v) 6 65 efficiency (%) 70 75 80 85 6.5 7 7.5 8 3497 ta08b 8.5 9 1-100ma led/6 leds downloaded from: http:///
lt3497 19 3497f 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. package description ddb package 10-lead plastic dfn (3mm 2mm) (reference ltc dwg # 05-08-1722 rev ?) 2.00 0.10 (2 sides) note:1. drawing conforms to version (wecd-1) in jedec package outline m0-229 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom viewexposed pad 0.64 0.05 (2 sides) 0.75 0.05 r = 0.115 typ r = 0.05 typ 2.39 0.05 (2 sides) 3.00 0.10 (2 sides) 1 5 10 6 pin 1 bar top mark (see note 6) 0.200 ref 0 0.05 (ddb10) dfn 0905 rev ? 0.25 0.05 0.50 bsc pin 1r = 0.20 or 0.25 45 chamfer 0.25 0.05 2.39 0.05 (2 sides) recommended solder pad pitch and dimensions 0.64 0.05 (2 sides) 1.15 0.05 0.70 0.05 2.55 0.05 packageoutline 0.50 bsc downloaded from: http:///
lt3497 20 3497f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2006 lt 1206 ? printed in usa related parts typical application 2 li-ion to 8/8 white leds conversion ef? ciency part number description comments lt1937 constant current, 1.2mhz, high ef? ciency white led boost regulator up to 4 white leds, v in : 2.5v to 10v, v out(max) = 34v, i q = 1.9ma, i sd < 1a, thinsot tm /sc70 packages ltc3200-5 low noise, 2mhz regulated charge pump white led driver up to 6 white leds, v in : 2.7v to 4.5v, i q = 8ma, i sd < 1a, thinsot package ltc3201 low noise, 1.7mhz regulated charge pump white led driver up to 6 white leds, v in : 2.7v to 4.5v, i q = 6.5ma, i sd < 1a, ms package ltc3202 low noise, 1.5mhz regulated charge pump white led driver up to 8 white leds, v in : 2.7v to 4.5v, i q = 5ma, i sd < 1a, ms package ltc3205 high ef? ciency, multidisplay led controller up to 4 (main), 2 (sub) and rgb, v in : 2.8v to 4.5v, i q = 50a, i sd < 1a, 24-lead qfn package lt3465/lt3465a constant current, 1.2mhz/2.7mhz, high ef? ciency white led boost regulator with integrated schottky diode up to 6 white leds, v in : 2.7v to 16v, v out(max) = 34v, i q = 1.9ma, i sd < 1a, thinsot 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 white led driver in sc70 with integrated schottky drives up to 6 20ma white leds, v in : 2.5v to 12v, v out(max) = 27v, 8-lead sc70 package thinsot is a trademark of linear technology corporation. sw1 v in lt3497 gnd sw2 l215 h r sense2 10 ? r sense1 10 ? c31 f c21 f 3497 ta11a c1 1 f v in 6v to 9v l1 15 h cap1 cap2 led1 led2 ctrl1 shutdown and dimming control 1 shutdown and dimming control 2 ctrl2 off on off on c1, c2: taiyo yuden gmk212bj105kg c3: taiyo yuden lmk212bj105mg l1, l2: murata lqh32cn150k53 led current (ma) 0 70 75 85 15 3497 ta11b 65 60 51 0 2 0 5550 80 efficiency (%) v in = 7.2v 8/8leds downloaded from: http:///

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