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1 lt3466 3466fa dual full function white led step-up converter with built-in schottky diodes figure 1. li-ion powered driver for 8/8 white leds drives up to 20 white leds (10 in series per converter) from a 3.6v supply two independent step-up converters capable of driving asymmetric led strings independent dimming and shutdown control of the two led strings internal schottky diodes internal soft-start eliminates inrush current open led protection (39.5v max v out ) fixed frequency operation up to 2mhz 81% efficiency driving 16 white leds at 15ma (eight per driver) from a 3.6v supply wide input voltage range: 2.7v to 24v available in 10-pin dfn and 16-pin thermally enhanced tssop packages , ltc and lt are registered trademarks of linear technology corporation. main/sub displays digital cameras, sub-notebook pcs pdas, handheld computers automotive lt ? 3466 is a dual full function step-up dc/dc converter specifically designed to drive up to 20 white leds (10 in series per converter) with a constant current. series 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. the dimming of the two led strings can also be controlled independently. the lt3466 is ideal for providing backlight for main and sub-displays in cell phones and other handheld devices. the lt3466 operating frequency can be set with an external resistor over a 200khz to 2mhz range. a low 200mv feedback voltage minimizes power loss in the current setting resistor for better efficiency. additional features include output voltage limiting when leds are disconnected and internal soft-start. the lt3466 is available in the 10-pin (3mm 3mm 0.75mm) dfn and 16-pin thermally enhanced tssop packages. ctrl1 gnd ctrl2 r t sw1 sw2 v in 3v to 5v l2 47 h 1 f 2.2 f 2.2 f led1 led2 l1 47 h lt3466 shutdown and dimming control 2 shutdown and dimming control 1 v out1 fb1 10 ? 10 ? 3466 f01a v out2 fb2 63.4k off on off on conversion efficiency led current (ma) 0 efficiency (%) 70 75 20 3466 f01b 60 50 65 55 5 10 15 85 v in = 3.6v 8/8 leds 80 descriptio u features applicatio s u typical applicatio u
2 lt3466 3466fa input voltage (v in ) ................................................... 24v sw1, sw2 voltages ................................................ 44v v out1 , v out2 voltages ............................................. 44v ctrl1, ctrl2 voltages ........................................... 24v fb1, fb2, r t voltages ................................................ 2v operating temperature range (note 2) ... C40 c to 85 c absolute axi u rati gs w ww u package/order i for atio uu w t jmax = 125 c, ja = 43 c/w, jc = 2.96 c/w exposed pad (pin 11) is gnd must be soldered to pcb order part number dd part marking lbbh lt3466edd consult ltc marketing for parts specified with wider operating temperature ranges. top view 11 dd package 10-lead (3mm 3mm) plastic dfn 10 9 6 7 8 4 5 3 2 1 fb1 ctrl1 r t ctrl2 fb2 v out1 sw1 v in sw2 v out2 (note 1) maximum junction temperature ......................... 125 c storage temperature range dfn .................................................. C65 c to 125 c tssop .............................................. C65 c to 150 c lead temperature (soldering, 10 sec, tssop) ..... 300 c order part number fe part marking 3466efe lt3466efe fe package 16-lead plastic tssop 1 2 3 4 5 6 7 8 top view 16 15 14 13 12 11 10 9 gnd nc v out1 sw1 v in sw2 v out2 gnd gnd fb1 ctrl1 nc r t ctrl2 fb2 gnd 17 t jmax = 125 c, ja = 38 c/w, jc(pad) = 10 c/w exposed pad (pin 17) is gnd must be soldered to pcb electrical characteristics the denotes specifications that apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3v, v ctrl1 = 3v, v ctrl2 = 3v, unless otherwise specified. parameter conditions min typ max units minimum operating voltage 2.7 v maximum operating voltage 24 v fb1 voltage 192 200 208 mv fb2 voltage 192 200 208 mv offset voltage (v os ) between fb1 and fb2 voltages v os = |fb1 C fb2| 0 1.5 7.5 mv fb1 pin bias current v fb1 = 0.2v (note 3) 10 50 na fb2 pin bias current v fb2 = 0.2v (note 3) 10 50 na quiescent current v fb1 = v fb2 = 0.3v 5 7.5 ma ctrl1 = ctrl2 = 0v 16 25 a switching frequency r t = 48.7k 0.8 1 1.2 mhz oscillator frequency range (note 4) 200 2000 khz nominal r t pin voltage r t = 48.7k 0.54 v maximum duty cycle r t = 48.7k 90 96 % r t = 20.5k 92 % r t = 267k 99 %
3 lt3466 3466fa electrical characteristics the denotes specifications that apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3v, v ctrl1 = 3v, v ctrl2 = 3v, unless otherwise specified. parameter conditions min typ max units converter 1 current limit (note 5) 320 400 ma converter 2 current limit (note 5) 320 400 ma converter 1 v cesat i sw1 = 300ma 360 mv converter 2 v cesat i sw2 = 300ma 360 mv switch 1 leakage current v sw1 = 10v 0.01 5 a switch 2 leakage current v sw2 = 10v 0.01 5 a ctrl1 voltage for full led current 1.8 v ctrl2 voltage for full led current 1.8 v ctrl1 or ctrl2 voltage to turn-on the ic 150 mv ctrl1 and ctrl2 voltages to shut down the ic 50 mv ctrl1, ctrl2 pin bias current v ctrl1 = v ctrl2 = 1v 81012 a v out1 overvoltage-lockout threshold v out1 rising 39.5 v v out2 overvoltage-lockout threshold v out2 rising 39.5 v schottky 1 forward drop i schottky1 = 300ma 0.85 v schottky 2 forward drop i schottky2 = 300ma 0.85 v schottky 1 reverse leakage v out1 = 20v 5 a schottky 2 reverse leakage v out2 = 20v 5 a soft-start time (switcher 1) 600 s soft-start time (switcher 2) 600 s note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the lt3466e is guaranteed to meet specified performance from 0 c to 70 c. specifications over the C40 c to 85 c operating range are assured by design, characterization and correlation with statistical process controls. typical perfor a ce characteristics uw switching waveforms transient response v out1 50mv/div v sw1 20v/div i l1 100ma/div v in = 3.6v 0.5 s/div 3466 g01 circuit of figure 1 v out1 0.5v/div v ctrl1 2v/div i l1 200ma/div v in = 3.6v 50 s/div 3466 g02 i led1 = 20ma to 10ma circuit of figure 1 note 3: current flows out of the pin. note 4: guaranteed by design and test correlation, not production tested. note 5: current limit is guaranteed by design and/or correlation to static test. slope compensation reduces current limit at high duty cycle.
4 lt3466 3466fa typical perfor a ce characteristics uw switch saturation voltage (v cesat ) switch current limit vs duty cycle shutdown quiescent current (ctrl1 = ctrl2 = 0v) open-circuit clamp voltage vs v in switch current (ma) 0 switch saturation voltage (mv) 250 300 350 400 3466 g04 200 150 0 100 200 300 50 150 250 350 100 50 450 400 t a = 25 c v ce1 , v ce2 duty cycle (%) 0 current limit (ma) 300 400 80 3466 g05 200 100 250 350 450 500 150 50 0 20 40 60 100 t a = C50 c t a = 85 c t a = 25 c v in (v) 4 shutdown current ( a) 60 80 100 20 3466 g06 40 20 50 70 90 30 10 0 8 12 16 6 222 10 14 18 24 t a = C50 c t a = 100 c t a = 25 c v in (v) 2 output clamp voltage (v) 39.5 40.0 18 3466 g07 39.0 38.5 6 10 12 24 40.5 14 4 8 20 22 16 v out2 v out1 t a = 25 c r t = 63.4k temperature ( c) C50 output clamp voltage (v) 39 40 3466 g08 38 37 0 50 100 42 41 v in = 3.6v r t = 63.4k v out2 v out1 v in (v) 2 input current (ma) 15 20 25 18 3466 g09 10 5 0 468 10 12 14 16 20 22 24 t a = 25 c r t = 63.4k open-circuit clamp voltage vs temperature input current with output 1 and output 2 open circuit v fb vs v ctrl control voltage (v) 0 feedback voltage (mv) 100 150 2 3466 g03 50 0 0.5 1 1.5 250 200 v in = 3v t a = 25 c distribution of v fb vs v ctrl v fb vs v ctrl (temperature variation) control voltage (v) 0 feedback voltage (mv) 100 150 max 4mv typ min 2 3466 g16 50 0 0.5 1 1.5 250 v in = 3v t a = 25 c 200 4mv control voltage (v) 0 feedback voltage (mv) 100 150 2 3466 g17 50 0 0.5 1 1.5 250 200 5mv t a = C45 c t a = 25 c t a = 85 c
5 lt3466 3466fa typical perfor a ce characteristics uw schottky forward voltage drop schottky leakage current quiescent current (ctrl1 = ctrl2 = 3v) v in (v) 0 0 quiescent current (ma) 1 2 3 4 6 4 81216 3466 g13 20 24 5 t a = 25 c schottky forward drop (mv) 0 schottky forward current (ma) 150 200 250 600 1000 3466 g14 100 50 0 200 400 800 300 350 400 t a = 25 c temperature ( c) C50 0 schottky leakage current ( a) 1 2 3 4 6 050 3466 g15 100 v r = 36v 5 v r = 20v oscillator frequency vs temperature temperature ( c) C50 oscillator frequency (khz) 1250 1500 1750 3466 g12 1000 750 500 050 2000 2250 2500 100 v in = 3.6v r t = 20.5k r t = 48.7k r t vs oscillator frequency oscillator frequency (khz) r t (k ? ) 1000 3466 g10 10 100 600 1800 1400 1000 200 oscillator frequency vs v in v in (v) 2 oscillator frequency (khz) 1000 1100 18 3466 g11 900 800 6 10 12 24 1200 14 4 8 20 22 16 r t = 48.7k
6 lt3466 3466fa uu u pi fu ctio s v out1 (pin 1/pin 3): output of converter 1. this pin is connected to the cathode of the internal schottky diode. connect an output capacitor from this pin to ground. sw1 (pin 2/pin 4): switch pin for converter 1. connect the inductor at this pin. v in (pin 3/pin 5): input supply pin. must be locally bypassed with a 1 f, x5r or x7r type ceramic capacitor. sw2 (pin 4/pin 6): switch pin for converter 2. connect the inductor at this pin. v out2 (pin 5/pin 7): output of converter 2. this pin is connected to the cathode of the internal schottky diode. connect an output capacitor from this pin to ground. fb2 (pin 6/pin 10): feedback pin for converter 2. the nominal voltage at this pin is 200mv. connect cathode of the lowest led and the feedback resisitor at this pin. the led current can be programmed by : i led2 (200mv/r fb2 ), when v ctrl2 > 1.6v i led2 (v ctrl2 /5 ? r fb2 ), when v ctrl2 < 1v ctrl2 (pin 7/pin 11): dimming and shutdown pin for converter 2. connect this pin to ground to disable the converter. as the pin voltage is ramped from 0v to 1.6v, the led current ramps from 0 to i led2 (= 200mv/r fb2 ). any voltage above 1.6v does not affect the led current. r t (pin 8/pin 12): timing resistor to program the switch- ing frequency. the switching frequency can be pro- grammed from 200khz to 2mhz. ctrl1 (pin 9/pin 14): dimming and shutdown pin for converter 1. connect this pin to ground to disable the converter. as the pin voltage is ramped from 0v to 1.6v, the led current ramps from 0 to i led1 (= 200mv/r fb1 ). any voltage above 1.6v does not affect the led current. fb1 (pin 10/pin 15): feedback pin for converter 1. the nominal voltage at this pin is 200mv. connect cathode of the lowest led and the feedback resistor at this pin. the led current can be programmed by : i led1 (200mv/r fb1 ), when v ctrl1 > 1.6v i led1 (v ctrl1 /5 ? r fb1 ), when v ctrl1 < 1v exposed pad (pin 11/pin 17): the exposed pad must be soldered to the pcb system ground. gnd (na/pins 1, 8, 9, 16): these pins are internally fused to the exposed pad (tssop package only). connect these gnd pins and the exposed pad to the pcb system ground. (dd/tssop)
7 lt3466 3466fa block diagra w C + C + C + + ea ea pwm comp r sns1 r sns2 osc c3 v out2 driver l2 sw2 0.2v 20k exposed pad 20k fb1 converter 1 converter 2 0.2v 80k 80k shdn ctrl2 ctrl1 pin numbers correspond to the 10-pin dfn package C + C + + start-up control ref 1.25v pwm logic v in v in r t r t fb2 r fb2 r fb1 3466 f02 C + osc sw1 c1 l1 driver v out1 c2 pwm logic osc ramp gen osc overvolt detection overvolt detection q1 q2 a2 a1 a1 a2 a3 pwm comp a3 1 2 8 3 4 5 6 11 7 9 10 figure 2. lt3466 block diagram
8 lt3466 3466fa operatio u main control loop the lt3466 uses a constant frequency, current mode control scheme to provide excellent line and load regula- tion. it incorporates two identical, but fully independent pwm converters. operation can be best understood by referring to the block diagram in figure 2. the oscillator, start-up bias and the bandgap reference are shared be- tween the two converters. the control circuitry, power switch, schottky diode etc., are all identical for both the converters. at power-up, the output voltages v out1 and v out2 are charged up to v in (input supply voltage) via their respec- tive inductor and the internal schottky diode. if either ctrl1 and ctrl2 or both are pulled high, the bandgap reference, start-up bias and the oscillator are turned on. working of 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 amplifier a1, and is simply an amplified version of the difference between the feedback voltage and the 200mv reference voltage. in this manner, the error amplifier a1 regulates the feedback voltage to 200mv reference voltage. the output of the error amplifier a1 sets the correct peak current level in inductor l1 to keep the output in regulation. the ctrl1 pin voltage is used to adjust the reference voltage. if only one of the converters is turned on, the other con- verter will stay off and its output will remain charged up to v in (input supply voltage). the lt3466 enters into shut- down, when both ctrl1 and ctrl2 are pulled lower than 50mv. the ctrl1 and ctrl2 pins perform independent dimming and shutdown control for the two converters. minimum output current the lt3466 can drive an 8-led string at 2.5ma 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 led current remains regulated on an average basis down to zero. the photo in figure 3 shows circuit operation with 16 white leds (eight per converter) at 2.5ma current driven from 3.6v supply. peak inductor current is less than 50ma and the regulator operates in discontinuous mode imply- ing that the inductor current reached zero during the discharge phase. after the inductor current reaches zero, the switch pin exhibits ringing due to the lc tank circuit formed by the inductor in combination with switch and diode capacitance. this ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. the ringing can be damped by applica- tion of a 300 ? resistor across the inductors, although this will degrade efficiency. open-circuit protection the lt3466 has internal open-circuit protection for both the converters. when the leds are disconnected from the circuit or fail open, the converter output voltage is clamped at 39.5v (typ). figure 4a shows the transient response of figure 1s 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 finally gets clamped at 39.5v (typ). the converter will then switch at low inductor current to regulate the converter output at the clamp voltage. output voltage and input current during output open circuit are shown in the typical performance characteristics graphs. in the event one of the converters has an output open- circuit, its output voltage will be clamped at 39.5v. figure 3. switching waveforms v out1 10mv/div v sw1 20v/div i l1 50ma/div v in = 3.6v 0.5 s/div 3466 f03 i led1 = 2.5ma circuit of figure 1
9 lt3466 3466fa however, the other converter will continue functioning properly. the photo in figure 4b shows circuit operation with converter 1 output open-circuit and converter 2 driv- ing eight leds at 20ma. converter 1 starts switching at a lower peak inductor current and begins skipping pulses, thereby reducing its input current. soft-start the lt3466 has a separate internal soft-start circuitry for each converter. soft-start helps to limit the inrush current during start-up. soft-start is achieved by clamping the output of the error amplifier during the soft-start period. this limits the peak inductor current and ramps up the output voltage in a controlled manner. the converter enters into soft-start mode whenever the respective ctrl pin is pulled from low to high. figure 5 shows the start-up waveforms with converter 1 driving four leds at 20ma. the filtered input current, as shown in figure 5, is well controlled. the soft-start circuit is less effective when driving a higher number of leds. undervoltage lockout the lt3466 has an undervoltage lockout circuit which shuts down both the converters when the input voltage drops below 2.1v (typ). this prevents the converter from operating in an erratic mode when powered from low supply voltages. operatio u figure 4a. transient response of switcher 1 with led1 disconnected from the output figure 5. start-up waveforms i in 100ma/div v fb1 200mv/div crtl1 2v/div v in = 3.6v 100 s/div 3466 f05 4 leds, 20ma l = 15 h c = 0.47 f v out1 5v/div v out1 10v/div i l1 200ma/div 200 s/div 3466 f04a led1 disconnected at this instant v in = 3.3v circuit of figure 1 i l1 50ma/div v sw1 50v/div i l2 100ma/div v sw2 50v/div figure 4b. switching waveforms with output 1 open-circuit v in = 3.3v 1 s/div 3466 f04b circuit of figure 1 led1 disconnected
10 lt3466 3466fa duty cycle the duty cycle for a step-up converter is given by: d vvv vvv out d in out d cesat = + + C C where: v out = output voltage v d = schottky forward voltage drop v cesat = saturation voltage of the switch v in = input battery voltage the maximum duty cycle achievable for lt3466 is 96% (typ) when running at 1mhz switching frequency. it in- creases to 99% (typ) when run at 200khz and drops to 92% (typ) at 2mhz. always ensure that the converter is not duty-cycle limited when powering the leds at a given switching frequency. setting the switching frequency the lt3466 uses a constant frequency architecture that can be programmed over a 200khz to 2mhz range with a single external timing resistor from the r t pin to ground. the nominal voltage on the r t pin is 0.54v, and the current that flows into the timing resistor is used to charge and discharge an internal oscillator capacitor. a graph for selecting the value of r t for a given operating frequency is shown in figure 6. operating frequency selection the choice of operating frequency is determined by sev- eral factors. there is a tradeoff between efficiency and component size. higher switching frequency allows the use of smaller inductors albeit at the cost of increased switching losses and decreased efficiency. another consideration is the maximum duty cycle achiev- able. in certain applications, the converter needs to oper- ate at the maximum duty cycle in order to light up the maximum number of leds. the lt3466 has a fixed oscillator off-time and a variable on-time. as a result, the maximum duty cycle increases as the switching frequency is decreased. the circuit of figure 1 is operated with different values of timing resistor (r t ). r t is chosen so as to run the converters at 800khz (r t = 63.4k), 1.25mhz (r t = 39.1k) and 2mhz (r t = 20.5k). the efficiency comparison for different r t values is shown in figure 7. applicatio s i for atio wu uu figure 6. timing resistor (r t ) value figure 7. efficiency comparison for different r t resistors oscillator frequency (khz) r t (k ? ) 1000 3466 f06 10 100 600 1800 1400 1000 200 led current (ma) 0 70 75 85 15 3466 f07 65 60 510 20 55 50 80 efficiency (%) r t = 63.4k r t = 39.1k r t = 20.5k circuit of figure 1 v in = 3.6v 8/8 leds
11 lt3466 3466fa applicatio s i for atio wu uu inductor selection the choice of the inductor will depend on the selection of the switching frequency of the lt3466. the switching frequency can be programmed from 200khz to 2mhz. higher switching frequency allows the use of smaller inductors albeit at the cost of increased switching losses. the inductor current ripple ( ? i l ), neglecting the drop across the schottky diode and the switch, is given by : ? = () i vv v vfl l in min out max in min out max () ( ) () () ?C ?? where: l = inductor f = operating frequency v in(min) = minimum input voltage v out(max) = maximum output voltage the ? i l is typically set to 20% to 40% of the maximum inductor current. the inductor should have a saturation current rating greater than the peak inductor current required for the application. also, ensure that the inductor has a low dcr (copper wire resistance) to minimize i 2 r power losses. recommended inductor values range from 10 h to 68 h. several inductors that work well with the lt3466 are listed in table 1. consult each manufacturer for more detailed information and for their entire selection of related parts. table 1. recommended inductors max current l dcr rating part ( h) ( ? ) (ma) vendor lqh32cn100 10 0.44 300 murata lqh32cn150 15 0.58 300 (814) 237-1431 lqh43cn330 33 1.00 310 www.murata.com ell6rh330m 33 0.38 600 panasonic ell6sh680m 68 0.52 500 (714) 373-7939 www.panasonic.com a914byw330m 33 0.45 440 toko a914byw470m 47 0.73 360 www.toko.com a920cy680m 68 0.40 400 cdrh2d18150nc 15 0.22 350 sumida cdrh4d18-330 33 0.51 310 (847) 956-0666 cdrh5d18-680 68 0.84 430 www.sumida.com capacitor selection the small size of ceramic capacitors make them ideal for lt3466 applications. use only x5r and x7r types be- cause they retain their capacitance over wider voltage and temperature ranges than other types such as y5v or z5u. a 1 f input capacitor is sufficient for most applications. always use a capacitor with sufficient voltage rating. table 2 shows a list of several ceramic capacitor manufac- turers. consult the manufacturers for detailed information on their entire selection of ceramic parts. table 2. ceramic capacitor manufacturers taiyo yuden (408) 573-4150 www.t-yuden.com avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com inrush current the lt3466 has built-in schottky diodes. when supply voltage is applied to the v in pin, an inrush current flows through the inductor and the schottky diode and charges up the output voltage. both the schottky diodes in the lt3466 can sustain a maximum of 1a current. the selec- tion of inductor and capacitor value should ensure the peak of the inrush current to be below 1a. for low dcr inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: i v l where lc pk in out = = C. : 06 1 table 3 gives inrush peak current for some component selections.
12 lt3466 3466fa table 3. inrush peak current v in (v) l ( h) c out ( f) i p (a) 5 15 0.47 0.78 5 33 1.00 0.77 5 47 2.2 0.95 5 68 1.00 0.53 9 47 0.47 0.84 12 33 0.22 0.93 typically peak inrush current will be less than the value calculated above. this is due to the fact that the dc resistance in the inductor provides some damping result- ing in a lower peak inrush current. programming led current the led current of each led string can be set indepen- dently by the choice of resistors r fb1 and r fb2 respec- tively (figure 2). the feedback reference is 200mv. in order to have accurate led current, precision resistors are preferred (1% is recommended). r mv i r mv i fb led fb led 1 1 2 2 200 200 = = table 4. r fb value selection i led (ma) r fb ( ? ) 5 40.2 10 20.0 15 13.3 20 10.0 25 8.06 most white leds are driven at maximum currents of 15ma to 20ma. dimming control there are two different types of dimming control circuits. the led current in the two drivers can be set indepen- dently by modulating the ctrl1 and ctrl2 pins respectively. applicatio s i for atio wu uu 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 dimming of the respective led string. as the voltage on the ctrl pin increases from 0v to 1.6v, the led current increases from 0 to i led . as the ctrl pin voltage increases beyond 1.6v, it has no effect on the led current. the led current can be set by: i led (200mv/r fb ), when v ctrl > 1.6v i led (v ctrl /5 ? r fb ), when v ctrl < 1v feedback voltage variation versus control voltage is given in the typical performance characteristics graphs. using a filtered pwm signal a variable duty cycle pwm can be used to control the brightness of the led string. the pwm signal is filtered (figure 8) by an 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 100k ? . 3466 f08 c1 1 f pwm 10khz typ r1 10k lt3466 ctrl1,2 figure 8. dimming control using a filtered pwm signal low input voltage applications the lt3466 can be used in low input voltage applications. the input supply voltage to the lt3466 must be 2.7v or higher. however, the inductors can be run off a lower battery voltage. this technique allows the leds to be powered off two alkaline cells. most portable devices have a 3.3v logic supply voltage which can be used to power the lt3466. the leds can be driven straight from the battery, resulting in higher efficiency.
13 lt3466 3466fa applicatio s i for atio wu uu figure 9 shows four leds being powered off two aa cells. the battery is connected to the inductors and the chip is powered off 3.3v logic supply voltage. ctrl1 ctrl2 r t sw1 sw2 v in lt3466 v out1 63.4k 1% 3466 f09 fb1 10 ? v out2 fb2 l1 15 h 2 aa cells 1.8v to 3v 1 f l2 15 h 0.1 f 3.3v 1 f 1 f 10 ? off on off on figure 9. 2 aa cells to four white leds 1 2 3 4 5 10 9 8 7 6 c out1 r fb1 r t ctrl1 ctrl2 3466 f10 r fb2 c out2 c in v in gnd gnd l1 l2 11 figure 10. recommended component placement (dfn package) high input voltage applications the input voltage to the lt3466 can be as high as 24v. this gives it the flexibility of driving a large number of leds when being powered off a higher voltage. the maximum number of leds that can be driven is constrained by the converter output voltages being clamped at 39.5v (typ). the lt3466 can be used to drive 20 white leds (10 per converter) at 20ma when powered off two li-ion cells in series. board layout consideration 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 essen- tial. minimize the length and area of all traces connected to the switching node pins (sw1 and sw2). keep the feed- back pins (fb1 and fb2) away from the switching nodes. the exposed paddle for both dfn and tssop packages must be connected to the system ground. the ground connection for the feedback resistors should be tied directly to the ground plane and not shared with any other component, except the r t resistor, ensuring a clean, noise-free connection. recommended component place- ment for the dfn package is shown in figure 10.
14 lt3466 3466fa typical applicatio s u ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 15 h c in 1 f c out1 1 f c out2 0.47 f 38.3k 1% l1 15 h lt3466 c in : taiyo yuden jmk107bj105 c out1 : taiyo yuden lmk212bj105 c out2 : taiyo yuden emk212bj474 l1, l2: murata lqh32cn150 v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta01a v out2 fb2 off on off on li-ion to 2/4 white leds conversion efficiency ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 15 h c in 1 f c out1 0.47 f c out2 0.47 f 38.3k 1% l1 15 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden gmk212bj474 l1, l2: murata lqh32cn150 v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta02a v out2 fb2 off on off on li-ion to 5/5 white leds conversion efficiency led current (ma) 0 70 75 85 15 3466 ta01b 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 2/4 leds led current (ma) 0 70 75 85 15 3466 ta02b 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 5/5 leds
15 lt3466 3466fa typical applicatio s u li-ion to 6/6 white leds conversion efficiency li-ion to 7/7 white leds conversion efficiency ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 33 h c in 1 f c out1 1 f c out2 1 f 63.4k 1% l1 33 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden gmk316bj105 l1, l2: toko a914byw-330m v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta03a v out2 fb2 off on off on ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 33 h c in 1 f c out1 1 f c out2 1 f 63.4k 1% l1 33 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden gmk316bj105 l1, l2: toko a914byw-330m v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta04a v out2 fb2 off on off on led current (ma) 0 70 75 85 15 3466 ta03b 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 6/6 leds led current (ma) 0 70 75 85 15 3466 ta04b 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 7/7 leds
16 lt3466 3466fa typical applicatio s u li-ion to 8/8 white leds conversion efficiency li-ion to 9/9 white leds conversion efficiency ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 47 h c in 1 f c out1 2.2 f c out2 2.2 f 63.4k 1% l1 47 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden gmk325bj225 l1, l2: toko a918ce-470m v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta05a v out2 fb2 off on off on ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 68 h c in 1 f c out1 1 f c out2 1 f 147k 1% l1 68 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden umk325bj105 l1, l2: toko a920cy-680m v out1 fb1 r fb2 16.5 ? r fb1 16.5 ? 3466 ta06a v out2 fb2 off on off on led current (ma) 0 70 75 85 15 3466 ta05b 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 8/8 leds led current (ma) 0 70 75 85 90 12 3466 ta06b 65 60 48 80 efficiency (%) v in = 3.6v 9/9 leds
17 lt3466 3466fa typical applicatio s u li-ion to 10/10 white leds conversion efficiency 2 aa cells to 2/2 white leds conversion efficiency ctrl1 ctrl2 r t sw1 sw2 v in 3v to 5v l2 68 h c in 1 f c out1 1 f c out2 1 f 147k 1% l1 68 h lt3466 c in : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden umk325bj105 l1, l2: toko a920cy-680m v out1 fb1 r fb1 16.5 ? r fb2 16.5 ? 3466 ta07a v out2 fb2 off on off on ctrl1 ctrl2 r t sw1 sw2 v in 3.3v l2 15 h c in1 0.1 f c in2 1 f c out1 1 f c out2 1 f l1 15 h v cc 1.8v to 3v lt3466 c in1 : taiyo yuden emk107bj104 c in2 : taiyo yuden jmk107bj105 c out1 , c out2 : taiyo yuden gmk316bj105 l1, l2: murata lqh32cn150 v out1 fb1 r fb2 10 ? 63.4k 1% r fb1 10 ? 3466 ta08a v out2 fb2 off on off on led current (ma) 0 70 75 85 90 12 3466 ta07b 65 60 48 80 efficiency (%) v in = 3.6v 10/10 leds led current (ma) 0 70 75 15 3466 ta08b 65 60 510 20 55 50 efficiency (%) v in = 2.4v 2/2 leds
18 lt3466 3466fa typical applicatio s u 2 li-ion cells to 10/10 white leds conversion efficiency ctrl1 ctrl2 r t sw1 sw2 v in 6v to 9v l2 47 h c in 1 f c out1 0.47 f c out2 0.47 f l1 47 h lt3466 c in : taiyo yuden lmk212bj105 c out1 , c out2 : taiyo yuden umk316bj474 l1, l2: toko a914byw-470m v out1 fb1 r fb1 10 ? r fb2 10 ? 63.4k 1% 3466 ta09a v out2 fb2 off on off on led current (ma) 0 efficiency (%) 70 75 80 20 3466 ta09b 65 60 50 5 10 15 55 90 85 v in = 7v 10/10 leds 2 li-ion cells to 16/16 white leds ctrl1 ctrl2 r t sw1 sw2 v in 6v to 9v v led1 16 leds 16 leds v led2 c in 1 f c3 0.22 f 38.3k 1% c6 0.22 f c4 0.1 f c1 0.1 f l1 47 h l2 47 h d1 d2 c2 0.1 f c5 0.1 f d4 d3 lt3466 c in : taiyo yuden lmk212bj105 c1, c2, c4, c5: taiyo yuden umk212bj104 c3, c6: taiyo yuden umk316bj224 d1-d4: philips bav99 l1, l2: toko a914byw-470m v out1 fb1 r fb1 10 ? r fb2 10 ? 3466 ta10a v out2 fb2 off on off on led current (ma) 0 efficiency (%) 70 75 80 20 3466 ta11b 65 60 50 5 10 15 55 90 85 v in = 7v 16/16 leds conversion efficiency
19 lt3466 3466fa u package descriptio information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. fe package 16-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663) exposed pad variation bb fe16 (bb) 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) 134 5 6 7 8 10 9 4.90 C 5.10* (.193 C .201) 16 1514 13 12 11 1.10 (.0433) max 0.05 C 0.15 (.002 C .006) 0.65 (.0256) bsc 2.94 (.116) 0.195 C 0.30 (.0077 C .0118) typ 2 recommended solder pad layout 0.45 0.05 0.65 bsc 4.50 0.10 6.60 0.10 1.05 0.10 2.94 (.116) 3.58 (.141) 3.58 (.141) 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 dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699) 3.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (weed-2). check the ltc website data sheet for current status of variation assignment 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 0.38 0.10 bottom viewexposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.115 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 C 0.05 (dd10) dfn 1103 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50 bsc 0.675 0.05 3.50 0.05 package outline 0.25 0.05 0.50 bsc
20 lt3466 3466fa lt/lt 0305 rev a ?printed in usa ? linear technology corporation 2004 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com typical applicatio u 12v to 25/25 white leds conversion efficiency part number description comments lt1618 constant current, constant voltage 1.24mhz, high efficiency up to 16 white leds, v in : 1.6v to 18v, v out(max) = 34v, boost regulator i q = 1.8ma, i sd < 1 a, ms package lt1932 constant current, 1.2mhz, high efficiency white led boost up to 8 white leds, v in : 1v to 10v, v out(max) = 34v, regulator i q = 1.2ma, i sd < 1 a, thinsot tm package lt1937 constant current, 1.2mhz, high efficiency white led boost up to 4 white leds, v in : 2.5v to 10v, v out(max) = 34v, regulator i q = 1.9ma, i sd < 1 a, thinsot, sc70 packages ltc3200 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 < 1 a, ms 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 < 1 a, 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 < 1 a, ms package ltc3205/ltc3206 high efficiency, multidisplay led controller up to 4 (main), 2 (sub) and rgb, v in : 2.8v to 4.5v, i q = 50 a, i sd < 1 a, qfn-24 package lt3465/lt3465a constant current, 1.2mhz/2.7mhz, high efficiency white led up to six white leds, v in : 2.7v to 16v, v out(max) = 34v, boost regulator with integrated schottky diode i q = 1.9ma, i sd < 1 a, thinsot package thinsot is a trademark of linear technology corporation. related parts ctrl1 ctrl2 r t sw1 sw2 v in v led1 25 leds 25 leds v led2 c in 3.3v c6 0.22 f 20.5k 1% c11 0.22 f c10 0.1 f c9 0.1 f c4 0.1 f c5 0.1 f l1 33 h car battery 12v (typ) 9v to 18v l2 33 h d5 d6 d7 d8 c2 0.1 f c7 0.1 f c8 0.1 f c3 0.1 f d3 d4 d2 d1 d10 lt3466 c in : taiyo yuden jmk107bj105 c2-c5, c7-c10: taiyo yuden umk212bj104 c6, c11: taiyo yuden umk316bj224 d1-d8: philips bav99 d9, d10: philips bas16 l1, l2: toko a914byw-330m v out1 fb1 r fb1 13.3 ? r fb2 13.3 ? 3466 ta10a v out2 fb2 d9 off on off on led current (ma) 0 85 v in = 12v 25/25 leds 80 75 70 65 60 55 50 3466 ta10b 5 10 15 efficiency (%)

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